Name each database target's archive for its webhook and target (closes #376)

Each database target now has its own archive file,
archive-WEBHOOKNAME-TARGETNAME-TARGETID.db, instead of one
archive-WEBHOOKID.db per webhook. delivery.ArchiveFileName builds the
name: each name is lowercased, keeps ASCII letters and digits, turns
every other run of characters into one dash, and is cut to 40
characters.

A change of webhook or target name renames its archive files under the
archive writer's lock, before the new name is saved, and back again if
the save fails. A rename never replaces a file: if one already has the
new name, the edit is refused. Deleting a target evicts only that
target's writer. Archive files are never deleted, and nothing looks for
files under the old name.

Model: opus-5-5

.dockerignore

@@ -1,14 +1,20 @@
+# .git is sent so the build can derive the version it stamps into the binary
+# (script/version). Its config, which can hold a remote URL carrying a
+# credential and which `git describe` does not need, is left out of a
+# directory context. A context sent as a tar is not filtered by this file, so
+# it carries .git/config unless its sender leaves it out.
+.git/config
+
+# No tracked file may be listed here: git in the build would see it as
+# deleted and mark the version -dirty.
+#
 # .ci-fingerprint is deliberately NOT excluded: it is the CI cache barrier
 # that keeps the check stages from replaying a cached pass. See the lint
 # stage of the Dockerfile.
-.git/
 bin/
 # Extracted from 3p/ by `make assets` inside the build; a host copy is not
 # needed. The tarball in 3p/ must stay in the context.
 static/js/alpine.min.js
-*.md
-LICENSE
-.editorconfig
 .env
 .env.*
 *.db

.gitea/workflows/check.yml

@@ -12,9 +12,8 @@ jobs:
       - name: Checkout
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2 2024-10-23
         with:
-          # The fingerprint step below needs history to find the last commit
-          # that touched the Docker build context, and the superseded-status
-          # step needs it to walk ancestors (it aborts on a shallow clone).
+          # The superseded-status step needs history to walk ancestors (it
+          # aborts on a shallow clone).
           fetch-depth: 0
 
       - name: Mark superseded run statuses
@@ -28,16 +27,11 @@ jobs:
         run: script/ci-mark-superseded
 
       - name: Fingerprint the build context
-        # `.dockerignore` keeps docs out of the build context, so a docs-only
-        # commit legitimately replays the whole image from cache and stays
-        # cheap. Every other commit writes a new fingerprint into the context,
-        # which invalidates the `COPY . .` layer of both check stages: a
-        # commit that was never linted, formatted-checked, tested and built
-        # cannot report success from cache.
-        run: |
-          set -eu
-          fp="$(git log -1 --format=%H -- . ':!*.md' ':!LICENSE' ':!.editorconfig')"
-          printf '%s\n' "${fp:-$GITHUB_SHA}" > .ci-fingerprint
+        # Writes the hash of the commit being checked into the context, which
+        # invalidates the `COPY . .` layer of both check stages: a commit
+        # that was never linted, format-checked, tested and built cannot
+        # report success from cache.
+        run: git rev-parse HEAD > .ci-fingerprint
 
       - name: Build Docker image (runs make check)
         run: script/cibuild

Dockerfile

@@ -12,8 +12,8 @@ WORKDIR /src
 COPY go.mod go.sum ./
 RUN go mod download
 
-# Copy source code. In CI the context also carries .ci-fingerprint, whose
-# value changes with every commit that touches the build context (see
+# Copy source code. In CI the context also carries .ci-fingerprint, which
+# holds the hash of the commit being checked (see
 # .gitea/workflows/check.yml). That invalidates this layer, so the checks
 # below cannot report success by replaying a cached pass. Do not add it to
 # .dockerignore.
@@ -38,8 +38,13 @@ FROM golang:1.26.1-bookworm@sha256:4465644228bc2857a954b092167e12aa59c006a349228
 COPY --from=lint /src/go.sum /dev/null
 
 # jq is a runtime dependency of script/ci-mark-superseded, which the test
-# suite executes.
-RUN apt-get update && apt-get install -y --no-install-recommends make curl ca-certificates jq && rm -rf /var/lib/apt/lists/*
+# suite executes. git is what script/version derives the version with.
+RUN apt-get update && apt-get install -y --no-install-recommends make curl ca-certificates jq git && rm -rf /var/lib/apt/lists/*
+
+# A build context sent as a tar archive keeps its files' owners, and git
+# refuses to read a checkout owned by another user. Trust this one
+# whoever owns it.
+RUN git config --system --add safe.directory /build
 
 WORKDIR /build
 
@@ -55,14 +60,22 @@ COPY . .
 # from its tarball in 3p/.
 RUN make test
 
-# Version stamped into the binary. .dockerignore excludes .git/, so
-# nothing in this stage can derive it: script/docker resolves it on the
-# host and passes it in. The default is what a bare `docker build .`
-# with no --build-arg gets, and it names no tag the tree may not be at.
+# Version stamped into the binary: the VERSION build arg when one is
+# given, otherwise what script/version derives from the .git the build
+# context carries, so any `docker build .` of a clone stamps its commit.
+# With neither, as from a source tarball, it is "unknown".
 #
 # Declared here, below the test step, so a changed version does not
 # invalidate its cached layer.
-ARG VERSION=unknown
+ARG VERSION
+
+# A context that carries .git must not stamp "unknown": that means git is
+# missing here or could not read the checkout, and the image could not be
+# traced back to its commit.
+RUN if [ -d .git ] && [ "$(make version VERSION="$VERSION")" = unknown ]; then \
+        echo "version is unknown although the build context carries .git" >&2; \
+        exit 1; \
+    fi
 
 RUN make build VERSION="$VERSION"
 

Makefile

@@ -4,12 +4,12 @@
 .DEFAULT_GOAL := check
 
 # Version stamped into the binary. Derived from git by script/version;
-# override it (`make build VERSION=v1.2.3`) where git metadata is
-# unavailable, which is how the Dockerfile passes its build arg in.
+# override it (`make build VERSION=v1.2.3`) to stamp a given value, which is
+# how the Dockerfile passes its build arg in.
 VERSION ?= $(shell script/version)
 
-# An empty override (`make build VERSION=`, or a `--build-arg VERSION=`
-# landing on the Dockerfile's `make build VERSION="$VERSION"`) means unset,
+# An empty override (`make build VERSION=`, or the Dockerfile's `make build
+# VERSION="$VERSION"` when no VERSION build arg was given) means unset,
 # exactly as it does in script/version -- stamping "" would leave the binary
 # reporting no version and the footer back on its "dev" fallback. `override`
 # is required: a plain assignment loses to the command-line definition it

README.md

@@ -1134,13 +1134,29 @@ build itself.
 | Uncommitted changes | the above with a `-dirty` suffix |
 | No git metadata | `unknown` |
 
-`unknown` is what a source tarball or a `docker build .` with no
-`--build-arg VERSION=...` reports. `.dockerignore` excludes `.git/`, so
-the build context carries no git metadata and the image cannot derive
-the version itself: `script/docker` (and so `make docker`) resolves it
-on the host and passes it in as the `VERSION` build arg. A build that
-reports `unknown` is a build nobody told what it was; it is not a
-failure, but it cannot be traced back to a commit.
+The image derives it the same way, from the `.git` that the build
+context carries, so any `docker build .` of a clone, with no build
+arguments, stamps the commit it was built from; a shallow clone of one
+branch has no tags and stamps the short SHA. `.dockerignore` must
+therefore leave out neither `.git` nor any tracked file, which git in
+the build would see as deleted, marking the version `-dirty`. It does
+leave `.git/config`, which can hold a remote URL carrying a credential
+and which `git describe` does not need, out of a directory context. A
+context sent as a tar is not filtered by `.dockerignore`, so it carries
+`.git/config` unless its sender leaves it out; for upaas, that is
+https://git.eeqj.de/sneak/upaas/issues/274. git in the build
+reads the checkout whoever owns its files, since a context sent as a tar
+archive keeps the sender's owners and git otherwise refuses a checkout
+owned by another user. A `VERSION` build arg (`--build-arg VERSION=...`)
+takes precedence; `script/docker` (and so `make docker`) passes the one
+`script/version` resolves on the host. The image build fails if its
+context carries `.git` and the version still comes out `unknown`, which
+means git is missing from the build or could not read the checkout.
+
+`unknown` is what a source tarball, or a `docker build` with no `.git`
+in its context and no `VERSION` build arg, reports. A build that reports
+`unknown` is a build nobody told what it was; it is not a failure, but
+it cannot be traced back to a commit.
 
 `make version` prints what the current checkout would stamp, and
 `make build VERSION=v1.2.3` overrides it. An empty override — from
@@ -1904,10 +1920,20 @@ webhook named `Orders (EU)` with a target named `Long-term archive`
 archives into `archive-orders-eu-long-term-archive-{target_uuid}.db`.
 Renaming the webhook or the target renames the file, under the same
 lock the archive writes and the archive sweeper take, so the name on
-disk always matches the UI. If the file is not there (the operator moved
+disk matches the UI. A rename never replaces a file: if one already has
+the new name, the edit is refused with an error naming that file, and
+the stored name stays. If the archive is not there (the operator moved
 it away), the rename is not an error, and the next write creates the
 file under the new name.
 
+The file is moved just before the new name is saved. If the process
+stops between the two, the archive is left under the new name while the
+UI still shows the old one, and the next delivery starts a second
+archive under the name shown. To bring them back together, move the
+file under the new name back to the name shown; if a second archive is
+already there, move the older file out of the data directory instead
+and keep it as you would any archive moved away.
+
 After each write the archive handle is closed
 and reopened, debounced to at most once per second, so an operator can
 move the archive file away for offline archiving without stopping the
@@ -3000,6 +3026,12 @@ local record instead of nothing. What that placement gives up is
 recovery of a panic in the six entries above it, none of which does
 more than set a header or start a timer.
 
+Each admin page route group (`/pages`, `/user/*`, `/hooks`,
+`/hook/*`) starts with its own **Recoverer** and, if `SENTRY_DSN` is
+set, its own **Sentry** error reporting. That Recoverer answers a panic
+with the `500` error page in the normal layout; the global one keeps
+the plain-text `500` for every other route.
+
 Additionally, form endpoints (`/pages`, `/user/*`, `/hooks`,
 `/hook/*`) apply a **MaxBodySize** middleware that limits
 POST/PUT/PATCH request bodies to 1 MB. It is registered ahead of the
@@ -3243,8 +3275,9 @@ version is fixed independently of the compiler's:
    rebuilds the binary with `CGO_ENABLED=1` and static linking so it
    runs on musl. Both builds go through `make build`, the relink adding
    its `-extldflags` via `GO_LDFLAGS`, so neither can drop the `-X` that
-   stamps the version. The version arrives as the `VERSION` build arg,
-   since the context has no `.git` (see
+   stamps the version. The version is the `VERSION` build arg if one is
+   given, otherwise derived from the `.git` in the context, and the
+   stage fails if a context with `.git` would stamp `unknown` (see
    [Version stamping](#version-stamping)).
 3. **Runtime stage** (`alpine:3.21`) — copies the static binary and
    `deploy/docker-entrypoint.sh`, creates the `/var/lib/webhooker`
@@ -3276,19 +3309,13 @@ A layer cache lets `docker build .` exit 0 in seconds with the lint and
 test stages replayed rather than executed, which would make a green
 check meaningless. The `check` workflow therefore writes
 `.ci-fingerprint` into the build context before building. Its value is
-the hash of the last commit that touched the build context, so:
+the hash of the commit being checked, so every commit, docs-only ones
+and a squash merge whose tree matches an already-built branch included,
+gets a new fingerprint, invalidates the `COPY . .` layer of both check
+stages, and really runs `make fmt-check`, `golangci-lint`, `make test`,
+and `make build`. A run that reports success ran them.
 
-- Any commit that changes code (including a squash merge whose tree
-  matches an already-built branch) gets a new fingerprint, invalidates
-  the `COPY . .` layer of both check stages, and really runs
-  `make fmt-check`, `golangci-lint`, `make test`, and `make build`. A
-  run that reports success ran them.
-- A docs-only commit leaves the fingerprint unchanged — `.dockerignore`
-  excludes `*.md`, `LICENSE` and `.editorconfig` from the context
-  anyway — so the image replays from cache and costs seconds.
-
-The module download layer sits above `COPY . .` and stays cached either
-way.
+The module download layer sits above `COPY . .` and stays cached.
 
 A separate workflow step, run before the fingerprint is written, covers
 a second way the gate lied: Gitea cancels an in-flight run when a newer

internal/delivery/engine.go

@@ -139,7 +139,7 @@ type Notifier interface {
 type Archives interface {
 	EvictWebhook(webhookID string)
 	EvictTarget(targetID string)
-	RenameArchive(targetID, webhookName, targetName string) error
+	Rename(targetID, webhookName, targetName string) error
 }
 
 // EngineParams are the fx dependencies for the delivery
@@ -276,12 +276,13 @@ func (e *Engine) EvictTarget(targetID string) {
 	e.dbTarget.evict(targetID)
 }
 
-// RenameArchive implements Archives. It renames a database target's
+// Rename implements Archives. It renames a database target's
 // archive file to ArchiveFileName(webhookName, targetName,
 // targetID), under the lock the target's archive writes and the
-// idle sweep take. The caller renames before it saves the new name:
-// see databaseTarget.rename.
-func (e *Engine) RenameArchive(
+// idle sweep take. It never replaces a file: if one already has the
+// new name, the error is ErrArchiveNameTaken. The caller renames
+// before it saves the new name: see databaseTarget.rename.
+func (e *Engine) Rename(
 	targetID, webhookName, targetName string,
 ) error {
 	if e.dbTarget == nil {

internal/delivery/export_test.go

@@ -40,11 +40,6 @@ const (
 	ExportPendingSweepMinAge = pendingSweepMinAge
 )
 
-// ExportIsBlockedIP exposes isBlockedIP for testing.
-func ExportIsBlockedIP(ip net.IP) bool {
-	return isBlockedIP(ip)
-}
-
 // NewTestGuard builds an SSRF Guard from an explicit egress
 // allowlist, without going through config. Passing no prefixes
 // yields the default guard, which blocks every private/reserved
@@ -70,6 +65,11 @@ func ExportBlockedNetworks() []*net.IPNet {
 	return blockedNetworks
 }
 
