Light wrapper for the Go http client adding (essential) timeouts for both connect and readwrite.

httpclient.go

package httpclient

import (
    "net"
    "net/http"
    "time"
)

type Config struct {
    ConnectTimeout   time.Duration
    ReadWriteTimeout time.Duration
}

func TimeoutDialer(config *Config) func(net, addr string) (c net.Conn, err error) {
    return func(netw, addr string) (net.Conn, error) {
        conn, err := net.DialTimeout(netw, addr, config.ConnectTimeout)
        if err != nil {
            return nil, err
	    }
        conn.SetDeadline(time.Now().Add(config.ReadWriteTimeout))
        return conn, nil
    }
}

func NewTimeoutClient(args ...interface{}) *http.Client {
    // Default configuration
    config := &Config{
        ConnectTimeout:   1 * time.Second,
        ReadWriteTimeout: 1 * time.Second,
    }

    // merge the default with user input if there is one
    if len(args) == 1 {
        timeout := args[0].(time.Duration)
        config.ConnectTimeout = timeout
        config.ReadWriteTimeout = timeout
    }

    if len(args) == 2 {
        config.ConnectTimeout = args[0].(time.Duration)
        config.ReadWriteTimeout = args[1].(time.Duration)
    }

    return &http.Client{
        Transport: &http.Transport{
            Dial: TimeoutDialer(config),
        },
    }
}

httpclient_test.go

package httpclient

import (
	"io"
	"net"
	"net/http"
	"sync"
	"testing"
	"time"
)

var starter sync.Once
var addr net.Addr

func testHandler(w http.ResponseWriter, req *http.Request) {
	time.Sleep(500 * time.Millisecond)
	io.WriteString(w, "hello, world!\n")
}

func testDelayedHandler(w http.ResponseWriter, req *http.Request) {
	time.Sleep(2100 * time.Millisecond)
	io.WriteString(w, "hello, world ... in a bit\n")
}

func setupMockServer(t *testing.T) {
	http.HandleFunc("/test", testHandler)
	http.HandleFunc("/test-delayed", testDelayedHandler)
	ln, err := net.Listen("tcp", ":0")
	if err != nil {
		t.Fatalf("failed to listen - %s", err.Error())
	}
	go func() {
		err = http.Serve(ln, nil)
		if err != nil {
			t.Fatalf("failed to start HTTP server - %s", err.Error())
		}
	}()
	addr = ln.Addr()
}

func TestDefaultConfig(t *testing.T) {
	starter.Do(func() { setupMockServer(t) })

	httpClient := NewTimeoutClient()
	req, _ := http.NewRequest("GET", "http://"+addr.String()+"/test-delayed", nil)

	httpClient = NewTimeoutClient()

	_, err := httpClient.Do(req)
	if err == nil {
		t.Fatalf("request should have timed out")
	}

}

func TestHttpClient(t *testing.T) {
	starter.Do(func() { setupMockServer(t) })

	httpClient := NewTimeoutClient()

	req, _ := http.NewRequest("GET", "http://"+addr.String()+"/test", nil)

	resp, err := httpClient.Do(req)
	if err != nil {
		t.Fatalf("1st request failed - %s", err.Error())
	}
	defer resp.Body.Close()

	connectTimeout := (250 * time.Millisecond)
	readWriteTimeout := (50 * time.Millisecond)

	httpClient = NewTimeoutClient(connectTimeout, readWriteTimeout)

	resp, err = httpClient.Do(req)
	if err == nil {
		t.Fatalf("2nd request should have timed out")
	}

	resp, err = httpClient.Do(req)
	if resp != nil {
		t.Fatalf("3nd request should not have timed out")
	}

}

httpclient_usage.go

/*
    This wrapper takes care of both the connection timeout and the readwrite timeout.
    WARNING: You must instantiate this every time you want to use it, otherwise it is 
    likely that the timeout is reached before you actually make the call.

    One argument sets the connect timeout and the readwrite timeout to the same value.
    Other wise, 2 arguments are 1) connect and 2) readwrite

    It returns an *http.Client
*/

package main

import(
    "httpclient"
    "time"
)

func main() {
    httpClient := httpclient.NewWithTimeout(500*time.Millisecond, 1*time.Second)
    resp, err := httpClient.Get("http://google.com")
    if err != nil {
        fmt.Println("Rats! Google is down.")
    }
}

TimeoutDialer have problem in go.1.16 ;
it will cause i/o timeout , in a short duration , like 50 ms , but we set it more than 1 second.

because the code not using keepAlive and golang will using conn cache pool for sites.

so we should use http.Client{ Timeout: XXX , ... } to set one request timeout .
not this!!!!!!!!