feat(alerting): Implement ntfy provider

Closes #308

Work remaining:
- Add the documentation on the README.md
- Test it with an actual Ntfy instance (I've only used https://ntfy.sh/docs/examples/#gatus as a reference; I haven't actually tested it yet)

alerting/alert/type.go

@@ -26,6 +26,9 @@ const (
 	// TypeMessagebird is the Type for the messagebird alerting provider
 	TypeMessagebird Type = "messagebird"
 
+	// TypeNtfy is the Type for the ntfy alerting provider
+	TypeNtfy Type = "ntfy"
+
 	// TypeOpsgenie is the Type for the opsgenie alerting provider
 	TypeOpsgenie Type = "opsgenie"
 

alerting/config.go

@@ -10,6 +10,7 @@ import (
 	"github.com/TwiN/gatus/v4/alerting/provider/matrix"
 	"github.com/TwiN/gatus/v4/alerting/provider/mattermost"
 	"github.com/TwiN/gatus/v4/alerting/provider/messagebird"
+	"github.com/TwiN/gatus/v4/alerting/provider/ntfy"
 	"github.com/TwiN/gatus/v4/alerting/provider/opsgenie"
 	"github.com/TwiN/gatus/v4/alerting/provider/pagerduty"
 	"github.com/TwiN/gatus/v4/alerting/provider/slack"
@@ -41,6 +42,9 @@ type Config struct {
 	// Messagebird is the configuration for the messagebird alerting provider
 	Messagebird *messagebird.AlertProvider `yaml:"messagebird,omitempty"`
 
+	// Ntfy is the configuration for the ntfy alerting provider
+	Ntfy *ntfy.AlertProvider `yaml:"ntfy,omitempty"`
+
 	// Opsgenie is the configuration for the opsgenie alerting provider
 	Opsgenie *opsgenie.AlertProvider `yaml:"opsgenie,omitempty"`
 
@@ -105,6 +109,12 @@ func (config Config) GetAlertingProviderByAlertType(alertType alert.Type) provid
 			return nil
 		}
 		return config.Messagebird
+	case alert.TypeNtfy:
+		if config.Ntfy == nil {
+			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil
+			return nil
+		}
+		return config.Ntfy
 	case alert.TypeOpsgenie:
 		if config.Opsgenie == nil {
 			// Since we're returning an interface, we need to explicitly return nil, even if the provider itself is nil

alerting/provider/ntfy/ntfy.go

@@ -0,0 +1,73 @@
+package ntfy
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net/http"
+
+	"github.com/TwiN/gatus/v4/alerting/alert"
+	"github.com/TwiN/gatus/v4/client"
+	"github.com/TwiN/gatus/v4/core"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using Slack
+type AlertProvider struct {
+	URL      string `yaml:"url"`
+	Topic    string `yaml:"topic"`
+	Priority int    `yaml:"priority"`
+
+	// DefaultAlert is the default alert configuration to use for endpoints with an alert of the appropriate type
+	DefaultAlert *alert.Alert `yaml:"default-alert,omitempty"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	return len(provider.URL) > 0 && len(provider.Topic) > 0 && provider.Priority > 0 && provider.Priority < 6
+}
+
+// Send an alert using the provider
+func (provider *AlertProvider) Send(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) error {
+	buffer := bytes.NewBuffer([]byte(provider.buildRequestBody(endpoint, alert, result, resolved)))
+	request, err := http.NewRequest(http.MethodPost, provider.URL, buffer)
+	if err != nil {
+		return err
+	}
+	request.Header.Set("Content-Type", "application/json")
+	response, err := client.GetHTTPClient(nil).Do(request)
+	if err != nil {
+		return err
+	}
+	if response.StatusCode > 399 {
+		body, _ := io.ReadAll(response.Body)
+		return fmt.Errorf("call to provider alert returned status code %d: %s", response.StatusCode, string(body))
+	}
+	return err
+}
+
+// buildRequestBody builds the request body for the provider
+func (provider *AlertProvider) buildRequestBody(endpoint *core.Endpoint, alert *alert.Alert, result *core.Result, resolved bool) string {
+	var message, tag string
+	if len(alert.GetDescription()) > 0 {
+		message = endpoint.DisplayName() + " - " + alert.GetDescription()
+	} else {
+		message = endpoint.DisplayName()
+	}
+	if resolved {
+		tag = "x"
+	} else {
+		tag = "white_check_mark"
+	}
+	return fmt.Sprintf(`{
+  "topic": "%s",
+  "title": "Gatus",
+  "message": "%s",
+  "tags": ["%s"],
+  "priority": %d
+}`, provider.Topic, message, tag, provider.Priority)
+}
+
+// GetDefaultAlert returns the provider's default alert configuration
+func (provider AlertProvider) GetDefaultAlert() *alert.Alert {
+	return provider.DefaultAlert
+}

