gzhttp: Add TransportAlwaysDecompress option.

gzhttp/compress.go

@@ -306,7 +306,7 @@ func (w *GzipResponseWriter) startPlain() error {
 func (w *GzipResponseWriter) WriteHeader(code int) {
 	// Handle informational headers
 	// This is gated to not forward 1xx responses on builds prior to go1.20.
-	if shouldWrite1xxResponses() && code >= 100 && code <= 199 {
+	if code >= 100 && code <= 199 {
 		w.ResponseWriter.WriteHeader(code)
 		return
 	}

gzhttp/compress_test.go

@@ -18,6 +18,7 @@ import (
 	"testing"
 
 	"github.com/klauspost/compress/gzip"
+	"github.com/klauspost/compress/zstd"
 )
 
 var (
@@ -1756,14 +1757,32 @@ func runBenchmark(b *testing.B, req *http.Request, handler http.Handler) {
 }
 
 func newTestHandler(body []byte) http.Handler {
+	var gzBuf bytes.Buffer
+	var zstdBuf bytes.Buffer
+	gz := gzip.NewWriter(&gzBuf)
+	gz.Write(body)
+	gz.Close()
+	zs, _ := zstd.NewWriter(&zstdBuf)
+	zs.Write(body)
+	zs.Close()
 	return GzipHandler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		switch r.URL.Path {
 		case "/gzipped":
+			// Add header. Write body as is.
 			w.Header().Set("Content-Encoding", "gzip")
 			w.Write(body)
 		case "/zstd":
+			// Add header. Write body as is.
 			w.Header().Set("Content-Encoding", "zstd")
 			w.Write(body)
+		case "/gzipped/do":
+			// Add header. Write gzipped body.
+			w.Header().Set("Content-Encoding", "gzip")
+			w.Write(gzBuf.Bytes())
+		case "/zstd/do":
+			// Add header. Write zstd body.
+			w.Header().Set("Content-Encoding", "zstd")
+			w.Write(zstdBuf.Bytes())
 		default:
 			w.Write(body)
 		}
@@ -1803,11 +1822,6 @@ func TestGzipHandlerNilContentType(t *testing.T) {
 
 // This test is an adapted version of net/http/httputil.Test1xxResponses test.
 func Test1xxResponses(t *testing.T) {
-	// do not test 1xx responses on builds prior to go1.20.
-	if !shouldWrite1xxResponses() {
-		return
-	}
-
 	wrapper, _ := NewWrapper()
 	handler := wrapper(http.HandlerFunc(
 		func(w http.ResponseWriter, r *http.Request) {

gzhttp/transport.go

@@ -61,10 +61,21 @@ func TransportCustomEval(fn func(header http.Header) bool) transportOption {
 	}
 }
 
+// TransportAlwaysDecompress will always decompress the response,
+// regardless of whether we requested it or not.
+// Default is false, which will pass compressed data through
+// if we did not request compression.
+func TransportAlwaysDecompress(enabled bool) transportOption {
+	return func(c *gzRoundtripper) {
+		c.alwaysDecomp = enabled
+	}
+}
+
 type gzRoundtripper struct {
 	parent             http.RoundTripper
 	acceptEncoding     string
 	withZstd, withGzip bool
+	alwaysDecomp       bool
 	customEval         func(header http.Header) bool
 }
 
@@ -90,15 +101,19 @@ func (g *gzRoundtripper) RoundTrip(req *http.Request) (*http.Response, error) {
 	}
 
 	resp, err := g.parent.RoundTrip(req)
-	if err != nil || !requestedComp {
+	if err != nil {
 		return resp, err
 	}
-	decompress := false
+	decompress := g.alwaysDecomp
 	if g.customEval != nil {
 		if !g.customEval(resp.Header) {
 			return resp, nil
 		}
 		decompress = true
+	} else {
+		if !requestedComp && !g.alwaysDecomp {
+			return resp, nil
+		}
 	}
 	// Decompress
 	if (decompress || g.withGzip) && asciiEqualFold(resp.Header.Get("Content-Encoding"), "gzip") {

gzhttp/transport_test.go

@@ -251,6 +251,71 @@ func TestTransportCustomEval(t *testing.T) {
 	}
 }
 
+func TestTransportTransportAlwaysDecompress(t *testing.T) {
+	bin, err := os.ReadFile("testdata/benchmark.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// We will serve the data as zstd+gzip, but the client will not request it.
+	server := httptest.NewServer(newTestHandler(bin))
+	c := http.Client{Transport: Transport(http.DefaultTransport, TransportEnableZstd(false), TransportEnableGzip(false), TransportAlwaysDecompress(true))}
+	resp, err := c.Get(server.URL + "/zstd/do")
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err := io.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(got, bin) {
+		t.Errorf("data mismatch")
+	}
+	resp.Body.Close()
+
+	resp, err = c.Get(server.URL + "/gzip/do")
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err = io.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(got, bin) {
+		t.Errorf("data mismatch")
+	}
+	resp.Body.Close()
+
+	// We will serve the data as zstd+gzip, but the client will not request it.
+	// With TransportAlwaysDecompress(false) it should not be decompressed.
+	c = http.Client{Transport: Transport(http.DefaultTransport, TransportEnableZstd(false), TransportEnableGzip(false), TransportAlwaysDecompress(false))}
+	resp, err = c.Get(server.URL + "/zstd/do")
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err = io.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if bytes.Equal(got, bin) {
+		t.Errorf("data matches")
+	}
+	resp.Body.Close()
+
+	resp, err = c.Get(server.URL + "/gzip/do")
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err = io.ReadAll(resp.Body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(got, bin) {
+		t.Errorf("data matches")
+	}
+	resp.Body.Close()
+}
+
 func BenchmarkTransport(b *testing.B) {
 	raw, err := os.ReadFile("testdata/benchmark.json")
 	if err != nil {