fix(backend): report ingest correctness — propagate storage failure, 413 on oversize, global body cap (closes #23)

A buffer failure on POST /api/v1/reports now returns 500 instead of a
false `ok`, so clients can retry. An over-limit body returns 413
(errors.As on `*http.MaxBytesError`); malformed JSON stays 400. A
MaxBodyBytes middleware (1 MiB) caps every route, rejecting an
oversized Content-Length up front and capping the read otherwise; a
route group can only lower that limit. The raw geo blob is no longer
logged, only its length; client_id, timestamp and decode error text
are length-bounded before logging. A decodeJSON handler helper is
added. Panic recovery routes the stack through slog as structured
JSON. Storage failure uses 500: a full buffer or write error is
server-side and retryable.

Model: opus-5-5

Dockerfile.backend

@@ -1,8 +1,8 @@
 # Lint stage — fast feedback on formatting and lint issues. The
 # golangci/golangci-lint image ships Go, gofmt, make and the linter, so
 # nothing is installed here.
-# golangci/golangci-lint:v2.7.2 (2026-08-09)
+# golangci/golangci-lint:v2.12.2 (2026-08-10)
-FROM golangci/golangci-lint@sha256:5d6d5c70a61f1356adfd9dd6316ce286799fefc9d743421356ff1b00842368ba AS lint
+FROM golangci/golangci-lint@sha256:5cceeef04e53efe1470638d4b4b4f5ceefd574955ab3941b2d9a68a8c9ad5240 AS lint
 
 WORKDIR /src
 COPY backend/go.mod backend/go.sum ./

TODO.md

@@ -10,25 +10,27 @@
 
 # Status
 
-pre-1.0. No git tags. Backend work in flight on feat/reportbuf-storage (dirty:
+pre-1.0. No git tags. `feat/reportbuf-storage` is merged; the backend, the CI
-src/main.js). Frontend is functional; backend is new and unmerged.
+workflow, and the backend repo standard files are all on `main`. Frontend and
+backend are both functional. Working toward the 1.0.0 milestone by closing the
+remaining repo-compliance issues on the tracker.
 
 # Next Step
 
-Land feat/reportbuf-storage: finish the in-progress src/main.js change, get make
+Confirm the `.gitea/workflows/check.yml` run is green (main always green
-check green, and merge the branch to main. The branch adds the backend (buffered
+policy). The workflow file is already on `main`; what is unverified is that its
-zstd-compressed report storage), the CI workflow, and backend repo standard
+latest run passes.
-files, so merging it also closes most compliance gaps.
 
