如何在 GET 请求中发送结构

Question

If I create a struct, how do I send it with a HTTP GET request to a web server endpoint?

package main

import (
    "encoding/json"
    "net/http"
)

type Payload struct {
    Endpoint string `json:"endpoint"`
    Data map[string]interface{} `json:"data"`
}

/*
eg.
{"endpoint":"some-service", "data": {"userID": "abc123"}}
*/

func main() {

    http.HandleFunc("/service", func(w http.ResponseWriter, r *http.Request) {

        decoder := json.NewDecoder(r.Body)
        var p Payload
        err := decoder.Decode(&p)
        if err != nil {
            panic(err)
        }

        // How to attach 'p' ?
        resp, err := http.Get("www.example.com/" + p.Endpoint) // Add "data": p.Data
        if err != nil {
            log.Fatal(err)
        }
        defer resp.Body.Close()

        // handle response here

    })

    http.ListenAndServe(":8080", nil)

}

The endpoint receiving this data would ideally interpret it as JSON.

Answer 1

HTTP GET requests do not allow a request body.

If you must do it with a GET , basically you have 2 options: add the data as a query parameter, or send it in an HTTP Header field.

Note that both the URL and header fields have length limits, so if you want to "attach" a long JSON text, it might fail. To send arbitrary data, you should use another method, eg POST .

Example adding it as a query param:

u, err := url.Parse("http://www.example.com")
if err != nil {
    panic(err)
}

params := url.Values{}
params.Add("data", `{"a":1,"b":"c"}`)
u.RawQuery = params.Encode()

// use u.String() as the request URL

Example sending it in a Header field:

req, err := http.NewRequest("GET", "http://example.com", nil)
// ...
req.Header.Add("X-Data", `{"a":1,"b":"c"}`)
resp, err := client.Do(req)