How to add URL query parameters to HTTP GET request?

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!