Skip to content

thomasbabuj/gotips

BranchesTags

Folders and files

NameName
Last commit message
Last commit date

Latest commit

 

History

57 Commits
README.md
README.md
 
 
gophers.jpg
gophers.jpg
 
 

Repository files navigation

header

Golang short tips & trics

This list of short golang code tips & trics will help keep collected knowledge in one place.

Can you help make it better?

Please feel free to send a PR with your own Golang tip to be published here. Any improvements or suggestions are welcome!

Contributing

Make PR add new tip on top of list with title, date, description, code and links, please see tips as a reference.

Don't forget to Star the repo, as this will help to promote the project!

Tips list

#17 - Use context API

2016-16-02 by @beyondns

Some APIs are designed with context interface, google search is an example. Use context to send cancel signal.

	done := make(chan error,1)
	query := "golang context"
	ctx, cancel := context.WithCancel(context.Background())
	// or use ctx, cancel = context.WithTimeout(context.Background(), queryTimeLimit)
	go func() {
		start := time.Now()
		_, err := google.Search(ctx, query)
		elapsed := time.Since(start)
		fmt.Printf("search time %v", elapsed)
		done <- err
	}()
	select {
	case <-time.After(queryTimeLimit):
		cancel()
		<-done // wait
		fmt.Printf("time out")
	case err :=<- done:
		if err != nil {
			panic(err)
		}
	}	
	fmt.Printf("Done")

#16 - Go routines syncronization

2016-16-02 by @beyondns

  • Wait groups
	const N = 3
	var wg sync.WaitGroup
	wg.Add(N)
	for i := 0; i < N; i++ {
		go func(i int) {
			defer wg.Done()
			fmt.Println(i)
		}(i)
	}
	wg.Wait()
	fmt.Println("Done")

run

  • Channels
	const N = 3
	done := make(chan struct{})
	for i := 0; i < N; i++ {
		go func(i int) {
			defer func() { done <- struct{}{} }()
			fmt.Println(i)
		}(i)
	}
	var counter = 0
	for {
		select {
		case <-time.After(time.Second * 1):
			panic("time out")
		case <-done:
			counter++
			if counter == N {
				goto DONE
			}
		}
	}
DONE:
	fmt.Println("Done")

run

#15 - Time interval measurement

2016-14-02 by @beyondns

  start := time.Now()
  DoHardWork() // or time.Sleep(1 * time.Second)
  finish := time.Since(start)
  fmt.Printf("Hard work finished in %d ms.\n", finish.Nanoseconds()/10e6)

#14 - Benchmark switch vs else if

2016-14-02 by @beyondns

package boom

import (
	"fmt"
	"math/rand"
	"testing"
)

var words = []string{
	"alpha", "beta", "gamma", "delta", "epsilon", "zeta", "eta", "theta",
	"iota", "kappa", "lambda", "mu", "nu", "xi", "omicron", "pi", "rho",
	"sigma", "tau", "upsilon", "phi", "chi", "psi", "omega",
}
var wlen = len(words)

func BenchmarkSwitch(b *testing.B) {
	m := make(map[string]int)
	rand.Seed(376234242)
	for i := 0; i < b.N; i++ {
		j := rand.Intn(wlen)
		s := words[j]
		switch s {
		case "alpha":
			m[s]++
		case "beta":
			m[s]++
		case "gamma":
			m[s]++
		case "delta":
			m[s]++
		case "epsilon":
			m[s]++
		case "zeta":
			m[s]++
		case "eta":
			m[s]++
		case "theta":
			m[s]++
		case "iota":
			m[s]++
		case "kappa":
			m[s]++
		case "lambda":
			m[s]++
		case "mu":
			m[s]++
		case "nu":
			m[s]++
		case "xi":
			m[s]++
		case "omicron":
			m[s]++
		case "pi":
			m[s]++
		case "rho":
			m[s]++
		case "sigma":
			m[s]++
		case "tau":
			m[s]++
		case "upsilon":
			m[s]++
		case "phi":
			m[s]++
		case "chi":
			m[s]++
		case "psi":
			m[s]++
		case "omega":
			m[s]++
		}
	}
	var c int
	for _,v:=range m{
		c=c+v
	}
	fmt.Printf("%d %d\n", len(m),c)
}

