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

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
+}