How to Handle Mixed JSON Message Types in Go WebSocket using Gorilla Websocket?

Go WebSocket JSON Serialization/Deserialization: Handling Mixed Incoming Messages

In Go, using the gorilla websocket package for WebSocket communication, handling incoming messages of mixed types can pose a challenge. The library's conn.ReadJSON function is limited to deserializing into a single struct type.

Problem Statement

Consider two structs, Foo and Bar, representing incoming message types:

type Foo struct {
    A string `json:"a"`
    B string `json:"b"`
}

type Bar struct {
    C string `json:"c"`
    D string `json:"d"`
}

The requirement is to process these incoming messages, identifying their type (Foo or Bar) and accordingly deserializing them into the appropriate struct.

Solution

To handle mixed incoming messages, the following approach can be employed:

1. Use a Wrapper Struct:

Create a wrapper struct, Messages, that includes a Control field to specify the message type and a X field to hold the deserialized data.

type Messages struct {
    Control string `json:"control"`
    X json.RawMessage
}

2. ReadJSON into the Wrapper Struct:

Use conn.ReadJSON to deserialize the incoming message into the Messages struct.

var m Messages
err := c.ReadJSON(&m)
if err != nil {
    // handle error
}

3. Parse the Message Type:

Based on the value of m.Control, determine the actual message type (Foo or Bar).

switch m.Control {
case "Foo":
    // Convert the JSON to a Foo struct
case "Bar":
    // Convert the JSON to a Bar struct
}

Example Code:

switch m.Control {
case "Foo":
    var foo Foo
    if err := json.Unmarshal([]byte(m.X), &foo); err != nil {
       // handle error
    }
    // do something with foo

case "Bar":
   ... follow pattern for Foo
}

By using json.RawMessage in the Messages struct, the deserialized data can be handled dynamically based on the message type. This solution allows for flexible handling of incoming messages with different structures.

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