From e72a543eb9e6fd40918f628e741922edcf4411ea Mon Sep 17 00:00:00 2001
From: rajpreetcodes <rskkalt@gmail.com>
Date: Wed, 14 Oct 2026 19:43:52 +0530
Subject: [PATCH] fix(middleware): restore previous response writer in BodyDump

BodyDump installs a wrapped bodyDumpResponseWriter on the Echo Context via c.SetResponse, but previously never restored the original writer when the middleware returned. Because Echo invokes HTTPErrorHandler after the middleware chain has unwound, subsequent error handler writes went through the wrapped writer into a buffer that had already been returned to bodyDumpBufferPool, creating a data race and potential body corruption under concurrent load.

Defer restoring the original response writer so that c.Response is reset before the pooled buffer is returned and before downstream error handling runs. Add regression tests verifying response writer restoration and concurrent error handling.

Fixes #3173
---
 middleware/body_dump.go      |  4 ++-
 middleware/body_dump_test.go | 50 ++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/middleware/body_dump.go b/middleware/body_dump.go
index 0443a67ab..dc281d73b 100644
--- a/middleware/body_dump.go
+++ b/middleware/body_dump.go
@@ -127,11 +127,13 @@ func (config BodyDumpConfig) ToMiddleware() (echo.MiddlewareFunc, error) {
 			} else {
 				respWriter = io.MultiWriter(c.Response(), resBuf)
 			}
+			origResponse := c.Response()
 			writer := &bodyDumpResponseWriter{
 				Writer:         respWriter,
-				ResponseWriter: c.Response(),
+				ResponseWriter: origResponse,
 			}
 			c.SetResponse(writer)
+			defer c.SetResponse(origResponse)
 
 			err := next(c)
 
diff --git a/middleware/body_dump_test.go b/middleware/body_dump_test.go
index e5f64541a..ee7082bf8 100644
--- a/middleware/body_dump_test.go
+++ b/middleware/body_dump_test.go
@@ -4,11 +4,13 @@
 package middleware
 
 import (
+	"bytes"
 	"errors"
 	"io"
 	"net/http"
 	"net/http/httptest"
 	"strings"
+	"sync"
 	"testing"
 
 	"github.com/labstack/echo/v5"
@@ -579,3 +581,51 @@ func BenchmarkBodyDump_BufferPooling(b *testing.B) {
 		mw(h)(c)
 	}
 }
+
+func TestBodyDump_RestoreResponse(t *testing.T) {
+	e := echo.New()
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	rec := httptest.NewRecorder()
+	c := e.NewContext(req, rec)
+	origResponse := c.Response()
+
+	mw, err := BodyDumpConfig{
+		Handler: func(c *echo.Context, reqBody, resBody []byte, err error) {},
+	}.ToMiddleware()
+	assert.NoError(t, err)
+
+	var innerResponse http.ResponseWriter
+	h := func(c *echo.Context) error {
+		innerResponse = c.Response()
+		return c.String(http.StatusOK, "ok")
+	}
+
+	err = mw(h)(c)
+	assert.NoError(t, err)
+	assert.NotEqual(t, origResponse, innerResponse)
+	assert.Equal(t, origResponse, c.Response())
+}
+
+func TestBodyDump_ErrorHandlerRace(t *testing.T) {
+	e := echo.New()
+	e.HTTPErrorHandler = func(c *echo.Context, err error) {
+		_ = c.JSON(http.StatusOK, map[string]any{"error": err.Error()})
+	}
+	e.Pre(BodyDump(func(c *echo.Context, reqBody, rspBody []byte, err error) {}))
+	e.POST("/err", func(c *echo.Context) error {
+		return echo.NewHTTPError(http.StatusBadRequest, "boom")
+	})
+
+	var wg sync.WaitGroup
+	for i := 0; i < 16; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for j := 0; j < 200; j++ {
+				req := httptest.NewRequest(http.MethodPost, "/err", bytes.NewReader(make([]byte, 256)))
+				e.ServeHTTP(httptest.NewRecorder(), req)
+			}
+		}()
+	}
+	wg.Wait()
+}