api/slack: implement client for webhook

Unlike PostWebhook API which is close and open one connection at the
time, the WebhookClient is keep open.

Use the WebhookClient for long running program that post message every
minutes or seconds.

1 files changed, 94 insertions, 0 deletions

diff --git a/api/slack/webhook_client.go b/api/slack/webhook_client.go
new file mode 100644
index 00000000..597dbe1a
--- /dev/null
+++ b/api/slack/webhook_client.go
@@ -0,0 +1,94 @@
+// 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 (
+	"fmt"
+	"net/http"
+	"net/url"
+	"time"
+
+	libhttp "github.com/shuLhan/share/lib/http"
+)
+
+//
+// WebhookClient for slack.
+// Use this for long running program that post message every minutes or
+// seconds.
+//
+type WebhookClient struct {
+	*libhttp.Client
+	webhookPath string
+	user        string
+	channel     string
+}
+
+//
+// NewWebhookClient create new slack client that will write the message using
+// webhook URL and optional user and channel.
+//
+func NewWebhookClient(webhookURL, user, channel string) (wcl *WebhookClient, err error) {
+	wurl, err := url.Parse(webhookURL)
+	if err != nil {
+		return nil, fmt.Errorf("NewWebhookClient: %w", err)
+	}
+
+	host := fmt.Sprintf("%s://%s", wurl.Scheme, wurl.Host)
+	wcl = &WebhookClient{
+		Client:      libhttp.NewClient(host, nil, false),
+		webhookPath: wurl.Path,
+		user:        user,
+		channel:     channel,
+	}
+
+	wcl.Client.Timeout = 5 * time.Second
+
+	return wcl, nil
+}
+
+//
+// Post the Message as is.
+//
+func (wcl *WebhookClient) Post(msg *Message) (err error) {
+	if wcl.Client == nil {
+		return nil
+	}
+	httpRes, resBody, err := wcl.PostJSON(nil, wcl.webhookPath, msg)
+	if err != nil {
+		return fmt.Errorf("WebhookClient.Post: %w", err)
+	}
+	if httpRes.StatusCode != http.StatusOK {
+		return fmt.Errorf("Post: %s: %s\n", httpRes.Status, resBody)
+	}
+	return nil
+}
+
+//
+// Write wrap the raw bytes into Message with the user and channel previously
+// defined when creating the client, and post it to slack.
+//
+func (wcl *WebhookClient) Write(b []byte) (n int, err error) {
+	if wcl.Client == nil {
+		return 0, nil
+	}
+	msg := &Message{
+		Channel:  wcl.channel,
+		Username: wcl.user,
+		Text:     string(b),
+	}
+	err = wcl.Post(msg)
+	if err != nil {
+		return 0, fmt.Errorf("Write: %w", err)
+	}
+	return len(b), nil
+}
+
+//
+// Close the client connection.
+//
+func (wcl *WebhookClient) Close() (err error) {
+	wcl.Client = nil
+	return nil
+}