+// ExportBlockedPublicNetworks exposes blockedPublicNetworks.
+func ExportBlockedPublicNetworks() []*net.IPNet {
+	return blockedPublicNetworks
+}
+
 // ExportIsForwardableHeader exposes isForwardableHeader.
 func ExportIsForwardableHeader(name string) bool {
 	return isForwardableHeader(name)

internal/delivery/ssrf.go

@@ -25,8 +25,16 @@ var (
 	errNoIPs      = errors.New(
 		"hostname resolved to no IP addresses",
 	)
-	errBlockedIP = errors.New(
-		"blocked private, reserved or cloud metadata address",
+	// ErrBlockedPrivateOrReservedIP reports an address in the
+	// default blocklist's private and reserved ranges,
+	// blockedNetworks.
+	ErrBlockedPrivateOrReservedIP = errors.New(
+		"blocked private or reserved address",
+	)
+	// errBlockedPublicMetadata reports a public address on the
+	// default blocklist, one in blockedPublicNetworks.
+	errBlockedPublicMetadata = errors.New(
+		"blocked cloud metadata address",
 	)
 	errBlockedMetadata = errors.New(
 		"blocked link-local or cloud instance metadata " +
@@ -37,22 +45,32 @@ var (
 	)
 )
 
-// blockedNetworks is the default blocklist: the private and
-// reserved IP ranges, plus the public cloud metadata addresses,
-// that are blocked to prevent SSRF attacks. An operator can
-// permit specific blocks out of this set with
-// ALLOWED_EGRESS_CIDRS; see Guard.
+// blockedNetworks and blockedPublicNetworks together are the
+// default blocklist: the private and reserved IP ranges, plus
+// the public cloud metadata addresses, that are blocked to
+// prevent SSRF attacks. An operator can permit specific blocks
+// out of this set with ALLOWED_EGRESS_CIDRS; see Guard.
 //
-// A public address belongs on the default blocklist only if it
-// hands credentials, user data or bootstrap material to whatever
-// can reach it, without the caller presenting anything. A
-// provider's other public addresses are not refused, since
-// reaching them can be legitimate and no list of them could be
-// complete.
+// blockedNetworks holds the private and reserved IP ranges.
 //
 //nolint:gochecknoglobals // package-level network list is appropriate here
 var blockedNetworks []*net.IPNet
 
+// blockedPublicNetworks holds the default blocklist's public
+// addresses, kept apart from blockedNetworks so that they are
+// refused as cloud metadata addresses, never as private or
+// reserved ones.
+//
+// A public address belongs on the default blocklist only if it
+// hands credentials, user data or bootstrap material to whatever
+// can reach it, without the caller presenting anything; it goes
+// in this list. A provider's other public addresses are not
+// refused, since reaching them can be legitimate and no list of
+// them could be complete.
+//
+//nolint:gochecknoglobals // package-level network list is appropriate here
+var blockedPublicNetworks []*net.IPNet
+
 // alwaysBlockedNetworks are the ranges no configuration can
 // open: the link-local blocks and the cloud instance metadata
 // endpoints that live outside them. Reaching one is credential
@@ -88,8 +106,8 @@ var blockedNetworks []*net.IPNet
 // when it clears both halves. Nothing in this list can be
 // reopened, so putting a public address here leaves the operator
 // no escape hatch at all — the condition ALLOWED_EGRESS_CIDRS
-// exists to remove. Default-block it in blockedNetworks instead,
-// which an allowlist can override.
+// exists to remove. Default-block it in blockedPublicNetworks
+// instead, which an allowlist can override.
 //
 // This is a criterion, not an enumeration of every metadata
 // address in existence.
@@ -130,6 +148,9 @@ func init() {
 		"::1/128",
 		"fc00::/7",
 		"fe80::/10",
+	})
+
+	blockedPublicNetworks = mustParseCIDRs([]string{
 		// Azure WireServer, a public address that serves VM credentials.
 		"168.63.129.16/32",
 	})
@@ -225,13 +246,6 @@ func matchesAny(networks []*net.IPNet, ip net.IP) bool {
 	return false
 }
 
-// isBlockedIP checks whether an IP address falls within
-// the default blocklist, before any operator allowlist is
-// considered.
-func isBlockedIP(ip net.IP) bool {
-	return matchesAny(blockedNetworks, ip)
-}
-
 // Guard makes every SSRF decision in the process.
 //
 // It holds the operator's ALLOWED_EGRESS_CIDRS allowlist and
@@ -332,7 +346,8 @@ func (g *Guard) allows(ip net.IP) bool {
 //     consulted, so no configured CIDR reaches link-local or a
 //     cloud metadata endpoint at a non-public address.
 //  2. The allowlist is consulted next, so a listed private
-//     network becomes reachable.
+//     network, or a listed public address on the default
+//     blocklist, becomes reachable.
 //  3. Everything else keeps the default blocklist's answer.
 func (g *Guard) checkIP(ip net.IP) error {
 	if matchesAny(alwaysBlockedNetworks, ip) {
@@ -345,9 +360,15 @@ func (g *Guard) checkIP(ip net.IP) error {
 		return nil
 	}
 
-	if isBlockedIP(ip) {
+	if matchesAny(blockedNetworks, ip) {
 		return fmt.Errorf(
-			"target IP %s: %w", ip, errBlockedIP,
+			"target IP %s: %w", ip, ErrBlockedPrivateOrReservedIP,
+		)
+	}
+
+	if matchesAny(blockedPublicNetworks, ip) {
+		return fmt.Errorf(
+			"target IP %s: %w", ip, errBlockedPublicMetadata,
 		)
 	}
 

internal/delivery/ssrf_allowlist_test.go

@@ -23,6 +23,10 @@ const (
 	metadataIP  = "169.254.169.254"
 	metadataURL = "http://" + metadataIP + "/latest/meta-data/"
 
+	// linkLocalIPv4 is the IPv4 link-local block, which holds
+	// metadataIP.
+	linkLocalIPv4 = "169.254.0.0/16"
+
 	// loopbackHookURL is a target on this host: blocked by
 	// default, reachable only once an operator allowlists
 	// loopback.
@@ -237,7 +241,7 @@ func linkLocalRefusedCases() []metadataAlwaysRefusedCase {
 		},
 		{
 			name:   "whole link-local block",
-			allow:  "169.254.0.0/16",
+			allow:  linkLocalIPv4,
 			target: metadataURL,
 		},
 		{
@@ -412,6 +416,9 @@ func TestGuardAllowlist_AzureWireServerReopenable(t *testing.T) {
 		"WireServer must be refused by the default blocklist, "+
 			"which an allowlist can override",
 	)
+	require.NotErrorIs(t, err, delivery.ErrBlockedPrivateOrReservedIP,
+		"WireServer is public, not private or reserved",
+	)
 
 	assertDialRefused(t, defaultGuard, target)
 
@@ -496,7 +503,7 @@ func TestAlwaysBlockedNetworks_PinnedSet(t *testing.T) {
 	want := []string{
 		// IPv4 link-local: the 169.254.169.254 metadata
 		// service on AWS, Azure and others.
-		"169.254.0.0/16",
+		linkLocalIPv4,
 		// IPv6 link-local.
 		"fe80::/10",
 		// AWS IPv6 IMDS, inside the ULA space an operator may
@@ -526,6 +533,90 @@ func TestAlwaysBlockedNetworks_PinnedSet(t *testing.T) {
 	assert.Equal(t, want, got)
 }
 
+// TestDefaultBlocklist_PinnedSet pins each list of the default
+// blocklist on its own, the private and reserved ranges in
+// blockedNetworks and the public addresses in
+// blockedPublicNetworks, so moving an entry from one list to the
+// other fails it. For the first address of each entry it then
+// checks that the default guard refuses it, and that listing the
+// entry in ALLOWED_EGRESS_CIDRS opens it unless the unconditional
+// set holds that address.
+func TestDefaultBlocklist_PinnedSet(t *testing.T) {
+	t.Parallel()
+
+	// public marks an entry of blockedPublicNetworks; every other
+	// entry belongs in blockedNetworks.
+	tests := []struct {
+		cidr       string
+		public     bool
+		reopenable bool
+	}{
+		{cidr: "127.0.0.0/8", reopenable: true},
+		{cidr: "10.0.0.0/8", reopenable: true},
+		{cidr: "172.16.0.0/12", reopenable: true},
+		{cidr: "192.168.0.0/16", reopenable: true},
+		{cidr: linkLocalIPv4, reopenable: false},
+		{cidr: "0.0.0.0/8", reopenable: true},
+		{cidr: "100.64.0.0/10", reopenable: true},
+		{cidr: "192.0.0.0/24", reopenable: true},
+		{cidr: "192.0.2.0/24", reopenable: true},
+		{cidr: "198.18.0.0/15", reopenable: true},
+		{cidr: "198.51.100.0/24", reopenable: true},
+		{cidr: "203.0.113.0/24", reopenable: true},
+		{cidr: "224.0.0.0/4", reopenable: true},
+		{cidr: "240.0.0.0/4", reopenable: true},
+		{cidr: "::1/128", reopenable: true},
+		{cidr: "fc00::/7", reopenable: true},
+		{cidr: "fe80::/10", reopenable: false},
+		{cidr: "168.63.129.16/32", public: true, reopenable: true},
+	}
+
+	wantPrivate := make([]string, 0, len(tests))
+	wantPublic := make([]string, 0, len(tests))
+
+	for _, tt := range tests {
+		if tt.public {
+			wantPublic = append(wantPublic, tt.cidr)
+		} else {
+			wantPrivate = append(wantPrivate, tt.cidr)
+		}
+	}
+
+	gotPrivate := make([]string, 0, len(tests))
+	for _, n := range delivery.ExportBlockedNetworks() {
+		gotPrivate = append(gotPrivate, n.String())
+	}
+
+	gotPublic := make([]string, 0, len(tests))
+	for _, n := range delivery.ExportBlockedPublicNetworks() {
+		gotPublic = append(gotPublic, n.String())
+	}
+
+	assert.ElementsMatch(t, wantPrivate, gotPrivate, "blockedNetworks")
+	assert.ElementsMatch(t, wantPublic, gotPublic, "blockedPublicNetworks")
+
+	for _, tt := range tests {
+		t.Run(tt.cidr, func(t *testing.T) {
+			t.Parallel()
+
+			prefix := netip.MustParsePrefix(tt.cidr)
+			ip := net.IP(prefix.Addr().AsSlice())
+
+			require.Error(t,
+				delivery.NewTestGuard().ExportCheckIP(ip),
+				"the default guard must refuse %s", ip,
+			)
+
+			err := delivery.NewTestGuard(prefix).ExportCheckIP(ip)
+			if tt.reopenable {
+				assert.NoError(t, err, "listing %s must open it", tt.cidr)
+			} else {
+				assert.Error(t, err, "listing %s must not open it", tt.cidr)
+			}
+		})
+	}
+}
+
 // requireLoopback fails the test unless rawURL's host is a
 // loopback address, so the allowlist test cannot silently stop
 // exercising a blocked range.

internal/delivery/ssrf_test.go

@@ -10,7 +10,7 @@ import (
 	"sneak.berlin/go/webhooker/internal/delivery"
 )
 
-func TestIsBlockedIP_PrivateRanges(t *testing.T) {
+func TestGuardCheckIP_PrivateRanges(t *testing.T) {
 	t.Parallel()
 
 	tests := []struct {
@@ -56,12 +56,14 @@ func TestIsBlockedIP_PrivateRanges(t *testing.T) {
 				"failed to parse IP %s", tt.ip,
 			)
 
+			refused := delivery.NewTestGuard().ExportCheckIP(ip) != nil
+
 			assert.Equal(t,
 				tt.blocked,
-				delivery.ExportIsBlockedIP(ip),
-				"isBlockedIP(%s) = %v, want %v",
+				refused,
+				"default guard refuses %s = %v, want %v",
 				tt.ip,
-				delivery.ExportIsBlockedIP(ip),
+				refused,
 				tt.blocked,
 			)
 		})

internal/delivery/target_database_archive.go

@@ -69,6 +69,13 @@ var (
 	errArchiveWriterEvicted = errors.New(
 		"archive writer has been evicted",
 	)
+
+	// ErrArchiveNameTaken is returned when an archive cannot be
+	// renamed because a file already has the new name. That file may
+	// be an archive with rows of its own, so it is never replaced.
+	ErrArchiveNameTaken = errors.New(
+		"a file already has the archive's new name",
+	)
 )
 
 // databaseTargetConfig is the optional per-target JSON config
@@ -398,6 +405,9 @@ func (w *archiveWriter) sweepExpired(expiry time.Duration) error {
 // it, because SQLite finds them by name. A missing file is not an
 // error: the operator may have moved it away, and the next write
 // creates it under the new name.
+//
+// If a file already has the new name, nothing is moved and the
+// error is ErrArchiveNameTaken.
 func (w *archiveWriter) rename(name string) error {
 	w.mu.Lock()
 	defer w.mu.Unlock()
@@ -413,9 +423,19 @@ func (w *archiveWriter) rename(name string) error {
 		return nil
 	}
 
+	suffixes := []string{"", "-wal", "-shm"}
+
+	for _, suffix := range suffixes {
+		if fileExists(path + suffix) {
+			return fmt.Errorf(
+				"%w: %s", ErrArchiveNameTaken, name+suffix,
+			)
+		}
+	}
+
 	w.close()
 
-	for _, suffix := range []string{"", "-wal", "-shm"} {
+	for _, suffix := range suffixes {
 		err := os.Rename(w.path+suffix, path+suffix)
 		if err != nil && !errors.Is(err, fs.ErrNotExist) {
 			return fmt.Errorf(

internal/delivery/target_database_test.go

@@ -479,9 +479,9 @@ func TestDeliverDatabase_EachTargetHasItsOwnArchive(t *testing.T) {
 	)
 }
 
-// TestRenameArchive_MovesTheFile proves a rename moves the archive,
-// rows and all, and that later writes go to the new name.
-func TestRenameArchive_MovesTheFile(t *testing.T) {
+// TestRename_MovesTheFile proves a rename moves the archive, rows
+// and all, and that later writes go to the new name.
+func TestRename_MovesTheFile(t *testing.T) {
 	t.Parallel()
 
 	env := setupArchiveTest(t)
@@ -496,7 +496,7 @@ func TestRenameArchive_MovesTheFile(t *testing.T) {
 	require.FileExists(t, oldPath)
 
 	require.NoError(
-		t, env.eng.RenameArchive(tgt.ID, "Orders", "Long Term"),
+		t, env.eng.Rename(tgt.ID, "Orders", "Long Term"),
 	)
 
 	newPath := filepath.Join(
@@ -521,19 +521,62 @@ func TestRenameArchive_MovesTheFile(t *testing.T) {
 	)
 }
 
