Add support for Gotify notifications (#346)

This adds support for Gotify (https://gotify.net) notifications.

Work items:

* Two flags have been added to internal/flags/flags.go:
  "notification-gotify-url" and "notification-gotify-token".

* A Gotify notification driver has been added in
  notifications/gotify.go.

* "gotify" has been added to notification driver choices in
  notifications/notifier.go.

* Docs have been updated

docs/notifications.md

@@ -7,6 +7,7 @@ The types of notifications to send are passed via the comma-separated option `--
 - `email` to send notifications via e-mail
 - `slack` to send notifications through a Slack webhook
 - `msteams` to send notifications via MSTeams webhook
+- `gotify` to send notifications via Gotify
 
 ## Settings
 
@@ -90,3 +91,18 @@ docker run -d \
   -e WATCHTOWER_NOTIFICATION_MSTEAMS_USE_LOG_DATA=true \
   containrrr/watchtower
 ```
+
+### Gotify
+
+To push a notification to your Gotify instance, register a Gotify app and specify the Gotify URL and app token:
+
+
+```bash
+docker run -d \
+  --name watchtower \
+  -v /var/run/docker.sock:/var/run/docker.sock \
+  -e WATCHTOWER_NOTIFICATIONS=gotify \
+  -e WATCHTOWER_NOTIFICATION_GOTIFY_URL="https://my.gotify.tld/" \
+  -e WATCHTOWER_NOTIFICATION_GOTIFY_TOKEN="SuperSecretToken" \
+  containrrr/watchtower
+```

internal/flags/flags.go

@@ -98,7 +98,7 @@ func RegisterNotificationFlags(rootCmd *cobra.Command) {
 		"notifications",
 		"n",
 		viper.GetStringSlice("WATCHTOWER_NOTIFICATIONS"),
-		" notification types to send (valid: email, slack, msteams")
+		" notification types to send (valid: email, slack, msteams, gotify)")
 
 	flags.StringP(
 		"notifications-level",
@@ -192,6 +192,17 @@ Should only be used for testing.
 		"",
 		viper.GetBool("WATCHTOWER_NOTIFICATION_MSTEAMS_USE_LOG_DATA"),
 		"The MSTeams notifier will try to extract log entry fields as MSTeams message facts")
+
+	flags.StringP(
+		"notification-gotify-url",
+		"",
+		viper.GetString("WATCHTOWER_NOTIFICATION_GOTIFY_URL"),
+		"The Gotify URL to send notifications to")
+	flags.StringP(
+		"notification-gotify-token",
+		"",
+		viper.GetString("WATCHTOWER_NOTIFICATION_GOTIFY_TOKEN"),
+		"The Gotify Application required to query the Gotify API")
 }
 
 // SetDefaults provides default values for environment variables

notifications/gotify.go

@@ -0,0 +1,100 @@
+package notifications
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
+)
+
+const (
+	gotifyType = "gotify"
+)
+
+type gotifyTypeNotifier struct {
+	gotifyURL      string
+	gotifyAppToken string
+	logLevels      []log.Level
+}
+
+func newGotifyNotifier(c *cobra.Command, acceptedLogLevels []log.Level) typeNotifier {
+	flags := c.PersistentFlags()
+
+	gotifyURL, _ := flags.GetString("notification-gotify-url")
+	if len(gotifyURL) < 1 {
+		log.Fatal("Required argument --notification-gotify-url(cli) or WATCHTOWER_NOTIFICATION_GOTIFY_URL(env) is empty.")
+	} else if !(strings.HasPrefix(gotifyURL, "http://") || strings.HasPrefix(gotifyURL, "https://")) {
+		log.Fatal("Gotify URL must start with \"http://\" or \"https://\"")
+	} else if strings.HasPrefix(gotifyURL, "http://") {
+		log.Warn("Using an HTTP url fpr Gotify is insecure")
+	}
+
+	gotifyToken, _ := flags.GetString("notification-gotify-token")
+	if len(gotifyToken) < 1 {
+		log.Fatal("Required argument --notification-gotify-token(cli) or WATCHTOWER_NOTIFICATION_GOTIFY_TOKEN(env) is empty.")
+	}
+
+	n := &gotifyTypeNotifier{
+		gotifyURL:      gotifyURL,
+		gotifyAppToken: gotifyToken,
+		logLevels:      acceptedLogLevels,
+	}
+
+	log.AddHook(n)
+
+	return n
+}
+
+func (n *gotifyTypeNotifier) StartNotification() {}
+
+func (n *gotifyTypeNotifier) SendNotification() {}
+
+func (n *gotifyTypeNotifier) Levels() []log.Level {
+	return n.logLevels
+}
+
+func (n *gotifyTypeNotifier) getURL() string {
+	url := n.gotifyURL
+	if !strings.HasSuffix(url, "/") {
+		url += "/"
+	}
+	return url + "message?token=" + n.gotifyAppToken
+}
+
+func (n *gotifyTypeNotifier) Fire(entry *log.Entry) error {
+
+	go func() {
+		jsonBody, err := json.Marshal(gotifyMessage{
+			Message:  "(" + entry.Level.String() + "): " + entry.Message,
+			Title:    "Watchtower",
+			Priority: 0,
+		})
+		if err != nil {
+			fmt.Println("Failed to create JSON body for Gotify notification: ", err)
+			return
+		}
+
+		jsonBodyBuffer := bytes.NewBuffer([]byte(jsonBody))
+		resp, err := http.Post(n.getURL(), "application/json", jsonBodyBuffer)
+		if err != nil {
+			fmt.Println("Failed to send Gotify notification: ", err)
+		}
+		defer resp.Body.Close()
+
+		if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+			fmt.Printf("Gotify notification returned %d HTTP status code", resp.StatusCode)
+		}
+
+	}()
+	return nil
+}
+
+type gotifyMessage struct {
+	Message  string `json:"message"`
+	Title    string `json:"title"`
+	Priority int    `json:"priority"`
+}

pkg/notifications/notifier.go

@@ -38,6 +38,8 @@ func NewNotifier(c *cobra.Command) *Notifier {
 			tn = newSlackNotifier(c, acceptedLogLevels)
 		case msTeamsType:
 			tn = newMsTeamsNotifier(c, acceptedLogLevels)
+		case gotifyType:
+			tn = newGotifyNotifier(c, acceptedLogLevels)
 		default:
 			log.Fatalf("Unknown notification type %q", t)
 		}