Delete the oldest report files to stay under the size cap (closes #54)

When a report would take the report files past DATA_DIR_MAX_BYTES,
reportbuf now deletes the oldest report files until it fits, and does
the same at start when files left by an earlier run are already past
it. A file joins the files that may be deleted only once it is
completely written, so a file still being written is never deleted. A
report is refused with 507 only when the reports waiting to be written
fill the cap on their own, and then no file is deleted. The reports of
a failed write stop counting, and the part of its file written is
removed. A file whose deletion fails keeps counting; one already
deleted by hand counts as freed.

Model: opus-5-5

Dockerfile

@@ -20,7 +20,10 @@ RUN make lint
 # golang:1.25-alpine (2026-02-27)
 FROM golang:1.25-alpine@sha256:f6751d823c26342f9506c03797d2527668d095b0a15f1862cddb4d927a7a4ced AS builder
 
-RUN apk add --no-cache git make
+# gcc and musl-dev are for make test: its race detector needs cgo, which
+# Go turns on by itself once a C compiler is present. make build still
+# sets CGO_ENABLED=0, so the binary stays static.
+RUN apk add --no-cache gcc git make musl-dev
 
 WORKDIR /src
 

README.md

@@ -39,14 +39,16 @@ halves, so the root `make check` fails if either one is broken. We provide:
 - `script/bootstrap` — install all dependencies (the pinned node via nvm unless
   one new enough for the frontend's dependencies is installed, yarn via
   corepack, `yarn install --frozen-lockfile`, the pinned Go unless one at least
-  as new as `backend/go.mod` asks for is installed, and the Go modules), linking
+  as new as `backend/go.mod` asks for is installed, the Go modules, and gcc with
-  what it installs itself into `~/.local/bin`, which has to be on `PATH`. It
+  the C library headers unless gcc is installed, for the race detector in
-  installs no Go linter and not Docker: `make lint` runs the linter in Docker
+  `make test`), linking what it installs itself into `~/.local/bin`, which has
+  to be on `PATH`. It installs no Go linter and not Docker: `make lint` runs the
+  linter in Docker
 - `script/setup` — make a fresh clone ready for development: bootstrap plus the
   git pre-commit hook
 - `script/projectname` — print the project name (used for the Docker image tag)
-- `script/test` — run `script/frontend-test`, then the backend's Go tests, both
+- `script/test` — run `script/frontend-test`, then the backend's Go tests, each
-  within one 30-second timeout
+  under its own 30-second timeout
 - `script/lint` — run `script/frontend-lint`, then golangci-lint in Docker, by
   building the lint stage of `Dockerfile` without the cache
 - `script/fmt` — format all files (writes): prettier, then gofmt over `backend/`

TODO.md

@@ -32,6 +32,17 @@ latest run passes.
   write stop counting, and the part of its file written is removed. A file that
   cannot be deleted still counts until the next start; one already deleted by
   hand counts as freed
+- 2026-10-03: the Go tests run with the race detector and coverage (issue #88):
+  `backend/script/test` runs `go test -timeout 30s -race -cover ./...` and, if
+  that fails, runs it again with `-v` and fails. Go's `-timeout` bounds the
+  tests, not their compile; the root `script/test` no longer puts one 30-second
+  timeout around both halves, which a cold Go build cache could use up on
+  compiling alone. The race detector needs a C compiler: the builder stage of
+  `Dockerfile` has gcc and musl-dev, and `script/bootstrap` installs gcc, with
+  the C library headers on apt and apk, when gcc is missing; the binary is still
+  built with `CGO_ENABLED=0`. New tests cover the health check's answer, a valid
+  report's answer, a report file's exact contents, and the flush when the buffer
+  reaches 10 MiB; the handlers' `TestImport` stub is gone
 - 2026-10-03: each target check times out after 80% of the refresh interval
   (issue #78), 24 seconds at 30 seconds, where it was capped at 3 seconds. A
   round started early, after an interval change or when the recovery probe finds

