How to exchange context value between servers? - go

Question

I'm studying Golang and have question on context.
I want to send request from server1 to server2 with context and want to read context value set by server1.
But it seems context of sercer2 doesn't carry server1's context value.
When I send request to server1 by curl http://localhost:8080
server1's console.
Send request to http://localhost:8082
server2's console.
request coming in
<nil>
How can I retrieve context value set by server1?
And if it is possible, I also want to know whether it is a correct way of exchanging value's like authentication between servers.
Middleware pattern is more desirable?
Thank you.
Codes
package main
import (
"context"
"fmt"
"net/http"
"github.com/go-chi/chi/v5"
)
func main() {
r := chi.NewRouter()
r.HandleFunc("/", hello)
fmt.Println("Starting listening on port 8080...")
http.ListenAndServe(":8080", r)
}
// Context's key.
type Sample string
var sampleKey Sample = "sample"
func hello(w http.ResponseWriter, r *http.Request) {
fmt.Println("Send request to http://localhost:8082")
ctx := context.WithValue(context.Background(), sampleKey, "1234")
req, err := http.NewRequestWithContext(ctx, http.MethodGet, "http://localhost:8082", nil)
if err != nil {
fmt.Println("Error while sending request: ", err)
}
// Send request.
var c http.Client
c.Do(req)
}
package main
import (
"fmt"
"net/http"
"github.com/go-chi/chi/v5"
)
func main() {
r := chi.NewRouter()
r.HandleFunc("/", receive)
fmt.Println("Start listening on port 8082...")
http.ListenAndServe(":8082", r)
}
type Sample string
var sampleKey Sample
func receive(w http.ResponseWriter, r *http.Request) {
fmt.Println("request coming in")
fmt.Println(r.Context().Value(sampleKey))
}

Answer 1

The context is supposed to be used in a function call stack to share information and cancellation point between these functions. There is no automatic mechanism to serialize the value bound in the context over http. If you want to send data over http between these two servers, you mostly have three solution, you can:
encode that as an url parameter in the path somewhere
GET /hello/1234
send that in the http body, for example in JSON
POST /hello
{
"sample": 1234
}
as url key/value encoded as url parameters
/hello?sample=1234