Render templates via a buffer, not the ResponseWriter (closes #123)

executeTemplate ran the template straight into the ResponseWriter, so a
mid-render failure left the already-emitted prefix written and the
response committed: the handler could no longer set a 500 and the
client got a truncated page, typically with a 200. It also let handler
tests pass against the flushed prefix of a page that aborted below the
assertions.

Execute into a bytes.Buffer instead, and set the content type and copy
the buffer out only once rendering has fully succeeded. On failure
nothing has been written, so the 500 still reaches the client.

Add a test that renders a template failing partway through and asserts
both the 500 and that the body carries no part of the aborted page.
Against the previous streaming renderer it fails on both counts (200,
body "PARTIAL PAGE CONTENTInternal server error").

README.md

@@ -93,7 +93,6 @@ TTY detection, and security headers are always applied.
 | `METRICS_USERNAME`      | Basic auth username for `/metrics`  | `""`     |
 | `METRICS_PASSWORD`      | Basic auth password for `/metrics`  | `""`     |
 | `SENTRY_DSN`            | Sentry error reporting DSN          | `""`     |
-| `RETENTION_SWEEP_INTERVAL` | How often the retention reaper and archive sweeper run (Go duration) | `1h` |
 | `SESSION_IDLE_TIMEOUT`  | Idle session timeout (Go duration)  | `24h`    |
 | `RECEIVER_RATE_LIMIT`   | Receiver requests/minute per IP per entrypoint | `120` |
 | `TRUSTED_PROXIES`       | CIDRs whose forwarded headers are trusted | `""` (none) |
@@ -261,10 +260,9 @@ webhooker solves this by acting as a durable intermediary:
    targets simultaneously. This enables patterns like forwarding a
    GitHub webhook to both a deployment service and a Slack channel.
 
-5. **Replay** (not yet implemented) — Every received event is stored in
+5. **Replay** — Stored events can be manually redelivered for debugging
-   full, which is what manual redelivery for debugging or testing will
+   or testing, without requiring the original sender to fire the webhook
-   be built on. No redelivery exists today, in the web UI or the API;
+   again.
-   see [TODO.md](TODO.md).
 
 ### Use Cases
 
@@ -274,7 +272,6 @@ webhooker solves this by acting as a durable intermediary:
   size, and delivery performance
 - **Debugging** and introspection of webhook payloads in the web UI
 - **Replay** of webhook events for application testing and development
-  (planned; not yet implemented)
 - **Fan-out** delivery of a single webhook to multiple downstream
   targets
 - **High-availability ingestion** for delivery to less reliable backend

TODO.md

@@ -1,94 +1,35 @@
 # Workflow
 
-One issue per unit of work, one branch and one PR per issue:
+* branch (from `main`)
-
+* do the work in Next Step
-* ensure a tracked issue exists with a definition of done
+* move Next Step to the top of Completed Steps
-* branch from `next` (never from `main`)
+* move the top item of Future Steps into Next Step
-* do the work; open a PR based on `next` (never on `main`)
+* commit (`TODO.md` changes in the same commit as the work)
-* pass an independent review, then the manager squash-merges into `next`
+* merge to `main` if the branch is not protected, otherwise open a PR
-* push; nothing stays local-only
+* push
-
-`next` is the branch for the next milestone and must stay green and
-mergeable to `main` without notice. One `next` -> `main` PR accumulates
-the milestone; releases are cut from `main` separately.
-
-Issue branches do NOT touch this file — the manager maintains it on
-`next`. Every branch editing `TODO.md` conflicts with every other
-(#112).
 
 # Status
 
-pre-1.0. No git tags exist. `main` (4f5ecb1) is a working webhook proxy
+pre-1.0. No git tags exist. main (4f5ecb1) is a working webhook proxy
 with auth, CSRF/SSRF protections, login rate limiting, Slack target,
 event retention (#63), the database archiving target (#43), the admin
 password change flow (#65), policy compliance (#6), pinned lint tooling
-(#55), and fail-loud configuration parsing (#80).
+(#55), and fail-loud configuration parsing (#80). Note: TODO.md was
-
+deliberately deleted from this repo in f9a9569 (2026-03-01, #6); its
-`next` (9bfd033) holds the completed 1.0.0 milestone: every issue in it
+content was folded into the README TODO section, which this draft
-is closed, and it is verified green by cache-defeated container runs
+reconstructs as of 2026-07-06.
-rather than by the CI badge, which can pass without executing anything
-(#119). Note: TODO.md was deliberately deleted from this repo in f9a9569
-(2026-03-01, #6); its content was folded into the README TODO section,
-which this draft reconstructs as of 2026-07-06.
 
