rest: remove workaround for content-length handling bug

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
 }