How do you send a struct in a GET request - json

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, e.g. 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)