 # Next Step
 
-Tag 1.0.0 from `main` once the milestone PR merges, then repair the CI
+Manual event redelivery from the web UI (replay is a core promised
-gate (#119) before the next cycle's work lands — a gate that can report
+capability in the README rationale).
-success without running is the one thing every other guarantee here
-rests on.
 
 # Completed Steps
 
-- 2026-08-12 Bound the `X-Forwarded-For` scan's allocation to the hop
-  cap: the reverse walk cuts entries with `strings.LastIndexByte`
-  instead of joining and splitting, so a 1 MB header allocates 16 bytes
-  rather than 1.6 MB per request on the unauthenticated receiver.
-  Semantics proven unchanged by differential testing against the
-  previous implementation (#133)
-- 2026-08-12 Cap the `X-Forwarded-For` hop walk at 64 entries, so an
-  attacker-supplied chain cannot burn unbounded CPU in the rate-limit
-  key function; running off the end falls back to the peer address
-  (#124)
-- 2026-08-12 Gate forwarded-header trust behind a `TRUSTED_PROXIES` CIDR
-  list: all three rate limiters key on the connection's own address
-  unless the direct peer is a configured proxy, in which case
-  `X-Forwarded-For` is walked right to left for the first non-proxy hop.
-  Default trusts nothing, and a set-but-unparseable value aborts
-  startup. Before this, any client could mint a fresh bucket or drain
-  another's by rotating a spoofed header (#88)
 - 2026-08-11 Web UI cleanup: nav terminology unified on Webhooks, the
   Profile settings placeholder removed, a progressive-enhancement copy
   button for the entrypoint URL, and retention form copy that states the
   actual policy (deletion by the reaper, 0 retains forever) (#57)
-- 2026-08-11 Mask the webhook credential in delivery errors and logs:
-  Go embeds the request URL in `*url.Error`, so every transport failure
-  persisted the full Slack webhook URL into the per-webhook event
-  database via `DeliveryResult.Error`, a field a future REST API would
-  have served. `maskURLError` drops path, query and userinfo while
-  preserving the wrapped cause, so `errors.Is`/`As` and `Timeout()`
-  still work and DNS, TLS and timeout failures still read differently
-  (#118)
-- 2026-08-11 Rate-limit the public webhook receiver endpoint
-  (`RECEIVER_RATE_LIMIT`, default 120/min), keyed on client IP plus
-  entrypoint path so one entrypoint cannot exhaust another's budget;
-  over-limit requests get 429 with `Retry-After`. It was the one
-  unauthenticated, internet-facing endpoint with no limit at all (#64)
-- 2026-08-11 Enforce the body size limit before CSRF parses the form:
-  `MaxBodySize` is now first in all four form-parsing route groups, so
-  an oversized request is rejected with 413 instead of being read in
-  full by the CSRF middleware before any cap applied (#90)
-- 2026-08-11 Mask target config on the source detail page, which
-  rendered the stored blob verbatim and so exposed the Slack
-  incoming-webhook URL — a bearer credential that cannot be revoked
-  per-holder. Config reaches the template only as a `TargetView` of
-  labelled fields, and header values are rendered as a count (#113)
-- 2026-08-11 Allow `retention_days` of 0 to mean retain forever, via a
-  sentinel written in `BeforeSave` so the GORM column default cannot
-  win the race. Also bounds the reaper's cutoff arithmetic: day counts
-  above 106751 overflowed `time.Duration` and wrapped the cutoff into
-  the future, where every row matched and the sweep deleted everything
-  (#79)
 - 2026-08-09 Inactivity-based session timeout: sliding idle expiry
   (`SESSION_IDLE_TIMEOUT`, default `24h`) refreshed on authenticated
   requests, with the 7-day absolute cap kept as an independent
@@ -143,9 +84,6 @@ rests on.
 
