feat(server): monitor model + checker package

server/internal/checker/checker.go

@@ -0,0 +1,222 @@
+// Package checker runs service checks (http/tcp/icmp/tls) and returns a uniform
+// Result. It has no dependency on models or pb so it can be duplicated verbatim
+// into the agent module (agent-run monitors) — callers map their own monitor
+// representation onto Spec.
+package checker
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+)
+
+// Check types (mirror models.Monitor* constants).
+const (
+	TypeHTTP = "http"
+	TypeTCP  = "tcp"
+	TypeICMP = "icmp"
+	TypeTLS  = "tls"
+)
+
+// Spec is a self-contained description of a single check.
+type Spec struct {
+	Type           string
+	URL            string
+	Host           string
+	Port           int
+	Method         string
+	ExpectedStatus int
+	Keyword        string
+	TLSWarnDays    int
+	TimeoutSec     int
+}
+
+// Result is the uniform outcome of running a check.
+type Result struct {
+	Up         bool
+	LatencyMs  int
+	Message    string
+	CertExpiry *time.Time
+}
+
+func (s Spec) timeout() time.Duration {
+	t := s.TimeoutSec
+	if t <= 0 || t > 10 {
+		t = 10
+	}
+	return time.Duration(t) * time.Second
+}
+
+// Run executes the check described by s.
+func Run(ctx context.Context, s Spec) Result {
+	switch s.Type {
+	case TypeHTTP:
+		return runHTTP(ctx, s)
+	case TypeTCP:
+		return runTCP(ctx, s)
+	case TypeICMP:
+		return runICMP(ctx, s)
+	case TypeTLS:
+		return runTLS(ctx, s)
+	default:
+		return Result{Message: "unknown check type: " + s.Type}
+	}
+}
+
+func runHTTP(ctx context.Context, s Spec) Result {
+	method := s.Method
+	if method == "" {
+		method = http.MethodGet
+	}
+	expect := s.ExpectedStatus
+	if expect == 0 {
+		expect = 200
+	}
+	client := &http.Client{Timeout: s.timeout()}
+	start := time.Now()
+	req, err := http.NewRequestWithContext(ctx, method, s.URL, nil)
+	if err != nil {
+		return Result{Message: err.Error()}
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return Result{LatencyMs: msSince(start), Message: err.Error()}
+	}
+	defer resp.Body.Close()
+	res := Result{LatencyMs: msSince(start), Up: true}
+	if resp.TLS != nil && len(resp.TLS.PeerCertificates) > 0 {
+		exp := resp.TLS.PeerCertificates[0].NotAfter
+		res.CertExpiry = &exp
+	}
+	if resp.StatusCode != expect {
+		return Result{LatencyMs: res.LatencyMs, CertExpiry: res.CertExpiry, Message: fmt.Sprintf("status %d (want %d)", resp.StatusCode, expect)}
+	}
+	if s.Keyword != "" {
+		body, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+		if !strings.Contains(string(body), s.Keyword) {
+			return Result{LatencyMs: res.LatencyMs, CertExpiry: res.CertExpiry, Message: "keyword not found"}
+		}
+	}
+	return res
+}
+
+func runTCP(ctx context.Context, s Spec) Result {
+	addr := net.JoinHostPort(s.Host, fmt.Sprint(s.Port))
+	start := time.Now()
+	d := net.Dialer{Timeout: s.timeout()}
+	conn, err := d.DialContext(ctx, "tcp", addr)
+	if err != nil {
+		return Result{LatencyMs: msSince(start), Message: err.Error()}
+	}
+	conn.Close()
+	return Result{Up: true, LatencyMs: msSince(start)}
+}
+
+func runTLS(ctx context.Context, s Spec) Result {
+	port := s.Port
+	if port == 0 {
+		port = 443
+	}
+	addr := net.JoinHostPort(s.Host, fmt.Sprint(port))
+	start := time.Now()
+	d := net.Dialer{Timeout: s.timeout()}
+	conn, err := tls.DialWithDialer(&d, "tcp", addr, &tls.Config{ServerName: s.Host})
+	if err != nil {
+		return Result{LatencyMs: msSince(start), Message: err.Error()}
+	}
+	defer conn.Close()
+	certs := conn.ConnectionState().PeerCertificates
+	if len(certs) == 0 {
+		return Result{LatencyMs: msSince(start), Message: "no peer certificate"}
+	}
+	exp := certs[0].NotAfter
+	res := Result{LatencyMs: msSince(start), CertExpiry: &exp}
+	warn := s.TLSWarnDays
+	if warn <= 0 {
+		warn = 14
+	}
+	remaining := time.Until(exp)
+	if remaining <= 0 {
+		res.Message = "certificate expired"
+		return res
+	}
+	if remaining <= time.Duration(warn)*24*time.Hour {
+		res.Message = fmt.Sprintf("certificate expires in %d days", int(remaining.Hours()/24))
+		return res
+	}
+	res.Up = true
+	return res
+}
+
+func msSince(t time.Time) int { return int(time.Since(t).Milliseconds()) }
+
+// runICMP sends a single ICMP echo request and waits for the reply. Requires
+// raw-socket privileges (the agent and server run as root). Returns down with a
+// descriptive message when the socket cannot be opened or no reply arrives.
+func runICMP(ctx context.Context, s Spec) Result {
+	dst, err := net.ResolveIPAddr("ip4", s.Host)
+	if err != nil {
+		return Result{Message: err.Error()}
+	}
+	conn, err := net.ListenPacket("ip4:icmp", "0.0.0.0")
+	if err != nil {
+		return Result{Message: "icmp socket: " + err.Error()}
+	}
+	defer conn.Close()
+
+	id := os.Getpid() & 0xffff
+	pkt := icmpEcho(id, 1)
+	deadline := time.Now().Add(s.timeout())
+	if d, ok := ctx.Deadline(); ok && d.Before(deadline) {
+		deadline = d
+	}
+	_ = conn.SetDeadline(deadline)
+
+	start := time.Now()
+	if _, err := conn.WriteTo(pkt, dst); err != nil {
+		return Result{Message: err.Error()}
+	}
+	reply := make([]byte, 1500)
+	for {
+		n, peer, err := conn.ReadFrom(reply)
+		if err != nil {
+			return Result{LatencyMs: msSince(start), Message: "no reply"}
+		}
+		// Skip the IPv4 header (20 bytes) to reach the ICMP message.
+		if n < 28 || peer.String() != dst.String() {
+			continue
+		}
+		if reply[20] == 0 { // ICMP echo reply type
+			return Result{Up: true, LatencyMs: msSince(start)}
+		}
+	}
+}
+
+func icmpEcho(id, seq int) []byte {
+	// Type(8)=echo request, Code=0, Checksum, ID, Seq, no payload.
+	b := []byte{8, 0, 0, 0, byte(id >> 8), byte(id), byte(seq >> 8), byte(seq)}
+	cs := icmpChecksum(b)
+	b[2] = byte(cs >> 8)
+	b[3] = byte(cs)
+	return b
+}
+
+func icmpChecksum(b []byte) uint16 {
+	var sum uint32
+	for i := 0; i < len(b)-1; i += 2 {
+		sum += uint32(b[i])<<8 | uint32(b[i+1])
+	}
+	if len(b)%2 == 1 {
+		sum += uint32(b[len(b)-1]) << 8
+	}
+	for sum>>16 != 0 {
+		sum = (sum & 0xffff) + (sum >> 16)
+	}
+	return ^uint16(sum)
+}