primeiro commit

internal/probe/ping.go

@@ -0,0 +1,153 @@
+package probe
+
+import (
+	"context"
+	"crypto/rand"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"net"
+	"time"
+)
+
+const (
+	icmpEchoReply = 0
+	icmpEcho      = 8
+)
+
+// PingResult contains the outcome of one ICMP echo request.
+type PingResult struct {
+	Reachable bool
+	RTT       time.Duration
+	Err       error
+}
+
+// Ping sends one ICMP echo request to an IPv4 host.
+func Ping(ctx context.Context, host string, timeout time.Duration) (result PingResult) {
+	start := time.Now()
+	ip, err := resolveIPv4(ctx, host)
+	if err != nil {
+		return PingResult{Err: err}
+	}
+
+	conn, err := net.ListenPacket("ip4:icmp", "0.0.0.0")
+	if err != nil {
+		return PingResult{Err: fmt.Errorf("opening icmp socket: %w", err)}
+	}
+	defer func() {
+		if closeErr := conn.Close(); closeErr != nil && result.Err == nil {
+			result = PingResult{Err: fmt.Errorf("closing icmp socket: %w", closeErr)}
+		}
+	}()
+
+	deadline := time.Now().Add(timeout)
+	if ctxDeadline, ok := ctx.Deadline(); ok && ctxDeadline.Before(deadline) {
+		deadline = ctxDeadline
+	}
+	if err := conn.SetDeadline(deadline); err != nil {
+		return PingResult{Err: fmt.Errorf("setting icmp deadline: %w", err)}
+	}
+
+	id, seq, err := echoIdentifiers()
+	if err != nil {
+		return PingResult{Err: err}
+	}
+	packet := echoPacket(id, seq)
+	if _, err := conn.WriteTo(packet, &net.IPAddr{IP: ip}); err != nil {
+		return PingResult{Err: fmt.Errorf("sending icmp echo to %s: %w", host, err)}
+	}
+
+	buffer := make([]byte, 1500)
+	for {
+		n, addr, err := conn.ReadFrom(buffer)
+		if err != nil {
+			if ctxErr := ctx.Err(); ctxErr != nil {
+				return PingResult{Err: fmt.Errorf("ping canceled: %w", ctxErr)}
+			}
+			return PingResult{Err: fmt.Errorf("reading icmp reply from %s: %w", host, err)}
+		}
+		if !sameIP(addr, ip) {
+			continue
+		}
+		if echoReplyMatches(buffer[:n], id, seq) {
+			return PingResult{Reachable: true, RTT: time.Since(start)}
+		}
+	}
+}
+
+func resolveIPv4(ctx context.Context, host string) (net.IP, error) {
+	if parsed := net.ParseIP(host); parsed != nil {
+		if ipv4 := parsed.To4(); ipv4 != nil {
+			return ipv4, nil
+		}
+		return nil, fmt.Errorf("%s is not an IPv4 address", host)
+	}
+	addrs, err := net.DefaultResolver.LookupIPAddr(ctx, host)
+	if err != nil {
+		return nil, fmt.Errorf("resolving ping host %s: %w", host, err)
+	}
+	for _, addr := range addrs {
+		if ipv4 := addr.IP.To4(); ipv4 != nil {
+			return ipv4, nil
+		}
+	}
+	return nil, fmt.Errorf("resolving ping host %s: no IPv4 address found", host)
+}
+
+func echoIdentifiers() (uint16, uint16, error) {
+	var data [4]byte
+	if _, err := rand.Read(data[:]); err != nil {
+		return 0, 0, fmt.Errorf("generating icmp identifiers: %w", err)
+	}
+	return binary.BigEndian.Uint16(data[0:2]), binary.BigEndian.Uint16(data[2:4]), nil
+}
+
+func echoPacket(id uint16, seq uint16) []byte {
+	payload := []byte("statuspanel")
+	packet := make([]byte, 8+len(payload))
+	packet[0] = icmpEcho
+	binary.BigEndian.PutUint16(packet[4:6], id)
+	binary.BigEndian.PutUint16(packet[6:8], seq)
+	copy(packet[8:], payload)
+	checksum := icmpChecksum(packet)
+	binary.BigEndian.PutUint16(packet[2:4], checksum)
+	return packet
+}
+
+func echoReplyMatches(packet []byte, id uint16, seq uint16) bool {
+	if len(packet) < 8 {
+		return false
+	}
+	if packet[0] == 69 && len(packet) >= 28 {
+		packet = packet[20:]
+	}
+	return len(packet) >= 8 &&
+		packet[0] == icmpEchoReply &&
+		binary.BigEndian.Uint16(packet[4:6]) == id &&
+		binary.BigEndian.Uint16(packet[6:8]) == seq
+}
+
+func sameIP(addr net.Addr, ip net.IP) bool {
+	ipAddr, ok := addr.(*net.IPAddr)
+	if !ok {
+		return false
+	}
+	return ipAddr.IP.Equal(ip)
+}
+
+func icmpChecksum(data []byte) uint16 {
+	var sum uint32
+	for len(data) > 1 {
+		sum += uint32(binary.BigEndian.Uint16(data[:2]))
+		data = data[2:]
+	}
+	if len(data) == 1 {
+		sum += uint32(data[0]) << 8
+	}
+	for sum>>16 != 0 {
+		sum = (sum & 0xffff) + (sum >> 16)
+	}
+	return ^uint16(sum)
+}
+
+var errUnsupportedGateway = errors.New("gateway discovery is unsupported on this platform")