Post messages to Slack in Go

slack.go

package main

import (
	"context"
	"encoding/json"
	"io/ioutil"
	"net/http"
	"strings"
	"time"

	"github.com/pkg/errors"
)

type SlackMessage struct {
	Blocks []SlackBlock `json:"blocks"`
}

type SlackText struct {
	Type string `json:"type"`
	Text string `json:"text"`
}

type SlackAccessory struct {
	Type     string     `json:"type"`
	Text     *SlackText `json:"text,omitempty"`
	URL      string     `json:"url,omitempty"`
	Style    string     `json:"style,omitempty"`
	ImageURL string     `json:"image_url,omitempty"`
	AltText  string     `json:"alt_text,omitempty"`
}

type SlackBlock struct {
	Type      string          `json:"type"`
	Text      *SlackText      `json:"text,omitempty"`
	Elements  []SlackText     `json:"elements,omitempty"`
	Accessory *SlackAccessory `json:"accessory,omitempty"`
}

func (m SlackMessage) Encode() (string, error) {
	b, err := json.Marshal(m)
	if err != nil {
		return "", err
	}
	return string(b), nil
}

func (m SlackMessage) Post(ctx context.Context, WebhookURL string) error {
	encoded, err := m.Encode()
	if err != nil {
		return err
	}
	client := &http.Client{
		Timeout: 2 * time.Second,
	}
	req, err := http.NewRequest(http.MethodPost, WebhookURL, strings.NewReader(encoded))
	if err != nil {
		return err
	}
	req = req.WithContext(ctx)
	req.Header.Set("Content-Type", "application/json")
	resp, err := client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		bod, err := ioutil.ReadAll(resp.Body)
		if err != nil {
			return errors.New("Not OK and couldn't read body")
		}
		return errors.New("Not OK: " + string(bod))
	}
	return nil
}