feat(alerting): Add message-content parameter for Discord pings (#1335)

* feat(discord-alerts): add option for prefix-messages outside of embeds

* chore(docs): add discord prefix-message to README

* chore(discord-alerts): rename prefix-message to message-content

---------

Co-authored-by: TwiN <twin@linux.com>

README.md

@@ -920,6 +920,7 @@ endpoints:
 | `alerting.discord`                   | Configuration for alerts of type `discord`                                                 | `{}`                                |
 | `alerting.discord.webhook-url`       | Discord Webhook URL                                                                        | Required `""`                       |
 | `alerting.discord.title`             | Title of the notification                                                                  | `":helmet_with_white_cross: Gatus"` |
+| `alerting.discord.message-content`   | Message content to send before the embed (useful for pinging users/roles, e.g. `<@123>`)   | `""`                                |
 | `alerting.discord.default-alert`     | Default alert configuration. <br />See [Setting a default alert](#setting-a-default-alert) | N/A                                 |
 | `alerting.discord.overrides`         | List of overrides that may be prioritized over the default configuration                   | `[]`                                |
 | `alerting.discord.overrides[].group` | Endpoint group for which the configuration will be overridden by this configuration        | `""`                                |

alerting/provider/discord/discord.go

@@ -20,8 +20,9 @@ var (
 )
 
 type Config struct {
-	WebhookURL string `yaml:"webhook-url"`
+	WebhookURL     string `yaml:"webhook-url"`
-	Title      string `yaml:"title,omitempty"` // Title of the message that will be sent
+	Title          string `yaml:"title,omitempty"`           // Title of the message that will be sent
+	MessageContent string `yaml:"message-content,omitempty"` // Message content for pinging users or groups (e.g. "<@123456789>" or "<@&987654321>")
 }
 
 func (cfg *Config) Validate() error {
@@ -38,6 +39,9 @@ func (cfg *Config) Merge(override *Config) {
 	if len(override.Title) > 0 {
 		cfg.Title = override.Title
 	}
+	if len(override.MessageContent) > 0 {
+		cfg.MessageContent = override.MessageContent
+	}
 }
 
 // AlertProvider is the configuration necessary for sending an alert using Discord
@@ -142,7 +146,7 @@ func (provider *AlertProvider) buildRequestBody(cfg *Config, ep *endpoint.Endpoi
 		title = cfg.Title
 	}
 	body := Body{
-		Content: "",
+		Content: cfg.MessageContent,
 		Embeds: []Embed{
 			{
 				Title:       title,

