How to Efficiently Parse Partially a JSON Map in Go?

Parsing JSON Data into a Map in Go

Websocket servers often receive JSON data wrapped in key-value pairs that indicate the type of value. While the "encoding/json" package provides convenient unmarshalling capabilities, there is a need to parse the JSON data partially into a map for further processing.

Approach Using a map[string]json.RawMessage

To achieve partial unmarshalling, one can utilize a map[string]json.RawMessage. This approach allows the JSON data to be unmarshaled into a map, with the keys being the property names and the values being the unparsed JSON data.

import (
    "encoding/json"
    "fmt"
)

func main() {
    data := []byte(`{"sendMsg":{"user":"ANisus","msg":"Trying to send a message"},"say":"Hello"}`)

    var objmap map[string]json.RawMessage
    err := json.Unmarshal(data, &objmap)
    if err != nil {
        fmt.Printf("Error unmarshaling JSON: %v", err)
        return
    }

    // Unpack Individual Values

    // Parsing sendMsg
    var s sendMsg
    err = json.Unmarshal(objmap["sendMsg"], &s)
    if err != nil {
        fmt.Printf("Error unmarshaling 'sendMsg': %v", err)
        return
    }
    fmt.Println("sendMsg:", s)

    // Parsing say
    var str string
    err = json.Unmarshal(objmap["say"], &str)
    if err != nil {
        fmt.Printf("Error unmarshaling 'say': %v", err)
        return
    }
    fmt.Println("say:", str)
}

type sendMsg struct {
    User string
    Msg  string
}

In this approach, the objmap will contain a key "sendMsg" with a value that is the raw JSON data representing the sendMsg object. By further unmarshaling this data into a sendMsg struct, the individual fields (User and Msg) can be accessed.

Note: To ensure successful unmarshalling, remember to export the fields in the sendMsg struct (i.e., User and Msg).

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