What causes "failed to buffer stream to temp file: %w" in argoproj/argo-workflows?

Inspect the wrapped error: read errors indicate upstream/network problems; write errors (ENOSPC) indicate disk space.

failed to buffer stream to temp file: %w

Error message

failed to buffer stream to temp file: %w

What it means

After creating the temp file, BufferReaderToTempFile copies the artifact stream into it with io.Copy. If the source reader errors mid-copy (or writing to the temp file fails, e.g. disk full), the temp file is closed/removed and this error is returned wrapping the cause.

Source

Thrown at workflow/artifacts/common/streaming.go:43

// function that removes it; cleanup is safe to call more than once. On error, any partially
// written temp file is removed before returning, so callers only need to defer cleanup
// after a nil error.
func BufferReaderToTempFile(reader io.Reader, pattern string) (path string, cleanup func(), err error) {
	noop := func() {}

	tmpFile, err := os.CreateTemp("", pattern)
	if err != nil {
		return "", noop, fmt.Errorf("failed to create temp file: %w", err)
	}
	name := tmpFile.Name()
	cleanup = func() {
		_ = os.Remove(name)
	}

	if _, err := io.Copy(tmpFile, reader); err != nil {
		_ = tmpFile.Close()
		cleanup()
		return "", noop, fmt.Errorf("failed to buffer stream to temp file: %w", err)
	}
	if err := tmpFile.Close(); err != nil {
		cleanup()
		return "", noop, fmt.Errorf("failed to close temp file: %w", err)
	}

	return name, cleanup, nil
}

View on GitHub (pinned to 35bff19146)

Solutions

Inspect the wrapped error: read errors indicate upstream/network problems; write errors (ENOSPC) indicate disk space.
Retry the operation — the temp file is cleaned up automatically so no stale artifacts remain.
Free/expand disk on the temp filesystem before re-running large artifacts.
Add timeouts/retries upstream or fetch from a more reliable replica of the artifact.
If streaming from HTTP artifacts, ensure the artifact server / source URL supports stable long-lived transfers.

Defensive patterns

Strategy: retry

Validate before calling

// ensure space for the expected artifact size before buffering
if st, ok := reader.(interface{ Len() int }); ok {
    if free, _ := diskFree(os.TempDir()); free < uint64(st.Len()) {
        return errors.New("insufficient temp disk space for artifact stream")
    }
}

Try / catch

err := artifactscommon.SaveStreamViaTempFile(reader, "upload-*", save)
if err != nil && strings.Contains(err.Error(), "failed to buffer stream") {
    if errors.Is(err, syscall.ENOSPC) {
        return fmt.Errorf("temp volume full during transfer: %w", err)
    }
    return fmt.Errorf("transient stream error, retry: %w", err) // temp file already cleaned up
}

Prevention

Size the temp volume for the largest expected artifact.
Use retryable readers (fresh HTTP requests per attempt) so retries can restart the stream.
Monitor node disk pressure conditions in Kubernetes.
Set read/write timeouts on upstream artifact sources to fail fast rather than hang.

When it happens

Trigger: io.Copy fails because the upstream reader errors: HTTP/S3/Azure stream broken mid-download, TLS timeout, or the temp filesystem fills up while writing (ENOSPC).

Common situations: Streaming large artifacts from flaky networks; storage backend returning 200-then-truncated body; disk quota on the node reached during save; interrupted upstream artifact service.

Related errors

AI-assisted analysis of argoproj/argo-workflows@35bff19146 (2026-09-03). Data as JSON: /api/errors/62bc212273c6a2a8. Report an issue: GitHub.