first commit

app/tap.py

@@ -0,0 +1,42 @@
+from __future__ import annotations
+
+import fcntl
+import os
+import struct
+import subprocess
+import threading
+
+TUNSETIFF = 0x400454CA
+IFF_TAP = 0x0002
+IFF_NO_PI = 0x1000
+
+
+class TapDevice:
+    def __init__(self, name: str, mtu: int = 9000) -> None:
+        self.name = name
+        self.mtu = mtu
+        self.fd: int | None = None
+        self._lock = threading.Lock()
+
+    def open(self) -> None:
+        if self.fd is not None:
+            return
+        fd = os.open("/dev/net/tun", os.O_RDWR)
+        ifreq = struct.pack("16sH22x", self.name.encode("ascii"), IFF_TAP | IFF_NO_PI)
+        fcntl.ioctl(fd, TUNSETIFF, ifreq)
+        subprocess.run(["ip", "link", "set", "dev", self.name, "mtu", str(self.mtu)], check=True)
+        subprocess.run(["ip", "link", "set", "dev", self.name, "up"], check=True)
+        self.fd = fd
+
+    def write(self, frame: bytes) -> int:
+        if self.fd is None:
+            raise RuntimeError("TAP is not open")
+        with self._lock:
+            return os.write(self.fd, frame)
+
+    def close(self) -> None:
+        if self.fd is not None:
+            try:
+                os.close(self.fd)
+            finally:
+                self.fd = None