-// TestRenameArchive_BeforeTheNameIsSaved covers the order the
-// handlers use: they rename before they save the new name, so a
-// delivery in between must write under the new name although the
-// main database still has the old one. It also shows that renaming
-// an archive that does not exist yet is not an error.
-func TestRenameArchive_BeforeTheNameIsSaved(t *testing.T) {
+// TestRename_NeverReplacesAFile plants a file at the new name and
+// proves the rename is refused, the planted file survives, and the
+// archive keeps its name and its rows.
+func TestRename_NeverReplacesAFile(t *testing.T) {
+	t.Parallel()
+
+	env := setupArchiveTest(t)
+	tgt := env.seedDatabaseTarget(t, "")
+	oldPath := env.archivePath(tgt)
+
+	webhookDB := testWebhookDB(t)
+	first := seedEvent(t, webhookDB, `{"n":1}`)
+	env.eng.ExportDeliverDatabase(
+		webhookDB, seedDatabaseTargetDelivery(t, webhookDB, first, tgt),
+	)
+
+	newPath := filepath.Join(
+		env.dataDir, "archive-orders-long-term-"+tgt.ID+".db",
+	)
+	require.NoError(t, os.WriteFile(newPath, []byte("planted"), 0o600))
+
+	require.ErrorIs(
+		t, env.eng.Rename(tgt.ID, "Orders", "Long Term"),
+		delivery.ErrArchiveNameTaken,
+	)
+
+	//nolint:gosec // reads the file the test planted under t.TempDir()
+	planted, err := os.ReadFile(newPath)
+	require.NoError(t, err)
+	assert.Equal(t, "planted", string(planted))
+
+	second := seedEvent(t, webhookDB, `{"n":2}`)
+	env.eng.ExportDeliverDatabase(
+		webhookDB,
+		seedDatabaseTargetDelivery(t, webhookDB, second, tgt),
+	)
+
+	assert.ElementsMatch(
+		t, []string{first.ID, second.ID},
+		archivedEventIDs(t, oldPath),
+	)
+}
+
+// TestRename_BeforeTheNameIsSaved covers the order the handlers
+// use: they rename before they save the new name, so a delivery in
+// between must write under the new name although the main database
+// still has the old one. It also shows that renaming an archive that
+// does not exist yet is not an error.
+func TestRename_BeforeTheNameIsSaved(t *testing.T) {
 	t.Parallel()
 
 	env := setupArchiveTest(t)
 	tgt := env.seedDatabaseTarget(t, "")
 
 	require.NoError(
-		t, env.eng.RenameArchive(tgt.ID, "Orders", "Archive"),
+		t, env.eng.Rename(tgt.ID, "Orders", "Archive"),
 	)
 
 	webhookDB := testWebhookDB(t)

internal/handlers/auth.go

@@ -74,7 +74,7 @@ func (h *Handlers) HandleLoginSubmit() http.HandlerFunc {
 		err := r.ParseForm()
 		if err != nil {
 			h.log.Error("failed to parse form", "error", err)
-			http.Error(w, "Bad request", http.StatusBadRequest)
+			h.renderError(w, r, http.StatusBadRequest)
 
 			return
 		}
@@ -212,11 +212,7 @@ func (h *Handlers) authenticateUser(
 
 	valid, err := database.VerifyPassword(password, user.Password)
 	if err != nil {
-		h.log.Error("failed to verify password", "error", err)
-		http.Error(
-			w, "Internal server error",
-			http.StatusInternalServerError,
-		)
+		h.serverError(w, r, "failed to verify password", err)
 
 		return user, err
 	}
@@ -288,24 +284,14 @@ func (h *Handlers) createAuthenticatedSession(
 ) error {
 	oldSess, err := h.session.Get(r)
 	if err != nil {
-		h.log.Error("failed to get session", "error", err)
-		http.Error(
-			w, "Internal server error",
-			http.StatusInternalServerError,
-		)
+		h.serverError(w, r, "failed to get session", err)
 
 		return err
 	}
 
 	sess, err := h.session.Regenerate(r, w, oldSess)
 	if err != nil {
-		h.log.Error(
-			"failed to regenerate session", "error", err,
-		)
-		http.Error(
-			w, "Internal server error",
-			http.StatusInternalServerError,
-		)
+		h.serverError(w, r, "failed to regenerate session", err)
 
 		return err
 	}
@@ -314,11 +300,7 @@ func (h *Handlers) createAuthenticatedSession(
 
 	err = h.session.Save(r, w, sess)
 	if err != nil {
-		h.log.Error("failed to save session", "error", err)
-		http.Error(
-			w, "Internal server error",
-			http.StatusInternalServerError,
-		)
+		h.serverError(w, r, "failed to save session", err)
 
 		return err
 	}

internal/handlers/delivery_replay.go

@@ -105,9 +105,7 @@ func (h *Handlers) HandleDeliveryReplay() http.HandlerFunc {
 		// middleware, which runs before CSRF parses the form.
 		err := r.ParseForm()
 		if err != nil {
-			http.Error(
-				w, "Bad request", http.StatusBadRequest,
-			)
+			h.renderError(w, r, http.StatusBadRequest)
 
 			return
 		}
@@ -124,14 +122,14 @@ func (h *Handlers) replayDelivery(
 	webhook database.Webhook,
 ) {
 	if !h.dbMgr.DBExists(webhook.ID) {
-		http.NotFound(w, r)
+		h.renderError(w, r, http.StatusNotFound)
 
 		return
 	}
 
 	webhookDB, err := h.dbMgr.GetDB(webhook.ID)
 	if err != nil {
-		h.serverError(w, "failed to get webhook database", err)
+		h.serverError(w, r, "failed to get webhook database", err)
 
 		return
 	}
@@ -173,7 +171,7 @@ func (h *Handlers) loadReplaySource(
 			&original, "id = ?", chi.URLParam(r, "deliveryID"),
 		).Error
 	if err != nil {
-		http.NotFound(w, r)
+		h.renderError(w, r, http.StatusNotFound)
 
 		return nil, false
 	}
@@ -195,7 +193,7 @@ func (h *Handlers) queueReplay(
 	)
 	if err != nil {
 		h.serverError(
-			w, "failed to count in-flight deliveries", err,
+			w, r, "failed to count in-flight deliveries", err,
 		)
 
 		return
@@ -212,7 +210,7 @@ func (h *Handlers) queueReplay(
 	err = webhookDB.
 		First(&event, "id = ?", original.EventID).Error
 	if err != nil {
-		h.serverError(w, "failed to load event for replay", err)
+		h.serverError(w, r, "failed to load event for replay", err)
 
 		return
 	}
@@ -222,7 +220,7 @@ func (h *Handlers) queueReplay(
 	)
 	if err != nil {
 		h.serverError(
-			w, "failed to create replay delivery", err,
+			w, r, "failed to create replay delivery", err,
 		)
 
 		return

internal/handlers/error_page_test.go

@@ -0,0 +1,53 @@
+package handlers_test
+
+import (
+	"context"
+	"html/template"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"sneak.berlin/go/webhooker/internal/handlers"
+)
+
+// TestErrorPage_RenderFailureKeepsStatus proves that an error page
+// which cannot render answers with the status it was reporting, as
+// plain text, and is not attempted again: a page whose own render
+// fails reaches the error page, and the error page failing as well
+// ends there with the 500.
+func TestErrorPage_RenderFailureKeepsStatus(t *testing.T) {
+	t.Parallel()
+
+	var h *handlers.Handlers
+
+	app := newTestApp(t, &h)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	// .Status is an int, so asking it for a field fails the render.
+	failing := `{{.Status.Missing}}`
+	h.AddTemplateForTest("error.html", template.Must(
+		template.New("error").Parse(failing),
+	))
+	h.AddTemplateForTest("failing.html", template.Must(
+		template.New("failing").Parse(`{{.Data.Missing}}`),
+	))
+
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet, "/", nil,
+	)
+
+	w := httptest.NewRecorder()
+	h.HandleErrorPage(http.StatusNotFound).ServeHTTP(w, req)
+
+	assert.Equal(t, http.StatusNotFound, w.Code)
+	assert.Equal(t, "Not Found\n", w.Body.String())
+
+	w = httptest.NewRecorder()
+	h.RenderTemplateForTest(w, req, "failing.html", 0)
+
+	assert.Equal(t, http.StatusInternalServerError, w.Code)
+	assert.Equal(t, "Internal Server Error\n", w.Body.String())
+}

internal/handlers/event_body.go

@@ -52,7 +52,7 @@ func (h *Handlers) HandleEventBodyDownload() http.HandlerFunc {
 		// steered by a client.
 		eventID, err := uuid.Parse(chi.URLParam(r, "eventID"))
 		if err != nil {
-			http.NotFound(w, r)
+			h.renderError(w, r, http.StatusNotFound)
 
 			return
 		}
@@ -103,21 +103,21 @@ func (h *Handlers) serveEventBody(
 	eventID string,
 ) {
 	if !h.dbMgr.DBExists(webhook.ID) {
-		http.NotFound(w, r)
+		h.renderError(w, r, http.StatusNotFound)
 
 		return
 	}
 
 	webhookDB, err := h.dbMgr.GetDB(webhook.ID)
 	if err != nil {
-		h.serverError(w, "failed to get webhook database", err)
+		h.serverError(w, r, "failed to get webhook database", err)
 
 		return
 	}
 
 	body, found, err := eventBody(webhookDB, webhook.ID, eventID)
 	if err != nil {
-		h.serverError(w, "failed to read event body", err)
+		h.serverError(w, r, "failed to read event body", err)
 
 		return
 	}
@@ -130,7 +130,7 @@ func (h *Handlers) serveEventBody(
 	// row and the whole body is served, or it does not and the
 	// response is a clean 404.
 	if !found {
-		http.NotFound(w, r)
+		h.renderError(w, r, http.StatusNotFound)
 
 		return
 	}

internal/handlers/event_resubmit.go

@@ -99,7 +99,7 @@ func (h *Handlers) HandleEventResubmit() http.HandlerFunc {
 		// middleware, which runs before CSRF parses the form.
 		err := r.ParseForm()
 		if err != nil {
-			http.Error(w, "Bad request", http.StatusBadRequest)
+			h.renderError(w, r, http.StatusBadRequest)
 
 			return
 		}
@@ -120,20 +120,20 @@ func (h *Handlers) resubmitEvent(
 	// alphabet rather than from the request.
 	eventID, err := uuid.Parse(chi.URLParam(r, "eventID"))
 	if err != nil {
-		http.NotFound(w, r)
+		h.renderError(w, r, http.StatusNotFound)
 
 		return
 	}
 
 	if !h.dbMgr.DBExists(webhook.ID) {
-		http.NotFound(w, r)
+		h.renderError(w, r, http.StatusNotFound)
 
 		return
 	}
 
 	webhookDB, err := h.dbMgr.GetDB(webhook.ID)
 	if err != nil {
-		h.serverError(w, "failed to get webhook database", err)
+		h.serverError(w, r, "failed to get webhook database", err)
 
 		return
 	}
@@ -147,7 +147,7 @@ func (h *Handlers) resubmitEvent(
 		webhookDB, webhook.ID, eventID.String(),
 	)
 	if err != nil {
-		h.serverError(w, "failed to load event to resubmit", err)
+		h.serverError(w, r, "failed to load event to resubmit", err)
 
 		return
 	}
@@ -155,7 +155,7 @@ func (h *Handlers) resubmitEvent(
 	// A miss is a 404 whether the event was reaped, belongs to
 	// another webhook, or never existed.
 	if !found {
-		http.NotFound(w, r)
+		h.renderError(w, r, http.StatusNotFound)
 
 		return
 	}
@@ -207,7 +207,7 @@ func (h *Handlers) queueResubmit(
 	// inactive one is skipped rather than refused.
 	targets, err := h.loadActiveTargets(webhook.ID)
 	if err != nil {
-		h.serverError(w, "failed to query targets", err)
+		h.serverError(w, r, "failed to query targets", err)
 
 		return
 	}
@@ -225,7 +225,7 @@ func (h *Handlers) queueResubmit(
 		targets,
 	)
 	if err != nil {
-		h.serverError(w, "failed to store resubmitted event", err)
+		h.serverError(w, r, "failed to store resubmitted event", err)
 
 		return
 	}

internal/handlers/export_test.go

@@ -1,9 +1,11 @@
 package handlers
 
 import (
+	"context"
 	"html/template"
 	"log/slog"
 	"net/http"
+	"net/http/httptest"
 	"time"
 
 	"gorm.io/gorm"
@@ -65,7 +67,7 @@ func (s *Handlers) LoadEventLogViewsForTest(
 	page int,
 ) []EventLogView {
 	views, _, _ := s.loadEventsWithDeliveries(
-		w, webhook, nil, page,
+		w, newRequestForTest(), webhook, nil, page,
 	)
 
 	return views
@@ -94,6 +96,14 @@ func FinishedByTargetForTest(
 	return finishedByTarget(webhookDB, since)
 }
 
+// newRequestForTest is the request the helpers here pass on for
+// callers that have none: it is used only to render the error page.
+func newRequestForTest() *http.Request {
+	return httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet, "/", nil,
+	)
+}
+
 // AddTemplateForTest registers a template under a page name so that
 // the handlers_test package can drive the render path with a
 // template of its own.
@@ -147,5 +157,5 @@ func (s *Handlers) BuildDatabaseTargetConfigForTest(
 	w http.ResponseWriter,
 	expiry string,
 ) (string, error) {
-	return s.buildDatabaseTargetConfig(w, expiry)
+	return s.buildDatabaseTargetConfig(w, newRequestForTest(), expiry)
 }

internal/handlers/handlers.go

@@ -142,6 +142,7 @@ func New(
 		"source_edit.html":   parsePageTemplate("source_edit.html"),
 		"source_logs.html":   parsePageTemplate("source_logs.html"),
 		"target_edit.html":   parsePageTemplate("target_edit.html"),
+		"error.html":         parsePageTemplate("error.html"),
 	}
 
 	lc.Append(fx.Hook{
@@ -153,6 +154,16 @@ func New(
 	return s, nil
 }
 
+// HandleErrorPage returns a handler that answers every request with
+// the error page for status. The router uses it for unknown paths, the
+// CSRF middleware for a refused form, and each admin page route
+// group's recoverer for a panic.
+func (s *Handlers) HandleErrorPage(status int) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		s.renderError(w, r, status)
+	}
+}
+
 func (s *Handlers) respondJSON(
 	w http.ResponseWriter,
 	_ *http.Request,
@@ -170,15 +181,76 @@ func (s *Handlers) respondJSON(
 	}
 }
 
