init work of uptime

internal/monitor/dns.go

@@ -0,0 +1,69 @@
+package monitor
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"time"
+
+	"arclineit/arcline-uptime/internal/config"
+)
+
+// DNSChecker resolves a hostname and optionally asserts a specific IP is returned.
+type DNSChecker struct {
+	cfg     config.MonitorConfig
+	timeout time.Duration
+}
+
+func NewDNSChecker(cfg config.MonitorConfig, timeout time.Duration) *DNSChecker {
+	return &DNSChecker{cfg: cfg, timeout: timeout}
+}
+
+func (d *DNSChecker) Name()     string        { return d.cfg.Name }
+func (d *DNSChecker) Interval() time.Duration { return time.Duration(d.cfg.Interval) * time.Second }
+
+func (d *DNSChecker) Check() Result {
+	start := time.Now()
+	result := Result{
+		MonitorName: d.cfg.Name,
+		CheckedAt:   start,
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), d.timeout)
+	defer cancel()
+
+	addrs, err := net.DefaultResolver.LookupHost(ctx, d.cfg.Host)
+	result.ResponseTime = time.Since(start)
+	if err != nil {
+		result.Error = err.Error()
+		return result
+	}
+
+	if d.cfg.ExpectedIP != "" {
+		want := normalizeIP(d.cfg.ExpectedIP)
+		found := false
+		for _, addr := range addrs {
+			if normalizeIP(addr) == want {
+				found = true
+				break
+			}
+		}
+		if !found {
+			result.Error = fmt.Sprintf("expected IP %q not found in results %v", d.cfg.ExpectedIP, addrs)
+			return result
+		}
+	}
+
+	result.Up = true
+	applyThreshold(&result, d.cfg.MaxResponseMS)
+	return result
+}
+
+// normalizeIP parses and re-serialises an IP string so different representations
+// of the same address compare equal (e.g. "::1" and "0:0:0:0:0:0:0:1").
+func normalizeIP(s string) string {
+	if ip := net.ParseIP(s); ip != nil {
+		return ip.String()
+	}
+	return s
+}