remote build: fix streaming and error handling

Address a number of issues in the streaming logic in remote build, most
importantly an error in using buffered channels on the server side.

The pattern below does not guarantee that the channel is entirely read
before the context fires.

for {
	select {
		case <- bufferedChannel:
		...
		case <- ctx.Done():
		...
	}
}

Fixes: #10154
Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

1 files changed, 23 insertions, 15 deletions

diff --git a/pkg/bindings/images/build.go b/pkg/bindings/images/build.go
index 142204f27..a35f461a7 100644
--- a/pkg/bindings/images/build.go
+++ b/pkg/bindings/images/build.go
@@ -391,42 +391,50 @@ func Build(ctx context.Context, containerFiles []string, options entities.BuildO
 	dec := json.NewDecoder(body)
 
 	var id string
-	var mErr error
 	for {
 		var s struct {
 			Stream string `json:"stream,omitempty"`
 			Error  string `json:"error,omitempty"`
 		}
-		if err := dec.Decode(&s); err != nil {
-			if errors.Is(err, io.EOF) {
-				if mErr == nil && id == "" {
-					mErr = errors.New("stream dropped, unexpected failure")
-				}
-				break
-			}
-			s.Error = err.Error() + "\n"
-		}
 
 		select {
+		// FIXME(vrothberg): it seems we always hit the EOF case below,
+		// even when the server quit but it seems desirable to
+		// distinguish a proper build from a transient EOF.
 		case <-response.Request.Context().Done():
-			return &entities.BuildReport{ID: id}, mErr
+			return &entities.BuildReport{ID: id}, nil
 		default:
 			// non-blocking select
 		}
 
+		if err := dec.Decode(&s); err != nil {
+			if errors.Is(err, io.ErrUnexpectedEOF) {
+				return nil, errors.Wrap(err, "server probably quit")
+			}
+			// EOF means the stream is over in which case we need
+			// to have read the id.
+			if errors.Is(err, io.EOF) && id != "" {
+				break
+			}
+			return &entities.BuildReport{ID: id}, errors.Wrap(err, "decoding stream")
+		}
+
 		switch {
 		case s.Stream != "":
-			stdout.Write([]byte(s.Stream))
-			if iidRegex.Match([]byte(s.Stream)) {
+			raw := []byte(s.Stream)
+			stdout.Write(raw)
+			if iidRegex.Match(raw) {
 				id = strings.TrimSuffix(s.Stream, "\n")
 			}
 		case s.Error != "":
-			mErr = errors.New(s.Error)
+			// If there's an error, return directly.  The stream
+			// will be closed on return.
+			return &entities.BuildReport{ID: id}, errors.New(s.Error)
 		default:
 			return &entities.BuildReport{ID: id}, errors.New("failed to parse build results stream, unexpected input")
 		}
 	}
-	return &entities.BuildReport{ID: id}, mErr
+	return &entities.BuildReport{ID: id}, nil
 }
 
 func nTar(excludes []string, sources ...string) (io.ReadCloser, error) {