From 4e2c3fc7d85a6bbecf03c5b651dcd68b9126f954 Mon Sep 17 00:00:00 2001
From: Landry Benguigui <lbenguigui@gmail.com>
Date: Fri, 21 Mar 2025 15:55:07 +0100
Subject: [PATCH] fix: ensure bufferWriter returns an error when exceeding
 maxResponseBodyBytes

---
 buffer/buffer.go      | 22 ++++++++++++++--------
 buffer/buffer_test.go |  8 ++++++--
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/buffer/buffer.go b/buffer/buffer.go
index 4c528228..cf312c87 100644
--- a/buffer/buffer.go
+++ b/buffer/buffer.go
@@ -164,6 +164,19 @@ func (b *Buffer) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 
 	outReq := b.copyRequest(req, body, totalSize)
 
+	defer func() {
+		if err := recover(); err != nil {
+			if err == http.ErrAbortHandler {
+				b.log.Error("vulcand/oxy/buffer: failed to read response, err: %v", err)
+
+				b.errHandler.ServeHTTP(w, req, err.(error))
+				return
+			}
+
+			panic(err)
+		}
+	}()
+
 	attempt := 1
 	for {
 		// We create a special writer that will limit the response size, buffer it to disk if necessary
@@ -292,14 +305,7 @@ func (b *bufferWriter) Header() http.Header {
 }
 
 func (b *bufferWriter) Write(buf []byte) (int, error) {
-	length, err := b.buffer.Write(buf)
-	if err != nil {
-		// Since go1.11 (https://github.com/golang/go/commit/8f38f28222abccc505b9a1992deecfe3e2cb85de)
-		// if the writer returns an error, the reverse proxy panics
-		b.log.Error("write: %v", err)
-		length = len(buf)
-	}
-	return length, nil
+	return b.buffer.Write(buf)
 }
 
 // WriteHeader sets rw.Code.
diff --git a/buffer/buffer_test.go b/buffer/buffer_test.go
index 972692f3..e996553f 100644
--- a/buffer/buffer_test.go
+++ b/buffer/buffer_test.go
@@ -2,6 +2,7 @@ package buffer
 
 import (
 	"bufio"
+	"crypto/rand"
 	"crypto/tls"
 	"fmt"
 	"io"
@@ -173,8 +174,11 @@ func TestBuffer_requestLimitReached(t *testing.T) {
 }
 
 func TestBuffer_responseLimitReached(t *testing.T) {
+	payload := make([]byte, 40000)
+	_, _ = rand.Read(payload)
+
 	srv := testutils.NewHandler(func(w http.ResponseWriter, _ *http.Request) {
-		_, _ = w.Write([]byte("hello, this response is too large"))
+		_, _ = w.Write(payload)
 	})
 	t.Cleanup(srv.Close)
 
@@ -188,7 +192,7 @@ func TestBuffer_responseLimitReached(t *testing.T) {
 	})
 
 	// stream handler will forward requests to redirect
-	st, err := New(rdr, MaxResponseBodyBytes(4))
+	st, err := New(rdr, MaxResponseBodyBytes(10000))
 	require.NoError(t, err)
 
 	proxy := httptest.NewServer(st)