func BenchmarkIf(b *testing.B) {
	m := make(map[string]int)
	rand.Seed(376234242)
	for i := 0; i < b.N; i++ {
		j:= rand.Intn(wlen)
		w := words[j]
		if w == "alpha" {
			m[w]++
		} else if w == "beta" {
			m[w]++
		} else if w == "gamma" {
			m[w]++
		} else if w == "delta" {
			m[w]++
		} else if w == "epsilon" {
			m[w]++
		} else if w == "zeta" {
			m[w]++
		} else if w == "eta" {
			m[w]++
		} else if w == "theta" {
			m[w]++
		} else if w == "iota" {
			m[w]++
		} else if w == "kappa" {
			m[w]++
		} else if w == "lambda" {
			m[w]++
		} else if w == "mu" {
			m[w]++
		} else if w == "nu" {
			m[w]++
		} else if w == "xi" {
			m[w]++
		} else if w == "omicron" {
			m[w]++
		} else if w == "pi" {
			m[w]++
		} else if w == "rho" {
			m[w]++
		} else if w == "sigma" {
			m[w]++
		} else if w == "tau" {
			m[w]++
		} else if w == "upsilon" {
			m[w]++
		} else if w == "phi" {
			m[w]++
		} else if w == "chi" {
			m[w]++
		} else if w == "psi" {
			m[w]++
		} else if w == "omega" {
			m[w]++
		}
	}
	c:=0
	for _,v:=range m{
		c=c+v
	}
	fmt.Printf("%d %d\n", len(m),c)
}
go test -bench=.

#13 - Use ASM in Go Code

2016-10-02 by @beyondns

Place add.go & add_asm.s in src/add sub folder, then build.

// add_asm.s
TEXT add(SB),$0
        MOVL x+0(FP), BX
        MOVL y+4(FP), BP
        ADDL BP, BX
        MOVL BX, ret+8(FP)
        RET
// main.go
func add(x, y int32) int32

func main() {
	r:=add(2,5)
	fmt.Println(r)
}
export GOPATH=$PWD 
go build add

To play with go/asm code compile

go tool compile -S code.go > code.s

#12 - JSON with unknown structure

2016-08-02 by @papercompute

Parse JSON with unknown structure, just pass map[string]interface{} to json.Unmarshal

func ProcessJSON(s string) map[string]interface{} {
	var m map[string]interface{}

	if err := json.Unmarshal([]byte(s), &m); err != nil {
		panic(err)
	}

	if err := passM(m); err != nil {
		panic(err)
	}
	return m
}

func passKV(k string, v interface{}) error {
	var ok bool

	if _, ok = v.(map[string]interface{}); ok {
		err := passM(v.(map[string]interface{}))
		if err != nil {
			return err
		}
	}

	if _, ok = v.([]interface{}); ok {
		err := passA(v.([]interface{}))
		if err != nil {
			return err
		}
	}

	fmt.Printf("%s : %v\n", k, v)

	return nil
}

func passM(m map[string]interface{}) error {
	for k, v := range m {
		if err := passKV(k, v); err != nil {
			return err
		}
	}
	return nil
}

func passA(a []interface{}) error {
	for _, v := range a {
		switch v.(type) {
		case map[string]interface{}:
			if err := passM(v.(map[string]interface{})); err != nil {
				return err
			}
		case []interface{}:
			if err := passA(v.([]interface{})); err != nil {
				return err
			}
		default:
			return errors.New("wrong expression in array")
		}
	}
	return nil
}

#11 - Websocket over HTTP2

2016-08-02 by @beyondns

In go 1.6 HTTP2 is supported out of the box with http.ListenAndServeTLS and can be used with websockets. Just use wss connection.