alerting/provider/ntfy/ntfy_test.go

@@ -0,0 +1,44 @@
+package ntfy
+
+import "testing"
+
+func TestAlertDefaultProvider_IsValid(t *testing.T) {
+	scenarios := []struct {
+		name     string
+		provider AlertProvider
+		expected bool
+	}{
+		{
+			name:     "valid",
+			provider: AlertProvider{URL: "https://ntfy.sh", Topic: "example", Priority: 1},
+			expected: true,
+		},
+		{
+			name:     "invalid-url",
+			provider: AlertProvider{URL: "", Topic: "example", Priority: 1},
+			expected: false,
+		},
+		{
+			name:     "invalid-topic",
+			provider: AlertProvider{URL: "https://ntfy.sh", Topic: "", Priority: 1},
+			expected: false,
+		},
+		{
+			name:     "invalid-priority-too-high",
+			provider: AlertProvider{URL: "https://ntfy.sh", Topic: "example", Priority: 6},
+			expected: false,
+		},
+		{
+			name:     "invalid-priority-too-low",
+			provider: AlertProvider{URL: "https://ntfy.sh", Topic: "example", Priority: 0},
+			expected: false,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.name, func(t *testing.T) {
+			if scenario.provider.IsValid() != scenario.expected {
+				t.Errorf("expected %t, got %t", scenario.expected, scenario.provider.IsValid())
+			}
+		})
+	}
+}

alerting/provider/provider.go

@@ -9,6 +9,7 @@ import (
 	"github.com/TwiN/gatus/v4/alerting/provider/matrix"
 	"github.com/TwiN/gatus/v4/alerting/provider/mattermost"
 	"github.com/TwiN/gatus/v4/alerting/provider/messagebird"
+	"github.com/TwiN/gatus/v4/alerting/provider/ntfy"
 	"github.com/TwiN/gatus/v4/alerting/provider/opsgenie"
 	"github.com/TwiN/gatus/v4/alerting/provider/pagerduty"
 	"github.com/TwiN/gatus/v4/alerting/provider/slack"
@@ -61,6 +62,7 @@ var (
 	_ AlertProvider = (*matrix.AlertProvider)(nil)
 	_ AlertProvider = (*mattermost.AlertProvider)(nil)
 	_ AlertProvider = (*messagebird.AlertProvider)(nil)
+	_ AlertProvider = (*ntfy.AlertProvider)(nil)
 	_ AlertProvider = (*opsgenie.AlertProvider)(nil)
 	_ AlertProvider = (*pagerduty.AlertProvider)(nil)
 	_ AlertProvider = (*slack.AlertProvider)(nil)

config/config.go

@@ -306,6 +306,7 @@ func validateAlertingConfig(alertingConfig *alerting.Config, endpoints []*core.E
 		alert.TypeMatrix,
 		alert.TypeMattermost,
 		alert.TypeMessagebird,
+		alert.TypeNtfy,
 		alert.TypeOpsgenie,
 		alert.TypePagerDuty,
 		alert.TypeSlack,