gzhttp: Remove header before writing (#639)

flate/stateless.go

@@ -59,9 +59,9 @@ var bitWriterPool = sync.Pool{
 	},
 }
 
-// StatelessDeflate allows to compress directly to a Writer without retaining state.
+// StatelessDeflate allows compressing directly to a Writer without retaining state.
 // When returning everything will be flushed.
-// Up to 8KB of an optional dictionary can be given which is presumed to presumed to precede the block.
+// Up to 8KB of an optional dictionary can be given which is presumed to precede the block.
 // Longer dictionaries will be truncated and will still produce valid output.
 // Sending nil dictionary is perfectly fine.
 func StatelessDeflate(out io.Writer, in []byte, eof bool, dict []byte) error {

gzhttp/compress.go

@@ -196,12 +196,13 @@ func (w *GzipResponseWriter) startGzip() error {
 
 // startPlain writes to sent bytes and buffer the underlying ResponseWriter without gzip.
 func (w *GzipResponseWriter) startPlain() error {
+	w.Header().Del(HeaderNoCompression)
 	if w.code != 0 {
 		w.ResponseWriter.WriteHeader(w.code)
 		// Ensure that no other WriteHeader's happen
 		w.code = 0
 	}
-	delete(w.Header(), HeaderNoCompression)
+
 	w.ignore = true
 	// If Write was never called then don't call Write on the underlying ResponseWriter.
 	if len(w.buf) == 0 {