api/slack: a simple API to post message to Slack

This package only depends on standard packages.

Currently, it provide function to send message using incoming webhook
URL.

3 files changed, 92 insertions, 0 deletions

diff --git a/api/slack/message.go b/api/slack/message.go
new file mode 100644
index 00000000..fd4805be
--- /dev/null
+++ b/api/slack/message.go
@@ -0,0 +1,16 @@
+// Copyright 2021, Shulhan <ms@kilabit.info>. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package slack
+
+//
+// Message define the standard message payload with JSON tags.
+//
+type Message struct {
+	Channel   string `json:"channel,omitempty"`
+	Username  string `json:"username,omitempty"`
+	IconEmoji string `json:"icon_emoji,omitempty"`
+	IconUrl   string `json:"icon_url,omitempty"`
+	Text      string `json:"text"`
+}
diff --git a/api/slack/slack.go b/api/slack/slack.go
new file mode 100644
index 00000000..360a43db
--- /dev/null
+++ b/api/slack/slack.go
@@ -0,0 +1,48 @@
+// Copyright 2021, Shulhan <ms@kilabit.info>. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//
+// Package slack provide a simple API for sending message to Slack using only
+// standard packages.
+//
+package slack
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+)
+
+//
+// PostWebhook send a message using "Incoming Webhook".
+//
+func PostWebhook(webhookUrl string, msg *Message) (err error) {
+	payload, err := json.Marshal(&msg)
+	if err != nil {
+		return fmt.Errorf("PostWebhook: %w", err)
+	}
+
+	res, err := http.DefaultClient.Post(webhookUrl, "application/json",
+		bytes.NewReader(payload))
+	if err != nil {
+		return fmt.Errorf("PostWebhook: %w", err)
+	}
+
+	if res.StatusCode != http.StatusOK {
+		resBody, err := ioutil.ReadAll(res.Body)
+		if err != nil {
+			return fmt.Errorf("PostWebhook: %w", err)
+		}
+		return fmt.Errorf("PostWebhook: %s: %s\n", res.Status, resBody)
+	}
+
+	err = res.Body.Close()
+	if err != nil {
+		return fmt.Errorf("PostWebhook: %w", err)
+	}
+
+	return nil
+}
diff --git a/api/slack/slack_example_test.go b/api/slack/slack_example_test.go
new file mode 100644
index 00000000..4f2d4e9d
--- /dev/null
+++ b/api/slack/slack_example_test.go
@@ -0,0 +1,28 @@
+// Copyright 2021, Shulhan <ms@kilabit.info>. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package slack
+
+import (
+	"log"
+	"os"
+)
+
+func ExamplePostWebhook() {
+	webhookURL := os.Getenv("SLACK_WEBHOOK_URL")
+	if len(webhookURL) == 0 {
+		return
+	}
+	msg := &Message{
+		Channel:   "test",
+		Username:  "Test",
+		IconEmoji: ":ghost:",
+		Text:      "Hello, world!",
+	}
+	err := PostWebhook(webhookURL, msg)
+	if err != nil {
+		log.Fatal(err)
+	}
+	//Output:
+}