http3: return http.ErrContentLength when writing too large response (#3953)

http3/response_writer.go

@@ -23,6 +23,8 @@ type responseWriter struct {
 	header        http.Header
 	status        int // status code passed to WriteHeader
 	headerWritten bool
+	contentLen    int64 // if handler set valid Content-Length header
+	numWritten    int64 // bytes written
 
 	logger utils.Logger
 }
@@ -61,6 +63,16 @@ func (w *responseWriter) WriteHeader(status int) {
 		if _, ok := w.header["Date"]; !ok {
 			w.header.Set("Date", time.Now().UTC().Format(http.TimeFormat))
 		}
+		// Content-Length checking
+		if clen := w.header.Get("Content-Length"); clen != "" {
+			if cl, err := strconv.ParseInt(clen, 10, 64); err == nil {
+				w.contentLen = cl
+			} else {
+				// emit a warning for malformed Content-Length and remove it
+				w.logger.Errorf("Malformed Content-Length %s", clen)
+				w.header.Del("Content-Length")
+			}
+		}
 	}
 	w.status = status
 
@@ -111,6 +123,12 @@ func (w *responseWriter) Write(p []byte) (int, error) {
 	if !bodyAllowed {
 		return 0, http.ErrBodyNotAllowed
 	}
+
+	w.numWritten += int64(len(p))
+	if w.contentLen != 0 && w.numWritten > w.contentLen {
+		return 0, http.ErrContentLength
+	}
+
 	df := &dataFrame{Length: uint64(len(p))}
 	w.buf = w.buf[:0]
 	w.buf = df.Append(w.buf)

http3/response_writer_test.go

@@ -167,4 +167,15 @@ var _ = Describe("Response Writer", func() {
 		Expect(rw.SetReadDeadline(time.Now().Add(1 * time.Second))).To(BeNil())
 		Expect(rw.SetWriteDeadline(time.Now().Add(1 * time.Second))).To(BeNil())
 	})
+
+	It(`checks Content-Length header`, func() {
+		rw.Header().Set("Content-Length", "6")
+		n, err := rw.Write([]byte("foobar"))
+		Expect(n).To(Equal(6))
+		Expect(err).To(BeNil())
+
+		n, err = rw.Write([]byte("foobar"))
+		Expect(n).To(Equal(0))
+		Expect(err).To(Equal(http.ErrContentLength))
+	})
 })