 # Completed Steps
 
-- 2026-09-21: report ingest correctness (issue #23): a storage failure now
+- 2026-09-28: report ingest correctness (issue #23): a storage failure now
   returns 500 instead of a false `ok`; oversize bodies return 413 (distinguished
   from malformed JSON, which stays 400); a `MaxBodyBytes` middleware caps every
   route, not just the report route; the raw attacker-controlled `geo` blob is no
-  longer logged (only its length) and `client_id`/`timestamp` are length-bounded
+  longer logged (only its length), and `client_id`, `timestamp` and decode error
-  before logging; a `decodeJSON` handler helper was added; and panic recovery
+  text are length-bounded before logging; a `decodeJSON` handler helper was
-  now routes the stack through slog instead of chi's plain-text stderr
+  added; and panic recovery now routes the stack through slog instead of chi's
+  plain-text stderr
 - 2026-09-21: shutdown lifecycle correctness. The process now shuts down through
   fx instead of `os.Exit`, so every component's `OnStop` runs and buffered
   reports are flushed to disk on `SIGTERM` — previously a full flush window of
@@ -43,6 +45,14 @@ files, so merging it also closes most compliance gaps.
   frame/sniff/referrer/permissions headers) registered before CORS, and
   trusted-proxy client IP resolution honouring `X-Forwarded-For` / `X-Real-IP`
   only from a `TRUSTED_PROXIES` allowlist (loopback plus RFC1918 by default)
+- 2026-08-10: adopted the org-standard `backend/.golangci.yml` verbatim and
+  moved the pinned golangci-lint from v2.7.2 to v2.12.2 (the `lint` stage of
+  `Dockerfile.backend` now pins the `golangci/golangci-lint:v2.12.2` image by
+  digest); the previous config declared `version: "2"` but used v1 schema keys,
+  so every threshold in it was inert and its green result was meaningless.
+  `backend/Makefile`'s `lint` target now asserts the config's sha256 against the
+  canonical file first, so drift from the org standard fails the build instead
+  of silently degrading to defaults
 - 2026-08-10: every interactive control now meets the 44x44 CSS px minimum tap
   target (`.pin-btn`, `#interval-select`, the debug-log label and, on narrow
   viewports, `#pause-btn`). The pin button's hit area grows via matching
@@ -72,7 +82,7 @@ files, so merging it also closes most compliance gaps.
   shims, README Entrypoints section
 - 2026-02-27: backend with buffered zstd-compressed report storage; CI workflow
   and backend repo standard files; backend Dockerfile fixed (Go 1.25,
-  golangci-lint) and moved to repo root (feat/reportbuf-storage, unmerged)
+  golangci-lint) and moved to repo root (feat/reportbuf-storage)
 - 2026-02-26: host row layout redesigned with CSS grid; overflow and spacing
   fixes; nginx config extracted; port hardcoded to 8080
 - 2026-02-26: debug log panel, median stats, recovery probe, Docker build fix,
@@ -94,3 +104,9 @@ files, so merging it also closes most compliance gaps.
   (main always green policy)
 - Decide what to do with untracked resume.sh: commit it, gitignore it, or delete
   it
+- Upstream fix needed in `sneak/prompts`: the org-standard `.golangci.yml`
+  enables `gomodguard`, which golangci-lint v2.12.2 reports as deprecated since
+  v2.12.0 and replaced by `gomodguard_v2`, so every backend lint run prints a
+  deprecation warning. The file is standardized and must never be edited in this
+  repo, so nothing can be done here beyond tracking it — tracked at
+  <https://git.eeqj.de/sneak/netwatch/issues/41>

backend/.golangci.yml

@@ -1,5 +1,9 @@
 version: "2"
 
+# Config schema uses the golangci-lint v2 layout (settings live under
+# linters.settings, not top-level linters-settings) so that the
+# thresholds below are actually applied by golangci-lint >= v2.
+
 run:
   timeout: 5m
   modules-download-mode: readonly
@@ -14,19 +18,17 @@ linters:
     - wsl              # Deprecated, replaced by wsl_v5
     - wrapcheck        # Too verbose for internal packages
     - varnamelen       # Short names like db, id are idiomatic Go
-
+  settings:
-linters-settings:
+    lll:
-  lll:
+      line-length: 88
-    line-length: 88
+    funlen:
-  funlen:
+      lines: 80
-    lines: 80
+      statements: 50
-    statements: 50
+    cyclop:
-  cyclop:
+      max-complexity: 15
-    max-complexity: 15
+    dupl:
-  dupl:
+      threshold: 100
-    threshold: 100
 
 issues:
-  exclude-use-default: false
   max-issues-per-linter: 0
   max-same-issues: 0

backend/Makefile

@@ -10,6 +10,17 @@ GOLDFLAGS += -s -w
 GOLDFLAGS += -X main.Version=$(VERSION)
 GOLDFLAGS += -X main.Buildarch=$(BUILDARCH)
 
