Golang handlefunc with channel - go

Question

I think this question has been asked before (and probably more than once) but I can't find it...
Im learning Go, and I wanted to extend the classical web server example by sending a channel to the "handler".
I have this standard thing:
func hello(w http.ResponseWriter, r *http.Request) {
io.WriteString(w, "Hello world!")
}
func main() {
http.HandleFunc("/", hello)
http.ListenAndServe(":8000", nil)
}
And now I would like the "hello" function to be able to write stuff on a channel, for someone to consume... The way I have done with "normal" functions is to create a channel:
c := make(chan string)
and pass c in the call to the function. Something like:
dosomething(c)
But... how would I go about doing that if I want "hello" to get access to the channel c?

Answer 1

There are two other ways to do this (other than exporting your channels as in the previous answer).
The first is to use a function to return another handler function. When the function is returned, it will create a closure around the channel.
func makeHello(logger chan string) func(http.ResponseWriter, *http.Request) {
return func(w http.ResponseWriter, r *http.Request) {
logger <- r.Host
io.WriteString(w, "Hello world!")
}
}
The second is to use a struct which holds the channel as a member and use pointer receiver methods to handle the request...
type DataPasser struct {
logs chan string
}
func (p *DataPasser) handleHello(w http.ResponseWriter, r *http.Request) {
p.logs <- r.URL.String()
io.WriteString(w, "Hello world")
}
This is a full working example (just hit /1 and /2 to see the two examples)
package main
import (
"fmt"
"io"
"net/http"
)
func main() {
// METHOD 1
logs := make(chan string)
go logLogs(logs)
handleHello := makeHello(logs)
// METHOD 2
passer := &DataPasser{logs: make(chan string)}
go passer.log()
http.HandleFunc("/1", handleHello)
http.HandleFunc("/2", passer.handleHello)
http.ListenAndServe(":9999", nil)
}
// METHOD 1
func makeHello(logger chan string) func(http.ResponseWriter, *http.Request) {
return func(w http.ResponseWriter, r *http.Request) {
logger <- r.Host
io.WriteString(w, "Hello world!")
}
}
func logLogs(logger chan string) {
for item := range logger {
fmt.Println("1. Item", item)
}
}
// METHOD 2
type DataPasser struct {
logs chan string
}
func (p *DataPasser) handleHello(w http.ResponseWriter, r *http.Request) {
p.logs <- r.URL.String()
io.WriteString(w, "Hello world")
}
func (p *DataPasser) log() {
for item := range p.logs {
fmt.Println("2. Item", item)
}
}

Answer 2

There a few ways to solve this problem, the simplest is to define an exported channel in a package and import said package where ever you want to use the channel.
package mychannel
var Chan = make(chan string)