backend/README.md

@@ -35,7 +35,10 @@ pattern as the repo root: the targets in `backend/Makefile` are thin shims over
   stamped in. The version is `VERSION` from the environment;
   when that is unset or empty, it falls back to `git describe` inside a git
   checkout, then to `dev`
-- `script/test` — run the Go tests under a 30-second timeout
+- `script/test` — run the Go tests with the race detector and coverage. Go's
+  `-timeout 30s` bounds the tests, not their compile. If they fail, they run
+  again with `-v` for the details, and the script fails. The race detector needs
+  a C compiler
 - `script/lint` — check `.golangci.yml` against its pinned sha256, then run
   golangci-lint. It runs inside the golangci-lint image of the lint stage of
   the root `Dockerfile`; from a checkout, run `make lint` at the repo root,
@@ -125,10 +128,11 @@ Reports are written as `reports-<timestamp>-<number>.jsonl.zst` files in
 `DATA_DIR`. The timestamp is in UTC to the millisecond, so the names sort by
 time. The number starts at 1 when the server starts and goes up by one for each
 file the server starts to write, so two files written in the same millisecond
-still get different names. A failed write uses up its number, leaving a gap in
+still get different names. A failed write uses up its number and leaves a gap in
-the numbers if the file could not be created and otherwise a file under that
+the numbers: its file, if it was created, is removed. The file stays, counted
-number that may be incomplete. Each file contains one JSON object per line,
+toward `DATA_DIR_MAX_BYTES` from the next start, only if removing it fails too.
-compressed with zstd. Files are created with `O_EXCL` to prevent overwrites.
+Each file contains one JSON object per line, compressed with zstd. Files are
+created with `O_EXCL` to prevent overwrites.
 
 ### Report limits
 

backend/internal/handlers/handlers_test.go

@@ -1,13 +0,0 @@
-package handlers_test
-
-import (
-	"testing"
-
-	_ "sneak.berlin/go/netwatch/internal/handlers"
-)
-
-func TestImport(t *testing.T) {
-	t.Parallel()
-	// Compilation check — verifies the package parses
-	// and all imports resolve.
-}

