add src/lan_utils.py

src/lan_utils.py

@@ -0,0 +1,155 @@
+"""
+LAN utilities for detecting network interfaces and IPv4 addresses.
+
+Provides functionality to enumerate local IPv4 addresses for LAN proxy
+sharing. IPv6 is intentionally not reported — this project only exposes
+the proxy over IPv4 LANs, which is what every consumer router and
+phone/desktop client actually uses.
+
+Implementation notes
+--------------------
+This module relies only on the Python standard library so it works
+out-of-the-box on every supported OS (Windows, Linux, macOS,
+Android/Termux, *BSD) without requiring a C compiler or native build
+tools (previous versions depended on ``netifaces``, which needs
+"Microsoft Visual C++ 14.0 or greater" on Windows and was a frequent
+install blocker for users on slow connections).
+
+Strategy (in order):
+1. "UDP connect trick" to reliably discover the primary outbound
+   IPv4 address on any OS.
+2. ``socket.getaddrinfo(hostname, AF_INET)`` to enumerate any additional
+   IPv4 addresses bound to the host (covers multi-homed machines).
+"""
+
+import ipaddress
+import logging
+import socket
+from typing import Dict, List, Optional, Set
+
+log = logging.getLogger("LAN")
+
+
+# ---------------------------------------------------------------------------
+# Primary-IP discovery (UDP connect trick)
+# ---------------------------------------------------------------------------
+def _primary_ipv4() -> Optional[str]:
+    """
+    Return the primary local IPv4 the OS would use for outbound traffic.
+
+    Uses a connected UDP socket which does *not* actually send packets —
+    the kernel just picks the source address from its routing table.
+    Works identically on Windows, Linux, macOS, and Android.
+    """
+    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    try:
+        s.settimeout(0.5)
+        # TEST-NET-1 address, port is arbitrary; no packet is sent for UDP connect().
+        s.connect(('192.0.2.1', 80))
+        return s.getsockname()[0]
+    except OSError:
+        return None
+    finally:
+        s.close()
+
+
+# ---------------------------------------------------------------------------
+# Public API
+# ---------------------------------------------------------------------------
+def get_network_interfaces() -> Dict[str, List[str]]:
+    """
+    Get network interfaces and their associated non-loopback IPv4 addresses.
+
+    Returns:
+        Dict[str, List[str]]: Interface label -> list of IPv4 addresses.
+        Labels are best-effort synthetic names such as ``"primary"``
+        and ``"host"``.
+    """
+    interfaces: Dict[str, List[str]] = {}
+    seen_ips: Set[str] = set()
+
+    def _add(label: str, ip: Optional[str]) -> None:
+        if not ip or ip in seen_ips:
+            return
+        if ip.startswith('127.'):
+            return
+        seen_ips.add(ip)
+        interfaces.setdefault(label, []).append(ip)
+
+    # 1) Primary outbound IPv4 (most reliable, cross-platform).
+    _add('primary', _primary_ipv4())
+
+    # 2) Enumerate via hostname resolution (picks up multi-homed hosts).
+    try:
+        hostname = socket.gethostname()
+    except OSError:
+        hostname = ''
+
+    if hostname:
+        try:
+            for info in socket.getaddrinfo(hostname, None, socket.AF_INET):
+                _add('host', info[4][0])
+        except (socket.gaierror, OSError):
+            pass
+
+    return interfaces
+
+
+def get_lan_ips(port: int = 8085) -> List[str]:
+    """
+    Get list of LAN-accessible proxy addresses (IPv4 only).
+
+    Returns a list of IP:port combinations that can be used to access
+    the proxy from other devices on the local network.
+
+    Args:
+        port: The port the proxy is listening on
+
+    Returns:
+        List[str]: List of "IP:port" strings for LAN access
+    """
+    interfaces = get_network_interfaces()
+    lan_addresses: List[str] = []
+
+    for iface_ips in interfaces.values():
+        for ip in iface_ips:
+            try:
+                addr = ipaddress.IPv4Address(ip)
+            except (ValueError, ipaddress.AddressValueError):
+                continue
+            if addr.is_loopback or addr.is_unspecified:
+                continue
+            if addr.is_private or addr.is_link_local:
+                lan_addresses.append(f"{ip}:{port}")
+
+    # Remove duplicates while preserving order.
+    seen: Set[str] = set()
+    unique_addresses: List[str] = []
+    for addr in lan_addresses:
+        if addr not in seen:
+            seen.add(addr)
+            unique_addresses.append(addr)
+
+    return unique_addresses
+
+
+def log_lan_access(port: int = 8085, socks_port: Optional[int] = None):
+    """
+    Log the LAN-accessible proxy addresses for user convenience.
+
+    Args:
+        port: HTTP proxy port
+        socks_port: Optional SOCKS5 proxy port
+    """
+    lan_http = get_lan_ips(port)
+    if lan_http:
+        log.info("LAN HTTP proxy   : %s", ", ".join(lan_http))
+    else:
+        log.warning("No LAN IP addresses detected for HTTP proxy")
+
+    if socks_port:
+        lan_socks = get_lan_ips(socks_port)
+        if lan_socks:
+            log.info("LAN SOCKS5 proxy : %s", ", ".join(lan_socks))
+        else:
+            log.warning("No LAN IP addresses detected for SOCKS5 proxy")