Using a handler function

HandleFunc registers the handler function for the given pattern in the server mux (router).

You can pass define an anonymous function, as we have seen in the basic Hello World example:

http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, "Hello, world!")
}

But we can also pass a HandlerFunc type. In other words, we can pass any function that respects the following signature:

func FunctionName(w http.ResponseWriter, req *http.Request)

We can rewrite the previous example passing the reference to a previously defined HandlerFunc. Here’s the full example:

package main

import (
    "fmt"
    "net/http"
)

// A HandlerFunc function
// Notice the signature of the function
func RootHandler(w http.ResponseWriter, req *http.Request) {
    fmt.Fprintln(w, "Hello, world!")
}

func main() {
    // Here we pass the reference to the `RootHandler` handler function
    http.HandleFunc("/", RootHandler)
    panic(http.ListenAndServe(":8080", nil))
}

Of course, you can define several function handlers for different paths.

package main

import (
    "fmt"
    "log"
    "net/http"
)

func FooHandler(w http.ResponseWriter, req *http.Request) {
    fmt.Fprintln(w, "Hello from foo!")
}

func BarHandler(w http.ResponseWriter, req *http.Request) {
    fmt.Fprintln(w, "Hello from bar!")
}

func main() {
    http.HandleFunc("/foo", FooHandler)
    http.HandleFunc("/bar", BarHandler)

    log.Fatal(http.ListenAndServe(":8080", nil))
}

Here’s the output using cURL:

$ curl -i localhost:8080/foo
HTTP/1.1 200 OK
Date: Wed, 20 Jul 2016 18:23:08 GMT
Content-Length: 16
Content-Type: text/plain; charset=utf-8

Hello from foo!

$ curl -i localhost:8080/bar
HTTP/1.1 200 OK
Date: Wed, 20 Jul 2016 18:23:10 GMT
Content-Length: 16
Content-Type: text/plain; charset=utf-8

Hello from bar!

$ curl -i localhost:8080/
HTTP/1.1 404 Not Found
Content-Type: text/plain; charset=utf-8
X-Content-Type-Options: nosniff
Date: Wed, 20 Jul 2016 18:23:13 GMT
Content-Length: 19

404 page not found

Found a mistake? Have a question or improvement idea? Let me know.

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