func WSServer(ws *websocket.Conn) {
	var err error
	for {
		var reply string

		if err = websocket.Message.Receive(ws, &reply); err != nil {
			fmt.Println("Can't receive")
			break
		}

		fmt.Println("Received back from client: " + reply)

		msg := "Received:  " + reply
		fmt.Println("Sending to client: " + msg)

		if err = websocket.Message.Send(ws, msg); err != nil {
			fmt.Println("Can't send")
			break
		}
	}
}

func main() {
	http.Handle("/ws", websocket.Handler(WSServer))
	http.Handle("/", http.FileServer(http.Dir(".")))
	err := http.ListenAndServeTLS(":8000", "srv.cert", "srv.key", nil)
	if err != nil {
		log.Fatal(err)
	}
}

JS Client

<script type="text/javascript">
    function WebSocketTest() {
        if ("WebSocket" in window) {
            console.log("WebSocket is supported by your Browser!");

            var ws = new WebSocket("wss:https://localhost:8000/ws");

            ws.onopen = function() {
                ws.send("Message from client");
                console.log("Message is sent...");
            };

            ws.onmessage = function(evt) {
                console.log("Message is received...", evt.data);
            };

            ws.onclose = function() {
                console.log("Connection is closed...");
            };
        } else {
            console.log("WebSocket NOT supported by your Browser!");
        }
    }
</script>

#10 - HTTP2

2016-07-02 by @beyondns

Go 1.6's net/http package supports HTTP/2 for both the client and server out of the box.

In go 1.6+ HTTP2 is supported transparently, just use http.ListenAndServeTLS

Generate key & cert files with openssl

openssl req -x509 -newkey rsa:2048 -nodes -keyout srv.key -out srv.cert -days 365

HTTP2 server

import (
	"fmt"
	"log"
	"flag"
	"net/http"	
	"golang.org/x/net/http2" // optional in go 1.6+
)

func Handler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Hello http2")
}

func main() {
	var server http.Server

	host := flag.String("h", ":8000", "h host:port")
	flag.BoolVar(&http2.VerboseLogs, "verbose", false, "Verbose HTTP/2 debugging.")
	flag.Parse()

	server.Addr = *host
	http2.ConfigureServer(&server, nil)

	http.HandleFunc("/", Handler)

	log.Println("ListenAndServe on ", *host)

	log.Fatal(server.ListenAndServeTLS("srv.cert", "srv.key"))
}

CURL

curl --http2 --insecure https://localhost:8080

HTTP2 client

	host := flag.String("h", "https://127.0.0.1:8000", "h host:port")

	flag.Parse()
	tr := &http.Transport{TLSClientConfig: tlsConfigInsecure}
	defer tr.CloseIdleConnections()

	req, err := http.NewRequest("GET", *host, nil)
	if err != nil {
		panic(err)
	}
	res, err := tr.RoundTrip(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()

	log.Printf("Got res: %+v\n", res)
	if g, w := res.StatusCode, 200; g != w {
		panic(fmt.Sprintf("StatusCode = %v; want %v", g, w))
	}

	data, err := ioutil.ReadAll(res.Body)
	if err != nil {
		panic(fmt.Sprintf("Body read error: %v", err))
	}
	fmt.Printf("%s\n", string(data))

#9 - Error handling

2016-06-02 by @beyondns

Use last return variable in function as an error
Use panic / defer / recover to handle more complex errors

func MyFunc1(v interface{}) (interface{}, error) {
	var ok bool

	if !ok {
		return nil, errors.New("not ok error")
	}
	return v, nil
}

func MyFunc2() {
	defer func() {
		if err := recover(); err != nil {
			// recover from panic
			fmt.Println("recover: ", err)
		}
	}()
	v := struct{}{}
	if _, err := MyFunc1(v); err != nil {
		panic(err) // panic
	}

	fmt.Println("never happen")
}

func main() {
	MyFunc2()
	fmt.Println("main finish")
}

#8 - Memory management with pools of objects

2016-04-02 by @beyondns

Use thread safe pools to collect objects for reuse.

