promise's Introduction

Promise

When you need to restrict execution time of an API you can make use of Go context.Context and set the timeout using context.WithTimeout(Context,time.Duration) but it's not very handy if you always listen to ctx.Done() channel everytime you need to execute function that could take long time. With Promise you can easily wrap the desired function to respect the deadline of the context.

Install

go get -u github.com/ahmadmuzakki/promise

Usage

package main

import (
    "time"
    "fmt"
    "context"
    "github.com/ahmadmuzakki/promise"
)

func main() {
	ctx := context.Background()
	// timeout for the whole operation is 2 seconds
	timeout := time.Duration(2) * time.Second
	ctx, done := context.WithTimeout(ctx, timeout)
    defer done()

	// return result with Do()
	val, err := promise.Promise(ctx, dbTx).Do()
	fmt.Println("dbTx result:",val,"error:",err)

	// or we can do callback style like this
	promise.Promise(ctx, httpTx).Then(func(val interface{}){
		fmt.Println("httpTx result:",val)
	},func(err error){
		fmt.Println("httpTx error:",err)
	})
}

// let's say we have transaction that takes sometimes here
func dbTx() (interface{}, error) {
	time.Sleep(time.Duration(1) * time.Second)
	return "success", nil
}

// another transaction
func httpTx() (interface{}, error) {
	time.Sleep(time.Duration(2) * time.Second)
	return "success", nil
}

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