What causes "unsupported protocol %s" in probelabs/goreplay?

Set protocol to one of: '', 'http', 'binary' (lowercase).

unsupported protocol %s

Error message

unsupported protocol %s

What it means

TCPProtocol.Set converts a string protocol value into the typed TCPProtocol enum; only '' (empty), 'http', and 'binary' are supported. Any other value returns 'unsupported protocol %s', indicating an invalid protocol configuration for the TCP input/output.

Source

Thrown at internal/tcp/tcp_message.go:33

// TCPProtocol is a number to indicate type of protocol
type TCPProtocol uint8

const (
	// ProtocolHTTP ...
	ProtocolHTTP TCPProtocol = iota
	// ProtocolBinary ...
	ProtocolBinary
)

// Set is here so that TCPProtocol can implement flag.Var
func (protocol *TCPProtocol) Set(v string) error {
	switch v {
	case "", "http":
		*protocol = ProtocolHTTP
	case "binary":
		*protocol = ProtocolBinary
	default:
		return fmt.Errorf("unsupported protocol %s", v)
	}
	return nil
}

func (protocol *TCPProtocol) String() string {
	switch *protocol {
	case ProtocolBinary:
		return "binary"
	case ProtocolHTTP:
		return "http"
	default:
		return ""
	}
}

// Stats every message carry its own stats object
type Stats struct {
	LostData  int

View on GitHub (pinned to 251e45abd2)

Solutions

Set protocol to one of: '', 'http', 'binary' (lowercase).
If TLS is needed, keep protocol as http/binary and configure TLS separately, not via the protocol field.
Check the config key casing and spelling; the match is exact.
If a new protocol is required, add a case to TCPProtocol.Set and a corresponding String() branch.

Example fix

// before
protocol.Set("https")
// after
protocol.Set("http") // or "binary"; TLS is configured separately

Defensive patterns

Strategy: validation

Validate before calling

var validProtocols = map[string]bool{"": true, "http": true, "binary": true}
func validProtocol(v string) bool { return validProtocols[strings.ToLower(strings.TrimSpace(v))] }

Try / catch

var p tcp.Protocol
if err := p.Set(cfgValue); err != nil {
	return fmt.Errorf("tcp protocol must be http or binary, got %q", cfgValue)
}

Prevention

Whitelist protocol values at config-load time
Keep values lowercase and trimmed
Note that TLS is configured separately from protocol
Add enum validation to config schema (e.g. JSON schema enum)

When it happens

Trigger: Setting a TCP connection's protocol via Set with a string other than 'http' or 'binary' (or empty) — e.g. from a config value like 'https', 'raw', 'tcp', 'grpc'.

Common situations: YAML/JSON config for a TCP module with protocol: https (author assuming TLS implies a protocol type); typos like 'binay'; copying config from another product that supports more protocol names.

Related errors

AI-assisted analysis of probelabs/goreplay@251e45abd2 (2026-09-02). Data as JSON: /api/errors/5cc939db5c932fab. Report an issue: GitHub.