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feat: Add option to define which DNS server a DNS monitor queries (#2389)

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This commit is contained in:
Sven van Ginkel
2026-09-25 01:01:10 +02:00
committed by GitHub
parent a20a7d2edc
commit f7528a0208
10 changed files with 220 additions and 20 deletions
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70
agent/network_monitor_test.go
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@@ -376,15 +376,79 @@ func tcpMonitorTestResolver(ips []string) *net.Resolver {
}}
}
// udpDNSTestServer starts a UDP server on loopback that answers A queries with the
// given IPs, and returns its listen address (host:port).
func udpDNSTestServer(t *testing.T, ips []string) string {
t.Helper()
conn, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.ParseIP("127.0.0.1")})
require.NoError(t, err)
t.Cleanup(func() { conn.Close() })
go func() {
buf := make([]byte, 512)
for {
n, addr, err := conn.ReadFromUDP(buf)
if err != nil {
return
}
var msg dnsmessage.Message
if err := msg.Unpack(buf[:n]); err != nil {
continue
}
msg.Header.Response = true
msg.Header.RecursionAvailable = true
for _, question := range msg.Questions {
if question.Type != dnsmessage.TypeA {
continue
}
for _, ip := range ips {
msg.Answers = append(msg.Answers, dnsmessage.Resource{
Header: dnsmessage.ResourceHeader{Name: question.Name, Type: dnsmessage.TypeA, Class: dnsmessage.ClassINET},
Body: &dnsmessage.AResource{A: [4]byte(net.ParseIP(ip).To4())},
})
}
}
packet, err := msg.Pack()
if err != nil {
continue
}
_, _ = conn.WriteToUDP(packet, addr)
}
}()
return conn.LocalAddr().String()
}
func TestMonitorDNS(t *testing.T) {
t.Run("success", func(t *testing.T) {
responseUs, err := monitorDNS(context.Background(), "localhost")
responseUs, err := monitorDNS(context.Background(), "localhost", "")
require.NoError(t, err)
assert.GreaterOrEqual(t, responseUs, int64(0))
})
t.Run("lookup failure", func(t *testing.T) {
responseUs, err := monitorDNS(context.Background(), "")
responseUs, err := monitorDNS(context.Background(), "", "")
assert.Equal(t, int64(-1), responseUs)
require.Error(t, err)
})
t.Run("custom server", func(t *testing.T) {
serverAddr := udpDNSTestServer(t, []string{"192.0.2.10"})
responseUs, err := monitorDNS(context.Background(), "example.test.", serverAddr)
require.NoError(t, err)
assert.GreaterOrEqual(t, responseUs, int64(0))
})
t.Run("custom server without port defaults to 53", func(t *testing.T) {
resolver := dnsResolverForServer("127.0.0.1")
conn, err := resolver.Dial(context.Background(), "udp", "")
require.NoError(t, err)
defer conn.Close()
assert.Equal(t, "127.0.0.1:53", conn.RemoteAddr().String())
})
t.Run("custom server unreachable", func(t *testing.T) {
responseUs, err := monitorDNS(context.Background(), "example.test.", "127.0.0.1:1")
assert.Equal(t, int64(-1), responseUs)
require.Error(t, err)
})
@@ -479,7 +543,7 @@ func TestMonitorResolutionCancellation(t *testing.T) {
case "tcp":
_, err = monitorTCP(ctx, "monitor-cancellation.invalid.", 80)
case "dns":
_, err = monitorDNS(ctx, "monitor-cancellation.invalid.")
_, err = monitorDNS(ctx, "monitor-cancellation.invalid.", "")
case "icmp":
_, err = monitorICMP(ctx, "monitor-cancellation.invalid.")
}