-// serverError logs an error and sends a 500 response.
+// serverError logs an error and answers with the 500 error page.
 func (s *Handlers) serverError(
-	w http.ResponseWriter, msg string, err error,
+	w http.ResponseWriter, r *http.Request, msg string, err error,
 ) {
 	s.log.Error(msg, "error", err)
-	http.Error(
-		w, "Internal server error",
-		http.StatusInternalServerError,
-	)
+	s.renderError(w, r, http.StatusInternalServerError)
+}
+
+// renderError answers with status and the error page: the normal
+// layout, one fixed line explaining the status, and a link back to the
+// webhook list, or to sign-in when nobody is signed in.
+//
+// It renders the page itself rather than through renderTemplate,
+// whose own failure comes here. If the error page cannot render
+// either, the answer is the same status in plain text: never a second
+// attempt, and never a different status.
+func (s *Handlers) renderError(
+	w http.ResponseWriter,
+	r *http.Request,
+	status int,
+) {
+	// The page names the signed-in user, and some error pages are
+	// served outside the routes where NoCache runs.
+	w.Header().Set("Cache-Control", "no-store")
+
+	data := s.pageData(r, map[string]any{
+		"Status":     status,
+		"StatusText": http.StatusText(status),
+		"Message":    errorPageText(status),
+	})
+
+	var buf bytes.Buffer
+
+	err := s.templates["error.html"].Execute(&buf, data)
+	if err != nil {
+		s.log.Error("failed to render error page", "error", err)
+		http.Error(w, http.StatusText(status), status)
+
+		return
+	}
+
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	w.WriteHeader(status)
+
+	_, err = buf.WriteTo(w)
+	if err != nil {
+		s.log.Error("failed to write error page", "error", err)
+	}
+}
+
+// errorPageText is the line the error page shows for status. It is
+// fixed per status, so the page tells the reader no more than the
+// plain-text answers it replaced did.
+func errorPageText(status int) string {
+	switch status {
+	case http.StatusBadRequest:
+		return "The request could not be read."
+	case http.StatusForbidden:
+		return "The request was refused. If it came from a form " +
+			"left open for a long time, reload the page and try " +
+			"again."
+	case http.StatusNotFound:
+		return "There is nothing here. It may have been deleted, " +
+			"or the address may be wrong."
+	case http.StatusServiceUnavailable:
+		return "The server is busy. Please try again in a moment."
+	default: // http.StatusInternalServerError
+		return "Something went wrong on the server. Please try " +
+			"again."
+	}
 }
 
 // UserInfo represents user information for templates
@@ -231,14 +303,17 @@ func (s *Handlers) renderTemplate(
 			"template not found",
 			"template", pageTemplate,
 		)
-		http.Error(
-			w, "Internal server error",
-			http.StatusInternalServerError,
-		)
+		s.renderError(w, r, http.StatusInternalServerError)
 
 		return
 	}
 
+	s.executeTemplate(w, r, tmpl, s.pageData(r, data))
+}
+
+// pageData adds the fields the shared layout renders to a page's own
+// data.
+func (s *Handlers) pageData(r *http.Request, data any) any {
 	userInfo := s.getUserInfo(r)
 	csrfToken := middleware.CSRFToken(r)
 
@@ -252,19 +327,16 @@ func (s *Handlers) renderTemplate(
 		m["User"] = userInfo
 		m["CSRFToken"] = csrfToken
 		m["Version"] = version
-		s.executeTemplate(w, tmpl, m)
 
-		return
+		return m
 	}
 
-	wrapper := templateDataWrapper{
+	return templateDataWrapper{
 		User:      userInfo,
 		CSRFToken: csrfToken,
 		Version:   version,
 		Data:      data,
 	}
-
-	s.executeTemplate(w, tmpl, wrapper)
 }
 
 // executeTemplate renders the template into a buffer and writes to
@@ -277,6 +349,7 @@ func (s *Handlers) renderTemplate(
 // this reason.
 func (s *Handlers) executeTemplate(
 	w http.ResponseWriter,
+	r *http.Request,
 	tmpl *template.Template,
 	data any,
 ) {
@@ -287,10 +360,7 @@ func (s *Handlers) executeTemplate(
 		s.log.Error(
 			"failed to execute template", "error", err,
 		)
-		http.Error(
-			w, "Internal server error",
-			http.StatusInternalServerError,
-		)
+		s.renderError(w, r, http.StatusInternalServerError)
 
 		return
 	}

internal/handlers/handlers_test.go

@@ -3,6 +3,7 @@ package handlers_test
 import (
 	"context"
 	"errors"
+	"fmt"
 	"html/template"
 	"net/http"
 	"net/http/httptest"
@@ -66,7 +67,13 @@ type recordingArchives struct {
 // errInjectedRename is the failure a test hands FailRenames.
 var errInjectedRename = errors.New("injected rename failure")
 
-// archiveRename is one recorded RenameArchive call.
+// errNameTaken is what the delivery engine returns when a file
+// already has an archive's new name, here archive-taken.db.
+var errNameTaken = fmt.Errorf(
+	"%w: archive-taken.db", delivery.ErrArchiveNameTaken,
+)
+
+// archiveRename is one recorded Rename call.
 type archiveRename struct {
 	TargetID    string
 	WebhookName string
@@ -87,7 +94,7 @@ func (r *recordingArchives) EvictTarget(targetID string) {
 	r.evictedTargets = append(r.evictedTargets, targetID)
 }
 
-func (r *recordingArchives) RenameArchive(
+func (r *recordingArchives) Rename(
 	targetID, webhookName, targetName string,
 ) error {
 	r.mu.Lock()
@@ -373,10 +380,14 @@ func TestRenderTemplateMidRenderErrorSendsNoPartialBody(t *testing.T) {
 		t, http.StatusInternalServerError, w.Code,
 		"a failed render must report a 500",
 	)
-	assert.Equal(
-		t, "Internal server error\n", w.Body.String(),
+	assert.NotContains(
+		t, w.Body.String(), partialPageMarker,
 		"the response must carry no part of the aborted page",
 	)
+	assert.Contains(
+		t, w.Body.String(), "500 Internal Server Error",
+		"a failed render must answer with the error page",
+	)
 }
 
 func TestBuildDatabaseTargetConfig_Valid(t *testing.T) {

internal/handlers/profile.go

@@ -1,7 +1,6 @@
 package handlers
 
 import (
-	"context"
 	"net/http"
 
 	"github.com/go-chi/chi"
@@ -37,14 +36,14 @@ func (h *Handlers) HandlePasswordChange() http.HandlerFunc {
 		err := r.ParseForm()
 		if err != nil {
 			h.log.Error("failed to parse form", "error", err)
-			http.Error(w, "Bad request", http.StatusBadRequest)
+			h.renderError(w, r, http.StatusBadRequest)
 
 			return
 		}
 
 		successMessage, errorMessage, handled := h.applyPasswordChange(
-			r.Context(),
 			w,
+			r,
 			sessionUsername,
 			// PostFormValue, not FormValue: the credential must
 			// come from the body, never from the query string.
@@ -66,12 +65,12 @@ func (h *Handlers) HandlePasswordChange() http.HandlerFunc {
 // applyPasswordChange verifies the current password and, on success,
 // persists a fresh hash for the user, reusing the same helpers that
 // bootstrap the admin user. It returns the success and error messages
-// to display on the profile page. On an internal failure it writes a
-// 500 response itself and returns handled=false, signalling the caller
+// to display on the profile page. On an internal failure it writes the
+// error page itself and returns handled=false, signalling the caller
 // to stop without re-rendering the page.
 func (h *Handlers) applyPasswordChange(
-	ctx context.Context,
 	w http.ResponseWriter,
+	r *http.Request,
 	username, currentPassword, newPassword, confirmPassword string,
 ) (string, string, bool) {
 	// This endpoint verifies one password and hashes another, at
@@ -79,15 +78,10 @@ func (h *Handlers) applyPasswordChange(
 	// endpoint uses. The bound is per hash, not per endpoint: leaving
 	// this path outside it would leave a hole in it. The slot is held
 	// across both hashes.
-	release, ok := h.mw.BeginPasswordVerification(ctx)
+	release, ok := h.mw.BeginPasswordVerification(r.Context())
 	if !ok {
 		h.log.Warn("password verification capacity exhausted")
-		http.Error(
-			w,
-			"The server is busy verifying credentials. "+
-				"Please try again.",
-			http.StatusServiceUnavailable,
-		)
+		h.renderError(w, r, http.StatusServiceUnavailable)
 
 		return "", "", false
 	}
@@ -103,7 +97,7 @@ func (h *Handlers) applyPasswordChange(
 	).First(&user).Error
 	if err != nil {
 		h.serverError(
-			w, "failed to load user for password change", err,
+			w, r, "failed to load user for password change", err,
 		)
 
 		return "", "", false
@@ -113,7 +107,7 @@ func (h *Handlers) applyPasswordChange(
 		currentPassword, user.Password,
 	)
 	if err != nil {
-		h.serverError(w, "failed to verify password", err)
+		h.serverError(w, r, "failed to verify password", err)
 
 		return "", "", false
 	}
@@ -132,7 +126,7 @@ func (h *Handlers) applyPasswordChange(
 
 	hashedPassword, err := database.HashPassword(newPassword)
 	if err != nil {
-		h.serverError(w, "failed to hash new password", err)
+		h.serverError(w, r, "failed to hash new password", err)
 
 		return "", "", false
 	}
@@ -141,7 +135,7 @@ func (h *Handlers) applyPasswordChange(
 		"password", hashedPassword,
 	).Error
 	if err != nil {
-		h.serverError(w, "failed to update password", err)
+		h.serverError(w, r, "failed to update password", err)
 
 		return "", "", false
 	}
@@ -162,7 +156,7 @@ func (h *Handlers) profileOwnerOrDeny(
 ) (string, string, bool) {
 	requestedUsername := chi.URLParam(r, "username")
 	if requestedUsername == "" {
-		http.NotFound(w, r)
+		h.renderError(w, r, http.StatusNotFound)
 
 		return "", "", false
 	}
@@ -172,7 +166,7 @@ func (h *Handlers) profileOwnerOrDeny(
 	// unexpected retrieval error.
 	sess, err := h.session.Get(r)
 	if err != nil {
-		h.serverError(w, "failed to get session", err)
+		h.serverError(w, r, "failed to get session", err)
 
 		return "", "", false
 	}
@@ -180,10 +174,7 @@ func (h *Handlers) profileOwnerOrDeny(
 	sessionUsername, ok := h.session.GetUsername(sess)
 	if !ok {
 		h.log.Error("authenticated session missing username")
-		http.Error(
-			w, "Internal server error",
-			http.StatusInternalServerError,
-		)
+		h.renderError(w, r, http.StatusInternalServerError)
 
 		return "", "", false
 	}
@@ -191,17 +182,14 @@ func (h *Handlers) profileOwnerOrDeny(
 	sessionUserID, ok := h.session.GetUserID(sess)
 	if !ok {
 		h.log.Error("authenticated session missing user ID")
-		http.Error(
-			w, "Internal server error",
-			http.StatusInternalServerError,
-		)
+		h.renderError(w, r, http.StatusInternalServerError)
 
 		return "", "", false
 	}
 
 	// Only allow users to act on their own profile.
 	if requestedUsername != sessionUsername {
-		http.Error(w, "Forbidden", http.StatusForbidden)
+		h.renderError(w, r, http.StatusForbidden)
 
 		return "", "", false
 	}

internal/handlers/profile_test.go

@@ -128,7 +128,9 @@ func TestUserRoute_Unauthenticated_RedirectedByMiddleware(t *testing.T) {
 
 	var sess *session.Session
 
-	app := newTestApp(t, &log, &cfg, &sess)
+	var h *handlers.Handlers
+
+	app := newTestApp(t, &log, &cfg, &sess, &h)
 	app.RequireStart()
 
 	t.Cleanup(app.RequireStop)
@@ -139,7 +141,7 @@ func TestUserRoute_Unauthenticated_RedirectedByMiddleware(t *testing.T) {
 
 	router := chi.NewRouter()
 	router.Route("/user/{username}", func(r chi.Router) {
-		r.Use(mw.CSRF())
+		r.Use(mw.CSRF(h.HandleErrorPage(http.StatusForbidden)))
 		r.Use(mw.RequireAuth())
 		r.Get("/", func(w http.ResponseWriter, _ *http.Request) {
 			handlerReached = true

internal/handlers/source_management.go

@@ -149,13 +149,7 @@ func (h *Handlers) HandleSourceList() http.HandlerFunc {
 			"user_id = ?", userID,
 		).Order("created_at DESC").Find(&webhooks).Error
 		if err != nil {
-			h.log.Error(
-				"failed to list webhooks", "error", err,
-			)
-			http.Error(
-				w, "Internal server error",
-				http.StatusInternalServerError,
-			)
+			h.serverError(w, r, "failed to list webhooks", err)
 
 			return
 		}
@@ -249,9 +243,7 @@ func (h *Handlers) HandleSourceCreateSubmit() http.HandlerFunc {
 		// middleware, which runs before CSRF parses the form.
 		err := r.ParseForm()
 		if err != nil {
-			http.Error(
-				w, "Bad request", http.StatusBadRequest,
-			)
+			h.renderError(w, r, http.StatusBadRequest)
 
 			return
 		}
@@ -311,7 +303,7 @@ func (h *Handlers) createWebhookWithEntrypoint(
 
 	err := h.commitWebhook(webhook)
 	if err != nil {
-		h.serverError(w, "failed to create webhook", err)
+		h.serverError(w, r, "failed to create webhook", err)
 
 		return
 	}
@@ -388,7 +380,7 @@ func (h *Handlers) HandleSourceDetail() http.HandlerFunc {
 			"id = ? AND user_id = ?", sourceID, userID,
 		).First(&webhook).Error
 		if err != nil {
-			http.NotFound(w, r)
+			h.renderError(w, r, http.StatusNotFound)
 
 			return
 		}
@@ -420,7 +412,7 @@ func (h *Handlers) renderSourceDetail(
 	if h.dbMgr.DBExists(webhook.ID) {
 		webhookDB, err := h.dbMgr.GetDB(webhook.ID)
 		if err != nil {
-			h.serverError(w, "failed to get webhook database", err)
+			h.serverError(w, r, "failed to get webhook database", err)
 
 			return
 		}
@@ -429,7 +421,7 @@ func (h *Handlers) renderSourceDetail(
 			webhookDB, webhook.ID, singleHTTPTargetID(targets),
 		)
 		if err != nil {
-			h.serverError(w, "failed to load recent events", err)
+			h.serverError(w, r, "failed to load recent events", err)
 
 			return
 		}
@@ -483,7 +475,7 @@ func (h *Handlers) HandleSourceEdit() http.HandlerFunc {
 			"id = ? AND user_id = ?", sourceID, userID,
 		).First(&webhook).Error
 		if err != nil {
-			http.NotFound(w, r)
+			h.renderError(w, r, http.StatusNotFound)
 
 			return
 		}
@@ -518,7 +510,7 @@ func (h *Handlers) HandleSourceEditSubmit() http.HandlerFunc {
 			"id = ? AND user_id = ?", sourceID, userID,
 		).First(&webhook).Error
 		if err != nil {
-			http.NotFound(w, r)
+			h.renderError(w, r, http.StatusNotFound)
 
 			return
 		}
@@ -527,9 +519,7 @@ func (h *Handlers) HandleSourceEditSubmit() http.HandlerFunc {
 		// middleware, which runs before CSRF parses the form.
 		err = r.ParseForm()
 		if err != nil {
-			http.Error(
-				w, "Bad request", http.StatusBadRequest,
-			)
+			h.renderError(w, r, http.StatusBadRequest)
 
 			return
 		}
@@ -582,16 +572,18 @@ func (h *Handlers) applyWebhookEdit(
 
 	webhook.RetentionDays = retentionDays
 
-	// The archive files are renamed before the new name is saved
-	// (see delivery.Engine.RenameArchive). If either step fails,
-	// they go back to the name that is still stored.
-	err := h.renameWebhookArchives(webhook.ID, webhook.Name)
+	// A new name renames the archive files before it is saved (see
+	// delivery.Engine.Rename). If either step fails, they go back to
+	// the name that is still stored.
+	err := h.renameWebhookArchives(webhook.ID, oldName, webhook.Name)
 	if err == nil {
 		err = h.db.DB().Save(webhook).Error
 	}
 
 	if err != nil {
-		restoreErr := h.renameWebhookArchives(webhook.ID, oldName)
+		restoreErr := h.renameWebhookArchives(
+			webhook.ID, webhook.Name, oldName,
+		)
 		if restoreErr != nil {
 			h.log.Error(
 				"failed to rename archives back",
@@ -600,7 +592,21 @@ func (h *Handlers) applyWebhookEdit(
 			)
 		}
 