backend/internal/handlers/healthcheck_test.go

@@ -0,0 +1,120 @@
+package handlers_test
+
+import (
+	"encoding/json"
+	"maps"
+	"net/http"
+	"net/http/httptest"
+	"slices"
+	"testing"
+	"time"
+
+	"sneak.berlin/go/netwatch/internal/globals"
+	"sneak.berlin/go/netwatch/internal/handlers"
+	"sneak.berlin/go/netwatch/internal/healthcheck"
+	"sneak.berlin/go/netwatch/internal/logger"
+
+	"go.uber.org/fx/fxtest"
+)
+
+// newStartedHandlers builds Handlers with a real health check for the
+// server named in g, and starts them, which records the time the
+// uptime counts from.
+func newStartedHandlers(t *testing.T, g *globals.Globals) *handlers.Handlers {
+	t.Helper()
+
+	lc := fxtest.NewLifecycle(t)
+
+	log, err := logger.New(lc, logger.Params{Globals: g})
+	if err != nil {
+		t.Fatalf("logger: %v", err)
+	}
+
+	hc, err := healthcheck.New(lc,
+		healthcheck.Params{Globals: g, Logger: log})
+	if err != nil {
+		t.Fatalf("health check: %v", err)
+	}
+
+	h, err := handlers.New(lc,
+		handlers.Params{Globals: g, Healthcheck: hc, Logger: log})
+	if err != nil {
+		t.Fatalf("handlers: %v", err)
+	}
+
+	lc.RequireStart()
+	t.Cleanup(lc.RequireStop)
+
+	return h
+}
+
+// TestHandleHealthCheck checks the health check's answer: 200, a JSON
+// content type, and a JSON object with exactly the fields of
+// healthcheck.Response, carrying this server's name and version and
+// an uptime counted from its start.
+func TestHandleHealthCheck(t *testing.T) {
+	t.Parallel()
+
+	g := &globals.Globals{Appname: "netwatch-server", Version: "v1.2.3"}
+	h := newStartedHandlers(t, g)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(t.Context(),
+		http.MethodGet, "/.well-known/healthcheck", http.NoBody)
+
+	h.HandleHealthCheck().ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusOK)
+	}
+
+	contentType := rec.Header().Get("Content-Type")
+	if contentType != "application/json; charset=utf-8" {
+		t.Errorf("Content-Type = %q, want %q",
+			contentType, "application/json; charset=utf-8")
+	}
+
+	var body map[string]any
+
+	err := json.Unmarshal(rec.Body.Bytes(), &body)
+	if err != nil {
+		t.Fatalf("body not a JSON object: %v (%q)", err, rec.Body.String())
+	}
+
+	fields := []string{
+		"appname", "now", "status", "uptimeHuman", "uptimeSeconds", "version",
+	}
+	if got := slices.Sorted(maps.Keys(body)); !slices.Equal(got, fields) {
+		t.Fatalf("fields = %v, want %v", got, fields)
+	}
+
+	for field, want := range map[string]string{
+		"appname": g.Appname, "status": "ok", "version": g.Version,
+	} {
+		if body[field] != want {
+			t.Errorf("%s = %v, want %q", field, body[field], want)
+		}
+	}
+
+	now, _ := body["now"].(string)
+
+	at, err := time.Parse(time.RFC3339Nano, now)
+	if err != nil || time.Since(at).Abs() > time.Minute {
+		t.Errorf("now = %q, want the current time in RFC 3339 (%v)", now, err)
+	}
+
+	// Started just now, so the uptime is well under a minute.
+	human, _ := body["uptimeHuman"].(string)
+
+	uptime, err := time.ParseDuration(human)
+	if err != nil || uptime > time.Minute {
+		t.Errorf("uptimeHuman = %q, want a duration under a minute (%v)",
+			human, err)
+	}
+
+	seconds, ok := body["uptimeSeconds"].(float64)
+	if !ok || seconds < 0 || seconds > time.Minute.Seconds() {
+		t.Errorf("uptimeSeconds = %v, want a number of seconds under a minute",
+			body["uptimeSeconds"])
+	}
+}

backend/internal/handlers/report_test.go

@@ -46,6 +46,63 @@ func decodeStatus(t *testing.T, body []byte) string {
 	return resp.Status
 }
 
+// TestHandleReportAcceptsValidReports checks the answer to a valid
+// report, one with no hosts and one shaped as the frontend sends them:
+// 200 and {"status":"ok"} as JSON.
+func TestHandleReportAcceptsValidReports(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name string
+		body string
+	}{
+		{
+			name: "no hosts",
+			body: `{"clientId":"c1","geo":null,"hosts":[],` +
+				`"timestamp":"2026-10-03T12:00:00.000Z"}`,
+		},
+		{
+			name: "a host with a latency and an error sample",
+			body: `{"clientId":"c1","geo":null,"hosts":[{` +
+				`"name":"Example","url":"https://example.com/",` +
+				`"status":"error","history":[` +
+				`{"t":1790000000000,"latency":42,"error":null},` +
+				`{"t":1790000003000,"latency":null,"error":"timeout"}]}],` +
+				`"timestamp":"2026-10-03T12:00:00.000Z"}`,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			h := newTestHandlers(stubAppender{}, io.Discard)
+
+			rec := httptest.NewRecorder()
+			req := httptest.NewRequestWithContext(t.Context(),
+				http.MethodPost, "/api/v1/reports",
+				strings.NewReader(tt.body),
+			)
+
+			h.HandleReport().ServeHTTP(rec, req)
+
+			if rec.Code != http.StatusOK {
+				t.Fatalf("status = %d, want %d", rec.Code, http.StatusOK)
+			}
+
+			contentType := rec.Header().Get("Content-Type")
+			if contentType != "application/json; charset=utf-8" {
+				t.Errorf("Content-Type = %q, want %q",
+					contentType, "application/json; charset=utf-8")
+			}
+
+			if got := rec.Body.String(); got != "{\"status\":\"ok\"}\n" {
+				t.Errorf("body = %q, want %q", got, "{\"status\":\"ok\"}\n")
+			}
+		})
+	}
+}
+
 func TestHandleReportStorageFailureIsNon2xx(t *testing.T) {
 	t.Parallel()
 

backend/internal/reportbuf/export_test.go

@@ -5,6 +5,10 @@ import (
 	"time"
 )
 