var p sync.Pool
var o *T 
if v := p.Get(); v != nil {
	o = v.(*T)
} else {
	o = new(T)
}

// use o

p.Put(o) // return to reuse

#7 - Sort slice of time periods

2016-02-02 by @beyondns

For custom data structures it's necessary to use custom compare function to sort elements in slice.

type xTime struct {
	time.Time
}

func (t *xTime) UnmarshalJSON(buf []byte) error {
	tm, err := time.Parse("2006-01-02", strings.Trim(string(buf), `"`))
	if err != nil {
		return err
	}
	t.Time = tm
	return nil
}

type Period struct {
	Start xTime `json:"start"`
	End   xTime `json:"end"`
}

type Data struct {
	Ps []Period `json:"periods"`
}

type Periods []Period

func (a Periods) Len() int           { return len(a) }
func (a Periods) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
func (a Periods) Less(i, j int) bool { return compDate(a[i].Start, a[j].Start) < 0 }

func compDate(a, b xTime) int {
	ay, am, ad := a.Time.Date()
	by, bm, bd := b.Time.Date()
	if ay > by {
		return 1
	}
	if ay < by {
		return -1
	}

	if am > bm {
		return 1
	}
	if am < bm {
		return -1
	}

	if ad > bd {
		return 1
	}
	if ad < bd {
		return -1
	}

	return 0
}

func main() {

	data := `
{"periods": [
    {"start": "2015-11-01", "end": "2015-11-01"},
    {"start": "2015-12-02", "end": "2015-12-03"},
    {"start": "2015-12-07", "end": "2015-12-13"},
    {"start": "2015-10-18", "end": "2016-10-30"}
  ]}
`
	var d Data
	if err := json.Unmarshal([]byte(data), &d); err != nil {
		panic(err)
	}
	sort.Sort(Periods(d.Ps))
	fmt.Printf("%v", d)

}

#6 - Fast http server

2016-01-02 by @beyondns

If you don't need net/http package functionality just use net and "tcp"

func main() {

	host := flag.String("h", "127.0.0.1:8000", "h host:port")

	flag.Parse()

	l, err := net.Listen("tcp", *host)
	if err != nil {
		fmt.Println("Error listening:", err.Error())
		os.Exit(1)
	}

	defer l.Close()

	fmt.Printf("Listening on %s\n", *host)
	var i = 0
	for {
		conn, err := l.Accept()
		if err != nil {
			continue
		}

		go handleRequest(&conn)
	}

}

func handleRequest(c *net.Conn) {
	defer (*c).Close()
	buf := make([]byte, 2048) // tip: use preallocated
	n, err := (*c).Read(buf)
	if err != nil || n <= 0 {
		return
	}

	// parse http if necessary 

	(*c).Write([]byte("HTTP/1.1 200 Ok\r\nConnection: close\r\nContent-Length: 5\r\n\r\nhello"))
}

Just test it

./wrk -c 1024 -d 20s http:https://127.0.0.1:8000

#5 - Close channel to notify many

2016-28-01 by @beyondns

	c:=make(chan int)

	for i:=0;i<5;i++{
		go func(i int){ 
			_, ok :=<-c;
			fmt.Printf("closed %d, %t\n",i,ok) // random order
		}(i)
	}


	// c<-1
	close(c)
	time.Sleep(time.Second)

#4 - Is channel closed?

