micro/go-micro · error

ErrInvalidMessage

ErrInvalidMessage

Error message

invalid message

What it means

ErrInvalidMessage in codec/codec.go:17 is the sentinel error returned by codec operations (Marshal, Unmarshal, ReadBody, Write) when a message type is not one of the supported MessageType values (Request, Response, Event). The codec cannot determine how to encode/decode a message of unknown classification.

Source

Thrown at codec/codec.go:17

// Package codec is an interface for encoding messages
package codec

import (
	"errors"
	"io"
)

const (
	Error MessageType = iota
	Request
	Response
	Event
)

var (
	ErrInvalidMessage = errors.New("invalid message")
)

type MessageType int

// Takes in a connection/buffer and returns a new Codec.
type NewCodec func(io.ReadWriteCloser) Codec

// Codec encodes/decodes various types of messages used within go-micro.
// ReadHeader and ReadBody are called in pairs to read requests/responses
// from the connection. Close is called when finished with the
// connection. ReadBody may be called with a nil argument to force the
// body to be read and discarded.
type Codec interface {
	Reader
	Writer
	Close() error
	String() string
}

View on GitHub (pinned to 24529f1404)

Solutions

1. Ensure every message has Type explicitly set to codec.Request, codec.Response, or codec.Event before Write/Marshal
2. Check for zero-valued Message structs passed to the codec (Go zero value of MessageType is not valid here)
3. Align client and server library versions so message type enums match
4. Validate message construction in tests to catch unset Type fields early

Example fix

// before
msg := rpc.Message{Id: id}
err := codec.Write(&m, msg) // Type unset -> invalid message
// after
msg := rpc.Message{Id: id, Type: codec.Request}
err := codec.Write(&m, msg)

if msg.Type != codec.Request && msg.Type != codec.Response && msg.Type != codec.Event {
    return fmt.Errorf("refusing to write message with invalid type %v", msg.Type)
}

func isValidMessageType(t codec.MessageType) bool {
    return t == codec.Request || t == codec.Response || t == codec.Event
}

if err := codec.Write(m, msg); errors.Is(err, codec.ErrInvalidMessage) {
    return fmt.Errorf("message type %v unsupported by codec: %w", msg.Type, err)
}

When it happens

Trigger: Calling codec.Write/Marshal/Unmarshal/ReadBody with a MessageType outside the declared enum (e.g. zero value MessageType, or a custom/extended type the codec doesn't know).

Common situations: Constructing Messages manually without setting Type; custom middleware adding a new message type without extending the codec; version drift between client and server libraries using different message type sets.

Related errors

• unknown request path
• unsupported Content-Type
• failed to marshal: %v is not type of *bytes.Frame or proto.M
• failed to unmarshal: %v is not type of proto.Message
• failed to marshal: %v is not type of *[]byte

AI-assisted analysis of micro/go-micro@24529f1404 (2026-09-01). Data as JSON: /api/errors/dffe7d9c3a0c877a. Report an issue: GitHub.