How to add URL query parameters to HTTP GET request? - http

Question

I am trying to add a query parameter to a HTTP GET request but somehow methods pointed out on SO (e.g. here) don't work.
I have the following piece of code:
package main
import (
"fmt"
"log"
"net/http"
)
func main() {
req, err := http.NewRequest("GET", "/callback", nil)
req.URL.Query().Add("code", "0xdead 0xbeef")
req.URL.Query().Set("code", "0xdead 0xbeef")
// this doesn't help
//req.URL.RawQuery = req.URL.Query().Encode()
if err != nil {
log.Fatal(err)
}
fmt.Printf("URL %+v\n", req.URL)
fmt.Printf("RawQuery %+v\n", req.URL.RawQuery)
fmt.Printf("Query %+v\n", req.URL.Query())
}
which prints:
URL /callback
RawQuery
Query map[]
Any suggestions on how to achieve this?
Playground example: https://play.golang.org/p/SYN4yNbCmo

Answer 1

Check the docs for req.URL.Query():
Query parses RawQuery and returns the corresponding values.
Since it "parses RawQuery and returns" the values what you get is just a copy of the URL query values, not a "live reference", so modifying that copy does nothing to the original query. In order to modify the original query you must assign to the original RawQuery.
q := req.URL.Query() // Get a copy of the query values.
q.Add("code", "0xdead 0xbeef") // Add a new value to the set.
req.URL.RawQuery = q.Encode() // Encode and assign back to the original query.
// URL /callback?code=0xdead+0xbeef
// RawQuery code=0xdead+0xbeef
// Query map[code:[0xdead 0xbeef]]
Note that your original attempt to do so didn't work because it simply parses the query values, encodes them, and assigns them right back to the URL:
req.URL.RawQuery = req.URL.Query().Encode()
// This is basically a noop!

Answer 2

You can directly build the query params using url.Values
func main() {
req, err := http.NewRequest("GET", "/callback", nil)
req.URL.RawQuery = url.Values{
"code": {"0xdead 0xbeef"},
}.Encode()
...
}
Notice the extra braces because each key can have multiple values.