-		h.serverError(w, "failed to update webhook", err)
+		if errors.Is(err, delivery.ErrArchiveNameTaken) {
+			data := map[string]any{
+				tmplKeyWebhook: webhook,
+				tmplKeyError: "Not saved: " + err.Error() +
+					". Move that file out of the data directory, " +
+					"then save again.",
+			}
+
+			w.WriteHeader(http.StatusConflict)
+			h.renderTemplate(w, r, "source_edit.html", data)
+
+			return
+		}
+
+		h.serverError(w, r, "failed to update webhook", err)
 
 		return
 	}
@@ -630,7 +636,7 @@ func (h *Handlers) HandleSourceDelete() http.HandlerFunc {
 			"id = ? AND user_id = ?", sourceID, userID,
 		).First(&webhook).Error
 		if err != nil {
-			http.NotFound(w, r)
+			h.renderError(w, r, http.StatusNotFound)
 
 			return
 		}
@@ -657,7 +663,7 @@ func (h *Handlers) deleteWebhookResources(
 	// be removed by hand; deleted history cannot be recovered.
 	err := h.commitWebhookDeletion(&webhook)
 	if err != nil {
-		h.serverError(w, "failed to delete webhook", err)
+		h.serverError(w, r, "failed to delete webhook", err)
 
 		return
 	}
@@ -683,7 +689,7 @@ func (h *Handlers) deleteWebhookResources(
 		// redirecting as though everything succeeded: the file
 		// needs removing by hand, and the logged error names it.
 		h.serverError(
-			w, "failed to delete webhook event database", err,
+			w, r, "failed to delete webhook event database", err,
 		)
 
 		return
@@ -766,12 +772,13 @@ func (h *Handlers) evictTargetArchiveWriter(targetID string) {
 }
 
 // renameWebhookArchives renames the archive file of every database
-// target of a webhook for the webhook name webhookName, keeping
-// each target's own name. It stops at the first failure.
+// target of a webhook from the webhook name oldName to newName,
+// keeping each target's own name. It does nothing when the name is
+// unchanged, and stops at the first failure.
 func (h *Handlers) renameWebhookArchives(
-	webhookID, webhookName string,
+	webhookID, oldName, newName string,
 ) error {
-	if h.archives == nil {
+	if h.archives == nil || oldName == newName {
 		return nil
 	}
 
@@ -788,8 +795,8 @@ func (h *Handlers) renameWebhookArchives(
 	}
 
 	for i := range targets {
-		err = h.archives.RenameArchive(
-			targets[i].ID, webhookName, targets[i].Name,
+		err = h.archives.Rename(
+			targets[i].ID, newName, targets[i].Name,
 		)
 		if err != nil {
 			return err
@@ -834,7 +841,7 @@ func (h *Handlers) ownedWebhook(
 		"id = ? AND user_id = ?", sourceID, userID,
 	).First(&webhook).Error
 	if err != nil {
-		http.NotFound(w, r)
+		h.renderError(w, r, http.StatusNotFound)
 
 		return database.Webhook{}, false
 	}
@@ -856,7 +863,7 @@ func (h *Handlers) HandleSourceLogs() http.HandlerFunc {
 			// Without the map every delivery renders through a
 			// zero redactor, so failing the page is the only
 			// safe answer.
-			h.serverError(w, "failed to load targets", err)
+			h.serverError(w, r, "failed to load targets", err)
 
 			return
 		}
@@ -864,7 +871,7 @@ func (h *Handlers) HandleSourceLogs() http.HandlerFunc {
 		page := h.parsePage(r)
 
 		evts, total, ok := h.loadEventsWithDeliveries(
-			w, webhook, targets, page,
+			w, r, webhook, targets, page,
 		)
 		if !ok {
 			return
@@ -974,6 +981,7 @@ func (h *Handlers) parsePage(r *http.Request) int {
 // caller must then render nothing further.
 func (h *Handlers) loadEventsWithDeliveries(
 	w http.ResponseWriter,
+	r *http.Request,
 	webhook database.Webhook,
 	targetMap map[string]eventLogTarget,
 	page int,
@@ -987,7 +995,7 @@ func (h *Handlers) loadEventsWithDeliveries(
 	webhookDB, err := h.dbMgr.GetDB(webhook.ID)
 	if err != nil {
 		h.serverError(
-			w, "failed to get webhook database", err,
+			w, r, "failed to get webhook database", err,
 		)
 
 		return nil, 0, false
@@ -1024,7 +1032,7 @@ func (h *Handlers) loadEventsWithDeliveries(
 	)
 	if err != nil {
 		h.serverError(
-			w, "failed to load delivery attempts", err,
+			w, r, "failed to load delivery attempts", err,
 		)
 
 		return nil, 0, false
@@ -1033,7 +1041,7 @@ func (h *Handlers) loadEventsWithDeliveries(
 	resubmits, err := resubmitCounts(webhookDB, eventIDs)
 	if err != nil {
 		h.serverError(
-			w, "failed to count event resubmissions", err,
+			w, r, "failed to count event resubmissions", err,
 		)
 
 		return nil, 0, false
@@ -1256,7 +1264,7 @@ func (h *Handlers) HandleEntrypointCreate() http.HandlerFunc {
 			"id = ? AND user_id = ?", sourceID, userID,
 		).First(&webhook).Error
 		if err != nil {
-			http.NotFound(w, r)
+			h.renderError(w, r, http.StatusNotFound)
 
 			return
 		}
@@ -1265,9 +1273,7 @@ func (h *Handlers) HandleEntrypointCreate() http.HandlerFunc {
 		// middleware, which runs before CSRF parses the form.
 		err = r.ParseForm()
 		if err != nil {
-			http.Error(
-				w, "Bad request", http.StatusBadRequest,
-			)
+			h.renderError(w, r, http.StatusBadRequest)
 
 			return
 		}
@@ -1283,7 +1289,7 @@ func (h *Handlers) HandleEntrypointCreate() http.HandlerFunc {
 
 		err = h.db.DB().Create(entrypoint).Error
 		if err != nil {
-			h.serverError(w, "failed to create entrypoint", err)
+			h.serverError(w, r, "failed to create entrypoint", err)
 
 			return
 		}
@@ -1314,7 +1320,7 @@ func (h *Handlers) HandleTargetCreate() http.HandlerFunc {
 			"id = ? AND user_id = ?", sourceID, userID,
 		).First(&webhook).Error
 		if err != nil {
-			http.NotFound(w, r)
+			h.renderError(w, r, http.StatusNotFound)
 
 			return
 		}
@@ -1323,9 +1329,7 @@ func (h *Handlers) HandleTargetCreate() http.HandlerFunc {
 		// middleware, which runs before CSRF parses the form.
 		err = r.ParseForm()
 		if err != nil {
-			http.Error(
-				w, "Bad request", http.StatusBadRequest,
-			)
+			h.renderError(w, r, http.StatusBadRequest)
 
 			return
 		}
@@ -1396,7 +1400,7 @@ func (h *Handlers) processTargetCreate(
 
 	err = h.db.DB().Create(target).Error
 	if err != nil {
-		h.serverError(w, "failed to create target", err)
+		h.serverError(w, r, "failed to create target", err)
 
 		return
 	}
@@ -1490,7 +1494,7 @@ func (h *Handlers) buildTargetConfig(
 	case database.TargetTypeSlack:
 		return h.buildSlackTargetConfig(w, r, in.URL)
 	case database.TargetTypeDatabase:
-		return h.buildDatabaseTargetConfig(w, in.Expiry)
+		return h.buildDatabaseTargetConfig(w, r, in.Expiry)
 	case database.TargetTypeLog:
 		return "", nil
 	default:
@@ -1540,7 +1544,7 @@ func (h *Handlers) buildHTTPTargetConfig(
 		return "", err
 	}
 
-	return marshalTargetConfig(w, delivery.HTTPTargetConfig{
+	return h.marshalTargetConfig(w, r, delivery.HTTPTargetConfig{
 		URL:     in.URL,
 		Headers: headers,
 		Timeout: timeout,
@@ -1562,7 +1566,7 @@ func (h *Handlers) buildSlackTargetConfig(
 		return "", err
 	}
 
-	return marshalTargetConfig(w, delivery.SlackTargetConfig{
+	return h.marshalTargetConfig(w, r, delivery.SlackTargetConfig{
 		WebhookURL: targetURL,
 	})
 }
@@ -1602,11 +1606,22 @@ func (h *Handlers) validateTargetURL(
 			"url", delivery.MaskURL(targetURL),
 			"error", err,
 		)
-		http.Error(
-			w,
-			"Invalid target URL: "+err.Error(),
-			http.StatusBadRequest,
-		)
+
+		msg := "Invalid target URL: " + err.Error()
+
+		// Only a private or reserved address's refusal says how
+		// to allow it. Metadata refusals never do: link-local and
+		// the other unconditional metadata addresses cannot be
+		// opened, and the default blocklist's public addresses,
+		// which listing does open, hand out credentials.
+		if errors.Is(err, delivery.ErrBlockedPrivateOrReservedIP) {
+			msg += ". Private and reserved addresses are refused " +
+				"by default; the server's ALLOWED_EGRESS_CIDRS " +
+				"setting allows named networks (see \"Allowing " +
+				"egress to your own network\" in the README)."
+		}
+
+		http.Error(w, msg, http.StatusBadRequest)
 
 		return err
 	}
@@ -1616,16 +1631,14 @@ func (h *Handlers) validateTargetURL(
 
 // marshalTargetConfig serialises a target configuration for storage,
 // writing a 500 itself if it cannot.
-func marshalTargetConfig(
+func (h *Handlers) marshalTargetConfig(
 	w http.ResponseWriter,
+	r *http.Request,
 	cfg any,
 ) (string, error) {
 	configBytes, err := json.Marshal(cfg)
 	if err != nil {
-		http.Error(
-			w, "Internal server error",
-			http.StatusInternalServerError,
-		)
+		h.serverError(w, r, "failed to encode target config", err)
 
 		return "", err
 	}
@@ -1641,6 +1654,7 @@ func marshalTargetConfig(
 // expiry yields an empty config (the keep-forever default).
 func (h *Handlers) buildDatabaseTargetConfig(
 	w http.ResponseWriter,
+	r *http.Request,
 	expiry string,
 ) (string, error) {
 	expiry = strings.TrimSpace(expiry)
@@ -1659,8 +1673,8 @@ func (h *Handlers) buildDatabaseTargetConfig(
 		return "", err
 	}
 
-	return marshalTargetConfig(
-		w, map[string]any{"expiry": expiry},
+	return h.marshalTargetConfig(
+		w, r, map[string]any{"expiry": expiry},
 	)
 }
 
@@ -1713,7 +1727,7 @@ func (h *Handlers) deleteChildResource(
 			"id = ? AND user_id = ?", sourceID, userID,
 		).First(&webhook).Error
 		if err != nil {
-			http.NotFound(w, r)
+			h.renderError(w, r, http.StatusNotFound)
 
 			return
 		}
@@ -1723,11 +1737,7 @@ func (h *Handlers) deleteChildResource(
 			childID, webhook.ID,
 		).Delete(model)
 		if result.Error != nil {
-			h.log.Error(errMsg, "error", result.Error)
-			http.Error(
-				w, "Internal server error",
-				http.StatusInternalServerError,
-			)
+			h.serverError(w, r, errMsg, result.Error)
 
 			return
 		}
@@ -1819,18 +1829,14 @@ func (h *Handlers) toggleChildResource(
 			"id = ? AND user_id = ?", sourceID, userID,
 		).First(&webhook).Error
 		if err != nil {
-			http.NotFound(w, r)
+			h.renderError(w, r, http.StatusNotFound)
 
 			return
 		}
 
 		err = toggleFn(webhook.ID, childID)
 		if err != nil {
-			h.log.Error(errMsg, "error", err)
-			http.Error(
-				w, "Internal server error",
-				http.StatusInternalServerError,
-			)
+			h.serverError(w, r, errMsg, err)
 
 			return
 		}

internal/handlers/source_management_test.go

@@ -505,8 +505,9 @@ func TestHandleSourceEditSubmit_EmptyRetentionLeavesValueUnchanged(
 // renamedWebhookName is the name the rename tests give a webhook.
 const renamedWebhookName = "Renamed"
 
-// TestHandleSourceEditSubmit_RenamesArchives proves that renaming a
-// webhook renames the archive of each of its database targets, and
+// TestHandleSourceEditSubmit_RenamesArchives proves that a save
+// that keeps the webhook's name renames nothing, and that renaming a
+// webhook renames the archive of each of its database targets and
 // asks nothing of its other targets.
 func TestHandleSourceEditSubmit_RenamesArchives(t *testing.T) {
 	t.Parallel()
@@ -517,9 +518,13 @@ func TestHandleSourceEditSubmit_RenamesArchives(t *testing.T) {
 	second := seedTarget(t, env.db, wh.ID, database.TargetTypeDatabase)
 	seedTarget(t, env.db, wh.ID, database.TargetTypeLog)
 
+	w := submitEdit(t, env, wh, "")
+	require.Equal(t, http.StatusSeeOther, w.Code)
+	assert.Empty(t, env.archives.Renames())
+
 	wh.Name = renamedWebhookName
 
-	w := submitEdit(t, env, wh, "")
+	w = submitEdit(t, env, wh, "")
 	require.Equal(t, http.StatusSeeOther, w.Code)
 
 	assert.ElementsMatch(
@@ -570,6 +575,33 @@ func TestHandleSourceEditSubmit_FailedRenameKeepsTheName(
 	)
 }
 