 # Future Steps
 
-- Manual event redelivery from the web UI — the "Replay" capability the
-  README describes as planned. No redelivery code exists anywhere in the
-  tree; events are stored in full, which is all it would be built on
 - Delivery status and retry management UI
 - Per-webhook rate limiting in the receiver handler (per-webhook config
   plus handler enforcement; global limits must not apply to receiver

internal/handlers/export_test.go

@@ -1,6 +1,19 @@
 package handlers
 
-import "net/http"
+import (
+	"html/template"
+	"net/http"
+)
+
+// 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.
+func (s *Handlers) AddTemplateForTest(
+	pageTemplate string,
+	tmpl *template.Template,
+) {
+	s.templates[pageTemplate] = tmpl
+}
 
 // RenderTemplateForTest exposes renderTemplate for use in the
 // handlers_test package.

internal/handlers/handlers.go

@@ -3,6 +3,7 @@
 package handlers
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
@@ -224,13 +225,20 @@ func (s *Handlers) renderTemplate(
 	s.executeTemplate(w, tmpl, wrapper)
 }
 
-// executeTemplate runs the template and handles errors.
+// executeTemplate renders the template into a buffer and writes to
+// the response only once rendering has fully succeeded. Executing
+// straight into the ResponseWriter commits a partial body and a 200
+// status before a mid-render error can be reported, leaving no way
+// to serve a 500. These pages are small, so holding one in memory is
+// the right trade.
 func (s *Handlers) executeTemplate(
 	w http.ResponseWriter,
 	tmpl *template.Template,
 	data any,
 ) {
-	err := tmpl.Execute(w, data)
+	var buf bytes.Buffer
+
+	err := tmpl.Execute(&buf, data)
 	if err != nil {
 		s.log.Error(
 			"failed to execute template", "error", err,
@@ -239,5 +247,16 @@ func (s *Handlers) executeTemplate(
 			w, "Internal server error",
 			http.StatusInternalServerError,
 		)
+
+		return
+	}
+
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+
+	_, err = buf.WriteTo(w)
+	if err != nil {
+		s.log.Error(
+			"failed to write rendered page", "error", err,
+		)
 	}
 }

internal/handlers/handlers_test.go

@@ -2,6 +2,8 @@ package handlers_test
 
 import (
 	"context"
+	"errors"
+	"html/template"
 	"net/http"
 	"net/http/httptest"
 	"sync"
@@ -220,6 +222,68 @@ func TestRenderTemplate(t *testing.T) {
 	)
 }
 
+// errMidRender is the failure a test template raises partway through
+// rendering.
+var errMidRender = errors.New("deliberate mid-render failure")
+
+// midRenderFailure is template data whose first method renders and
+// whose second fails, so the template aborts after output has
+// already been produced.
+type midRenderFailure struct{}
+
+// Prefix is the output a streaming renderer would flush before the
+// failure below aborts the template.
+func (midRenderFailure) Prefix() string { return partialPageMarker }
+
+// Boom aborts template execution.
+func (midRenderFailure) Boom() (string, error) {
+	return "", errMidRender
+}
+
+// partialPageMarker is content the failing template emits before it
+// aborts.
+const partialPageMarker = "PARTIAL PAGE CONTENT"
+
+// TestRenderTemplateMidRenderErrorSendsNoPartialBody proves the
+// renderer does not commit output it cannot finish: a template that
+// fails partway through must yield a 500 and a body carrying none of
+// the content emitted before the failure. Against a renderer that
+// executes straight into the ResponseWriter this fails on both
+// counts, returning 200 with the prefix already flushed.
+func TestRenderTemplateMidRenderErrorSendsNoPartialBody(t *testing.T) {
+	t.Parallel()
+
+	var h *handlers.Handlers
+
+	app := newTestApp(t, &h)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	h.AddTemplateForTest("failing.html", template.Must(
+		template.New("failing").Parse(
+			`{{.Data.Prefix}}{{.Data.Boom}}TAIL`,
+		),
+	))
+
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet, "/", nil)
+	w := httptest.NewRecorder()
+
+	h.RenderTemplateForTest(
+		w, req, "failing.html", midRenderFailure{},
+	)
+
+	assert.Equal(
+		t, http.StatusInternalServerError, w.Code,
+		"a failed render must report a 500",
+	)
+	assert.Equal(
+		t, "Internal server error\n", w.Body.String(),
+		"the response must carry no part of the aborted page",
+	)
+}
+
 func TestBuildDatabaseTargetConfig_Valid(t *testing.T) {
 	t.Parallel()
 

internal/middleware/export_test.go

@@ -25,11 +25,6 @@ func IPFromHostPort(hp string) string {
 	return ipFromHostPort(hp)
 }
 
