pushWriter: correctly propagate errors

In the refactor from 926b9c72f61b5be6bf8d952512f1d0932fbaf898, the error
handling was substantially reworked, and changed the types of errors
returned.

Notably, in the case of a network error, instead of propogating the
error through to return from pushWriter.Write (as previously), it would
be propagated through to pushWriter.Commit - however, this is too late,
since we've already closed the io.Pipe by the time we would have reached
this function. Therefore, we get the generic error message  "io:
read/write on closed pipe" for *every network error*.

This patch corrects this behavior to ensure that the correct error
object is always returned as early as possible, by checking the error
result after writing and detecting a closed pipe.

Additionally, we do some additional hardening - specifically we prevent
falling through when resetting the content or detecting errors, and
update the tests to explicitly check for the ErrReset message.

Signed-off-by: Justin Chadwell <me@jedevc.com>

remotes/docker/pusher.go

@@ -380,17 +380,24 @@ func (pw *pushWriter) Write(p []byte) (n int, err error) {
 
 			// If content has already been written, the bytes
 			// cannot be written and the caller must reset
-			if status.Offset > 0 {
-				status.Offset = 0
-				status.UpdatedAt = time.Now()
-				pw.tracker.SetStatus(pw.ref, status)
-				return 0, content.ErrReset
-			}
+			status.Offset = 0
+			status.UpdatedAt = time.Now()
+			pw.tracker.SetStatus(pw.ref, status)
+			return 0, content.ErrReset
 		default:
 		}
 	}
 
 	n, err = pw.pipe.Write(p)
+	if errors.Is(err, io.ErrClosedPipe) {
+		// if the pipe is closed, we might have the original error on the error
+		// channel - so we should try and get it
+		select {
+		case err2 := <-pw.errC:
+			err = err2
+		default:
+		}
+	}
 	status.Offset += int64(n)
 	status.UpdatedAt = time.Now()
 	pw.tracker.SetStatus(pw.ref, status)
@@ -431,7 +438,7 @@ func (pw *pushWriter) Digest() digest.Digest {
 
 func (pw *pushWriter) Commit(ctx context.Context, size int64, expected digest.Digest, opts ...content.Opt) error {
 	// Check whether read has already thrown an error
-	if _, err := pw.pipe.Write([]byte{}); err != nil && err != io.ErrClosedPipe {
+	if _, err := pw.pipe.Write([]byte{}); err != nil && !errors.Is(err, io.ErrClosedPipe) {
 		return fmt.Errorf("pipe error before commit: %w", err)
 	}
 
@@ -442,9 +449,7 @@ func (pw *pushWriter) Commit(ctx context.Context, size int64, expected digest.Di
 	var resp *http.Response
 	select {
 	case err := <-pw.errC:
-		if err != nil {
-			return err
-		}
+		return err
 	case resp = <-pw.respC:
 		defer resp.Body.Close()
 	case p, ok := <-pw.pipeC:
@@ -456,18 +461,17 @@ func (pw *pushWriter) Commit(ctx context.Context, size int64, expected digest.Di
 		}
 		pw.pipe.CloseWithError(content.ErrReset)
 		pw.pipe = p
+
+		// If content has already been written, the bytes
+		// cannot be written again and the caller must reset
 		status, err := pw.tracker.GetStatus(pw.ref)
 		if err != nil {
 			return err
 		}
-		// If content has already been written, the bytes
-		// cannot be written again and the caller must reset
-		if status.Offset > 0 {
-			status.Offset = 0
-			status.UpdatedAt = time.Now()
-			pw.tracker.SetStatus(pw.ref, status)
-			return content.ErrReset
-		}
+		status.Offset = 0
+		status.UpdatedAt = time.Now()
+		pw.tracker.SetStatus(pw.ref, status)
+		return content.ErrReset
 	}
 
 	// 201 is specified return status, some registries return

remotes/docker/pusher_test.go

@@ -117,26 +117,19 @@ func TestPusherErrReset(t *testing.T) {
 	}
 
 	w, err := p.push(context.Background(), desc, remotes.MakeRefKey(context.Background(), desc), false)
-	assert.Equal(t, err, nil, "no error should be there")
+	assert.NoError(t, err)
 
-	w.Write(ct)
+	// first push should fail with ErrReset
+	_, err = w.Write(ct)
+	assert.NoError(t, err)
+	err = w.Commit(context.Background(), desc.Size, desc.Digest)
+	assert.Equal(t, content.ErrReset, err)
 
-	pw, _ := w.(*pushWriter)
-
-	select {
-	case p := <-pw.pipeC:
-		p.Write(ct)
-	case e := <-pw.errC:
-		assert.Failf(t, "error: %v while retrying request", e.Error())
-	}
-
-	select {
-	case resp := <-pw.respC:
-		assert.Equalf(t, resp.StatusCode, http.StatusCreated,
-			"201 should be the response code when uploading new content")
-	case <-pw.errC:
-		assert.Fail(t, "should not give error")
-	}
+	// second push should succeed
+	_, err = w.Write(ct)
+	assert.NoError(t, err)
+	err = w.Commit(context.Background(), desc.Size, desc.Digest)
+	assert.NoError(t, err)
 }
 
 func tryUpload(ctx context.Context, t *testing.T, p dockerPusher, layerContent []byte) error {