Golang : How to use Gorilla webtoolkit context package properly



Tags : golang handler gorilla-webtoolkit context

Many new comers to Gorilla web toolkit are confused as why they cannot pass variables to another handler with the help of context package...as if it is not working as advertised. The assumption is that ... context works like a global variables within the source code page... but it is not meant to be.

If you read the manual carefully, it is clearly stated that - "context stores values shared during a request lifetime.". To pass values to another handlers(functions) OUTSIDE the request lifetime, you need the assistance of the session package.

This code example below will demonstrate how to use context package to pass data to another handler. Provided it is within the lifetime of the request (http.Request)

Here you go!

 package main

 import (
 "fmt"
 "github.com/gorilla/context"
 "github.com/gorilla/mux"
 "net/http"
 )

 type Key string

 const GlobalRequestVariable Key = ""

 func SetGlobalHandler(w http.ResponseWriter, r *http.Request) {
 context.Set(r, GlobalRequestVariable, "test")

 // will WORK because within request lifetime
 get, ok := context.GetOk(r, GlobalRequestVariable)
 w.Write([]byte(fmt.Sprintf("GetOK : [%v] and get what :[%v] ", ok, get)))

 // global variable still accessible as long the request is still alive
 // and everything is cleared because router from gorilla/mux will
 // automatically call context.Clear(r)
 // and cause GetGlobalHandler to fail
 // WHEN you point the browser url to example.com:8080/get

 // to make it work, you have to pass r down to inside SetGlobalHandler
 // while the request is still alive to InternalGetGlobalHandler
 InternalGetGlobalHandler(w, r)

 }

 func InternalGetGlobalHandler(w http.ResponseWriter, r *http.Request) {

 // will WORK because still within request lifetime
 get, ok := context.GetOk(r, GlobalRequestVariable)
 w.Write([]byte(fmt.Sprintf("\nInternal GetOK : [%v] and get what :[%v] ", ok, get)))

 }

 func GetGlobalHandler(w http.ResponseWriter, r *http.Request) {

 // will FAIL because NOT within request lifetime
 get, ok := context.GetOk(r, GlobalRequestVariable)
 w.Write([]byte(fmt.Sprintf("GetOK : [%v] and get what :[%v] ", ok, get)))

 }

 func main() {
 mx := mux.NewRouter()

 mx.HandleFunc("/", SetGlobalHandler)
 mx.HandleFunc("/get", GetGlobalHandler)

 http.ListenAndServe(":8080", mx)
 }

Hope this helps and happy coding!

Reference :

http://www.gorillatoolkit.org/pkg/context

  See also : Golang : How to feed or take banana with Gorilla Web Toolkit Session package



Tags : golang handler gorilla-webtoolkit context

By Adam Ng

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