2016-28-01

	c:=make(chan int)
	go func(){
		if _, ok :=<-c;ok{
			fmt.Println("not closed",<-c)
		} else {
			fmt.Println("closed",<-c)
		}
			
	}()
	// c<-1
	close(c)
	time.Sleep(time.Second)

#3 - Http request/response with close notify and timeout

2016-27-01 by @beyondns

const RequestMaxWaitTimeInterval = time.Second * 15

func Handler(w http.ResponseWriter, r *http.Request) {
	u:=r.URL.Query().Get("url")
	if u==""{
		http.Error(w, "url is not specified", http.StatusBadRequest)
		return
	}
	var err error
	u,err=url.QueryUnescape(u)
	if err!=nil{
		http.Error(w, fmt.Sprintf("url unescape error %v",err), http.StatusBadRequest)
		return
	}
	closeNotify := w.(http.CloseNotifier).CloseNotify()
	//flusher := w.(http.Flusher)

	tr := &http.Transport{}
	client := &http.Client{Transport: tr}
	c := make(chan error, 1)

	req, err := http.NewRequest("GET", u, nil)
	if err != nil {
		http.Error(w, fmt.Sprintf("error %v", err), http.StatusBadRequest)
		return
	}

	go func() {
		resp, err := client.Do(req)

		defer func() { c <- err }()
		defer func() {
			if resp != nil && resp.Body != nil {
				resp.Body.Close()
			}
		}()

		if err != nil {
			return
		}

		if resp.StatusCode != 200 {
			http.Error(w, fmt.Sprintf("resp.StatusCode %s", resp.Status), resp.StatusCode)
			return
		}

		data, err := ioutil.ReadAll(resp.Body)
		if err != nil {
			http.Error(w, fmt.Sprintf("ioutil.ReadAll, error %v", err), http.StatusBadRequest)
			return
		}

		w.Header().Set("My-custom-header", "my-header-data")
		w.WriteHeader(http.StatusOK)
		w.Write(data)

	}()
	select {
	case <-time.After(RequestMaxWaitTimeInterval):
		tr.CancelRequest(req)
		log.Printf("Request timeout")
		<-c // Wait for goroutine to return.
		return
	case <-closeNotify:
		tr.CancelRequest(req)
		log.Printf("Request canceled")
		<-c // Wait for goroutine to return.
		return
	case err := <-c:
		if err!=nil{
			log.Printf("Error in request goroutine %v",err)
		}
		return
	}
}

#2 - Import packages

2016-26-01 by @beyondns

import "fmt"    // fmt.Print()
import ft "fmt" // ft.Print()
import . "fmt"  // Print()
import _ "fmt"  // not use, but run init

#1 - Map

2016-26-01

Map is a hash table

// Set/Get/Test 
m[k]=v
v=m[k]
if _,ok:=m[k];ok{
	// m[k] exists
} 

// Iterate over map, random order
for k,v:=range m{
	// k - key
	// v - value
}

// Function argument
type M map[TK]TV
func f(m M) // m - passed by value, but memory the same 
func f(m *M)// m - passed by reference, but memory the same 

// Double, triple,... map
m := make(map[TK1]map[TK2]TV)
m[K1]=make(map[TK2]TV)
m[K1][K2]=V

// Implemet set with empty struct 
s := make(map[TK]struct{})
s[K]=struct{}{} // set K
delete(s,K)     // unset K

#0 - Slices

2016-24-01 by @beyondns

Slice is a dynamic array

// Iterate over slice
for i,v:=range s{ // use range, inc order
	// i - index
	// v - value
} 
for i:=0;i<len(s);i++{ // use index, inc order
	// i - index
	// s[i] - value
} 
for i:=len(s)-1;i>=0;i--{ // use index, reverse order
	// i - index
	// s[i] - value
} 


// Function argument
func f(s []T) // s - passed by value, but memory the same 
func f(s *[]T) // s - passed by refernce, but memory the same 

// Append
a = append(a, b...)

// Clone
b = make([]T, len(a))
copy(b,a)

// Remove element, keep order
a = a[:i+copy(a[i:], a[i+1:])]
// or
a = append(a[:i], a[i+1:]...)

// Remove element, change order
a[i] = a[len(a)-1] 
a = a[:len(a)-1]

General Golang links

Inspired by

License

CC0

About

golang tips

Resources

Readme
Activity

Stars

1 star

Watchers

1 watching

Forks

29 forks
Report repository

Releases

No releases published

Packages

No packages published