How to write a simple custom HTTP server in Go? - go

Question

I am new to Go and trying to write a custom HTTP server. I'm getting a compilation error. How can I implement the ServeHTTP method in my code?
My Code:
package main
import (
"net/http"
"fmt"
"io"
"time"
)
func myHandler(w http.ResponseWriter, req *http.Request) {
io.WriteString(w, "hello, world!\n")
}
func main() {
// Custom http server
s := &http.Server{
Addr: ":8080",
Handler: myHandler,
ReadTimeout: 10 * time.Second,
WriteTimeout: 10 * time.Second,
MaxHeaderBytes: 1 << 20,
}
err := s.ListenAndServe()
if err != nil {
fmt.Printf("Server failed: ", err.Error())
}
}
Error while compiling:
.\hello.go:21: cannot use myHandler (type func(http.ResponseWriter, *http.Request)) as type http.Handler in field value:
func(http.ResponseWriter, *http.Request) does not implement http.Handler (missing ServeHTTP method)

Answer 1

You either use a struct and define ServeHTTP on it or simply wrap your function in a HandlerFunc
s := &http.Server{
Addr: ":8080",
Handler: http.HandlerFunc(myHandler),
ReadTimeout: 10 * time.Second,
WriteTimeout: 10 * time.Second,
MaxHeaderBytes: 1 << 20,
}

Answer 2

in order to work properly, myHandler should be an object that satisfy the Handler Interface, in other words myHandler should have method called ServeHTTP.
For example, let's say that myHandler is custom handler for showing the current time. The code should be like this
package main
import (
"fmt"
"net/http"
"time"
)
type timeHandler struct {
zone *time.Location
}
func (th *timeHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
tm := time.Now().In(th.zone).Format(time.RFC1123)
w.Write([]byte("The time is: " + tm))
}
func newTimeHandler(name string) *timeHandler {
return &timeHandler{zone: time.FixedZone(name, 0)}
}
func main() {
myHandler := newTimeHandler("EST")
//Custom http server
s := &http.Server{
Addr: ":8080",
Handler: myHandler,
ReadTimeout: 10 * time.Second,
WriteTimeout: 10 * time.Second,
MaxHeaderBytes: 1 << 20,
}
err := s.ListenAndServe()
if err != nil {
fmt.Printf("Server failed: ", err.Error())
}
}
run this code and access http://localhost:8080/ in your browser. you should see formatted text like this
The time is: Sat, 30 Aug 2014 18:19:46 EST
(you should see different time.)
hope this help,
Further more reading
A Recap of Request Handling in Go

Answer 3

You could also define a mux and add handlers to it before assigning it to the server like below.
func myHandler(w http.ResponseWriter, req *http.Request) {
io.WriteString(w, "hello, world!\n")
}
func main(){
// define a serveMux to handle routes
mux := http.NewServeMux()
// assign a route/todo to a handler myHandler
mux.HandleFunc("/todo", myHandler)
// assign a route/todo/notes to an anonymous func
mux.HandleFunc("/todo/notes", func(w http.ResponseWriter, req *http.Request) {
w.Write([]byte("Hello again."))
})
s := &http.Server{
Addr: ":8080",
Handler: mux,
ReadTimeout: 10 * time.Second,
WriteTimeout: 10 * time.Second,
MaxHeaderBytes: 1 << 20,
}
if err := s.ListenAndServe(); err != nil {
log.Fatalf("server failed to start with error %v", err.Error())
}
}