Initial commit

diff --git a/gps303.py b/gps303.py
new file mode 100755 (executable)
index 0000000..1d701ca
--- /dev/null
+++ b/gps303.py
@@ -0,0 +1,94 @@
+#!/usr/bin/env python3
+
+from enum import Enum
+from select import poll, POLLIN, POLLERR, POLLHUP, POLLPRI
+from socket import socket, AF_INET, SOCK_STREAM, SOL_SOCKET, SO_REUSEADDR
+from struct import pack, unpack
+import sys
+from time import time
+
+PORT = 4303
+
+class P(Enum):
+    UNKNOWN = 0x00
+    LOGIN = 0x01
+    STATUS = 0x13
+    HIBERNATION = 0x14
+    time = 0x30
+    SETUP = 0x57
+    
+
+
+def answer_setup(data):
+    return bytes.fromhex("0300310000000000000000000000000000000000000000000000003b3b3b")
+
+def handle_packet(packet, addr, when):
+    xx, length, proto = unpack("!2sBB", packet[:4])
+    crlf = packet[-2:]
+    data = packet[4:-2]
+    if xx != b"xx" or crlf != b"\r\n" or (length > 1 and len(packet) != length + 2):
+        print("bad packet:", packet.hex())
+    print("length", length, "proto", hex(proto))
+    try:
+        p = P(proto)
+    except ValueError:
+        p = P.UNKNOWN
+    payload = b""
+    if p == P.LOGIN:
+       print("imei", data[:-1].hex(), "ver", data[-1:].hex())
+    elif p == P.SETUP:
+        payload = answer_setup(data)
+    length = len(payload)+1
+    if length > 6:
+        length -= 6
+    return b"xx" + pack("B", length) + pack("B", proto) + payload + b"\r\n"
+
+if __name__ == "__main__":
+    ctlsock = socket(AF_INET, SOCK_STREAM)
+    ctlsock.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
+    ctlsock.bind(("", PORT))
+    ctlsock.listen(5)
+    ctlfd = ctlsock.fileno()
+    pollset = poll()
+    pollset.register(ctlfd, POLLIN | POLLERR | POLLHUP | POLLPRI)
+    clnt_dict = {}
+    while True:
+        try:
+            events = pollset.poll(1000)
+        except KeyboardInterrupt:
+            print("Exiting")
+            sys.exit(0)
+        for fd, ev in events:
+            if fd == ctlfd:
+                if ev & POLLIN:
+                    clntsock, clntaddr = ctlsock.accept()
+                    clntfd = clntsock.fileno()
+                    clnt_dict[clntfd] = (clntsock, clntaddr)
+                    pollset.register(clntfd, POLLIN | POLLERR | POLLHUP | POLLPRI)
+                    print("accepted connection from", clntaddr, "fd", clntfd)
+                if ev & ~POLLIN:
+                    print("unexpected event on ctlfd:", ev)
+            else:
+                try:
+                    clntsock, clntaddr = clnt_dict[fd]
+                except KeyError:  # this socket closed already
+                    continue
+                if ev & POLLIN:
+                    packet = clntsock.recv(4096)
+                    when = time()
+                    print("packet", packet, "from", clntaddr, "from fd", fd)
+                    if packet:
+                        response = handle_packet(packet, clntaddr, when)
+                        if response:
+                            try:
+                                # Ignore possibility of blocking
+                                clntsock.send(response)
+                            except OSError as e:
+                                print("sending to socket", fd, "error", e)
+                    else:
+                        print("disconnect")
+                        pollset.unregister(fd)
+                        clntsock.close()
+                        del clnt_dict[fd]
+                if ev & ~POLLIN:
+                    print("unexpected event", ev, "on fd", fd)