Test: cover client-IP/ARP resolution and SAIP schema lookup

Make get_mac_from_arp take an arp_path for testability (default unchanged), and
add tests for get_client_ip (X-Forwarded-For vs remote_addr), ARP MAC
resolution (match/no-match/missing), SAIP decode-unavailable, and the
SAIP_ASN_PATH override. Coverage: utils 100%, overall 93%; 108 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/utils.py

@@ -91,10 +91,10 @@ def get_client_ip(request) -> str:
     return request.remote_addr or ""
 
 
-def get_mac_from_arp(ip: str) -> Optional[str]:
-    """Attempt to resolve a MAC address from /proc/net/arp for the given IP."""
+def get_mac_from_arp(ip: str, arp_path: str = "/proc/net/arp") -> Optional[str]:
+    """Attempt to resolve a MAC address from the ARP table for the given IP."""
     try:
-        with open("/proc/net/arp") as f:
+        with open(arp_path) as f:
             for line in f:
                 parts = line.split()
                 if len(parts) >= 4 and parts[0] == ip:

tests/test_saip.py

@@ -41,6 +41,22 @@ class TestSaipEncoding:
             saip.create_saip_profile("302720000000001", generate_ki(),
                                      b"\x00" * 16, generate_iccid())
 
+    def test_decode_unavailable_raises(self, monkeypatch):
+        monkeypatch.setattr(saip, "_compiler", lambda: None)
+        with pytest.raises(RuntimeError, match="unavailable"):
+            saip.decode_saip_profile(b"\x00")
+
+    def test_find_asn_honours_env_override(self, tmp_path, monkeypatch):
+        fake = tmp_path / "schema.asn"
+        fake.write_text("-- placeholder\n")
+        monkeypatch.setenv("SAIP_ASN_PATH", str(fake))
+        assert saip.find_saip_asn() == str(fake)
+
+    def test_find_asn_ignores_missing_override(self, monkeypatch):
+        monkeypatch.setenv("SAIP_ASN_PATH", "/no/such/schema.asn")
+        # Falls through to the pySim lookup (or None); never returns the bad path.
+        assert saip.find_saip_asn() != "/no/such/schema.asn"
+
     @saip_required
     def test_produces_der_bytes(self):
         ki = generate_ki()

tests/test_utils.py

@@ -2,6 +2,8 @@ import pytest
 
 from server.utils import (
     ensure_parent_dir,
+    get_client_ip,
+    get_mac_from_arp,
     load_config,
     normalize_mac,
     validate_imsi,
@@ -10,6 +12,41 @@ from server.utils import (
 )
 
 
+class _FakeRequest:
+    def __init__(self, headers=None, remote_addr=None):
+        self.headers = headers or {}
+        self.remote_addr = remote_addr
+
+
+class TestClientResolution:
+    def test_client_ip_prefers_forwarded(self):
+        req = _FakeRequest(headers={"X-Forwarded-For": "203.0.113.7, 10.0.0.1"},
+                           remote_addr="10.0.0.1")
+        assert get_client_ip(req) == "203.0.113.7"
+
+    def test_client_ip_falls_back_to_remote_addr(self):
+        assert get_client_ip(_FakeRequest(remote_addr="192.168.4.10")) == "192.168.4.10"
+
+    def test_client_ip_empty_when_unknown(self):
+        assert get_client_ip(_FakeRequest()) == ""
+
+    def test_mac_from_arp_match(self, tmp_path):
+        arp = tmp_path / "arp"
+        arp.write_text(
+            "IP address       HW type     Flags       HW address            Mask     Device\n"
+            "192.168.4.10     0x1         0x2         AA:BB:CC:DD:EE:FF     *        wlan0\n"
+        )
+        assert get_mac_from_arp("192.168.4.10", str(arp)) == "aa:bb:cc:dd:ee:ff"
+
+    def test_mac_from_arp_no_match(self, tmp_path):
+        arp = tmp_path / "arp"
+        arp.write_text("IP address ...\n192.168.4.99 0x1 0x2 11:22:33:44:55:66 * wlan0\n")
+        assert get_mac_from_arp("192.168.4.10", str(arp)) is None
+
+    def test_mac_from_arp_missing_file(self):
+        assert get_mac_from_arp("192.168.4.10", "/no/such/arp") is None
+
+
 class TestEnsureParentDir:
     def test_bare_filename_does_not_crash(self):
         # No directory component -> must be a no-op, not FileNotFoundError.