fix(backend): rate-limit and cap report ingest, drop wildcard CORS (closes #20)

POST /api/v1/reports stays unauthenticated but is bounded. Each client
address, as the trusted-proxy logic resolves it, may send
REPORTS_PER_MINUTE reports a minute (default 60, all at once if it
likes), using golang.org/x/time/rate; past that it gets 429 with
Retry-After. Buckets that have refilled are dropped once a minute, so
idle addresses do not pile up. reportbuf refuses a report that would
take the report files past DATA_DIR_MAX_BYTES (default 1 GiB) with
ErrFull, answered with 507; the count starts from the files already in
DATA_DIR, and reports not yet written count at their uncompressed size.
CORS adds nothing unless CORS_ALLOWED_ORIGINS lists origins. A limit
that is not a positive number stops the server from starting.

Model: opus-5-5

backend/internal/server/routes_test.go

@@ -19,16 +19,13 @@ import (
 	"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()
+// newServer builds the server from the same constructors as main,
+// never started: SetupRoutes is called directly, so nothing listens.
+func newServer(t *testing.T) *server.Server {
+	t.Helper()
 
 	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,
@@ -50,6 +47,48 @@ func TestHealthCheckRejectsOversizeBody(t *testing.T) {
 
 	srv.SetupRoutes()
 
+	return srv
+}
+
+// TestReportsAreRateLimited checks that POST /api/v1/reports is
+// behind the per-address rate limit, set here to two a minute.
+func TestReportsAreRateLimited(t *testing.T) {
+	t.Setenv("REPORTS_PER_MINUTE", "2")
+
+	srv := newServer(t)
+
+	post := func() int {
+		rec := httptest.NewRecorder()
+		req := httptest.NewRequestWithContext(t.Context(),
+			http.MethodPost, "/api/v1/reports",
+			strings.NewReader(`{"clientId":"c1","hosts":[]}`),
+		)
+		srv.ServeHTTP(rec, req)
+
+		return rec.Code
+	}
+
+	for i := range 2 {
+		if code := post(); code != http.StatusOK {
+			t.Fatalf("report %d: status = %d, want %d",
+				i+1, code, http.StatusOK)
+		}
+	}
+
+	if code := post(); code != http.StatusTooManyRequests {
+		t.Fatalf("third report in a minute: status = %d, want %d",
+			code, http.StatusTooManyRequests)
+	}
+}
+
+// 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()
+
+	srv := newServer(t)
+
 	rec := httptest.NewRecorder()
 	req := httptest.NewRequestWithContext(t.Context(),
 		http.MethodGet, "/.well-known/healthcheck",