alerting/provider/discord/discord_test.go

@@ -134,6 +134,16 @@ func TestAlertProvider_Send(t *testing.T) {
 			}),
 			ExpectedError: false,
 		},
+		{
+			Name:     "triggered-with-message-content",
+			Provider: AlertProvider{DefaultConfig: Config{WebhookURL: "http://example.com", MessageContent: "<@123456789>"}},
+			Alert:    alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved: false,
+			MockRoundTripper: test.MockRoundTripper(func(r *http.Request) *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, Body: http.NoBody}
+			}),
+			ExpectedError: false,
+		},
 	}
 	for _, scenario := range scenarios {
 		t.Run(scenario.Name, func(t *testing.T) {
@@ -200,6 +210,27 @@ func TestAlertProvider_buildRequestBody(t *testing.T) {
 			Resolved:     false,
 			ExpectedBody: "{\"content\":\"\",\"embeds\":[{\"title\":\"provider-title\",\"description\":\"An alert for **endpoint-name** has been triggered due to having failed 3 time(s) in a row:\\n\\u003e description-1\",\"color\":15158332}]}",
 		},
+		{
+			Name:         "triggered-with-message-content-user-mention",
+			Provider:     AlertProvider{DefaultConfig: Config{MessageContent: "<@123456789>"}},
+			Alert:        alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     false,
+			ExpectedBody: "{\"content\":\"\\u003c@123456789\\u003e\",\"embeds\":[{\"title\":\":helmet_with_white_cross: Gatus\",\"description\":\"An alert for **endpoint-name** has been triggered due to having failed 3 time(s) in a row:\\n\\u003e description-1\",\"color\":15158332,\"fields\":[{\"name\":\"Condition results\",\"value\":\":x: - `[CONNECTED] == true`\\n:x: - `[STATUS] == 200`\\n:x: - `[BODY] != \\\"\\\"`\\n\",\"inline\":false}]}]}",
+		},
+		{
+			Name:         "triggered-with-message-content-role-mention",
+			Provider:     AlertProvider{DefaultConfig: Config{MessageContent: "<@&987654321>"}},
+			Alert:        alert.Alert{Description: &firstDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     false,
+			ExpectedBody: "{\"content\":\"\\u003c@\\u0026987654321\\u003e\",\"embeds\":[{\"title\":\":helmet_with_white_cross: Gatus\",\"description\":\"An alert for **endpoint-name** has been triggered due to having failed 3 time(s) in a row:\\n\\u003e description-1\",\"color\":15158332,\"fields\":[{\"name\":\"Condition results\",\"value\":\":x: - `[CONNECTED] == true`\\n:x: - `[STATUS] == 200`\\n:x: - `[BODY] != \\\"\\\"`\\n\",\"inline\":false}]}]}",
+		},
+		{
+			Name:         "resolved-with-message-content",
+			Provider:     AlertProvider{DefaultConfig: Config{MessageContent: "<@123456789>"}},
+			Alert:        alert.Alert{Description: &secondDescription, SuccessThreshold: 5, FailureThreshold: 3},
+			Resolved:     true,
+			ExpectedBody: "{\"content\":\"\\u003c@123456789\\u003e\",\"embeds\":[{\"title\":\":helmet_with_white_cross: Gatus\",\"description\":\"An alert for **endpoint-name** has been resolved after passing successfully 5 time(s) in a row:\\n\\u003e description-2\",\"color\":3066993,\"fields\":[{\"name\":\"Condition results\",\"value\":\":white_check_mark: - `[CONNECTED] == true`\\n:white_check_mark: - `[STATUS] == 200`\\n:white_check_mark: - `[BODY] != \\\"\\\"`\\n\",\"inline\":false}]}]}",
+		},
 	}
 	for _, scenario := range scenarios {
 		t.Run(scenario.Name, func(t *testing.T) {
@@ -313,6 +344,39 @@ func TestAlertProvider_GetConfig(t *testing.T) {
 			InputAlert:     alert.Alert{ProviderOverride: map[string]any{"webhook-url": "http://alert-example.com"}},
 			ExpectedOutput: Config{WebhookURL: "http://alert-example.com"},
 		},
+		{
+			Name: "provider-with-message-content-default",
+			Provider: AlertProvider{
+				DefaultConfig: Config{WebhookURL: "http://example.com", MessageContent: "<@123456789>"},
+			},
+			InputGroup:     "",
+			InputAlert:     alert.Alert{},
+			ExpectedOutput: Config{WebhookURL: "http://example.com", MessageContent: "<@123456789>"},
+		},
+		{
+			Name: "provider-with-message-content-group-override",
+			Provider: AlertProvider{
+				DefaultConfig: Config{WebhookURL: "http://example.com", MessageContent: "<@123456789>"},
+				Overrides: []Override{
+					{
+						Group:  "group",
+						Config: Config{WebhookURL: "http://group-example.com", MessageContent: "<@&987654321>"},
+					},
+				},
+			},
+			InputGroup:     "group",
+			InputAlert:     alert.Alert{},
+			ExpectedOutput: Config{WebhookURL: "http://group-example.com", MessageContent: "<@&987654321>"},
+		},
+		{
+			Name: "provider-with-message-content-alert-override",
+			Provider: AlertProvider{
+				DefaultConfig: Config{WebhookURL: "http://example.com", MessageContent: "<@123456789>"},
+			},
+			InputGroup:     "",
+			InputAlert:     alert.Alert{ProviderOverride: map[string]any{"message-content": "<@999999999>"}},
+			ExpectedOutput: Config{WebhookURL: "http://example.com", MessageContent: "<@999999999>"},
+		},
 	}
 	for _, scenario := range scenarios {
 		t.Run(scenario.Name, func(t *testing.T) {
@@ -323,6 +387,9 @@ func TestAlertProvider_GetConfig(t *testing.T) {
 			if got.WebhookURL != scenario.ExpectedOutput.WebhookURL {
 				t.Errorf("expected webhook URL to be %s, got %s", scenario.ExpectedOutput.WebhookURL, got.WebhookURL)
 			}
+			if got.MessageContent != scenario.ExpectedOutput.MessageContent {
+				t.Errorf("expected message content to be %s, got %s", scenario.ExpectedOutput.MessageContent, got.MessageContent)
+			}
 			// Test ValidateOverrides as well, since it really just calls GetConfig
 			if err = scenario.Provider.ValidateOverrides(scenario.InputGroup, &scenario.InputAlert); err != nil {
 				t.Errorf("unexpected error: %s", err)