Setup tun device

.gitignore

@@ -88,3 +88,5 @@ docs/_build/
 # PyBuilder
 target/
 
+# ---> Local ignores
+congestvpn

Makefile

@@ -0,0 +1,19 @@
+CXX=g++
+CXXFLAGS=-O2 -g -Wall -Wextra -std=c++17
+CXXLIBS=
+
+OBJS=TunDevice.o util.o main.o
+TARGET=congestvpn
+
+all: $(TARGET)
+
+$(TARGET): $(OBJS)
+	$(CXX) $(CXXFLAGS) $(CXXLIBS) -o $@ $^
+
+%.o: %.cpp
+	$(CXX) $(CXXFLAGS) -c -o $@ $<
+
+clean:
+	rm -f $(OBJS) $(TARGET)
+
+.PHONY: all clean

TunDevice.cpp

@@ -0,0 +1,46 @@
+#include <linux/if.h>
+#include <linux/if_tun.h>
+#include <sys/stat.h>
+#include <sys/ioctl.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <cstdlib>
+#include <cstring>
+
+#include "TunDevice.hpp"
+
+TunDevice::TunDevice(const std::string& dev)
+{
+    struct ifreq ifr;
+    int fd, err;
+
+    if( (fd = open("/dev/net/tun", O_RDWR)) < 0 )
+        throw TunDevice::InitializationError("Cannot open /dev/net/tun", fd);
+
+    memset(&ifr, 0, sizeof(ifr));
+
+    /* Flags: IFF_TUN   - TUN device (no Ethernet headers)
+     *        IFF_TAP   - TAP device
+     *
+     *        IFF_NO_PI - Do not provide packet information
+     */
+    ifr.ifr_flags = IFF_TUN;
+    if(!dev.empty()) {
+        if(dev.size() >= IFNAMSIZ - 2)
+            throw TunDevice::InitializationError("Device name is too long.");
+        strncpy(ifr.ifr_name, dev.c_str(), IFNAMSIZ-1);
+    }
+
+    if( (err = ioctl(fd, TUNSETIFF, (void *) &ifr)) < 0 ){
+        close(fd);
+        throw TunDevice::InitializationError(
+                "Tunnel interface failed [TUNSETIFF]", err
+                );
+    }
+    _dev_name = ifr.ifr_name;
+    _fd = fd;
+}
+
+TunDevice::~TunDevice() {
+    close(_fd);
+}

TunDevice.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <string>
+#include "util.hpp"
+
+class TunDevice {
+    public:
+        class InitializationError : public MsgException {
+            public:
+                InitializationError(const std::string& msg, int code=0)
+                    : MsgException(msg, code) {}
+        };
+
+        TunDevice(const std::string& dev);
+        ~TunDevice();
+
+        const std::string& get_dev_name() const { return _dev_name; }
+        int get_fd() const { return _fd; }
+    private:
+        int _fd;
+        std::string _dev_name;
+};

main.cpp

@@ -0,0 +1,17 @@
+#include <cstdio>
+#include <unistd.h>
+
+#include "TunDevice.hpp"
+
+int main(void) {
+    try {
+        TunDevice tun_dev("cvpn%d");
+        printf("Tunnel device opened: <%s>, fd <%d>.\nSleeping 10 seconds.\n",
+                tun_dev.get_dev_name().c_str(), tun_dev.get_fd());
+        sleep(10);
+        printf("Shutting down.\n");
+    } catch(const TunDevice::InitializationError& exn) {
+        fprintf(stderr, "ERROR: %s\n", exn.what());
+    }
+    return 0;
+}

util.cpp

@@ -0,0 +1,15 @@
+#include <cstdio>
+
+#include "util.hpp"
+
+MsgException::MsgException(const std::string& msg, int code)
+    : _msg(msg), _code(code)
+{
+    _what = _msg;
+
+    if(_code != 0) {
+        char remainder[20];
+        sprintf(remainder, " (code %d)", _code);
+        _what += remainder;
+    }
+}

util.hpp

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <exception>
+#include <string>
+
+// MsgException -- an exception bearing a passed explanation message
+class MsgException : public std::exception {
+    public:
+        MsgException(const std::string& msg, int code=0);
+        int errcode() const noexcept { return _code; }
+        const char* what() const noexcept { return _what.c_str(); };
+
+    private:
+        std::string _msg;
+        int _code;
+        std::string _what;
+};