dagger/dagger · error

short write %d/%d

Error message

short write %d/%d

What it means

Returned when rFile.write reports it wrote fewer bytes than the PACKET_DATA chunk contained (n != len(pkt.Data)). The io.PipeWriter normally returns either full writes or an error, so a short write indicates an unexpected pipe writer behavior; the file is closed with the error and Walk aborts.

Source

Thrown at engine/filesync/remotefs.go:170

				fs.filesMu.RLock()
				rFile, ok := fs.filesByID[pkt.ID]
				fs.filesMu.RUnlock()
				if !ok {
					return fmt.Errorf("invalid file request %d", pkt.ID)
				}
				if len(pkt.Data) == 0 {
					if err := rFile.CloseWrite(nil); err != nil {
						return fmt.Errorf("failed to close pipe %d: %w", pkt.ID, err)
					}
				} else {
					n, err := rFile.write(pkt.Data)
					if err != nil {
						err = fmt.Errorf("failed to write to pipe %d: %w", pkt.ID, err)
						rFile.CloseWrite(err)
						return err
					}
					if n != len(pkt.Data) {
						err := fmt.Errorf("short write %d/%d", n, len(pkt.Data))
						rFile.CloseWrite(err)
						return err
					}
				}
			}
		}
	}()

	for cp := range walkCh {
		if err := walkFn(cp.path, &StatInfo{cp.stat}, nil); err != nil {
			return err
		}
	}
	select {
	case err := <-errCh:
		return fmt.Errorf("receive failed: %w", err)
	default:
		return nil

View on GitHub (pinned to 82ba2681db)

Solutions

1. Retry the sync operation; this aborts the whole Walk so nothing is partially committed
2. Check the dagger version for known streaming bugs and upgrade CLI/engine together
3. Report with reproduction details if it recurs, including file size and include/exclude patterns

if err != nil && strings.Contains(err.Error(), "short write") {
    // whole Walk aborted; retry from scratch
    err = fs.Walk(ctx, ".", walkFn)
}

When it happens

Trigger: rFile.write (io.PipeWriter.Write) returns n < len(pkt.Data) with a nil error while streaming a file's data chunk during Walk.

Common situations: Practically rare; would indicate an anomalous pipe implementation or memory/contract violation in the streaming path rather than user misconfiguration.

Related errors

• failed to receive file bytes message: %w
• failed to close file: %w
• failed to close pipe %d: %w
• failed to write to pipe %d: %w
• count lines of added %s: %w

AI-assisted analysis of dagger/dagger@82ba2681db (2026-09-05). Data as JSON: /api/errors/1eed5f5b83bef6db. Report an issue: GitHub.