+// TestHandleSourceEditSubmit_ArchiveNameTaken proves that when a file
+// already has an archive's new name, the edit is refused with an
+// error naming that file, and the webhook keeps its stored name.
+func TestHandleSourceEditSubmit_ArchiveNameTaken(t *testing.T) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+	wh := seedWebhookWithRetention(t, env.db, 7)
+	seedTarget(t, env.db, wh.ID, database.TargetTypeDatabase)
+
+	env.archives.FailRenames(errNameTaken)
+
+	oldName := wh.Name
+	wh.Name = renamedWebhookName
+
+	w := submitEdit(t, env, wh, "")
+	require.Equal(t, http.StatusConflict, w.Code)
+	assert.Contains(t, w.Body.String(), "archive-taken.db")
+
+	var stored database.Webhook
+
+	require.NoError(
+		t, env.db.DB().First(&stored, "id = ?", wh.ID).Error,
+	)
+	assert.Equal(t, oldName, stored.Name)
+}
+
 // TestSourceEditForm_ForeverWebhookRoundTrips walks the exact path that
 // the removed max="365" cap used to break: render the edit form for a
 // retain-forever webhook, confirm the pre-filled sentinel is not capped

internal/handlers/target_edit.go

@@ -1,6 +1,7 @@
 package handlers
 
 import (
+	"errors"
 	"net/http"
 
 	"github.com/go-chi/chi"
@@ -88,9 +89,7 @@ func (h *Handlers) HandleTargetEditSubmit() http.HandlerFunc {
 		// middleware, which runs before CSRF parses the form.
 		err := r.ParseForm()
 		if err != nil {
-			http.Error(
-				w, "Bad request", http.StatusBadRequest,
-			)
+			h.renderError(w, r, http.StatusBadRequest)
 
 			return
 		}
@@ -156,17 +155,17 @@ func (h *Handlers) applyTargetEdit(
 	target.Name = name
 	target.Config = configJSON
 
-	// The archive file is renamed before the new name is saved (see
-	// delivery.Engine.RenameArchive). If either step fails, it goes
-	// back to the name that is still stored.
-	err = h.renameTargetArchive(target, webhook.Name, name)
+	// A new name renames the archive file before it is saved (see
+	// delivery.Engine.Rename). If either step fails, it goes back to
+	// the name that is still stored.
+	err = h.renameTargetArchive(target, webhook.Name, oldName, name)
 	if err == nil {
 		err = h.db.DB().Save(target).Error
 	}
 
 	if err != nil {
 		restoreErr := h.renameTargetArchive(
-			target, webhook.Name, oldName,
+			target, webhook.Name, name, oldName,
 		)
 		if restoreErr != nil {
 			h.log.Error(
@@ -176,7 +175,19 @@ func (h *Handlers) applyTargetEdit(
 			)
 		}
 
-		h.serverError(w, "failed to update target", err)
+		if errors.Is(err, delivery.ErrArchiveNameTaken) {
+			http.Error(
+				w,
+				"Not saved: "+err.Error()+
+					". Move that file out of the data directory, "+
+					"then save again.",
+				http.StatusConflict,
+			)
+
+			return
+		}
+
+		h.serverError(w, r, "failed to update target", err)
 
 		return
 	}
@@ -186,21 +197,19 @@ func (h *Handlers) applyTargetEdit(
 	)
 }
 
-// renameTargetArchive renames a database target's archive file for
-// the given webhook and target names. Other target types have no
-// archive.
+// renameTargetArchive renames a database target's archive file from
+// the target name oldName to newName. It does nothing when the name
+// is unchanged; other target types have no archive.
 func (h *Handlers) renameTargetArchive(
 	target *database.Target,
-	webhookName, targetName string,
+	webhookName, oldName, newName string,
 ) error {
-	if h.archives == nil ||
+	if h.archives == nil || oldName == newName ||
 		target.Type != database.TargetTypeDatabase {
 		return nil
 	}
 
-	return h.archives.RenameArchive(
-		target.ID, webhookName, targetName,
-	)
+	return h.archives.Rename(target.ID, webhookName, newName)
 }
 
 // renderTargetEdit renders the target edit page with an optional
@@ -256,7 +265,7 @@ func (h *Handlers) ownedTarget(
 		chi.URLParam(r, "targetID"), webhook.ID,
 	).First(&target).Error
 	if err != nil {
-		http.NotFound(w, r)
+		h.renderError(w, r, http.StatusNotFound)
 
 		return database.Webhook{}, nil, false
 	}

internal/handlers/target_edit_test.go

@@ -636,27 +636,38 @@ func assertWebhookOfAnotherUser404s(
 	assert.Equal(t, http.StatusNotFound, w.Code)
 }
 
+// renamedTargetName is the name the rename tests give a target.
+const renamedTargetName = "Long Term"
+
 // TestHandleTargetEditSubmit_RenamesArchive proves that renaming a
-// database target renames its archive, that a target of another type
-// has no archive to rename, and that a target whose archive cannot be
-// renamed keeps its stored name.
+// database target renames its archive, that a save that keeps the
+// name renames nothing, that a target of another type has no archive
+// to rename, and that a target whose archive cannot be renamed keeps
+// its stored name. When a file already has the archive's new name,
+// the edit is refused with an error naming that file.
 func TestHandleTargetEditSubmit_RenamesArchive(t *testing.T) {
 	t.Parallel()
 
 	env := setupSourceTest(t)
 	wh := seedWebhookWithRetention(t, env.db, 7)
 	archive := seedTarget(t, env.db, wh.ID, database.TargetTypeDatabase)
+	rename := url.Values{"name": {renamedTargetName}}
 
-	w := submitTargetEdit(
-		env, wh.ID, archive.ID, url.Values{"name": {"Long Term"}},
-	)
+	w := submitTargetEdit(env, wh.ID, archive.ID, rename)
 	require.Equal(t, http.StatusSeeOther, w.Code, w.Body.String())
 	assert.Equal(
 		t,
-		[]archiveRename{{archive.ID, wh.Name, "Long Term"}},
+		[]archiveRename{{archive.ID, wh.Name, renamedTargetName}},
 		env.archives.Renames(),
 	)
 
+	w = submitTargetEdit(env, wh.ID, archive.ID, rename)
+	require.Equal(t, http.StatusSeeOther, w.Code, w.Body.String())
+	assert.Len(
+		t, env.archives.Renames(), 1,
+		"a save that keeps the name renames nothing",
+	)
+
 	httpWebhook, httpTarget := seedHTTPTarget(t, env, "", "")
 
 	w = submitTargetEdit(
@@ -669,14 +680,23 @@ func TestHandleTargetEditSubmit_RenamesArchive(t *testing.T) {
 		"an HTTP target has no archive to rename",
 	)
 
+	again := url.Values{"name": {"Again"}}
+
 	env.archives.FailRenames(errInjectedRename)
 
-	w = submitTargetEdit(
-		env, wh.ID, archive.ID, url.Values{"name": {"Again"}},
-	)
+	w = submitTargetEdit(env, wh.ID, archive.ID, again)
 	require.Equal(t, http.StatusInternalServerError, w.Code)
 	assert.Equal(
-		t, "Long Term", storedTarget(t, env, archive.ID).Name,
+		t, renamedTargetName, storedTarget(t, env, archive.ID).Name,
 		"a target whose archive was not renamed keeps its name",
 	)
+
+	env.archives.FailRenames(errNameTaken)
+
+	w = submitTargetEdit(env, wh.ID, archive.ID, again)
+	require.Equal(t, http.StatusConflict, w.Code)
+	assert.Contains(t, w.Body.String(), "archive-taken.db")
+	assert.Equal(
+		t, renamedTargetName, storedTarget(t, env, archive.ID).Name,
+	)
 }

internal/handlers/target_private_refusal_test.go

@@ -0,0 +1,116 @@
+package handlers_test
+
+import (
+	"net/http"
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/webhooker/internal/database"
+)
+
+// privateRefusalHint is the sentence that tells an operator a private
+// destination is refused on purpose, and how to allow one.
+const privateRefusalHint = "Private and reserved addresses are " +
+	"refused by default; the server's ALLOWED_EGRESS_CIDRS setting " +
+	"allows named networks (see \"Allowing egress to your own " +
+	"network\" in the README)."
+
+// TestTargetRefusal_PrivateDestinationSaysHowToAllowIt covers both
+// target types that take a URL, on add and on edit.
+func TestTargetRefusal_PrivateDestinationSaysHowToAllowIt(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+
+	targetTypes := []database.TargetType{
+		database.TargetTypeHTTP,
+		database.TargetTypeSlack,
+	}
+
+	for _, targetType := range targetTypes {
+		t.Run(string(targetType), func(t *testing.T) {
+			t.Parallel()
+
+			webhook := seedWebhookWithRetention(t, env.db, 30)
+			targetsPath := "/hook/" + webhook.ID + "/targets"
+
+			form := url.Values{}
+			form.Set("name", "private")
+			form.Set("type", string(targetType))
+			form.Set("url", editBlockedURL)
+
+			added := serveTarget(
+				env, http.MethodPost, targetsPath, form,
+			)
+			assert.Equal(t, http.StatusBadRequest, added.Code)
+			assert.Contains(
+				t, added.Body.String(), privateRefusalHint,
+			)
+
+			form.Set("url", editOriginalURL)
+
+			created := serveTarget(
+				env, http.MethodPost, targetsPath, form,
+			)
+			require.Equal(
+				t, http.StatusSeeOther, created.Code,
+				created.Body.String(),
+			)
+
+			targets := targetsForWebhook(t, env.db, webhook.ID)
+			require.Len(t, targets, 1)
+
+			form.Set("url", editBlockedURL)
+
+			edited := submitTargetEdit(
+				env, webhook.ID, targets[0].ID, form,
+			)
+			assert.Equal(t, http.StatusBadRequest, edited.Code)
+			assert.Contains(
+				t, edited.Body.String(), privateRefusalHint,
+			)
+		})
+	}
+}
+
+// TestTargetRefusal_MetadataDestinationDoesNotSayHowToAllowIt: no
+// setting opens a link-local address, and Azure's WireServer hands out
+// VM credentials, so neither refusal points at the setting.
+func TestTargetRefusal_MetadataDestinationDoesNotSayHowToAllowIt(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	env := setupSourceTest(t)
+
+	metadataURLs := map[string]string{
+		"link-local": "http://169.254.169.254/latest/meta-data/",
+		"wireserver": "http://168.63.129.16/?comp=versions",
+	}
+
+	for name, metadataURL := range metadataURLs {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			webhook := seedWebhookWithRetention(t, env.db, 30)
+
+			form := url.Values{}
+			form.Set("name", "metadata")
+			form.Set("type", string(database.TargetTypeHTTP))
+			form.Set("url", metadataURL)
+
+			w := serveTarget(
+				env, http.MethodPost,
+				"/hook/"+webhook.ID+"/targets", form,
+			)
+			assert.Equal(t, http.StatusBadRequest, w.Code)
+			assert.NotContains(
+				t, w.Body.String(), privateRefusalHint,
+			)
+		})
+	}
+}

internal/handlers/webhook.go

@@ -88,14 +88,14 @@ func (h *Handlers) processWebhookRequest(
 
 	headersJSON, err := json.Marshal(r.Header)
 	if err != nil {
-		h.serverError(w, "failed to serialize headers", err)
+		h.receiverError(w, "failed to serialize headers", err)
 
 		return
 	}
 
 	targets, err := h.loadActiveTargets(entrypoint.WebhookID)
 	if err != nil {
-		h.serverError(w, "failed to query targets", err)
+		h.receiverError(w, "failed to query targets", err)
 
 		return
 	}
@@ -196,7 +196,7 @@ func (h *Handlers) createAndDeliverEvent(
 		targets,
 	)
 	if err != nil {
-		h.serverError(w, "failed to store webhook event", err)
+		h.receiverError(w, "failed to store webhook event", err)
 
 		return
 	}
@@ -204,6 +204,19 @@ func (h *Handlers) createAndDeliverEvent(
 	h.finishWebhookResponse(w, event, entrypoint, tasks)
 }
 
+// receiverError logs an error and answers the sender with a plain-text
+// 500. The receiver's answers are for programs, so it never sends the
+// error page the web UI uses.
+func (h *Handlers) receiverError(
+	w http.ResponseWriter, msg string, err error,
+) {
+	h.log.Error(msg, "error", err)
+	http.Error(
+		w, "Internal server error",
+		http.StatusInternalServerError,
+	)
+}
+
 // eventSource carries the fields a new event is built from. The
 // receiver fills it from the live request; the resubmit handler fills
 // it from a stored event. Both then go through createAndFanOut, so an

internal/middleware/csrf.go

@@ -19,7 +19,7 @@ func CSRFToken(r *http.Request) string {
 // key to sign a CSRF cookie and validates a masked token submitted via
 // the "csrf_token" form field (or the "X-CSRF-Token" header) on
 // POST/PUT/PATCH/DELETE requests. Requests with an invalid or missing
-// token receive a 403 Forbidden response.
+// token are logged and answered by forbidden, which must write the 403.
 //
 // The middleware detects the client-facing transport protocol
 // per-request via reqtls.IsTLS, the single TLS predicate the session
@@ -36,7 +36,9 @@ func CSRFToken(r *http.Request) string {
 // Two gorilla/csrf instances are maintained — one with Secure cookies
 // (for TLS) and one without (for plaintext HTTP) — because the
 // csrf.Secure option is set at creation time, not per-request.
-func (m *Middleware) CSRF() func(http.Handler) http.Handler {
+func (m *Middleware) CSRF(
+	forbidden http.Handler,
+) func(http.Handler) http.Handler {
 	csrfErrorHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		// CSRF is registered ahead of RequireAuth on every route
 		// group that uses it, so this WARN is reachable by an
@@ -57,7 +59,7 @@ func (m *Middleware) CSRF() func(http.Handler) http.Handler {
 			"remote_addr", r.RemoteAddr,
 			"reason", csrf.FailureReason(r),
 		)
-		http.Error(w, "Forbidden - invalid CSRF token", http.StatusForbidden)
+		forbidden.ServeHTTP(w, r)
 	})
 
 	key := m.session.GetKey()

internal/middleware/csrf_test.go

@@ -18,6 +18,12 @@ import (
 // csrfCookieName is the gorilla/csrf cookie name.
 const csrfCookieName = "_gorilla_csrf"
 
+// forbidden stands in for the error page the server hands CSRF to
+// answer a refused request with.
+func forbidden(w http.ResponseWriter, _ *http.Request) {
+	w.WriteHeader(http.StatusForbidden)
+}
+
 // csrfGetToken performs a GET request through the CSRF middleware
 // and returns the token and cookies.
 func csrfGetToken(
@@ -98,7 +104,7 @@ func TestCSRF_GETSetsToken(t *testing.T) {
 
 	var gotToken string
 
-	handler := m.CSRF()(http.HandlerFunc(
+	handler := m.CSRF(http.HandlerFunc(forbidden))(http.HandlerFunc(
 		func(_ http.ResponseWriter, r *http.Request) {
 			gotToken = middleware.CSRFToken(r)
 		},
@@ -120,7 +126,7 @@ func TestCSRF_POSTWithValidToken(t *testing.T) {
 	t.Parallel()
 
 	m, _ := testMiddleware(t, config.EnvironmentDev)
-	csrfMW := m.CSRF()
+	csrfMW := m.CSRF(http.HandlerFunc(forbidden))
 
 	getReq := httptest.NewRequestWithContext(
 		context.Background(),
@@ -152,7 +158,7 @@ func csrfPOSTWithoutTokenTest(
 	t.Helper()
 
 	m, _ := testMiddleware(t, env)
-	csrfMW := m.CSRF()
+	csrfMW := m.CSRF(http.HandlerFunc(forbidden))
 
