rest: remove workaround for content-length handling bug

changelog/unreleased/pull-4041

@@ -1,7 +1,7 @@
 Change: Update dependencies and require Go 1.18 or newer
 
 We've updated most dependencies. Since some libraries require newer language
-features we're dropping support for Go 1.15 - 1.17, which means that restic now
+features, we're dropping support for Go 1.15 - 1.17, which means that restic now
 requires at least Go 1.18 to build.
 
 https://github.com/restic/restic/pull/4041

internal/backend/rest/rest.go

@@ -8,10 +8,8 @@ import (
 	"io"
 	"io/ioutil"
 	"net/http"
-	"net/textproto"
 	"net/url"
 	"path"
-	"strconv"
 	"strings"
 
 	"github.com/restic/restic/internal/backend/layout"
@@ -214,44 +212,6 @@ func (b *Backend) Load(ctx context.Context, h restic.Handle, length int, offset
 	return err
 }
 
-// checkContentLength returns an error if the server returned a value in the
-// Content-Length header in an HTTP2 connection, but closed the connection
-// before any data was sent.
-//
-// This is a workaround for https://github.com/golang/go/issues/46071
-//
-// See also https://forum.restic.net/t/http2-stream-closed-connection-reset-context-canceled/3743/10
-func checkContentLength(resp *http.Response) error {
-	// the following code is based on
-	// https://github.com/golang/go/blob/b7a85e0003cedb1b48a1fd3ae5b746ec6330102e/src/net/http/h2_bundle.go#L8646
-
-	if resp.ContentLength != 0 {
-		return nil
-	}
-
-	if resp.ProtoMajor != 2 && resp.ProtoMinor != 0 {
-		return nil
-	}
-
-	if len(resp.Header[textproto.CanonicalMIMEHeaderKey("Content-Length")]) != 1 {
-		return nil
-	}
-
-	// make sure that if the server returned a content length and we can
-	// parse it, it is really zero, otherwise return an error
-	contentLength := resp.Header.Get("Content-Length")
-	cl, err := strconv.ParseUint(contentLength, 10, 63)
-	if err != nil {
-		return fmt.Errorf("unable to parse Content-Length %q: %w", contentLength, err)
-	}
-
-	if cl != 0 {
-		return errors.Errorf("unexpected EOF: got 0 instead of %v bytes", cl)
-	}
-
-	return nil
-}
-
 func (b *Backend) openReader(ctx context.Context, h restic.Handle, length int, offset int64) (io.ReadCloser, error) {
 	debug.Log("Load %v, length %v, offset %v", h, length, offset)
 	if err := h.Valid(); err != nil {
@@ -301,14 +261,6 @@ func (b *Backend) openReader(ctx context.Context, h restic.Handle, length int, o
 		return nil, errors.Errorf("unexpected HTTP response (%v): %v", resp.StatusCode, resp.Status)
 	}
 
-	// workaround https://github.com/golang/go/issues/46071
-	// see also https://forum.restic.net/t/http2-stream-closed-connection-reset-context-canceled/3743/10
-	err = checkContentLength(resp)
-	if err != nil {
-		_ = resp.Body.Close()
-		return nil, err
-	}
-
 	return resp.Body, nil
 }
 

internal/backend/rest/rest_int_go114_test.go

@@ -1,72 +0,0 @@
-//go:build go1.14 && !go1.18
-// +build go1.14,!go1.18
-
-// missing eof error is fixed in golang >= 1.17.3 or >= 1.16.10
-// remove the workaround from rest.go when the minimum golang version
-// supported by restic reaches 1.18.
-
-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")
-	}
-}