Bound every slog line against client-chosen text (closes #176)

internal/middleware/ratelimit.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/go-chi/httprate"
+	"sneak.berlin/go/webhooker/internal/logfield"
 )
 
 const (
@@ -225,11 +226,22 @@ func (m *Middleware) clientKey(r *http.Request) string {
 // rejection with logMessage and answers with responseMessage.
 // httprate adds the Retry-After header (RFC 6585). The aggregate
 // receiver limiter uses floodTooManyRequests instead.
+//
+// The path is capped against the same budget as the access log's url
+// field. The per-entrypoint receiver limiter is unauthenticated and
+// its path is a client-chosen segment of client-chosen length, so at
+// WARN an uncapped path would let a sender pick the size of the line
+// it writes — the same defect the access log capping closed.
 func (m *Middleware) tooManyRequests(
 	logMessage, responseMessage string,
 ) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		m.log.Warn(logMessage, "path", r.URL.Path)
+		m.log.Warn(
+			logMessage,
+			"path", logfield.Truncate(
+				r.URL.Path, logfield.MaxBytes,
+			),
+		)
 		http.Error(w, responseMessage, http.StatusTooManyRequests)
 	}
 }