Golang example showing how to use interfaces (Writer) to compose functionality, in this case, retrieve data from a url, encode response to a base64 string, compress it, and then save to a file. Also includes sample aspects for logging and timing

zipped_webrequest.go

package main

import (
	"bytes"
	"compress/gzip"
	"encoding/base64"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"time"

	"github.com/SteveBate/gomailer"
)

// types

type WebFilter func(wd *WebData)

type WebData struct {
	filename string
	url      string
	raw      []byte
}

// methods of WebData

func (wd *WebData) scrape() {

	var err error

	resp, err := http.Get(wd.url)
	if err != nil {
		log.Fatal(err)
	}

	wd.raw, err = ioutil.ReadAll(resp.Body)
	if err != nil {
		log.Fatal(err)
	}

	resp.Body.Close()
}

func (wd *WebData) encode() {

	buf := bytes.Buffer{}
	e := base64.NewEncoder(base64.URLEncoding, &buf)
	e.Write(wd.raw)
	e.Close()
	wd.raw = buf.Bytes()
}

func (wd *WebData) compress() {

	buf := bytes.Buffer{}
	w := gzip.NewWriter(&buf)
	w.Write(wd.raw)
	w.Close()
	wd.raw = buf.Bytes()
	wd.filename += ".gz"
}

func (wd *WebData) save() {

	fmt.Println("saving ", wd.filename)
	ioutil.WriteFile(wd.filename, wd.raw, 0666)
}

func (wd *WebData) send() {

	mail := gomailer.NewMail()
	mail.Subject = "test email"
	mail.Body = "Hello world"
	mail.To = "" // an email address
	mail.From = "" // a name
	if err := mail.AttachBytes(wd.filename, wd.raw); err != nil {
		fmt.Println(err)
	}

	client := gomailer.NewMailClient()
	client.Username = "" // credentials
	client.Password = ""
	err := client.Send(mail)
	if err != nil {
		fmt.Println(err)
	}

	fmt.Println("mail sent")
}

// aspects

func Log(f WebFilter) WebFilter {

	return func(wd *WebData) {
		fmt.Println("fetching from ", wd.url)
		f(wd)
		fmt.Println("done fetching from ", wd.url)
	}
}

func Time(f WebFilter) WebFilter {

	return func(wd *WebData) {
		start := time.Now()
		f(wd)
		end := time.Now().Sub(start)
		fmt.Println("request completed in", end.String())
	}
}

// program entry point

func main() {

	wd1 := &WebData{filename: "bbc.txt", url: "http://www.bbc.co.uk"}
	wd2 := &WebData{filename: "amazon.txt", url: "http://www.amazon.co.uk"}
	wd3 := &WebData{filename: "google.txt", url: "http://www.google.co.uk"}

	f1 := Log(Time(Execute))
	f2 := Log(Time(Execute))
	f3 := Log(Time(Execute))

	go f1(wd1)
	go f2(wd2)
	go f3(wd3)

	select {}
}

func Execute(wd *WebData) {

	wd.scrape()
	wd.encode()
	wd.compress()
	wd.save()
	wd.send()
}