encode: ignore flushing until after first write (#4318)

* encode: ignore flushing until after first write (fix #4314) The first write will determine if encoding has to be done and will add an Content-Encoding. Until then Flushing has to be delayed so the Content-Encoding header can be added before headers and status code is written. (A passthrough flush would write header and status code) * Update modules/caddyhttp/encode/encode.go Co-authored-by: Matt Holt <mholt@users.noreply.github.com>

Steffen Brüheim committed Aug 31, 2021 at 21:36 UTC 4ebf100f099021bbec7eaa5284fe18f5f72feeb4

1 file changed +16

modules/caddyhttp/encode/encode.go

+16

@@ -182,6 +182,7 @@ type responseWriter struct {

182 buf *bytes.Buffer

183 config *Encode

184 statusCode int

185 + wroteHeader bool

186 }

187

188 // WriteHeader stores the status to write when the time comes

@@ -195,6 +196,19 @@ func (enc *Encode) Match(rw *responseWriter) bool {

196 return enc.Matcher.Match(rw.statusCode, rw.Header())

197 }

198

199 +// Flush implements http.Flusher. It delays the actual Flush of the underlying ResponseWriterWrapper

200 +// until headers were written.

201 +func (rw *responseWriter) Flush() {

202 + if !rw.wroteHeader {

203 + // flushing the underlying ResponseWriter will write header and status code,

204 + // but we need to delay that until we can determine if we must encode and

205 + // therefore add the Content-Encoding header; this happens in the first call

206 + // to rw.Write (see bug in #4314)

207 + return

208 + }

209 + rw.ResponseWriterWrapper.Flush()

210 +}

211 +

212 // Write writes to the response. If the response qualifies,

213 // it is encoded using the encoder, which is initialized

214 // if not done so already.

@@ -225,6 +239,7 @@ func (rw *responseWriter) Write(p []byte) (int, error) {

239 if rw.statusCode > 0 {

240 rw.ResponseWriter.WriteHeader(rw.statusCode)

241 rw.statusCode = 0

242 + rw.wroteHeader = true

243 }

244

245 switch {

@@ -271,6 +286,7 @@ func (rw *responseWriter) Close() error {

286 // that rely on If-None-Match, for example

287 rw.ResponseWriter.WriteHeader(rw.statusCode)

288 rw.statusCode = 0

289 + rw.wroteHeader = true

290 }

291 if rw.w != nil {

292 err2 := rw.w.Close()