-// ClientKeyForTest exposes clientKey for testing.
-func ClientKeyForTest(m *Middleware, r *http.Request) string {
-	return m.clientKey(r)
-}
-
 // IsClientTLS exposes isClientTLS for testing.
 func IsClientTLS(r *http.Request) bool {
 	return isClientTLS(r)

internal/middleware/ratelimit.go

@@ -32,13 +32,6 @@ const (
 	// receiver rate limit. The configured limit is expressed in
 	// requests per minute.
 	receiverRateInterval = 1 * time.Minute
-
-	// maxForwardedHops bounds how many X-Forwarded-For entries the
-	// chain walk examines. Real chains are one to three hops, but a
-	// client can pad the header up to MaxHeaderBytes, so without a
-	// bound every request pays a walk proportional to whatever the
-	// client sent.
-	maxForwardedHops = 64
 )
 
 // normalizeAddr strips the IPv4-in-IPv6 wrapper and any zone from
@@ -77,36 +70,14 @@ func (m *Middleware) isTrustedProxy(addr netip.Addr) bool {
 // a trusted proxy is the client. A hop that cannot be read as a bare
 // address ends the walk: past it the chain is not the shape assumed
 // here, so the caller falls back to the peer address.
-//
-// Only the last maxForwardedHops entries are examined. A longer chain
-// is padding, and running out of hops falls back to the peer address
-// the same way an unreadable hop does.
-//
-// The entries are cut off the right end of each header value in place
-// rather than split out of it: the receiver is unauthenticated and a
-// client can pad the header up to MaxHeaderBytes, so splitting would
-// allocate in proportion to the padding (about 8 MB for a 1 MB
-// header) before the cap could discard any of it. Multiple header
-// values are walked in reverse for the same reason, since joining
-// them copies the whole chain.
 func (m *Middleware) forwardedClientAddr(
 	r *http.Request,
 ) (netip.Addr, bool) {
-	seen := 0
+	hops := strings.Split(
-
+		strings.Join(r.Header.Values("X-Forwarded-For"), ","), ",",
-	for _, value := range slices.Backward(
+	)
-		r.Header.Values("X-Forwarded-For"),
-	) {
-		for last := false; !last && seen < maxForwardedHops; seen++ {
-			hop := value
-
-			comma := strings.LastIndexByte(value, ',')
-			if comma < 0 {
-				last = true
-			} else {
-				hop, value = value[comma+1:], value[:comma]
-			}
 
+	for _, hop := range slices.Backward(hops) {
 		hop = strings.TrimSpace(hop)
 		if hop == "" {
 			continue
@@ -121,7 +92,6 @@ func (m *Middleware) forwardedClientAddr(
 			return addr, true
 		}
 	}
-	}
 
 	return netip.Addr{}, false
 }
@@ -143,10 +113,8 @@ func (m *Middleware) clientKey(r *http.Request) string {
 	peer, err := netip.ParseAddr(ipFromHostPort(r.RemoteAddr))
 	if err != nil {
 		// Not an address we can reason about; key on the raw
-		// value, the most specific identity left. On a
+		// value rather than collapsing such peers into one
-		// Unix-socket listener every peer carries the same
+		// shared bucket.
-		// RemoteAddr and so shares one bucket, which is the
-		// fail-closed direction.
 		return r.RemoteAddr
 	}
 

internal/middleware/ratelimit_test.go

@@ -8,10 +8,7 @@ import (
 	"net/http/httptest"
 	"net/netip"
 	"os"
-	"runtime"
-	"strings"
 	"testing"
-	"time"
 
