Decompress HTTP/1.1 responses regardless of who set Accept-Encoding

example_client_test.go

@@ -328,13 +328,12 @@ func TestCompressionBrotli(t *testing.T) {
 	}
 	defer resp.Body.Close()
 
-	// HTTP/2 decodes the body even though the caller set Accept-Encoding, HTTP/1.1 only when it set it itself.
-	if resp.ProtoMajor == 2 {
-		if !resp.Uncompressed {
-			t.Fatal("brotli body was not decoded")
-		}
-	} else if h := resp.Header.Get("content-encoding"); h != "br" {
-		t.Fatalf("Got content-encoding header %v, expected br", h)
+	// Both protocols decode the body even though the caller set Accept-Encoding.
+	if !resp.Uncompressed {
+		t.Fatal("brotli body was not decoded")
+	}
+	if h := resp.Header.Get("content-encoding"); h != "" {
+		t.Fatalf("Got content-encoding header %v, expected none", h)
 	}
 }
 
@@ -370,9 +369,9 @@ func deflateServer(t *testing.T, zlibWrapped bool) *httptest.Server {
 	}))
 }
 
-// A caller that sets accept-encoding itself owns the decoding: the transport
-// must not decompress the body or strip Content-Encoding. Verify that, and
-// that the library decodes both deflate flavours.
+// The transport decodes by the response's Content-Encoding even when the caller
+// set accept-encoding itself, and strips the header. Verify that for both deflate
+// flavours.
 func testCompressionDeflate(t *testing.T, zlibWrapped bool) {
 	t.Helper()
 
@@ -393,11 +392,11 @@ func testCompressionDeflate(t *testing.T, zlibWrapped bool) {
 	}
 	defer resp.Body.Close()
 
-	if h := resp.Header.Get("content-encoding"); h != "deflate" {
-		t.Fatalf("Expected content encoding deflate, got %q", h)
+	if h := resp.Header.Get("content-encoding"); h != "" {
+		t.Fatalf("Expected no content encoding, got %q", h)
 	}
 
-	got, err := io.ReadAll(http.DecompressBodyByType(resp.Body, "deflate"))
+	got, err := io.ReadAll(resp.Body)
 	if err != nil {
 		t.Fatal(err)
 	}

transport.go

@@ -2190,7 +2190,7 @@ func (pc *persistConn) readLoop() {
 
 		resp.Body = body
 
-		if rc.addedGzip {
+		if !pc.t.DisableCompression {
 			resp.Body = DecompressBody(resp)
 		}
 
@@ -2467,11 +2467,6 @@ type requestAndChan struct {
 	cancelKey cancelKey
 	ch        chan responseAndError // unbuffered; always send in select on callerGone
 
-	// whether the Transport (as opposed to the user client code)
-	// added the Accept-Encoding gzip header. If the Transport
-	// set it, only then do we transparently decode the gzip.
-	addedGzip bool
-
 	// Optional blocking chan for Expect: 100-continue (for send).
 	// If the request has an "Expect: 100-continue" header and
 	// the server responds 100 Continue, readLoop send a value
@@ -2541,11 +2536,10 @@ func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err err
 	}
 
 	// Ask for a compressed version if the caller didn't set their
-	// own value for Accept-Encoding. We only attempt to
-	// uncompress the gzip stream if we were the layer that
-	// requested it.
+	// own value for Accept-Encoding. The response body is
+	// transparently decoded based on the response's actual
+	// Content-Encoding regardless of which layer asked for it.
 
-	requestedGzip := false
 	if !pc.t.DisableCompression &&
 		req.Header.Get("Accept-Encoding") == "" &&
 		req.Header.get("accept-encoding") == "" &&
@@ -2562,15 +2556,9 @@ func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err err
 		// We don't request gzip if the request is for a range, since
 		// auto-decoding a portion of a gzipped document will just fail
 		// anyway. See https://golang.org/issue/8923
-		requestedGzip = true
 		req.extraHeaders().Set("Accept-Encoding", "gzip, deflate, br, zstd")
 	}
 
-	// Set gzip to true if the caller's Accept-Encoding includes gzip.
-	if !pc.t.DisableCompression && (strings.Contains(req.Header.Get("Accept-Encoding"), "gzip") || strings.Contains(req.Request.Header.get("accept-encoding"), "gzip")) {
-		requestedGzip = true
-	}
-
 	var continueCh chan struct{}
 	if req.ProtoAtLeast(1, 1) && req.Body != nil && req.expectsContinue() {
 		continueCh = make(chan struct{}, 1)
@@ -2605,7 +2593,6 @@ func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err err
 		req:        req.Request,
 		cancelKey:  req.cancelKey,
 		ch:         resc,
-		addedGzip:  requestedGzip,
 		continueCh: continueCh,
 		callerGone: gone,
 	}