reverseproxy: prevent body close on dial-error retries (#7547)

modules/caddyhttp/reverseproxy/reverseproxy.go

@@ -482,18 +482,31 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyht
 	reqHost := clonedReq.Host
 	reqHeader := clonedReq.Header
 
-	// If the cloned request body was fully buffered, keep a reference to its
-	// buffer so we can reuse it across retries and return it to the pool
-	// once we’re done.
+	// When retries are configured and there is a body, wrap it in
+	// io.NopCloser to prevent Go's transport from closing it on dial
+	// errors. cloneRequest does a shallow copy, so clonedReq.Body and
+	// r.Body share the same io.ReadCloser — a dial-failure Close()
+	// would kill the original body for all subsequent retry attempts.
+	// The real body is closed by the HTTP server when the handler
+	// returns.
+	//
+	// If the body was already fully buffered (via request_buffers),
+	// we also extract the buffer so the retry loop can replay it
+	// from the beginning on each attempt. (see #6259, #7546)
 	var bufferedReqBody *bytes.Buffer
-	if reqBodyBuf, ok := clonedReq.Body.(bodyReadCloser); ok && reqBodyBuf.body == nil && reqBodyBuf.buf != nil {
-		bufferedReqBody = reqBodyBuf.buf
-		reqBodyBuf.buf = nil
-
-		defer func() {
-			bufferedReqBody.Reset()
-			bufPool.Put(bufferedReqBody)
-		}()
+	if clonedReq.Body != nil && h.LoadBalancing != nil &&
+		(h.LoadBalancing.Retries > 0 || h.LoadBalancing.TryDuration > 0) {
+		if reqBodyBuf, ok := clonedReq.Body.(bodyReadCloser); ok && reqBodyBuf.body == nil && reqBodyBuf.buf != nil {
+			bufferedReqBody = reqBodyBuf.buf
+			reqBodyBuf.buf = nil
+			clonedReq.Body = io.NopCloser(bytes.NewReader(bufferedReqBody.Bytes()))
+			defer func() {
+				bufferedReqBody.Reset()
+				bufPool.Put(bufferedReqBody)
+			}()
+		} else {
+			clonedReq.Body = io.NopCloser(clonedReq.Body)
+		}
 	}
 
 	start := time.Now()