Post to slack in Go language

Introduction

I was curious about how to post to Slack without using an external library, so I built it myself. The Slack setting enables chat: write and files: write in Bot Token Scopes. And give the app permission to the channel you want to post Prepare an image file named test.png in advance

About the source

main.go

package main

import (
	"bytes"
	"context"
	"io"
	"io/ioutil"
	"mime/multipart"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"
	"time"
)

const (
	SLACKPOSTMESSAGE = "https://slack.com/api/chat.postMessage"
	SLACKPOSTFILE    = "https://slack.com/api/files.upload"
	TOKEN            = "{List the displayed token}"
	CHANNEL          = "general"
)

}

func postSlackfile() string {
	filename := "./test.png "
	file, err := os.Open(filename)
	if err != nil {
		return ""
	}
	defer file.Close()
	body := &bytes.Buffer{}
	writer := multipart.NewWriter(body)
	part, err := writer.CreateFormFile("file", filepath.Base(filename))
	if err != nil {
		return ""
	}
	_, err = io.Copy(part, file)
	if err != nil {
		return ""
	}
	err = writer.Close()
	if err != nil {
		return ""
	}

	values := url.Values{
		"token": {TOKEN},
	}
	values.Add("channels", CHANNEL)
	values.Add("filename", filepath.Base(filename))

	req, err := http.NewRequest("POST", SLACKPOSTFILE, body)
	if err != nil {
		return ""
	}
	req = req.WithContext(context.Background())
	req.URL.RawQuery = (values).Encode()
	req.Header.Add("Content-Type", writer.FormDataContentType())

	client := &http.Client{}
	// client.Timeout = time.Second * 15
	resp, err := client.Do(req)
	if err != nil {
		return ""
	}
	defer resp.Body.Close()
	body2, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return ""
	}
	return string(body2)
}

func postSlackMessage(text string) string {
	urldata := SLACKPOSTMESSAGE
	values := url.Values{}
	values.Set("token", TOKEN)
	values.Add("channel", CHANNEL)
	values.Add("text", text)

	client := &http.Client{}
	client.Timeout = time.Second * 15
	req, err := http.NewRequest("POST", urldata, strings.NewReader(values.Encode()))
	if err != nil {
		return ""
	}
	//
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	resp, err := client.Do(req)
	if err != nil {
		return ""
	}
	defer resp.Body.Close()
	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return ""
	}
	return string(body)

}

func main(){
	fmt.Println(postSlackMessage("Hello World\nbbb"))
	fmt.Println(postSlackfile())
}

result

When executed, it will be posted as follows.

Digression

It's easier to do with the library linked below, but if you want to see and understand the features, just the source code above is easier.

https://github.com/nlopes/slack