Add Signal alerts via signal-cli-rest-api gateways

Author: brvier

CHANGELOG.md

@@ -3,6 +3,13 @@
 All notable changes to Gjallar are documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
+## [0.4.0] - 2026-07-05
+
+### Added
+
+- Signal alerts (`type: signal`) through any signal-cli-rest-api compatible
+  gateway: POST to `/v2/send` with sender `number` and `recipients`.
+
 ## [0.3.0] - 2026-07-04
 
 ### Added

README.md

@@ -24,6 +24,8 @@ Rules: `> N`, `>= N`, `< N`, `<= N`, `== x`, `!= x`, `~ regex`, `rows > 0` (row
 - Any [shoutrrr](https://shoutrrr.nickfedor.com/) URL: Telegram, email/SMTP, ntfy,
   Discord, Slack, Gotify, Pushover, generic webhooks, ...
 - Free Mobile SMS API (`type: freemobile`).
+- Signal via a [signal-cli-rest-api](https://github.com/bbernhard/signal-cli-rest-api)
+  gateway (`type: signal`: `url` to `/v2/send`, sender `number`, `recipients`).
 
 A monitor alerts after `failure_threshold` consecutive failures (no flapping noise),
 and again on recovery. Open incidents survive restarts: no duplicate alerts.

gjallar.example.yaml

@@ -33,6 +33,11 @@ alerts:
     type: freemobile
     user: "12345678"       # your Free Mobile login
     pass: "AbCdEfGh1234"   # the API key from your subscriber area
+  signal-ops:              # signal-cli-rest-api gateway (POST /v2/send)
+    type: signal
+    url: "https://signal-api.example.com/v2/send"
+    number: "+33600000000"              # sender registered on the gateway
+    recipients: ["+33611111111", "+33622222222"]
 
 monitors:
   # --- HTTP/HTTPS: status code, body regex, TLS certificate expiry ---

internal/alert/notifiers.go

@@ -20,6 +20,8 @@ func BuildNotifiers(alerts map[string]config.Alert) (map[string]Notifier, error)
 			out[name] = n
 		case "freemobile":
 			out[name] = NewFreeMobile(a.User, a.Pass)
+		case "signal":
+			out[name] = NewSignal(a.URL, a.Number, a.Recipients)
 		default:
 			return nil, fmt.Errorf("alert %q: unknown type %q", name, a.Type)
 		}

internal/alert/signal.go

@@ -0,0 +1,50 @@
+package alert
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+)
+
+// Signal sends messages through a signal-cli-rest-api compatible gateway
+// (POST {url} with {"message", "number", "recipients"}).
+type Signal struct {
+	URL        string // full /v2/send endpoint
+	Number     string // sender number registered on the gateway
+	Recipients []string
+	Client     *http.Client
+}
+
+func NewSignal(url, number string, recipients []string) *Signal {
+	return &Signal{URL: url, Number: number, Recipients: recipients, Client: &http.Client{}}
+}
+
+func (s *Signal) Send(ctx context.Context, title, message string) error {
+	payload, err := json.Marshal(map[string]any{
+		"message":    title + "\n" + message,
+		"number":     s.Number,
+		"recipients": s.Recipients,
+	})
+	if err != nil {
+		return err
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, s.URL, bytes.NewReader(payload))
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := s.Client.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode < 200 || resp.StatusCode > 299 {
+		body, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
+		return fmt.Errorf("signal: status %d: %s", resp.StatusCode, bytes.TrimSpace(body))
+	}
+	return nil
+}