+// FlushSizeThreshold exposes the buffer size at which Append starts
+// writing a report file to the external tests.
+const FlushSizeThreshold = flushSizeThreshold
+
 // Flush writes the buffered reports to a file now, as the periodic
 // flush does, so tests need not wait a minute for it.
 func (b *Buffer) Flush() error {

backend/internal/reportbuf/reportbuf_test.go

@@ -424,15 +424,18 @@ func TestFileDeletedByHandFreesRoom(t *testing.T) {
 	}
 }
 
-// TestFileBeingWrittenIsNeverDeleted holds a write open, its file
+// TestFileBeingWrittenIsNeverDeleted holds the write of one report file
-// created but not complete, while a report needs room. The file may
+// open while a second write completes, then sends a report that needs
-// not be deleted to make it, so the report is refused. Once the write
+// room. Deleting either file would make it, and the one being written is
-// is complete, the file is deleted when room is needed.
+// the older, but only the complete one may be deleted. Once the first
+// write is complete, its file is deleted when room is needed.
 func TestFileBeingWrittenIsNeverDeleted(t *testing.T) {
 	report := map[string]string{"id": "writing"}
 
 	t.Setenv("DATA_DIR", t.TempDir())
-	t.Setenv("DATA_DIR_MAX_BYTES", strconv.Itoa(lineBytes(t, report)))
+	// Room for two reports waiting to be written, but not for two
+	// beside a report file.
+	t.Setenv("DATA_DIR_MAX_BYTES", strconv.Itoa(2*lineBytes(t, report)))
 
 	buf := startBuffer(t)
 
@@ -447,7 +450,7 @@ func TestFileBeingWrittenIsNeverDeleted(t *testing.T) {
 
 	err := buf.Append(report)
 	if err != nil {
-		t.Fatalf("report that fills the cap exactly: %v", err)
+		t.Fatalf("first report: %v", err)
 	}
 
 	flushed := make(chan error)
@@ -456,32 +459,47 @@ func TestFileBeingWrittenIsNeverDeleted(t *testing.T) {
 
 	writing := <-created
 
-	// Errorf, not Fatalf, until the write is released, so that a
+	// Only the first write is held; the second goes through, and
+	// so do the writes after it, the final one at stop included.
+	var complete string
+
+	buf.OnFileCreated(func(f *os.File) { complete = f.Name() })
+
+	// Errorf, not Fatalf, until the first write is released, so that a
 	// failure here does not leave it held.
 	err = buf.Append(report)
-	if !errors.Is(err, reportbuf.ErrFull) {
+	if err != nil {
-		t.Errorf("report while the first was being written: "+
+		t.Errorf("second report: %v", err)
-			"error = %v, want ErrFull", err)
+	}
+
+	err = buf.Flush()
+	if err != nil {
+		t.Errorf("flush of the second report: %v", err)
+	}
+
+	err = buf.Append(report)
+	if err != nil {
+		t.Errorf("report that needs room: %v", err)
 	}
 
 	if !exists(t, writing) {
 		t.Error("report file deleted while it was being written")
 	}
 
+	if exists(t, complete) {
+		t.Error("complete report file kept, though room was needed")
+	}
+
 	close(release)
 
 	err = <-flushed
 	if err != nil {
-		t.Fatalf("flush: %v", err)
+		t.Fatalf("flush of the first report: %v", err)
 	}
 
