message-envelope.md

Base 3: tinywasm/binary — Message Envelope

Change: Add Message type

// binary/message.go
package binary

import "github.com/tinywasm/fmt"

// Message is the standard inter-module communication envelope.
// All pub/sub messages are encoded as Message before transmission.
type Message struct {
    Topic   string          // routing key: "users.created", "auth.logout"
    Type    fmt.MessageType // Event, Request, Response, Error
    ID      uint32          // correlation ID for request/response pairs
    Payload []byte          // binary-encoded body (domain-specific struct)
}

Why in binary (not bus)?

Message is the wire format — it must be available on both sides (server = imports bus; modules = imports binary for encoding payloads). Keeping it in binary avoids a circular dependency (bus → binary, never binary → bus).

Encoding contract

• Message itself is encoded via binary.Encode(msg, &buf) — standard usage
• Payload inside is the caller's responsibility to encode with binary.Encode(domainStruct, &msg.Payload)