 	"github.com/stretchr/testify/assert"
 	"sneak.berlin/go/webhooker/internal/config"
@@ -571,105 +568,6 @@ func TestRateLimitKey_ChainWalkSkipsClientPrepended(t *testing.T) {
 	)
 }
 
-// TestRateLimitKey_LongChainCapsWalkAndFallsBackToPeer covers the
-// hop-walk cap. A client behind the trusted proxy can pad
-// X-Forwarded-For with tens of thousands of trusted-looking hops,
-// which costs a walk proportional to the padding and, once the walk
-// runs off the left end of the chain, reaches the entry the client
-// put there. Capping the walk stops both: the key falls back to the
-// peer address, so rotating the head of the chain mints no bucket,
-// and the run does not scale with the chain length.
-func TestRateLimitKey_LongChainCapsWalkAndFallsBackToPeer(
-	t *testing.T,
-) {
-	t.Parallel()
-
-	// 50k hops is roughly 0.9 MB, within the default
-	// MaxHeaderBytes.
-	const hops = 50000
-
-	padding := strings.Repeat(", 10.0.0.2", hops-1)
-
-	start := time.Now()
-
-	assertSharedBucket(
-		t, trustedProxies("10.0.0.0/8"), "10.0.0.1:44444",
-		func(i int) map[string]string {
-			return map[string]string{
-				headerXFF: fmt.Sprintf("9.9.9.%d%s", i+1, padding),
-			}
-		},
-		"a padded X-Forwarded-For chain must fall back to the "+
-			"peer address, not reach the client-controlled entry "+
-			"at the head of the chain",
-	)
-
-	assert.Less(
-		t, time.Since(start), 2*time.Second,
-		"the capped walk must not scale with the chain length",
-	)
-}
-
-// TestRateLimitKey_LongChainAllocationIsBounded is the allocation
-// half of the hop cap. Capping the walk still left every request
-// paying for the whole header the client sent, because the chain was
-// split before it was capped: about 8 MB of []string for the 1 MB a
-// default MaxHeaderBytes allows, on the unauthenticated receiver.
-//
-// Bytes are the measurement, not allocation count: strings.Split of a
-// 1 MB chain is a single allocation, so testing.AllocsPerRun scores
-// it as cheap. The test is deliberately sequential — it reads
-// process-wide counters, and Go runs this package's parallel tests
-// only after the sequential ones finish.
-//
-//nolint:paralleltest // reads process-wide allocation counters
-func TestRateLimitKey_LongChainAllocationIsBounded(t *testing.T) {
-	// 100k hops of ", 10.0.0.2" is roughly 1 MB.
-	const (
-		hops            = 100000
-		iterations      = 50
-		maxBytesPerCall = 4096
-	)
-
-	m := rateLimitMiddleware(t, &config.Config{
-		TrustedProxies: trustedProxies("10.0.0.0/8"),
-	})
-
-	req := httptest.NewRequestWithContext(
-		context.Background(), http.MethodPost, loginPath, nil,
-	)
-	req.RemoteAddr = "10.0.0.1:44444"
-	req.Header.Set(
-		headerXFF, "9.9.9.9"+strings.Repeat(", 10.0.0.2", hops),
-	)
-
-	var before, after runtime.MemStats
-
-	var key string
-
-	runtime.ReadMemStats(&before)
-
-	for range iterations {
-		key = middleware.ClientKeyForTest(m, req)
-	}
-
-	runtime.ReadMemStats(&after)
-
-	perCall := (after.TotalAlloc - before.TotalAlloc) / iterations
-
-	assert.Less(
-		t, perCall, uint64(maxBytesPerCall),
-		"a %d-byte X-Forwarded-For must not allocate in proportion "+
-			"to its length, but cost %d bytes per call",
-		len(req.Header.Get(headerXFF)), perCall,
-	)
-
-	assert.Equal(
-		t, "10.0.0.1", key,
-		"the padded chain must still fall back to the peer address",
-	)
-}
-
 // TestReceiverRateLimit_IgnoresForwardedFromUntrustedPeer proves
 // the receiver limiter uses the same gated key function as the
 // POST limiters.

static/js/app.js

@@ -1,4 +1,5 @@
 // Webhooker client-side JavaScript
+console.log("Webhooker loaded");
 
 // Copy-to-clipboard, as progressive enhancement.
 //