internal/alert/signal_test.go

@@ -0,0 +1,53 @@
+package alert
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"gjallar/internal/config"
+)
+
+func TestSignal(t *testing.T) {
+	var got map[string]any
+	status := 201
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost || r.Header.Get("Content-Type") != "application/json" {
+			t.Errorf("method=%s content-type=%s", r.Method, r.Header.Get("Content-Type"))
+		}
+		json.NewDecoder(r.Body).Decode(&got)
+		w.WriteHeader(status)
+	}))
+	defer srv.Close()
+
+	s := NewSignal(srv.URL, "+33616400522", []string{"+33689816957", "+33616400522"})
+	if err := s.Send(context.Background(), "[Gjallar] DOWN: web", "web — boom"); err != nil {
+		t.Fatal(err)
+	}
+	if got["number"] != "+33616400522" {
+		t.Errorf("number = %v", got["number"])
+	}
+	if recs, _ := got["recipients"].([]any); len(recs) != 2 || recs[0] != "+33689816957" {
+		t.Errorf("recipients = %v", got["recipients"])
+	}
+	if msg, _ := got["message"].(string); !strings.Contains(msg, "DOWN: web") || !strings.Contains(msg, "boom") {
+		t.Errorf("message = %q", got["message"])
+	}
+
+	status = 400
+	if err := s.Send(context.Background(), "t", "m"); err == nil || !strings.Contains(err.Error(), "status 400") {
+		t.Errorf("err = %v", err)
+	}
+}
+
+func TestBuildNotifiersSignal(t *testing.T) {
+	ns, err := BuildNotifiers(map[string]config.Alert{
+		"sig": {Type: "signal", URL: "http://h/v2/send", Number: "+336", Recipients: []string{"+337"}},
+	})
+	if err != nil || ns["sig"] == nil {
+		t.Fatalf("BuildNotifiers: %v", err)
+	}
+}

internal/config/config.go

@@ -46,12 +46,16 @@ type Defaults struct {
 }
 
 // Alert is a named notifier. Type "" (default) means a shoutrrr URL;
-// type "freemobile" uses the Free Mobile SMS API with User/Pass.
+// type "freemobile" uses the Free Mobile SMS API with User/Pass;
+// type "signal" posts to a signal-cli-rest-api /v2/send endpoint.
 type Alert struct {
 	Type string `yaml:"type"`
 	URL  string `yaml:"url"`
 	User string `yaml:"user"`
 	Pass string `yaml:"pass"`
+	// signal
+	Number     string   `yaml:"number"`     // sender number registered on the gateway
+	Recipients []string `yaml:"recipients"` // destination numbers
 }
 
 type Monitor struct {
@@ -196,8 +200,12 @@ func (c *Config) Validate() error {
 			if a.User == "" || a.Pass == "" {
 				return fmt.Errorf("alert %q: user and pass are required for type freemobile", name)
 			}
+		case "signal":
+			if a.URL == "" || a.Number == "" || len(a.Recipients) == 0 {
+				return fmt.Errorf("alert %q: url, number and recipients are required for type signal", name)
+			}
 		default:
-			return fmt.Errorf("alert %q: unknown type %q (supported: shoutrrr, freemobile)", name, a.Type)
+			return fmt.Errorf("alert %q: unknown type %q (supported: shoutrrr, freemobile, signal)", name, a.Type)
 		}
 	}
 	if len(c.Monitors) == 0 {

internal/config/config_test.go

@@ -178,6 +178,7 @@ func TestLoadErrors(t *testing.T) {
 		{"unknown alert ref", "monitors:\n  - name: x\n    type: ping\n    host: h\n    alerts: [nope]", `unknown alert "nope"`},
 		{"alert missing url", "alerts:\n  a: {}\nmonitors:\n  - name: x\n    type: ping\n    host: h", "url is required"},
 		{"freemobile missing pass", "alerts:\n  a:\n    type: freemobile\n    user: u\nmonitors:\n  - name: x\n    type: ping\n    host: h", "user and pass"},
+		{"signal missing recipients", "alerts:\n  a:\n    type: signal\n    url: http://h/v2/send\n    number: \"+336\"\nmonitors:\n  - name: x\n    type: ping\n    host: h", "url, number and recipients"},
 		{"bad duration", "monitors:\n  - name: x\n    type: ping\n    host: h\n    interval: fast", "invalid duration"},
 	}
 	for _, tc := range cases {