correctly handle recorded compressed response

see #1569 (comment)

_examples/request-body/read-query/main.go

@@ -1,4 +1,5 @@
-// package main contains an example on how to use the ReadForm, but with the same way you can do the ReadJSON & ReadJSON
+// package main contains an example on how to use the ReadQuery,
+// same way you can do the ReadJSON & ReadProtobuf and e.t.c.
 package main
 
 import (

context/compress.go

@@ -241,17 +241,22 @@ func releaseCompressResponseWriter(w *CompressResponseWriter) {
 // and writes the status code.
 // Called automatically before `EndResponse`.
 func (w *CompressResponseWriter) FlushResponse() {
+	w.FlushHeaders()
+
+	// write the status, after header set and before any flushed content sent.
+	w.ResponseWriter.FlushResponse()
+
+	w.CompressWriter.Close() // flushes and closes.
+}
+
+func (w *CompressResponseWriter) FlushHeaders() {
 	if w.Disabled {
 		w.Header().Del(VaryHeaderKey)
 		w.Header().Del(ContentEncodingHeaderKey)
 		w.CompressWriter.Reset(&noOpWriter{})
-		w.CompressWriter.Close()
 	} else {
 		w.ResponseWriter.Header().Del(ContentLengthHeaderKey)
-		w.CompressWriter.Close() // flushes and closes.
 	}
-
-	w.ResponseWriter.FlushResponse()
 }
 
 // EndResponse reeases the writers.

context/response_recorder.go

@@ -152,14 +152,24 @@ func (w *ResponseRecorder) FlushResponse() {
 		}
 	}
 
-	// NOTE: before the ResponseWriter.Write in order to:
-	// set the given status code even if the body is empty.
-	w.ResponseWriter.FlushResponse()
+	cw, mustWriteToClose := w.ResponseWriter.(*CompressResponseWriter)
+	if mustWriteToClose { // see #1569#issuecomment-664003098
+		cw.FlushHeaders()
+	} else {
+		// NOTE: before the ResponseWriter.Write in order to:
+		// set the given status code even if the body is empty.
+		w.ResponseWriter.FlushResponse()
+	}
 
 	if len(w.chunks) > 0 {
 		// ignore error
 		w.ResponseWriter.Write(w.chunks)
 	}
+
+	if mustWriteToClose {
+		cw.CompressWriter.Close()
+		cw.ResponseWriter.FlushResponse()
+	}
 }
 
 // Clone returns a clone of this response writer