vxcontrol/pentagi · error

failed to read list output for '%s': %w

Error message

failed to read list output for '%s': %w

What it means

demuxExecStdout reads the multiplexed exec stream and its error is wrapped with this message. Failures include a truncated frame (ErrUnexpectedEOF mid-header/frame), stdout exceeding the byte cap, or a daemon-injected systemerr frame. In all cases the listing is considered incomplete and is discarded rather than served partially.

Source

Thrown at backend/pkg/docker/client.go:1003

	// including a \n that is part of a filename — corrupting the name. Without a
	// TTY the exec stream is multiplexed and demuxed below.
	createResp, err := dc.ContainerExecCreate(ctx, containerID, client.ExecCreateOptions{
		Cmd:          []string{"find", dirPath, "-maxdepth", "1", "-mindepth", "1", "!", "-name", ".*", "-print0"},
		AttachStdout: true,
		AttachStderr: true,
	})
	if err != nil {
		return ContainerDirListing{}, fmt.Errorf("failed to create list exec for '%s': %w", dirPath, err)
	}

	resp, err := dc.ContainerExecAttach(ctx, createResp.ID, client.ExecAttachOptions{})
	if err != nil {
		return ContainerDirListing{}, fmt.Errorf("failed to attach list exec for '%s': %w", dirPath, err)
	}
	output, readErr := demuxExecStdout(resp.Reader, maxListStdoutBytes)
	resp.Close()
	if readErr != nil {
		return ContainerDirListing{}, fmt.Errorf("failed to read list output for '%s': %w", dirPath, readErr)
	}

	inspect, err := dc.ContainerExecInspect(ctx, createResp.ID)
	if err != nil {
		return ContainerDirListing{}, fmt.Errorf("failed to inspect list exec for '%s': %w", dirPath, err)
	}
	if inspect.ExitCode != 0 {
		return ContainerDirListing{}, fmt.Errorf("list command failed for '%s' with exit code %d: %s", dirPath, inspect.ExitCode, string(output))
	}

	entryPaths, truncated := parseFindEntries(output)

	stats, failures := statContainerEntries(ctx, entryPaths, containerListWorkers, func(ctx context.Context, entryPath string) (container.PathStat, error) {
		return dc.ContainerStatPath(ctx, containerID, entryPath)
	})

	// A cancelled context is a directory-level fault (the client is gone), not a
	// partial listing, so surface it as an error. Entries that individually failed

View on GitHub (pinned to ea665308ba)

Solutions

1. List a narrower subdirectory instead of a huge parent (reduce output below the cap)
2. Retry the listing if the cause was a transient stream reset
3. Check why the container exited mid-exec (OOM, kill signal) via `docker inspect`
4. If the cap is legitimately too small for your workload, raise maxListStdoutBytes

Example fix

// before: giant dir overflows the cap
listing, err := dc.ListContainerDir(ctx, id, "/")
// after: list the intended subtree
listing, err := dc.ListContainerDir(ctx, id, "/workspace/src")

listing, err := client.ListContainerDir(ctx, containerID, dir)
if err != nil {
    if strings.Contains(err.Error(), "failed to read list output") {
        // stream read failed: retry or narrow the directory
        return retryListing(ctx, containerID, dir)
    }
    return err
}

When it happens

Trigger: The exec stream ends mid-frame (connection reset, daemon killed the stream, container OOM-killed while find was writing), the directory listing produces more than maxListStdoutBytes of stdout, or Docker injects a systemerr frame (stream id 3).

Common situations: Listing a huge directory (node_modules, /usr, /proc) blowing the output cap; container killed mid-exec; flaky connection to a remote Docker daemon; sandboxed workload deliberately flooding output.

Related errors

• failed to attach list exec for '%s': %w
• truncated exec stream: %w
• listing output exceeded %d bytes
• docker exec systemerr: %s
• failed to copy output: %w

AI-assisted analysis of vxcontrol/pentagi@ea665308ba (2026-09-01). Data as JSON: /api/errors/c40605988da5d0bf. Report an issue: GitHub.