-	// Writes from here on, the final one at stop included, go
-	// through unheld.
-	buf.OnFileCreated(func(*os.File) {})
-
 	err = buf.Append(report)
 	if err != nil {
-		t.Fatalf("report after the write was complete: %v", err)
+		t.Fatalf("report after the first write was complete: %v", err)
 	}
 
 	if exists(t, writing) {
@@ -604,7 +622,11 @@ func TestTwoFlushesInOneMillisecond(t *testing.T) {
 		}
 	}
 
-	files := readReportFiles(t, dir)
+	files, err := readReportFiles(dir)
+	if err != nil {
+		t.Fatalf("read report files: %v", err)
+	}
+
 	if len(files) != flushes {
 		t.Fatalf("%d report files after %d flushes", len(files), flushes)
 	}
@@ -617,6 +639,88 @@ func TestTwoFlushesInOneMillisecond(t *testing.T) {
 	}
 }
 
+// TestReportFileHoldsTheLinesAppended flushes three reports and reads
+// their file back: it must decompress to exactly their JSON lines, in
+// the order they were appended.
+func TestReportFileHoldsTheLinesAppended(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("DATA_DIR", dir)
+
+	buf := startBuffer(t)
+
+	for _, id := range []int{1, 2, 3} {
+		err := buf.Append(map[string]int{"id": id})
+		if err != nil {
+			t.Fatalf("append report %d: %v", id, err)
+		}
+	}
+
+	err := buf.Flush()
+	if err != nil {
+		t.Fatalf("flush: %v", err)
+	}
+
+	files, err := readReportFiles(dir)
+	if err != nil {
+		t.Fatalf("read report files: %v", err)
+	}
+
+	want := `{"id":1}` + "\n" + `{"id":2}` + "\n" + `{"id":3}` + "\n"
+	if len(files) != 1 || files[0] != want {
+		t.Fatalf("report files = %q, want one holding %q", files, want)
+	}
+}
+
+// TestFlushAtSizeThreshold appends reports until the buffer holds
+// FlushSizeThreshold bytes. The append that gets it there must write
+// them all to one report file, with no call to Flush and the periodic
+// flush a minute away, and no earlier append may write one.
+func TestFlushAtSizeThreshold(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("DATA_DIR", dir)
+
+	buf := startBuffer(t)
+
+	// Large reports, so the threshold takes a few hundred appends.
+	pad := strings.Repeat("a", 64<<10)
+
+	var appended strings.Builder
+
+	for id := 0; appended.Len() < reportbuf.FlushSizeThreshold; id++ {
+		report := map[string]any{"id": id, "pad": pad}
+
+		err := buf.Append(report)
+		if err != nil {
+			t.Fatalf("append report %d: %v", id, err)
+		}
+
+		line, err := json.Marshal(report)
+		if err != nil {
+			t.Fatalf("marshal report %d: %v", id, err)
+		}
+
+		appended.Write(line)
+		appended.WriteByte('\n')
+	}
+
+	// Append writes the file in the background, so wait for it.
+	deadline := time.Now().Add(10 * time.Second)
+
+	for {
+		files, err := readReportFiles(dir)
+		if err == nil && len(files) == 1 && files[0] == appended.String() {
+			return
+		}
+
+		if time.Now().After(deadline) {
+			t.Fatalf("%d report files (error: %v), want one holding the "+
+				"%d bytes appended", len(files), err, appended.Len())
+		}
+
+		time.Sleep(10 * time.Millisecond)
+	}
+}
+
 // reportFilesBytes returns the total size of the report files in dir.
 func reportFilesBytes(t *testing.T, dir string) int64 {
 	t.Helper()
@@ -641,20 +745,19 @@ func reportFilesBytes(t *testing.T, dir string) int64 {
 }
 
 // readReportFiles returns the decompressed contents of each report
-// file in dir.
+// file in dir. A file still being written does not decompress, so it
-func readReportFiles(t *testing.T, dir string) []string {
+// gives an error.
-	t.Helper()
+func readReportFiles(dir string) ([]string, error) {
-
 	files := os.DirFS(dir)
 
 	names, err := fs.Glob(files, "reports-*.jsonl.zst")
 	if err != nil {
-		t.Fatalf("list report files: %v", err)
+		return nil, fmt.Errorf("list report files: %w", err)
 	}
 
 	dec, err := zstd.NewReader(nil)
 	if err != nil {
-		t.Fatalf("create zstd decoder: %v", err)
+		return nil, fmt.Errorf("create zstd decoder: %w", err)
 	}
 	defer dec.Close()
 
