config: autodetect advertise IP

(cherry picked from commit 937a57b43e4a0a53c09e66c71ce232c7a0735fc9)

internal/config/config_test.go

@@ -0,0 +1,49 @@
+package config
+
+import (
+	"net"
+	"testing"
+)
+
+func TestLoadUsesExplicitAdvertiseIP(t *testing.T) {
+	t.Setenv("TELESRV_ADVERTISE_IP", "10.172.61.102")
+
+	cfg, err := Load()
+	if err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+	if cfg.AdvertiseIP != "10.172.61.102" {
+		t.Fatalf("AdvertiseIP = %q, want explicit env", cfg.AdvertiseIP)
+	}
+}
+
+func TestPreferredAdvertiseIPPrefersPhysicalLANRanges(t *testing.T) {
+	got := preferredAdvertiseIP([]net.IP{
+		net.IPv4(172, 17, 0, 1),
+		net.IPv4(192, 168, 1, 20),
+		net.IPv4(10, 172, 61, 102),
+	})
+	if got != "10.172.61.102" {
+		t.Fatalf("preferredAdvertiseIP = %q, want 10.172.61.102", got)
+	}
+
+	got = preferredAdvertiseIP([]net.IP{
+		net.IPv4(172, 17, 0, 1),
+		net.IPv4(192, 168, 1, 20),
+	})
+	if got != "192.168.1.20" {
+		t.Fatalf("preferredAdvertiseIP = %q, want 192.168.1.20", got)
+	}
+}
+
+func TestPrivateIPv4AndVirtualInterfaceDetection(t *testing.T) {
+	if !isPrivateIPv4(net.IPv4(10, 172, 61, 102)) {
+		t.Fatal("10.172.61.102 should be private")
+	}
+	if isPrivateIPv4(net.IPv4(8, 8, 8, 8)) {
+		t.Fatal("8.8.8.8 should not be private")
+	}
+	if !likelyVirtualInterface("vEthernet (WSL)") {
+		t.Fatal("vEthernet (WSL) should be treated as virtual")
+	}
+}