intercept: use already buffered response if possible when intercepting (#7028)

WeidiDeng committed Oct 21, 2025 at 12:48 UTC a7885aabec375db38ac6c221c7c709dc83122535

1 file changed +28 -2

modules/caddyhttp/intercept/intercept.go

+28 -2

@@ -17,6 +17,7 @@ package intercept

17 import (

18 "bytes"

19 "fmt"

20 + "io"

21 "net/http"

22 "strconv"

23 "strings"

@@ -175,10 +176,35 @@ func (ir Intercept) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddy

176 c.Write(zap.Int("handler", rec.handlerIndex))

177 }

178

178 - // pass the request through the response handler routes

179 - return rec.handler.Routes.Compile(next).ServeHTTP(w, r)

179 + // response recorder doesn't create a new copy of the original headers, they're

180 + // present in the original response writer

181 + // create a new recorder to see if any response body from the new handler is present,

182 + // if not, use the already buffered response body

183 + recorder := caddyhttp.NewResponseRecorder(w, nil, nil)

184 + if err := rec.handler.Routes.Compile(emptyHandler).ServeHTTP(recorder, r); err != nil {

185 + return err

186 + }

187 +

188 + // no new response status and the status is not 0

189 + if recorder.Status() == 0 && rec.Status() != 0 {

190 + w.WriteHeader(rec.Status())

191 + }

192 +

193 + // no new response body and there is some in the original response

194 + // TODO: what if the new response doesn't have a body by design?

195 + // see: https://github.com/caddyserver/caddy/pull/6232#issue-2235224400

196 + if recorder.Size() == 0 && buf.Len() > 0 {

197 + _, err := io.Copy(w, buf)

198 + return err

199 + }

200 + return nil

201 }

202

203 +// this handler does nothing because everything we need is already buffered

204 +var emptyHandler caddyhttp.Handler = caddyhttp.HandlerFunc(func(_ http.ResponseWriter, req *http.Request) error {

205 + return nil

206 +})

207 +

208 // UnmarshalCaddyfile sets up the handler from Caddyfile tokens. Syntax:

209 //

210 // intercept [<matcher>] {