@@ -663,18 +766,18 @@ func readReportFiles(t *testing.T, dir string) []string {
 	for _, name := range names {
 		compressed, readErr := fs.ReadFile(files, name)
 		if readErr != nil {
-			t.Fatalf("read %s: %v", name, readErr)
+			return nil, fmt.Errorf("read %s: %w", name, readErr)
 		}
 
 		data, decErr := dec.DecodeAll(compressed, nil)
 		if decErr != nil {
-			t.Fatalf("decompress %s: %v", name, decErr)
+			return nil, fmt.Errorf("decompress %s: %w", name, decErr)
 		}
 
 		contents = append(contents, string(data))
 	}
 
-	return contents
+	return contents, nil
 }
 
 // reportFilePath returns the path in dir of a report file named as

backend/script/test

@@ -1,12 +1,20 @@
 #!/bin/sh
-# script/test: run the backend test suite.
+# script/test: run the backend test suite with the race detector and
+# coverage. Go's own -timeout bounds the tests and not their compile,
+# so a cold build cache cannot fail it. The race detector needs cgo,
+# and so a C compiler. If the tests fail, they run again with -v for
+# the details, and the script fails even if that run passes.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    timeout 30 go test ./...
+    go test -timeout 30s -race -cover ./... || {
+        echo "--- Rerunning with -v for details ---"
+        go test -timeout 30s -race -v ./...
+        exit 1
+    }
 }
 
 main "$@"

script/bootstrap

@@ -64,7 +64,8 @@ detect_pkgmgr() {
     fi
 }
 
-# pkg_install <nix-attr> <apt-pkg> <brew-formula> <apk-pkg>
+# pkg_install <nix-attr> <apt-pkgs> <brew-formula> <apk-pkgs>: the apt
+# and apk arguments may each list several packages, separated by spaces.
 pkg_install() {
     detect_pkgmgr
     case "$PKGMGR" in
@@ -74,10 +75,10 @@ pkg_install() {
                 $SUDO env DEBIAN_FRONTEND=noninteractive apt-get update
                 APT_UPDATED=1
             fi
-            $SUDO env DEBIAN_FRONTEND=noninteractive apt-get install -y "$2"
+            $SUDO env DEBIAN_FRONTEND=noninteractive apt-get install -y $2
             ;;
         brew) brew install "$3" ;;
-        apk) apk add --no-cache "$4" ;;
+        apk) apk add --no-cache $4 ;;
     esac
 }
 
@@ -253,6 +254,12 @@ main() {
 
     if missing make; then pkg_install gnumake make make make; fi
     if missing git; then pkg_install git git git git; fi
+    # The race detector in make test needs cgo, which Go turns on only
+    # when it finds its C compiler, gcc on Linux. apt and apk ship the C
+    # library headers apart from gcc.
+    if missing gcc; then
+        pkg_install gcc "gcc libc6-dev" gcc "gcc musl-dev"
+    fi
 
     ensure_node
     ensure_yarn

script/test

@@ -1,14 +1,17 @@
 #!/bin/sh
 # script/test: run the test suite for the whole repo: the frontend at
-# the repo root, then the Go backend in backend/. Both halves together
+# the repo root, then the Go backend in backend/. Each half has its own
-# get 30 seconds; each also keeps its own limit for the Dockerfiles.
+# 30-second limit, and there is none around both: from a cold Go build
+# cache, compiling the backend's tests with the race detector can take
+# 30 seconds on its own, and Go's -timeout leaves the compile out.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 main() {
     cd "$ROOT"
-    timeout 30 sh -c 'script/frontend-test && backend/script/test'
+    script/frontend-test
+    backend/script/test
 }
 
 main "$@"