feat(connectivity): Allow internet connection validation prior to endpoint execution (#461)

config/config.go

@@ -14,6 +14,7 @@ import (
 	"github.com/TwiN/gatus/v5/alerting"
 	"github.com/TwiN/gatus/v5/alerting/alert"
 	"github.com/TwiN/gatus/v5/alerting/provider"
+	"github.com/TwiN/gatus/v5/config/connectivity"
 	"github.com/TwiN/gatus/v5/config/maintenance"
 	"github.com/TwiN/gatus/v5/config/remote"
 	"github.com/TwiN/gatus/v5/config/ui"
@@ -91,6 +92,9 @@ type Config struct {
 	// WARNING: This is in ALPHA and may change or be completely removed in the future
 	Remote *remote.Config `yaml:"remote,omitempty"`
 
+	// Connectivity is the configuration for connectivity
+	Connectivity *connectivity.Config `yaml:"connectivity,omitempty"`
+
 	configPath      string    // path to the file or directory from which config was loaded
 	lastFileModTime time.Time // last modification time
 }
@@ -252,10 +256,20 @@ func parseAndValidateConfigBytes(yamlBytes []byte) (config *Config, err error) {
 		if err := validateRemoteConfig(config); err != nil {
 			return nil, err
 		}
+		if err := validateConnectivityConfig(config); err != nil {
+			return nil, err
+		}
 	}
 	return
 }
 
+func validateConnectivityConfig(config *Config) error {
+	if config.Connectivity != nil {
+		return config.Connectivity.ValidateAndSetDefaults()
+	}
+	return nil
+}
+
 func validateRemoteConfig(config *Config) error {
 	if config.Remote != nil {
 		if err := config.Remote.ValidateAndSetDefaults(); err != nil {

config/connectivity/connectivity.go

@@ -0,0 +1,53 @@
+package connectivity
+
+import (
+	"errors"
+	"strings"
+	"time"
+
+	"github.com/TwiN/gatus/v5/client"
+)
+
+var (
+	ErrInvalidInterval  = errors.New("connectivity.checker.interval must be 5s or higher")
+	ErrInvalidDNSTarget = errors.New("connectivity.checker.target must be suffixed with :53")
+)
+
+// Config is the configuration for the connectivity checker.
+type Config struct {
+	Checker *Checker `yaml:"checker,omitempty"`
+}
+
+func (c *Config) ValidateAndSetDefaults() error {
+	if c.Checker != nil {
+		if c.Checker.Interval == 0 {
+			c.Checker.Interval = 60 * time.Second
+		} else if c.Checker.Interval < 5*time.Second {
+			return ErrInvalidInterval
+		}
+		if !strings.HasSuffix(c.Checker.Target, ":53") {
+			return ErrInvalidDNSTarget
+		}
+	}
+	return nil
+}
+
+// Checker is the configuration for making sure Gatus has access to the internet.
+type Checker struct {
+	Target   string        `yaml:"target"` // e.g. 1.1.1.1:53
+	Interval time.Duration `yaml:"interval,omitempty"`
+
+	isConnected bool
+	lastCheck   time.Time
+}
+
+func (c Checker) Check() bool {
+	return client.CanCreateTCPConnection(c.Target, &client.Config{Timeout: 5 * time.Second})
+}
+
+func (c *Checker) IsConnected() bool {
+	if now := time.Now(); now.After(c.lastCheck.Add(c.Interval)) {
+		c.lastCheck, c.isConnected = now, c.Check()
+	}
+	return c.isConnected
+}

config/connectivity/connectivity_test.go

@@ -0,0 +1,62 @@
+package connectivity
+
+import (
+	"fmt"
+	"testing"
+	"time"
+)
+
+func TestConfig(t *testing.T) {
+	scenarios := []struct {
+		name             string
+		cfg              *Config
+		expectedErr      error
+		expectedInterval time.Duration
+	}{
+		{
+			name:             "good-config",
+			cfg:              &Config{Checker: &Checker{Target: "1.1.1.1:53", Interval: 10 * time.Second}},
+			expectedInterval: 10 * time.Second,
+		},
+		{
+			name:             "good-config-with-default-interval",
+			cfg:              &Config{Checker: &Checker{Target: "8.8.8.8:53", Interval: 0}},
+			expectedInterval: 60 * time.Second,
+		},
+		{
+			name:        "config-with-interval-too-low",
+			cfg:         &Config{Checker: &Checker{Target: "1.1.1.1:53", Interval: 4 * time.Second}},
+			expectedErr: ErrInvalidInterval,
+		},
+		{
+			name:        "config-with-invalid-target-due-to-missing-port",
+			cfg:         &Config{Checker: &Checker{Target: "1.1.1.1", Interval: 15 * time.Second}},
+			expectedErr: ErrInvalidDNSTarget,
+		},
+		{
+			name:        "config-with-invalid-target-due-to-invalid-dns-port",
+			cfg:         &Config{Checker: &Checker{Target: "1.1.1.1:52", Interval: 15 * time.Second}},
+			expectedErr: ErrInvalidDNSTarget,
+		},
+	}
+	for _, scenario := range scenarios {
+		t.Run(scenario.name, func(t *testing.T) {
+			err := scenario.cfg.ValidateAndSetDefaults()
+			if fmt.Sprintf("%s", err) != fmt.Sprintf("%s", scenario.expectedErr) {
+				t.Errorf("expected error %v, got %v", scenario.expectedErr, err)
+			}
+			if err == nil && scenario.expectedErr == nil {
+				if scenario.cfg.Checker.Interval != scenario.expectedInterval {
+					t.Errorf("expected interval %v, got %v", scenario.expectedInterval, scenario.cfg.Checker.Interval)
+				}
+			}
+		})
+	}
+}
+
+func TestChecker_IsConnected(t *testing.T) {
+	checker := &Checker{Target: "1.1.1.1:53", Interval: 10 * time.Second}
+	if !checker.IsConnected() {
+		t.Error("expected checker.IsConnected() to be true")
+	}
+}