hashicorp/packer · error

Unknown address type: %s

Error message

Unknown address type: %s

What it means

The handshake line's third field names the RPC network the plugin is listening on. Packer only knows how to resolve "tcp" and "unix" addresses; any other value is rejected with this error before an address can be resolved.

Source

Thrown at packer/plugin_client.go:360

		// Test the API versions
		if pluginMajorAPIVersion != pluginsdk.APIVersionMajor {
			err = fmt.Errorf("Incompatible API MAJOR version with plugin. "+
				"plugin MINOR API version: %s, Ours: %s", pluginMajorAPIVersion, pluginsdk.APIVersionMajor)
			return nil, err
		}
		if pluginMinorAPIVersion > pluginsdk.APIVersionMinor {
			err = fmt.Errorf("Incompatible API MINOR version with plugin. "+
				"plugin MINOR API version: %s, Ours: %s. Please upgrade Packer.", pluginMinorAPIVersion, pluginsdk.APIVersionMinor)
			return nil, err
		}

		switch network {
		case "tcp":
			c.address, err = net.ResolveTCPAddr("tcp", netAddr)
		case "unix":
			c.address, err = net.ResolveUnixAddr("unix", netAddr)
		default:
			return nil, fmt.Errorf("Unknown address type: %s", network)
		}
		log.Printf("Received %s RPC address for %s: addr is %s", network, cmd.Path, c.address)
	}

	return c.address, err
}

func (c *PluginClient) logStderr(r io.Reader) {
	logPrefix := filepath.Base(c.config.Cmd.Path)
	if logPrefix == "packer" {
		// we just called the normal packer binary with the plugin arg.
		// grab the last arg from the list which will match the plugin name.
		logPrefix = c.config.Cmd.Args[len(c.config.Cmd.Args)-1]
	}

	bufR := bufio.NewReader(r)
	for {
		line, err := bufR.ReadString('\n')

View on GitHub (pinned to eb36e3c3e4)

Solutions

1. Rebuild/reinstall the plugin with the official hashicorp/go-plugin and packer-plugin-sdk versions so it advertises tcp or unix.
2. Inspect the plugin's handshake output (run the binary directly) to see the malformed network field.
3. Use an official release of the plugin rather than a custom fork.

out, _ := exec.Command(pluginPath, "packer-plugin").Output()
parts := strings.Split(strings.TrimSpace(string(out)), "|")
if len(parts) >= 3 && parts[2] != "tcp" && parts[2] != "unix" { /* unsupported network type */ }

if _, err := client.Start(); err != nil {
  if strings.Contains(err.Error(), "Unknown address type") {
    // rebuild plugin with official go-plugin/SDK
  }
}

When it happens

Trigger: Client.Start() in packer/plugin_client.go reaches the network switch with a network value other than "tcp" or "unix" — i.e. the plugin advertised an unsupported or malformed network type in its handshake line.

Common situations: A plugin built with a forked/nonstandard SDK that negotiates a different network type; a corrupted or garbled handshake line causing a bogus network field; hand-rolled plugin wrappers that print their own handshake format.

Related errors

• The protocol of this plugin (protocol version 4 and lower) w
• Unrecognized remote plugin message: %s
• error retrieving iteration from HCP Packer registry: %s
• request Fulcio certificate: %w
• load keyless trusted root: %w

AI-assisted analysis of hashicorp/packer@eb36e3c3e4 (2026-09-05). Data as JSON: /api/errors/c80a95a6448dbf08. Report an issue: GitHub.