From a4b6a22868ccac778537e21137e949803b93a8e3 Mon Sep 17 00:00:00 2001
From: PoliEcho <poliecho@pupes.org>
Date: Sat, 31 May 2025 14:05:07 +0200
Subject: [PATCH] prepare to QUIC migration

---
 README.md              |  3 ++
 src/common/const.h     |  9 ++++
 src/server/capture.cpp | 97 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 109 insertions(+)
 create mode 100644 README.md
 create mode 100644 src/server/capture.cpp

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..828e2ce
--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+# Interface forwarder
+
+do not work with IPv6 Jumbograms
diff --git a/src/common/const.h b/src/common/const.h
index d96e9f4..d01926b 100644
--- a/src/common/const.h
+++ b/src/common/const.h
@@ -2,4 +2,13 @@
 #define _IF_CONST_HG_
 #define CERTS_DIR "certs/"
 #define PORT 11723
+
+enum message_type {
+  RESERVED_TYPE,
+  KEEP_ALIVE_TYPE,
+  KEEPING_ALIVE_TYPE,
+  SET_IP_ADDR_TYPE,
+  IP_PACKET_TYPE,
+  TERMINATE_CONNECTION_TYPE
+};
 #endif
\ No newline at end of file
diff --git a/src/server/capture.cpp b/src/server/capture.cpp
new file mode 100644
index 0000000..6f41d76
--- /dev/null
+++ b/src/server/capture.cpp
@@ -0,0 +1,97 @@
+
+#include <arpa/inet.h>
+#include <cstring>
+#include <ifaddrs.h>
+#include <iostream>
+#include <linux/if_packet.h>
+#include <net/if.h>
+#include <netinet/if_ether.h>
+#include <netinet/in.h>
+#include <netinet/ip.h>
+#include <string>
+#include <sys/socket.h>
+#include <unistd.h>
+
+// this is max size standard Ipv4/6 packet can be
+// what in understand in practise it is much lower around 1500 bytes
+#define IP_PACKET_BUFFER_SIZE 65536
+
+int get_interface_index(const char *interface_name) {
+  struct ifaddrs *ifaddr, *ifa;
+  int interface_index = -1;
+
+  if (getifaddrs(&ifaddr) == -1) {
+    return -1;
+  }
+
+  for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
+    if (ifa->ifa_addr == NULL)
+      continue;
+
+    if (strcmp(ifa->ifa_name, interface_name) == 0) {
+      interface_index = if_nametoindex(interface_name);
+      break;
+    }
+  }
+
+  freeifaddrs(ifaddr);
+  return interface_index;
+}
+
+int listen_for_ip_packets(const std::string interface_name) {
+  int raw_ip_scoketfd;
+  unsigned char buffer[IP_PACKET_BUFFER_SIZE];
+
+  struct sockaddr_ll saddr;
+  socklen_t saddr_len = sizeof(saddr);
+
+  // Create raw socket for packet capture
+  raw_ip_scoketfd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_IP));
+  if (raw_ip_scoketfd < 0) {
+    perror("Failed to create raw socket");
+    std::cerr << "Make sure you're running as root!" << std::endl;
+    return 1;
+  }
+
+  // Get interface index
+  int if_index = get_interface_index(interface_name.c_str());
+  if (if_index < 0) {
+    std::cerr << "Interface " << interface_name << " not found!" << std::endl;
+    close(raw_ip_scoketfd);
+    return 1;
+  }
+
+  // Bind socket to specific interface
+  memset(&saddr, 0, sizeof(saddr));
+  saddr.sll_family = AF_PACKET;
+  saddr.sll_protocol = htons(ETH_P_IP);
+  saddr.sll_ifindex = if_index;
+
+  if (bind(raw_ip_scoketfd, (struct sockaddr *)&saddr, sizeof(saddr)) < 0) {
+    perror("Failed to bind to interface");
+    close(raw_ip_scoketfd);
+    return 1;
+  }
+
+  std::cout << "Listening for IP packets on interface: " << interface_name
+            << " (index: " << if_index << ")" << std::endl;
+
+  // Main packet capture loop
+  while (true) {
+    int packet_size = recvfrom(raw_ip_scoketfd, buffer, IP_PACKET_BUFFER_SIZE,
+                               0, (struct sockaddr *)&saddr, &saddr_len);
+
+    if (packet_size < 0) {
+      perror("Error receiving packet");
+      continue;
+    }
+
+    // Only process IP packets (skip non-IP traffic)
+    if (packet_size >= sizeof(struct ethhdr) + sizeof(struct iphdr)) {
+      process_packet(buffer, packet_size);
+    }
+  }
+
+  close(raw_ip_scoketfd);
+  return 0;
+}