grafana/k6 · error

couldn't read protoset: %w

Error message

couldn't read protoset: %w

What it means

grpc.Client.load() opened the protoset file but io.ReadAll failed while reading its bytes (internal/js/modules/k6/grpc/client.go:113). A pure I/O failure after a successful open - the file is present and opened, but its content could not be read to completion. Rare and usually environmental.

Source

Thrown at internal/js/modules/k6/grpc/client.go:113

	if c.vu.State() != nil {
		return nil, errors.New("load must be called in the init context")
	}

	initEnv := c.vu.InitEnv()
	if initEnv == nil {
		return nil, errors.New("missing init environment")
	}

	absFilePath := initEnv.GetAbsFilePath(protosetPath)
	fdsetFile, err := initEnv.FileSystems["file"].Open(absFilePath)
	if err != nil {
		return nil, fmt.Errorf("couldn't open protoset: %w", err)
	}

	defer func() { _ = fdsetFile.Close() }()
	fdsetBytes, err := io.ReadAll(fdsetFile)
	if err != nil {
		return nil, fmt.Errorf("couldn't read protoset: %w", err)
	}

	fdset := &descriptorpb.FileDescriptorSet{}
	if err = proto.Unmarshal(fdsetBytes, fdset); err != nil {
		return nil, fmt.Errorf("couldn't unmarshal protoset file %s: %w", protosetPath, err)
	}

	return c.convertToMethodInfo(fdset)
}

// Note: this function was lifted from `lib/options.go`
func decryptPrivateKey(key, password []byte) ([]byte, error) {
	block, _ := pem.Decode(key)
	if block == nil {
		return nil, errors.New("failed to decode PEM key")
	}

	blockType := block.Type

View on GitHub (pinned to 93accf6570)

Solutions

1. Regenerate and redeploy the protoset (it may be truncated or corrupted)
2. Ensure nothing rewrites the file while k6 starts
3. Move the protoset to local disk next to the script to rule out network storage

try {
  client.load('./pb/service.protoset');
} catch (e) {
  if (/couldn't read protoset/.test(e.message)) {
    throw new Error('protoset unreadable; regenerate it and ensure nothing rewrites it at startup');
  }
  throw e;
}

When it happens

Trigger: client.load(path) where the opened file becomes unreadable mid-read: truncated or replaced between open and read, storage or permission errors at read time, or a corrupted archive entry that opens but fails to read.

Common situations: Data files being rewritten concurrently with test startup; flaky container volumes; partially synced/downloaded protoset files.

Related errors

• couldn't open protoset: %w
• couldn't unmarshal protoset file %s: %w
• gRPC exporter endpoint is required
• persisting screenshot: %w
• failed to close file %s: %w

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/4ec86630071bdc26. Report an issue: GitHub.