rest: test that zero-length replies over HTTP2 work correctly

The first test function ensures that the workaround works as expected.
And the second test function is intended to fail as soon as the issue
has been fixed in golang to allow us to eventually remove the
workaround.

internal/backend/rest/rest_int_go114_test.go

@@ -0,0 +1,94 @@
+// +build go1.14
+
+package rest_test
+
+import (
+	"context"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+
+	"github.com/restic/restic/internal/backend/rest"
+	"github.com/restic/restic/internal/restic"
+)
+
+func TestZeroLengthRead(t *testing.T) {
+	// Test workaround for https://github.com/golang/go/issues/46071. Can be removed once this is fixed in Go
+	// and the minimum golang version supported by restic includes the fix.
+	numRequests := 0
+	srv := httptest.NewUnstartedServer(http.HandlerFunc(func(res http.ResponseWriter, req *http.Request) {
+		numRequests++
+		t.Logf("req %v %v", req.Method, req.URL.Path)
+		if req.Method == "GET" {
+			res.Header().Set("Content-Length", "42")
+			// Now the handler fails for some reason and is unable to send data
+			return
+		}
+
+		t.Errorf("unhandled request %v %v", req.Method, req.URL.Path)
+	}))
+	srv.EnableHTTP2 = true
+	srv.StartTLS()
+	defer srv.Close()
+
+	srvURL, err := url.Parse(srv.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	cfg := rest.Config{
+		Connections: 5,
+		URL:         srvURL,
+	}
+	be, err := rest.Open(cfg, srv.Client().Transport)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		err = be.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	err = be.Load(context.TODO(), restic.Handle{Type: restic.ConfigFile}, 0, 0, func(rd io.Reader) error {
+		_, err := ioutil.ReadAll(rd)
+		if err == nil {
+			t.Fatal("ReadAll should have returned an 'Unexpected EOF' error")
+		}
+		return nil
+	})
+	if err == nil {
+		t.Fatal("Got no unexpected EOF error")
+	}
+}
+
+func TestGolangZeroLengthRead(t *testing.T) {
+	// This test is intended to fail once the underlying issue has been fixed in Go
+	ts := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Length", "42")
+		// Now the handler fails for some reason and is unable to send data
+	}))
+	ts.EnableHTTP2 = true
+	ts.StartTLS()
+	defer ts.Close()
+
+	res, err := ts.Client().Get(ts.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = ioutil.ReadAll(res.Body)
+	defer func() {
+		err = res.Body.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+	}()
+	if err != nil {
+		// This should fail with an 'Unexpected EOF' error
+		t.Fatal(err)
+	}
+}