+# macOS ships shasum rather than sha256sum.
+SHA256SUM := $(shell command -v sha256sum >/dev/null 2>&1 && echo sha256sum || echo shasum -a 256)
+
+# .golangci.yml is standardized org-wide and must never be edited here
+# (REPO_POLICIES.md). Its last silent drift replaced the v2 schema with
+# v1 keys, which left every threshold in the file inert while the build
+# stayed green. The lint target therefore asserts the file still matches
+# the canonical copy byte for byte. The check is a local hash comparison:
+# no network, no remote schema, nothing unpinned in the build path.
+GOLANGCI_CONFIG_SHA256 := 021cc83f4e6fc7c31b95b34b846723dfcf20b66b7baeea1dc40406e643346bcb
+
 .PHONY: all build test lint fmt fmt-check check docker hooks run clean
 
 all: build
@@ -22,6 +33,14 @@ test:
 	timeout 30 go test ./...
 
 lint:
+	@actual=$$($(SHA256SUM) .golangci.yml | cut -d' ' -f1); \
+	if [ "$$actual" != "$(GOLANGCI_CONFIG_SHA256)" ]; then \
+		echo ".golangci.yml has drifted from the org standard."; \
+		echo "  expected $(GOLANGCI_CONFIG_SHA256)"; \
+		echo "  actual   $$actual"; \
+		echo "Restore it verbatim from sneak/prompts; do not edit it."; \
+		exit 1; \
+	fi
 	golangci-lint run ./...
 
 fmt:

backend/internal/handlers/export_test.go

@@ -2,6 +2,9 @@ package handlers
 
 import "log/slog"
 
+// MaxLoggedFieldBytes exposes the log bound to the external tests.
+const MaxLoggedFieldBytes = maxLoggedFieldBytes
+
 // NewForTest builds a Handlers around a report sink and logger,
 // bypassing the fx graph so handler behaviour (including the
 // storage failure path) is exercisable in unit tests.

backend/internal/handlers/report.go

@@ -6,9 +6,9 @@ import (
 	"net/http"
 )
 
-// maxLoggedFieldBytes bounds untrusted string fields before they
+// maxLoggedFieldBytes bounds untrusted text (string fields,
-// are logged, so a caller cannot inflate log volume with an
+// decode error text) before it is logged, so a caller cannot
-// oversized value.
+// inflate log volume with an oversized value.
 const maxLoggedFieldBytes = 128
 
 type reportSample struct {
@@ -79,7 +79,11 @@ func (s *Handlers) decodeErrorStatus(err error) int {
 		return http.StatusRequestEntityTooLarge
 	}
 
-	s.log.Error("failed to decode report", "error", err)
+	// The decoder's error text can quote request bytes (a whole
+	// oversized number, for example), so it is bounded too.
+	s.log.Error("failed to decode report",
+		"error", boundedForLog(err.Error()),
+	)
 
 	return http.StatusBadRequest
 }

backend/internal/handlers/report_test.go

@@ -12,6 +12,7 @@ import (
 	"testing"
 
 	"sneak.berlin/go/netwatch/internal/handlers"
+	"sneak.berlin/go/netwatch/internal/middleware"
 )
 
 var errStorageFailed = errors.New("storage failed")
@@ -49,7 +50,7 @@ func TestHandleReportStorageFailureIsNon2xx(t *testing.T) {
 	h := newTestHandlers(stubAppender{err: errStorageFailed}, io.Discard)
 
 	rec := httptest.NewRecorder()
-	req := httptest.NewRequest(
+	req := httptest.NewRequestWithContext(t.Context(),
 		http.MethodPost, "/api/v1/reports",
 		strings.NewReader(`{"clientId":"c1","hosts":[]}`),
 	)
@@ -71,7 +72,7 @@ func TestHandleReportMalformedJSONIs400(t *testing.T) {
 	h := newTestHandlers(stubAppender{}, io.Discard)
 
 	rec := httptest.NewRecorder()
-	req := httptest.NewRequest(
+	req := httptest.NewRequestWithContext(t.Context(),
 		http.MethodPost, "/api/v1/reports",
 		strings.NewReader(`{not json`),
 	)
@@ -90,17 +91,20 @@ func TestHandleReportOversizeIs413(t *testing.T) {
 	const limit = 32
 
 	h := newTestHandlers(stubAppender{}, io.Discard)
+	handler := (&middleware.Middleware{}).MaxBodyBytes(limit)(
+		h.HandleReport(),
+	)
 
