init

.gitignore

+# Project exclude paths
+/cmake-build-debug/
+/.idea/
\ No newline at end of file

CMakeLists.txt

+cmake_minimum_required(VERSION 3.22)
+project(tun)
+
+set(CMAKE_CXX_STANDARD 23)
+
+add_executable(tun main.cpp)
+
+find_package(Threads REQUIRED)
+target_link_libraries(tun Threads::Threads)
+
+#target_link_libraries(tun fmt)
+

main.cpp

+#include <iostream>
+#include <thread>
+
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <fcntl.h>
+#include <linux/if.h>
+#include <linux/if_tun.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+#include <arpa/inet.h>
+
+// internet -> tun
+void inbound(int raw, int tun) {
+    char buf[ETH_DATA_LEN];
+    sockaddr_in addr{AF_INET};
+    size_t nread;
+    while ((nread = recvfrom(raw, buf, sizeof(buf), 0, (sockaddr *)&addr, nullptr)) >= 0) {
+        if (write(tun, buf, nread) < 0) {
+            perror("outbound write");
+        }
+    }
+    perror("outbound read");
+}
+
+in_addr_t remote;
+// tun -> internet
+void outbound(int raw, int tun) {
+    char buf[ETH_DATA_LEN];
+    sockaddr_in addr{AF_INET};
+    addr.sin_addr.s_addr = remote;
+    size_t nread;
+    while ((nread = read(tun, buf, sizeof(buf))) >= 0) {
+        if (sendto(raw, buf, nread, 0, (sockaddr *) &addr,  sizeof(addr)) < 0) {
+            perror("inbound write");
+        }
+    }
+    perror("inbound read");
+}
+
+int main(int argc, char* argv[]) {
+    ifreq ifr{};
+    ifr.ifr_flags = IFF_TUN | IFF_NO_PI;
+
+    auto raw = socket(AF_INET, SOCK_RAW, IPPROTO_IPIP);
+    auto tun = open("/dev/net/tun", O_RDWR);
+    ioctl(tun, TUNSETIFF, &ifr);
+
+    remote = inet_addr(argv[1]);
+
+    std::cout << raw << std::endl;
+    std::cout << tun << std::endl;
+
+    std::thread t1(inbound, raw, tun);
+    std::thread t2(outbound, raw, tun);
+    t1.join();
+    t2.join();
+}
\ No newline at end of file