What causes "invalid codec type %s" in geektutu/7days-golang?

Use geerpc.DefaultOption (CodecType 'gee-gob') or set CodecType to a registered codec name.

invalid codec type %s

Error message

invalid codec type %s

What it means

Day7-registry variant of the codec lookup failure: NewClient cannot find a constructor for opt.CodecType in codec.NewCodecFuncMap and returns this error after logging it. Guarantees the client never proceeds with an unknown serialization protocol.

Source

Thrown at gee-rpc/day7-registry/client.go:216

	// if opts is nil or pass nil as parameter
	if len(opts) == 0 || opts[0] == nil {
		return DefaultOption, nil
	}
	if len(opts) != 1 {
		return nil, errors.New("number of options is more than 1")
	}
	opt := opts[0]
	opt.MagicNumber = DefaultOption.MagicNumber
	if opt.CodecType == "" {
		opt.CodecType = DefaultOption.CodecType
	}
	return opt, nil
}

func NewClient(conn net.Conn, opt *Option) (*Client, error) {
	f := codec.NewCodecFuncMap[opt.CodecType]
	if f == nil {
		err := fmt.Errorf("invalid codec type %s", opt.CodecType)
		log.Println("rpc client: codec error:", err)
		return nil, err
	}
	// send options with server
	if err := json.NewEncoder(conn).Encode(opt); err != nil {
		log.Println("rpc client: options error: ", err)
		_ = conn.Close()
		return nil, err
	}
	return newClientCodec(f(conn), opt), nil
}

func newClientCodec(cc codec.Codec, opt *Option) *Client {
	client := &Client{
		seq:     1, // seq starts with 1, 0 means invalid call
		cc:      cc,
		opt:     opt,
		pending: make(map[uint64]*Call),

View on GitHub (pinned to cf36443821)

Solutions

Use geerpc.DefaultOption (CodecType 'gee-gob') or set CodecType to a registered codec name.
Import the codec implementation package so its init() registers the codec function.
Ensure the server accepts the same CodecType.

Example fix

// before
opt := &geerpc.Option{ConnectTimeout: time.Second} // CodecType missing
// after
opt := geerpc.DefaultOption // CodecType: "gee-gob"

Defensive patterns

Strategy: validation

Validate before calling

if _, ok := codec.NewCodecFuncMap[opt.CodecType]; !ok {
    opt = geerpc.DefaultOption // or set a registered CodecType
}

Try / catch

client, err := geerpc.NewClient(conn, opt)
if err != nil {
    if strings.Contains(err.Error(), "invalid codec type") {
        // retry once with DefaultOption
        client, err = geerpc.NewClient(conn, geerpc.DefaultOption)
    }
    if err != nil { return err }
}

Prevention

Derive Options from DefaultOption rather than zero-value structs.
Blank-import the codec package so registration init runs.
Use shared constants for codec names across services.
Check server logs — the server performs the same codec lookup.

When it happens

Trigger: NewClient/NewHTTPClient called with Option.CodecType empty or set to a name never registered via codec.NewCodecFuncMap (e.g. 'gob'), including manually built Options bypassing DefaultOption.

Common situations: Custom Option structs missing CodecType; importing client code without the codec package's registration init; client/server using different codec name strings after a rename.

Related errors

AI-assisted analysis of geektutu/7days-golang@cf36443821 (2026-09-03). Data as JSON: /api/errors/d944b0ba26ce0e49. Report an issue: GitHub.