 	rec := httptest.NewRecorder()
-	req := httptest.NewRequest(
+	req := httptest.NewRequestWithContext(t.Context(),
 		http.MethodPost, "/api/v1/reports",
 		strings.NewReader(`{"clientId":"`+strings.Repeat("x", 200)+`"}`),
 	)
-	// Emulate the body-size middleware capping the body so the
+	// No declared length, so only the middleware's read cap can
-	// handler observes a *http.MaxBytesError while decoding.
+	// stop this body.
-	req.Body = http.MaxBytesReader(rec, req.Body, limit)
+	req.ContentLength = -1
 
-	h.HandleReport().ServeHTTP(rec, req)
+	handler.ServeHTTP(rec, req)
 
 	if rec.Code != http.StatusRequestEntityTooLarge {
 		t.Fatalf("oversize status = %d, want %d",
@@ -118,7 +122,7 @@ func TestHandleReportDoesNotLogRawGeo(t *testing.T) {
 	h := newTestHandlers(stubAppender{}, &logbuf)
 
 	rec := httptest.NewRecorder()
-	req := httptest.NewRequest(
+	req := httptest.NewRequestWithContext(t.Context(),
 		http.MethodPost, "/api/v1/reports",
 		strings.NewReader(
 			`{"clientId":"c1","geo":{"raw":"`+sentinel+`"},"hosts":[]}`,
@@ -139,3 +143,73 @@ func TestHandleReportDoesNotLogRawGeo(t *testing.T) {
 		t.Fatal("expected a bounded geo_bytes field in the log")
 	}
 }
+
+func TestHandleReportLogsClientIDCutToBound(t *testing.T) {
+	t.Parallel()
+
+	long := strings.Repeat("c", 2*handlers.MaxLoggedFieldBytes)
+
+	var logbuf bytes.Buffer
+
+	h := newTestHandlers(stubAppender{}, &logbuf)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodPost, "/api/v1/reports",
+		strings.NewReader(
+			`{"clientId":"`+long+`","timestamp":"`+long+`","hosts":[]}`,
+		),
+	)
+
+	h.HandleReport().ServeHTTP(rec, req)
+
+	var logged struct {
+		ClientID  string `json:"client_id"`
+		Timestamp string `json:"timestamp"`
+	}
+
+	err := json.Unmarshal(logbuf.Bytes(), &logged)
+	if err != nil {
+		t.Fatalf("log line not JSON: %v (%q)", err, logbuf.String())
+	}
+
+	want := long[:handlers.MaxLoggedFieldBytes]
+
+	if logged.ClientID != want {
+		t.Fatalf("logged client_id is %d bytes, want %d",
+			len(logged.ClientID), len(want))
+	}
+
+	if logged.Timestamp != want {
+		t.Fatalf("logged timestamp is %d bytes, want %d",
+			len(logged.Timestamp), len(want))
+	}
+}
+
+func TestHandleReportDecodeErrorLogIsBounded(t *testing.T) {
+	t.Parallel()
+
+	// A number too large for its int64 field makes the decoder's
+	// error text quote the whole number.
+	huge := strings.Repeat("9", 2*handlers.MaxLoggedFieldBytes)
+
+	var logbuf bytes.Buffer
+
+	h := newTestHandlers(stubAppender{}, &logbuf)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodPost, "/api/v1/reports",
+		strings.NewReader(`{"hosts":[{"history":[{"t":`+huge+`}]}]}`),
+	)
+
+	h.HandleReport().ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusBadRequest)
+	}
+
+	if strings.Contains(logbuf.String(), huge) {
+		t.Fatal("the whole oversized number was written to the log")
+	}
+}

backend/internal/middleware/middleware.go

@@ -261,8 +261,8 @@ func writeJSONError(w http.ResponseWriter, status int) {
 // rejected immediately with 413. Bodies without a declared
 // length (or that understate it) are capped as they are read, so
 // a handler that reads the body sees a *http.MaxBytesError it can
-// map to 413. Mount it with a different limit on a route group
+// map to 413. Mounted again on a route group, it can only lower
-// that needs a different bound.
+// the limit: a cap applied earlier in the chain still holds.
 func (s *Middleware) MaxBodyBytes(
 	limit int64,
 ) func(http.Handler) http.Handler {

backend/internal/middleware/middleware_test.go

@@ -12,6 +12,15 @@ import (
 	"sneak.berlin/go/netwatch/internal/middleware"
 )
 
