Rewrite bridge build system

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

wireguard-go-bridge/src/tun/tun_ios.go

@@ -0,0 +1,83 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (C) 2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+package tun
+
+// #include <sys/types.h>
+// static ssize_t callFnWithCtx(const void *func, const void *ctx, const void *buffer, size_t len)
+// {
+// 	return ((ssize_t(*)(const void *, const unsigned char *, size_t))func)(ctx, buffer, len);
+// }
+import "C"
+
+import (
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+type nativeTun struct {
+	events  chan TUNEvent
+	mtu     int
+	readFn  unsafe.Pointer
+	writeFn unsafe.Pointer
+	ctx     unsafe.Pointer
+}
+
+func CreateTUN(mtu int, readFn unsafe.Pointer, writeFn unsafe.Pointer, ctx unsafe.Pointer) TUNDevice {
+	tun := &nativeTun{
+		events:  make(chan TUNEvent, 10),
+		mtu:     mtu,
+		readFn:  readFn,
+		writeFn: writeFn,
+		ctx:     ctx,
+	}
+	tun.events <- TUNEventUp
+	return tun
+}
+
+func (tun *nativeTun) Name() (string, error) {
+	return "tun", nil
+}
+
+func (tun *nativeTun) File() *os.File {
+	return nil
+}
+
+func (tun *nativeTun) Events() chan TUNEvent {
+	return tun.events
+}
+
+func (tun *nativeTun) Read(buff []byte, offset int) (int, error) {
+	ret := C.callFnWithCtx(tun.readFn, tun.ctx, unsafe.Pointer(&buff[offset]), C.size_t(len(buff) - offset))
+	if ret < 0 {
+		return 0, syscall.Errno(-ret)
+	}
+	return int(ret), nil
+}
+
+func (tun *nativeTun) Write(buff []byte, offset int) (int, error) {
+	ret := C.callFnWithCtx(tun.writeFn, tun.ctx, unsafe.Pointer(&buff[offset]), C.size_t(len(buff) - offset))
+	if ret < 0 {
+		return 0, syscall.Errno(-ret)
+	}
+	return int(ret), nil
+}
+
+func (tun *nativeTun) Close() error {
+	if tun.events != nil {
+		close(tun.events)
+	}
+	return nil
+}
+
+func (tun *nativeTun) setMTU(n int) error {
+	tun.mtu = n
+	return nil
+}
+
+func (tun *nativeTun) MTU() (int, error) {
+	return tun.mtu, nil
+}