micro/go-micro · error

grpc: received message larger than max (%d vs. %d)

Error message

grpc: received message larger than max (%d vs. %d)

What it means

The gRPC codec enforces MaxMessageSize when decoding a length-prefixed frame: if the declared message length exceeds MaxMessageSize, decode aborts with this error before allocating the buffer. The two values printed are the received length and the configured max.

Source

Thrown at codec/grpc/util.go:38

	}

	// get encoding format e.g compressed
	cf := header[0]

	// get message length
	length := binary.BigEndian.Uint32(header[1:])

	// no encoding format
	if length == 0 {
		return cf, nil, nil
	}

	//
	if int64(length) > int64(maxInt) {
		return cf, nil, fmt.Errorf("grpc: received message larger than max length allowed on current machine (%d vs. %d)", length, maxInt)
	}
	if int(length) > MaxMessageSize {
		return cf, nil, fmt.Errorf("grpc: received message larger than max (%d vs. %d)", length, MaxMessageSize)
	}

	msg := make([]byte, int(length))

	if _, err := r.Read(msg); err != nil {
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		}
		return cf, nil, err
	}

	return cf, msg, nil
}

func encode(cf uint8, buf []byte, w io.Writer) error {
	header := make([]byte, 5)

	// set compression

View on GitHub (pinned to 24529f1404)

Solutions

1. Increase MaxMessageSize on the codec for both client and server (micro codec options).
2. Chunk large payloads into smaller messages.
3. Compress payloads before sending.
4. Confirm both sides agree on the same MaxMessageSize configuration.

Example fix

// before
c := grpc.NewCodec()
// after
c := grpc.NewCodec(codec.MaxMessageSize(1024 * 1024 * 16)) // 16MB

// Enforce a client-side size limit before sending:
if len(payload) > maxAllowed {
	return fmt.Errorf("payload %d exceeds codec max %d; chunk or raise MaxMessageSize", len(payload), maxAllowed)
}

if err := client.Call(ctx, req, resp); err != nil {
	if strings.Contains(err.Error(), "grpc: received message larger than max") {
		// raise codec.MaxMessageSize on both sides or chunk the payload
	}
	return err
}

When it happens

Trigger: Server or client sends a message whose wire length exceeds codec.MaxMessageSize (default small, e.g. 8192 bytes in this codec) while reading a response or request body via ReadBody.

Common situations: Large RPC payloads (big files, bulk exports) exceeding the small default; one side configured with a larger max than the other; proxies buffering responses larger than the client's limit.

Related errors

• grpc: received message larger than max length allowed on cur
• 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

AI-assisted analysis of micro/go-micro@24529f1404 (2026-09-01). Data as JSON: /api/errors/34930e81140eb7c5. Report an issue: GitHub.