+const (
+	// loopbackPeer is a remote address inside the trusted-proxy allowlist.
+	loopbackPeer = "127.0.0.1:5000"
+	// forwardedIP is the client address presented via X-Forwarded-For.
+	forwardedIP = "203.0.113.7"
+	// realIP is the client address presented via X-Real-IP.
+	realIP = "203.0.113.9"
+)
+
 func mustPrefixes(t *testing.T, cidrs ...string) []netip.Prefix {
 	t.Helper()
 
@@ -44,32 +53,32 @@ func clientIPCases() []clientIPCase {
 	return []clientIPCase{
 		{
 			name:       "trusted proxy uses forwarded-for",
-			remoteAddr: "127.0.0.1:5000",
+			remoteAddr: loopbackPeer,
-			xff:        "203.0.113.7",
+			xff:        forwardedIP,
-			want:       "203.0.113.7",
+			want:       forwardedIP,
 		},
 		{
 			name:       "trusted proxy uses left-most of chain",
 			remoteAddr: "10.1.2.3:5000",
-			xff:        "203.0.113.7, 10.1.2.3",
+			xff:        forwardedIP + ", 10.1.2.3",
-			want:       "203.0.113.7",
+			want:       forwardedIP,
 		},
 		{
 			name:       "trusted proxy falls back to x-real-ip",
-			remoteAddr: "127.0.0.1:5000",
+			remoteAddr: loopbackPeer,
-			xRealIP:    "203.0.113.9",
+			xRealIP:    realIP,
-			want:       "203.0.113.9",
+			want:       realIP,
 		},
 		{
 			name:       "untrusted peer ignores forwarded-for",
 			remoteAddr: "198.51.100.4:5000",
-			xff:        "203.0.113.7",
+			xff:        forwardedIP,
 			want:       "198.51.100.4",
 		},
 		{
 			name:       "untrusted peer ignores x-real-ip",
 			remoteAddr: "198.51.100.4:5000",
-			xRealIP:    "203.0.113.9",
+			xRealIP:    realIP,
 			want:       "198.51.100.4",
 		},
 		{
@@ -79,7 +88,7 @@ func clientIPCases() []clientIPCase {
 		},
 		{
 			name:       "trusted proxy with garbage header uses peer",
-			remoteAddr: "127.0.0.1:5000",
+			remoteAddr: loopbackPeer,
 			xff:        "not-an-ip",
 			want:       "127.0.0.1",
 		},
@@ -122,7 +131,7 @@ func TestSecurityHeaders(t *testing.T) {
 	)
 
 	rec := httptest.NewRecorder()
-	req := httptest.NewRequest(http.MethodGet, "/", http.NoBody)
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", http.NoBody)
 	handler.ServeHTTP(rec, req)
 
 	want := map[string]string{
@@ -157,7 +166,7 @@ func TestMaxBodyBytesRejectsOversizeOnNonReadingRoute(t *testing.T) {
 	)
 
 	rec := httptest.NewRecorder()
-	req := httptest.NewRequest(
+	req := httptest.NewRequestWithContext(t.Context(),
 		http.MethodPost, "/.well-known/healthcheck",
 		strings.NewReader(strings.Repeat("x", limit+1)),
 	)
@@ -185,7 +194,7 @@ func TestMaxBodyBytesAllowsWithinLimit(t *testing.T) {
 	)
 
