unexpected multipart response during emit, please file a bug

Error message

unexpected multipart response during emit, please file a bugreport

What it means

In `finishCLIExport` (PostRun for `ipfs dag export`), the multipart response reader iterates over response parts. Since a CAR export should stream exactly one binary part, encountering a second multipart part after one was already processed indicates a protocol/encoding bug in the command framework, so it aborts with `CloseWithError` and asks the user to file a bugreport.

Source

Thrown at core/commands/dag/export.go:232

	bar := pb.New64(0).Set(pb.Bytes, true).SetWriter(os.Stderr).SetRefreshRate(500 * time.Millisecond)
	bar.SetTemplateString(progressBarTemplate)
	bar.Start()

	var processedOneResponse bool
	for {
		v, err := res.Next()
		if err != nil {
			if errors.Is(err, io.EOF) {
				// We only write the final bar update on success
				// On error it looks too weird
				bar.Finish()
				return re.Close()
			}
			return re.CloseWithError(err)
		}

		if processedOneResponse {
			return re.CloseWithError(errors.New("unexpected multipart response during emit, please file a bugreport"))
		}

		r, ok := v.(io.Reader)
		if !ok {
			// some sort of encoded response, this should not be happening
			return errors.New("unexpected non-stream passed to PostRun: please file a bugreport")
		}

		processedOneResponse = true

		if err = re.Emit(bar.NewProxyReader(r)); err != nil {
			return err
		}
	}
}

type dagStore struct {
	dag iface.APIDagService

View on GitHub (pinned to 329838acdf)

Solutions

File a bugreport at https://github.com/ipfs/kubo/issues including kubo version and the exact command.
Ensure CLI and daemon versions match (`ipfs version` on both).
Remove any API proxy/middleware that could alter the multipart stream and retry directly against the daemon.
Retry the export on a fresh invocation to rule out a transient framing issue.

Defensive patterns

Strategy: try-catch

Validate before calling

cliVer, _ := run("ipfs", "version")
daemonVer, _ := run("ipfs", "id") // or check daemon binary version
if cliVer != daemonVer {
    log.Println("version mismatch between CLI and daemon")
}

Try / catch

if strings.Contains(err.Error(), "unexpected multipart response during emit") {
    // capture versions + command, report at github.com/ipfs/kubo/issues
}

Prevention

Keep CLI and daemon on the same kubo version.
Avoid custom proxies/middleware in front of /api/v0 that rewrite multipart responses.
Pin kubo versions in CI to avoid mixed-version stacks.

When it happens

Trigger: The RPC layer returns more than one multipart part for a dag export response: a mismatch between the command's `Encoders`/streaming setup and the client's multipart decoding, or a server emitting extra parts it should not.

Common situations: Using a custom RPC client/proxy that re-encodes the response; a kubo version mismatch between CLI and daemon (older daemon, newer CLI or vice versa); proxying the API through a middleware that duplicates parts.

Related errors

AI-assisted analysis of ipfs/kubo@329838acdf (2026-09-03). Data as JSON: /api/errors/ad81b332ebeda120. Report an issue: GitHub.