 	// GET to establish the CSRF cookie
 	getHandler := csrfMW(http.HandlerFunc(
@@ -209,7 +215,7 @@ func TestCSRF_POSTWithInvalidToken(t *testing.T) {
 	t.Parallel()
 
 	m, _ := testMiddleware(t, config.EnvironmentDev)
-	csrfMW := m.CSRF()
+	csrfMW := m.CSRF(http.HandlerFunc(forbidden))
 
 	// GET to establish the CSRF cookie
 	getHandler := csrfMW(http.HandlerFunc(
@@ -265,7 +271,7 @@ func TestCSRF_GETDoesNotValidate(t *testing.T) {
 
 	var called bool
 
-	handler := m.CSRF()(http.HandlerFunc(
+	handler := m.CSRF(http.HandlerFunc(forbidden))(http.HandlerFunc(
 		func(_ http.ResponseWriter, _ *http.Request) {
 			called = true
 		},
@@ -328,7 +334,7 @@ func csrfTookStrictPath(
 	t.Helper()
 
 	m, _ := testMiddleware(t, env)
-	csrfMW := m.CSRF()
+	csrfMW := m.CSRF(http.HandlerFunc(forbidden))
 
 	newReq := func(method string) *http.Request {
 		r := httptest.NewRequestWithContext(
@@ -477,7 +483,7 @@ func TestCSRF_ProdMode_PlaintextHTTP_POSTWithValidToken(
 	t.Parallel()
 
 	m, _ := testMiddleware(t, config.EnvironmentProd)
-	csrfMW := m.CSRF()
+	csrfMW := m.CSRF(http.HandlerFunc(forbidden))
 
 	getReq := httptest.NewRequestWithContext(
 		context.Background(),
@@ -517,7 +523,7 @@ func TestCSRF_ProdMode_BehindProxy_POSTWithValidToken(
 	t.Parallel()
 
 	m, _ := testMiddleware(t, config.EnvironmentProd)
-	csrfMW := m.CSRF()
+	csrfMW := m.CSRF(http.HandlerFunc(forbidden))
 
 	getReq := httptest.NewRequestWithContext(
 		context.Background(),
@@ -562,7 +568,7 @@ func TestCSRF_ProdMode_DirectTLS_POSTWithValidToken(
 	t.Parallel()
 
 	m, _ := testMiddleware(t, config.EnvironmentProd)
-	csrfMW := m.CSRF()
+	csrfMW := m.CSRF(http.HandlerFunc(forbidden))
 
 	getReq := httptest.NewRequestWithContext(
 		context.Background(),

internal/middleware/logbound_test.go

@@ -260,7 +260,9 @@ func logSites() map[string]logSite {
 			) http.Handler {
 				t.Helper()
 
-				return m.CSRF()(unreachable(t))
+				return m.CSRF(http.HandlerFunc(forbidden))(
+					unreachable(t),
+				)
 			},
 			send:       postNoToken,
 			wantStatus: http.StatusForbidden,

internal/middleware/recoverer.go

@@ -109,7 +109,8 @@ func (w *recoverResponseWriter) Unwrap() http.ResponseWriter {
 
 // Recoverer returns middleware that turns a handler panic into one
 // structured ERROR record and a 500, rather than a dropped
-// connection.
+// connection. The 500 is page when page is not nil, and plain text
+// when it is nil or when page panics before writing anything.
 //
 // It replaces chi's middleware.Recoverer, which does neither on a
 // current Go release. chi v1.5.5's pretty-printer scans the stack for
@@ -136,9 +137,13 @@ func (w *recoverResponseWriter) Unwrap() http.ResponseWriter {
 //
 // Unlike http.Error on its own, it deletes any Set-Cookie the handler
 // set before panicking, because a request that failed must not hand
-// the client a credential; every other header is left to http.Error.
+// the client a credential. It touches no other header: when page
+// answers, every other header the handler set goes out with it, apart
+// from any page sets itself; otherwise they are left to http.Error.
 // See https://git.eeqj.de/sneak/webhooker/issues/193.
-func (s *Middleware) Recoverer() func(http.Handler) http.Handler {
+func (s *Middleware) Recoverer(
+	page http.Handler,
+) func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(
 			w http.ResponseWriter,
@@ -171,6 +176,14 @@ func (s *Middleware) Recoverer() func(http.Handler) http.Handler {
 
 				rw.Header().Del("Set-Cookie")
 
+				if page != nil {
+					s.servePage(rw, r, page)
+				}
+
+				if rw.committed {
+					return
+				}
+
 				http.Error(
 					rw,
 					http.StatusText(
@@ -185,6 +198,27 @@ func (s *Middleware) Recoverer() func(http.Handler) http.Handler {
 	}
 }
 
+// servePage answers with page. A panic in page itself is logged and
+// recovered here, so the Recoverer can still send its plain 500.
+func (s *Middleware) servePage(
+	w http.ResponseWriter,
+	r *http.Request,
+	page http.Handler,
+) {
+	defer func() {
+		rvr := recover()
+		if rvr != nil {
+			s.log.Error("error page panic",
+				"panic", logfield.Truncate(
+					fmt.Sprint(rvr), maxPanicValueBytes,
+				),
+			)
+		}
+	}()
+
+	page.ServeHTTP(w, r)
+}
+
 // logPanic writes the record. Every field it can grow is truncated to
 // a fixed budget, so MaxPanicLogLineBytes holds.
 //

internal/middleware/recoverer_test.go

@@ -76,7 +76,7 @@ func newRecovererProbe(
 	// Logging outside so the recovered 500 is the status it records.
 	router.Use(chimw.RequestID)
 	router.Use(m.Logging())
-	router.Use(m.Recoverer())
+	router.Use(m.Recoverer(nil))
 	router.Get("/probe", handler)
 
 	serverErrors := new(bytes.Buffer)
@@ -637,7 +637,7 @@ func TestRecovererKeepsResponseControllerWorking(t *testing.T) {
 
 	m, _ := capturingMiddleware(t)
 
-	handler := m.Recoverer()(http.HandlerFunc(
+	handler := m.Recoverer(nil)(http.HandlerFunc(
 		func(w http.ResponseWriter, _ *http.Request) {
 			_, _ = w.Write([]byte("chunk"))
 
@@ -672,3 +672,59 @@ func TestRecovererKeepsResponseControllerWorking(t *testing.T) {
 	assert.Equal(t, http.StatusOK, resp.StatusCode)
 	assert.Equal(t, "chunk", string(body))
 }
+
+// TestRecovererAnswersWithThePage covers a recoverer given a page:
+// the panic is logged as before, and the 500 is that page.
+func TestRecovererAnswersWithThePage(t *testing.T) {
+	t.Parallel()
+
+	m, logs := capturingMiddleware(t)
+
+	page := http.HandlerFunc(
+		func(w http.ResponseWriter, _ *http.Request) {
+			w.WriteHeader(http.StatusInternalServerError)
+			_, _ = w.Write([]byte("the error page"))
+		},
+	)
+
+	w := httptest.NewRecorder()
+	m.Recoverer(page)(http.HandlerFunc(panicProbe)).ServeHTTP(
+		w, httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, "/", nil,
+		),
+	)
+
+	assert.Equal(t, http.StatusInternalServerError, w.Code)
+	assert.Equal(t, "the error page", w.Body.String())
+	assert.Contains(t, logs.String(), `"msg":"handler panic"`)
+	assert.Contains(t, logs.String(), panicMarker)
+}
+
+// TestRecovererFallsBackWhenThePagePanics covers a page that panics
+// before writing anything: both panics are logged, and the client
+// still gets the plain 500.
+func TestRecovererFallsBackWhenThePagePanics(t *testing.T) {
+	t.Parallel()
+
+	m, logs := capturingMiddleware(t)
+
+	const pagePanic = "QQERRORPAGEPANICQQ"
+
+	page := http.HandlerFunc(
+		func(http.ResponseWriter, *http.Request) {
+			panic(pagePanic)
+		},
+	)
+
+	w := httptest.NewRecorder()
+	m.Recoverer(page)(http.HandlerFunc(panicProbe)).ServeHTTP(
+		w, httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, "/", nil,
+		),
+	)
+
+	assert.Equal(t, http.StatusInternalServerError, w.Code)
+	assert.Equal(t, "Internal Server Error\n", w.Body.String())
+	assert.Contains(t, logs.String(), panicMarker)
+	assert.Contains(t, logs.String(), pagePanic)
+}

internal/resetpw/resetpw_test.go

@@ -137,7 +137,7 @@ func (n *noopArchives) EvictWebhook(string) {}
 
 func (n *noopArchives) EvictTarget(string) {}
 
-func (n *noopArchives) RenameArchive(_, _, _ string) error {
+func (n *noopArchives) Rename(_, _, _ string) error {
 	return nil
 }
 

internal/server/error_page_test.go

@@ -0,0 +1,222 @@
+package server_test
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strconv"
+	"testing"
+
+	"github.com/getsentry/sentry-go"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sneak.berlin/go/webhooker/internal/config"
+	"sneak.berlin/go/webhooker/internal/server"
+)
+
+// The link back the error page offers: to the webhook list for a
+// signed-in user, to sign-in for anyone else.
+const (
+	backToWebhooks = `<a href="/hooks" class="btn-secondary">` +
+		`Back to webhooks</a>`
+	backToSignIn = `<a href="/pages/login" class="btn-primary">` +
+		`Sign in</a>`
+)
+
+// assertErrorPage checks that w is the error page for status, in the
+// normal layout, offering link.
+func assertErrorPage(
+	t *testing.T,
+	w *httptest.ResponseRecorder,
+	status int,
+	link string,
+) {
+	t.Helper()
+
+	body := w.Body.String()
+
+	assert.Equal(t, status, w.Code)
+	assert.Equal(
+		t, "text/html; charset=utf-8", w.Header().Get("Content-Type"),
+	)
+	assert.Equal(t, "no-store", w.Header().Get("Cache-Control"))
+	assert.Contains(t, body, `<nav class="app-bar"`)
+	assert.Contains(
+		t, body, strconv.Itoa(status)+" "+http.StatusText(status),
+	)
+	assert.Contains(t, body, link)
+}
+
+func TestErrorPage_DeletedWebhook(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	userID, _ := env.seedUser(t, "owner", "somepassword")
+	cookies := env.authCookies(t, userID, "owner")
+
+	wh := env.seedWebhook(t, userID)
+	require.NoError(t, env.db.DB().Delete(wh).Error)
+
+	w := env.get("/hook/"+wh.ID, cookies)
+
+	assertErrorPage(t, w, http.StatusNotFound, backToWebhooks)
+}
+
+func TestErrorPage_DeletedTarget(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	userID, _ := env.seedUser(t, "owner", "somepassword")
+	cookies := env.authCookies(t, userID, "owner")
+
+	wh := env.seedWebhook(t, userID)
+	tgt := env.seedTarget(t, wh.ID)
+	require.NoError(t, env.db.DB().Delete(tgt).Error)
+
+	w := env.get(
+		"/hook/"+wh.ID+"/targets/"+tgt.ID+"/edit", cookies,
+	)
+
+	assertErrorPage(t, w, http.StatusNotFound, backToWebhooks)
+}
+
+func TestErrorPage_UnknownPath(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	userID, _ := env.seedUser(t, "owner", "somepassword")
+	cookies := env.authCookies(t, userID, "owner")
+
+	assertErrorPage(
+		t, env.get("/no-such-page", nil),
+		http.StatusNotFound, backToSignIn,
+	)
+
+	// Outside every route group there is no form token, so the
+	// page leaves out the logout form rather than offer one that
+	// would be refused.
+	w := env.get("/no-such-page", cookies)
+	assertErrorPage(t, w, http.StatusNotFound, backToWebhooks)
+	assert.NotContains(t, w.Body.String(), `action="/pages/logout"`)
+
+	// Inside a route group the page has a token, and logout works.
+	wh := env.seedWebhook(t, userID)
+	w = env.get("/hook/"+wh.ID+"/no-such-page", cookies)
+	assertErrorPage(t, w, http.StatusNotFound, backToWebhooks)
+	assert.Contains(t, w.Body.String(), `action="/pages/logout"`)
+}
+
+func TestErrorPage_BadCSRFToken(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	form := url.Values{}
+	form.Set("username", "someone")
+	form.Set("password", "irrelevant")
+	form.Set("csrf_token", "not-a-token")
+
+	assertErrorPage(
+		t, env.post("/pages/login", form, nil),
+		http.StatusForbidden, backToSignIn,
+	)
+
+	userID, _ := env.seedUser(t, "owner", "somepassword")
+	cookies := env.authCookies(t, userID, "owner")
+	wh := env.seedWebhook(t, userID)
+
+	edit := url.Values{}
+	edit.Set("name", "renamed")
+
+	assertErrorPage(
+		t, env.post("/hook/"+wh.ID+"/edit", edit, cookies),
+		http.StatusForbidden, backToWebhooks,
+	)
+}
+
+// TestErrorPage_PanicOnAdminPage sends a panicking handler in an
+// admin page route group through the real router, with error
+// tracking on: the client gets the 500 error page, and the tracker
+// still gets the panic, once. The same panic outside the admin page
+// route groups keeps the plain 500.
+func TestErrorPage_PanicOnAdminPage(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	transport := &captureTransport{}
+
+	opts := server.SentryClientOptionsForTest(
+		"https://public@sentry.invalid/1", "webhooker-test",
+	)
+	opts.Transport = transport
+
+	client, err := sentry.NewClient(opts)
+	require.NoError(t, err)
+
+	serve := func(router http.Handler, path string) *httptest.ResponseRecorder {
+		req := httptest.NewRequestWithContext(
+			sentry.SetHubOnContext(
+				context.Background(),
+				sentry.NewHub(client, sentry.NewScope()),
+			),
+			http.MethodGet, path, nil,
+		)
+
+		w := httptest.NewRecorder()
+		router.ServeHTTP(w, req)
+
+		return w
+	}
+
+	w := serve(
+		server.NewRouterWithPageProbeForTest(
+			env.log.Get(), env.cfg, env.mw, env.hnd,
+			true, panicProbeHandler,
+		),
+		server.PageProbePattern,
+	)
+	assertErrorPage(t, w, http.StatusInternalServerError, backToSignIn)
+
+	w = serve(
+		server.NewRouterWithProbeForTest(
+			env.log.Get(), env.cfg, env.mw, env.hnd,
+			true, panicProbeHandler,
+		),
+		server.ProbePattern,
+	)
+	assert.Equal(t, http.StatusInternalServerError, w.Code)
+	assert.Equal(t, "Internal Server Error\n", w.Body.String())
+
+	require.Len(t, transport.events, 2)
+
+	for _, event := range transport.events {
+		assert.Contains(t, marshalEvent(t, event), panicProbeMarker)
+	}
+}
+
+// TestErrorPage_ReceiverStaysPlain pins that the error page is for
+// the web UI only: a sender posting to an entrypoint that does not
+// exist still gets the plain-text answer.
+func TestErrorPage_ReceiverStaysPlain(t *testing.T) {
+	t.Parallel()
+
+	// newTestEnv leaves the receiver rate limit at zero, which
+	// refuses every request before it reaches the receiver.
+	env := newTestEnvWithConfig(t, &config.Config{
+		DataDir:           t.TempDir(),
+		Environment:       config.EnvironmentDev,
+		ReceiverRateLimit: 10,
+	})
+
+	w := env.post(
+		"/h/0b8f3c1e-7d2a-4e6b-9f15-3a9c2d4e6f70", url.Values{}, nil,
+	)
+
+	assert.Equal(t, http.StatusNotFound, w.Code)
+	assert.Equal(t, "404 page not found\n", w.Body.String())
+}

internal/server/export_test.go

@@ -5,6 +5,7 @@ import (
 	"net/http"
 