 	rec := httptest.NewRecorder()
-	req := httptest.NewRequest(
+	req := httptest.NewRequestWithContext(t.Context(),
 		http.MethodPost, "/api/v1/reports",
 		strings.NewReader(`{"clientId":"c1"}`),
 	)
@@ -212,7 +221,7 @@ func TestRecovererReturns500AndLogsThroughSlog(t *testing.T) {
 	)
 
 	rec := httptest.NewRecorder()
-	req := httptest.NewRequest(http.MethodGet, "/", http.NoBody)
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", http.NoBody)
 	handler.ServeHTTP(rec, req)
 
 	if rec.Code != http.StatusInternalServerError {

backend/internal/reportbuf/reportbuf.go

@@ -169,7 +169,9 @@ func (b *Buffer) writeFile(data []byte) {
 	name := fmt.Sprintf("reports-%s.jsonl.zst", ts)
 	path := filepath.Join(b.dataDir, name)
 
-	f, err := os.OpenFile( //nolint:gosec // path built from controlled dataDir + timestamp
+	// path is built from the operator-supplied dataDir plus a
+	// generated timestamp, so it carries no external input.
+	f, err := os.OpenFile( //nolint:gosec // see comment above
 		path,
 		os.O_WRONLY|os.O_CREATE|os.O_EXCL,
 		filePerms,

backend/internal/server/export_test.go

@@ -0,0 +1,5 @@
+package server
+
+// MaxRequestBodyBytes exposes the router-wide body limit to the
+// external tests.
+const MaxRequestBodyBytes = maxRequestBodyBytes

backend/internal/server/routes.go

@@ -10,9 +10,9 @@ import (
 const (
 	requestTimeout = 60 * time.Second
 
-	// maxRequestBodyBytes caps every request body. A route that
+	// maxRequestBodyBytes caps every request body. A route group
-	// needs a different bound mounts s.mw.MaxBodyBytes with its
+	// can mount s.mw.MaxBodyBytes with a smaller value to lower
-	// own value on its group.
+	// its bound, but cannot raise it: this cap runs first.
 	maxRequestBodyBytes int64 = 1 << 20 // 1 MiB
 )
 

backend/internal/server/routes_test.go

@@ -0,0 +1,67 @@
+package server_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"sneak.berlin/go/netwatch/internal/config"
+	"sneak.berlin/go/netwatch/internal/globals"
+	"sneak.berlin/go/netwatch/internal/handlers"
+	"sneak.berlin/go/netwatch/internal/healthcheck"
+	"sneak.berlin/go/netwatch/internal/logger"
+	"sneak.berlin/go/netwatch/internal/middleware"
+	"sneak.berlin/go/netwatch/internal/reportbuf"
+	"sneak.berlin/go/netwatch/internal/server"
+
+	"go.uber.org/fx"
+	"go.uber.org/fx/fxtest"
+)
+
+// TestHealthCheckRejectsOversizeBody sends the health check, which
+// never reads its body, a body one byte over the limit. Only the
+// router-wide body limit can reject it.
+func TestHealthCheckRejectsOversizeBody(t *testing.T) {
+	t.Parallel()
+
+	var srv *server.Server
+
+	// The same constructors as main, never started: SetupRoutes is
+	// called directly, so nothing listens.
+	app := fxtest.New(t,
+		fx.Provide(
+			config.New,
+			globals.New,
+			handlers.New,
+			healthcheck.New,
+			logger.New,
+			middleware.New,
+			reportbuf.New,
+			server.New,
+		),
+		fx.Populate(&srv),
+	)
+
+	err := app.Err()
+	if err != nil {
+		t.Fatalf("build server: %v", err)
+	}
+
+	srv.SetupRoutes()
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodGet, "/.well-known/healthcheck",
+		strings.NewReader(
+			strings.Repeat("x", int(server.MaxRequestBodyBytes)+1),
+		),
+	)
+
+	srv.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusRequestEntityTooLarge {
+		t.Fatalf("status = %d, want %d",
+			rec.Code, http.StatusRequestEntityTooLarge)
+	}
+}