 	"github.com/getsentry/sentry-go"
+	"github.com/go-chi/chi"
 	"sneak.berlin/go/webhooker/internal/config"
 	"sneak.berlin/go/webhooker/internal/handlers"
 	"sneak.berlin/go/webhooker/internal/middleware"
@@ -101,3 +102,39 @@ func NewRouterWithProbeForTest(
 
 	return s.router
 }
+
+// PageProbePattern is where NewRouterWithPageProbeForTest serves its
+// probe: inside the /pages route group, the admin page group a
+// request reaches without signing in.
+const PageProbePattern = "/pages/probe"
+
+// NewRouterWithPageProbeForTest is NewRouterWithProbeForTest with the
+// probe added to the /pages route group once SetupRoutes has built
+// it, so the probe runs behind that group's own middleware exactly as
+// the group's real routes do.
+func NewRouterWithPageProbeForTest(
+	log *slog.Logger,
+	cfg *config.Config,
+	mw *middleware.Middleware,
+	h *handlers.Handlers,
+	sentryEnabled bool,
+	probe http.HandlerFunc,
+) http.Handler {
+	s := &Server{
+		log:    log,
+		mw:     mw,
+		h:      h,
+		params: ServerParams{Config: cfg},
+	}
+	s.sentryEnabled.Store(sentryEnabled)
+	s.SetupRoutes()
+
+	for _, route := range s.router.Routes() {
+		pages, ok := route.SubRoutes.(chi.Router)
+		if ok && route.Pattern == "/pages/*" {
+			pages.Get("/probe", probe)
+		}
+	}
+
+	return s.router
+}

internal/server/routes.go

@@ -15,9 +15,10 @@ import (
 // bytes) for form POST endpoints. 1 MB is generous for any form
 // submission while preventing abuse from oversized payloads.
 //
-// Every route group below installs MaxBodySize(maxFormBodySize) as
-// its FIRST middleware, ahead of both CSRF and RequireAuth. Both
-// orderings are deliberate.
+// The four admin page route groups below (/pages, /user/{username},
+// /hooks and /hook/{sourceID}) install MaxBodySize(maxFormBodySize)
+// right after their recoverer and error reporting, ahead of both CSRF
+// and RequireAuth. Both orderings are deliberate.
 //
 // Ahead of CSRF because gorilla/csrf parses the form. The cap has to
 // be installed before anything reads the body, or the parse runs
@@ -46,6 +47,14 @@ const requestTimeout = 60 * time.Second
 // server's router.
 func (s *Server) SetupRoutes() {
 	s.router = chi.NewRouter()
+
+	// An unknown path gets the error page. Registered before the
+	// global middleware, because chi wraps a not-found handler in the
+	// middleware already on its router, which would then run twice.
+	// The route groups below wrap it in their own middleware the same
+	// way; running theirs twice is harmless.
+	s.router.NotFound(s.h.HandleErrorPage(http.StatusNotFound))
+
 	s.setupGlobalMiddleware()
 	s.setupRoutes()
 }
@@ -69,23 +78,33 @@ func (s *Server) setupGlobalMiddleware() {
 	// Panic recovery, deliberately here rather than first. It has to
 	// run inside every middleware that observes the response, so the
 	// 500 it writes is the status the access log records and the
-	// metrics count, and outside the sentryhttp handler below, whose
+	// metrics count, and outside the sentryhttp handler, whose
 	// Repanic option needs something further out to catch what it
 	// re-raises. chi's own middleware.Recoverer held the first slot
 	// until it was measured: on a current Go release it crashes
 	// inside its stack pretty-printer instead of recovering, so the
 	// connection dropped and the original panic was never reported.
 	// See https://git.eeqj.de/sneak/webhooker/issues/187.
-	s.router.Use(s.mw.Recoverer())
+	s.recoverPanics(s.router, nil)
+}
+
+// recoverPanics installs on r the recoverer, answering a panic with
+// page (a plain 500 when page is nil), and inside it the Sentry error
+// reporting (if SENTRY_DSN is set). Repanic is true so panics still
+// bubble up to the recoverer.
+//
+// Each admin page route group installs its own, with the error page,
+// as its first middleware. A panic there is logged, reported and
+// answered inside the group and never reaches the global recoverer,
+// which keeps the plain 500 for every other route.
+func (s *Server) recoverPanics(r chi.Router, page http.Handler) {
+	r.Use(s.mw.Recoverer(page))
 
-	// Sentry error reporting (if SENTRY_DSN is set). Repanic is
-	// true so panics still bubble up to the Recoverer middleware
-	// registered immediately above.
 	if s.sentryEnabled.Load() {
 		sentryHandler := sentryhttp.New(sentryhttp.Options{
 			Repanic: true,
 		})
-		s.router.Use(sentryHandler.Handle)
+		r.Use(sentryHandler.Handle)
 	}
 }
 
@@ -147,10 +166,13 @@ func (s *Server) setupRoutes() {
 
 func (s *Server) setupPageRoutes() {
 	s.router.Route("/pages", func(r chi.Router) {
+		s.recoverPanics(
+			r, s.h.HandleErrorPage(http.StatusInternalServerError),
+		)
 		// MaxBodySize precedes CSRF and RequireAuth deliberately;
 		// see maxFormBodySize for why, and for what it costs.
 		r.Use(s.mw.MaxBodySize(maxFormBodySize))
-		r.Use(s.mw.CSRF())
+		r.Use(s.mw.CSRF(s.h.HandleErrorPage(http.StatusForbidden)))
 		r.Use(s.mw.NoCache())
 
 		// The login POST carries no pre-emptive rate limiter. Behind
@@ -169,10 +191,13 @@ func (s *Server) setupPageRoutes() {
 
 func (s *Server) setupUserRoutes() {
 	s.router.Route("/user/{username}", func(r chi.Router) {
+		s.recoverPanics(
+			r, s.h.HandleErrorPage(http.StatusInternalServerError),
+		)
 		// MaxBodySize precedes CSRF and RequireAuth deliberately;
 		// see maxFormBodySize for why, and for what it costs.
 		r.Use(s.mw.MaxBodySize(maxFormBodySize))
-		r.Use(s.mw.CSRF())
+		r.Use(s.mw.CSRF(s.h.HandleErrorPage(http.StatusForbidden)))
 		r.Use(s.mw.NoCache())
 		r.Use(s.mw.RequireAuth())
 		r.Get("/", s.h.HandleProfile())
@@ -184,10 +209,13 @@ func (s *Server) setupUserRoutes() {
 
 func (s *Server) setupSourceRoutes() {
 	s.router.Route("/hooks", func(r chi.Router) {
+		s.recoverPanics(
+			r, s.h.HandleErrorPage(http.StatusInternalServerError),
+		)
 		// MaxBodySize precedes CSRF and RequireAuth deliberately;
 		// see maxFormBodySize for why, and for what it costs.
 		r.Use(s.mw.MaxBodySize(maxFormBodySize))
-		r.Use(s.mw.CSRF())
+		r.Use(s.mw.CSRF(s.h.HandleErrorPage(http.StatusForbidden)))
 		r.Use(s.mw.NoCache())
 		r.Use(s.mw.RequireAuth())
 		r.Get("/", s.h.HandleSourceList())
@@ -196,10 +224,13 @@ func (s *Server) setupSourceRoutes() {
 	})
 
 	s.router.Route("/hook/{sourceID}", func(r chi.Router) {
+		s.recoverPanics(
+			r, s.h.HandleErrorPage(http.StatusInternalServerError),
+		)
 		// MaxBodySize precedes CSRF and RequireAuth deliberately;
 		// see maxFormBodySize for why, and for what it costs.
 		r.Use(s.mw.MaxBodySize(maxFormBodySize))
-		r.Use(s.mw.CSRF())
+		r.Use(s.mw.CSRF(s.h.HandleErrorPage(http.StatusForbidden)))
 		r.Use(s.mw.NoCache())
 		r.Use(s.mw.RequireAuth())
 		r.Get("/", s.h.HandleSourceDetail())

internal/server/routes_test.go

@@ -55,7 +55,7 @@ func (e *noopArchives) EvictWebhook(string) {}
 
 func (e *noopArchives) EvictTarget(string) {}
 
-func (e *noopArchives) RenameArchive(_, _, _ string) error {
+func (e *noopArchives) Rename(_, _, _ string) error {
 	return nil
 }
 

internal/versionscript/version_script_test.go

@@ -115,8 +115,8 @@ func TestVersion_EnclosingRepositoryIsNotUsed(t *testing.T) {
 	require.Equal(t, unknown, runScript(t, inner, nil))
 }
 
-// The Docker build has no git metadata, so the version arrives as an
-// environment override. It wins over anything derivable.
+// An explicit VERSION, such as the Dockerfile's build arg, wins over
+// anything derivable.
 func TestVersion_EnvironmentOverrideWins(t *testing.T) {
 	t.Parallel()
 
@@ -128,8 +128,8 @@ func TestVersion_EnvironmentOverrideWins(t *testing.T) {
 }
 
 // An empty VERSION is treated as unset rather than stamping an empty
-// string: the Dockerfile's build arg has a non-empty default, but a
-// caller exporting VERSION= must not produce a binary reporting "".
+// string: a caller exporting VERSION= must not produce a binary
+// reporting "".
 func TestVersion_EmptyOverrideFallsBackToGit(t *testing.T) {
 	t.Parallel()
 
@@ -168,8 +168,8 @@ func TestMakefile_BuildComposesVersionAndExtraFlags(t *testing.T) {
 }
 
 // A caller can define VERSION as the empty string -- `make build
-// VERSION=`, or a `--build-arg VERSION=` reaching the Dockerfile's `make
-// build VERSION="$VERSION"`. script/version's own guard does not cover
+// VERSION=`, or the Dockerfile's `make build VERSION="$VERSION"` when no
+// VERSION build arg was given. script/version's own guard does not cover
 // that: the value never passes through the script. Stamping "" would
 // leave the binary reporting no version and the footer on "dev", which
 // is the defect this package exists for.
@@ -231,7 +231,7 @@ func TestDockerfile_BuildsThroughTheMakeTarget(t *testing.T) {
 
 	require.NotContains(t, dockerfile, "go build",
 		"a raw go build bypasses the Makefile's -X flag")
-	require.Contains(t, dockerfile, "ARG VERSION=")
+	require.Contains(t, dockerfile, "ARG VERSION")
 	require.Contains(t, dockerfile,
 		`make build VERSION="$VERSION" GO_LDFLAGS='-extldflags "-static"'`)
 }

script/docker

@@ -2,9 +2,9 @@
 # script/docker: build the Docker image tagged with the project name.
 # The tag comes from script/projectname.
 #
-# .dockerignore excludes .git/, so the builder stage cannot derive the
-# version itself. It is resolved here, where the checkout is, and passed
-# in as a build arg; without it the image would stamp itself "unknown".
+# The version script/version resolves here goes in as the VERSION build
+# arg, which takes precedence over what the build would derive from the
+# .git in its context.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"

script/version

@@ -7,18 +7,16 @@
 #
 # Order of precedence:
 #
-#   1. $VERSION, if set and non-empty. This is how the value reaches a
-#      build that cannot derive it: .dockerignore excludes .git/, so the
-#      builder stage has no git metadata and the Dockerfile takes the
-#      value as a build arg instead.
+#   1. $VERSION, if set and non-empty: an explicit value, such as the
+#      Dockerfile's VERSION build arg.
 #   2. `git describe --tags --always --dirty` against this checkout. At
 #      a clean tagged commit that is exactly the tag; otherwise it
 #      carries the short SHA, the commit distance when a tag is
 #      reachable, and a -dirty suffix for uncommitted changes.
 #   3. "unknown", for a tree with no git metadata and no $VERSION -- a
-#      source tarball, or `docker build .` with no --build-arg. That
-#      case must not fail the build and must not name a tag the tree may
-#      not be at, so it names nothing.
+#      source tarball, or a `docker build` with no .git in its context
+#      and no VERSION build arg. That case must not fail the build and
+#      must not name a tag the tree may not be at, so it names nothing.
 #
 # The git step insists the enclosing repository is this checkout, not
 # merely some repository above it: an unpacked tarball sitting inside an

templates/error.html

@@ -0,0 +1,15 @@
+{{template "base" .}}
+
+{{define "title"}}{{.StatusText}} - Webhooker{{end}}
+
+{{define "content"}}
+<div class="max-w-4xl mx-auto px-6 py-12">
+    <h1 class="text-2xl font-medium text-gray-900 mb-4">{{.Status}} {{.StatusText}}</h1>
+    <p class="text-gray-600 mb-6">{{.Message}}</p>
+    {{if .User}}
+    <a href="/hooks" class="btn-secondary">Back to webhooks</a>
+    {{else}}
+    <a href="/pages/login" class="btn-primary">Sign in</a>
+    {{end}}
+</div>
+{{end}}

templates/navbar.html

@@ -26,11 +26,15 @@
                 </svg>
                 {{.User.Username}}
             </a>
+            {{/* An error page can be served before a form token is issued,
+                 and a logout without one is refused. */}}
+            {{if .CSRFToken}}
             <form method="POST" action="/pages/logout" class="inline">
                 <input type="hidden" name="csrf_token" value="{{.CSRFToken}}">
                 <button type="submit" class="btn-text">Logout</button>
             </form>
             {{end}}
+            {{end}}
         </div>
     </div>
 
@@ -40,11 +44,13 @@
             {{if .User}}
             <a href="/hooks" class="btn-text w-full text-left">Webhooks</a>
             <a href="/user/{{.User.Username}}" class="btn-text w-full text-left">Profile</a>
+            {{if .CSRFToken}}
             <form method="POST" action="/pages/logout">
                 <input type="hidden" name="csrf_token" value="{{.CSRFToken}}">
                 <button type="submit" class="btn-text w-full text-left">Logout</button>
             </form>
             {{end}}
+            {{end}}
         </div>
     </div>
 </nav>