Add VpnPacket class

Makefile

@@ -5,6 +5,7 @@ CXXLIBS=
 OBJS= \
 	  UdpVpn.o UdpVpnClient.o UdpVpnServer.o \
 	  VpnPeer.o \
+	  VpnPacket.o \
 	  TunDevice.o \
 	  ip_header.o util.o main.o
 TARGET=congestvpn

VpnPacket.cpp

@@ -0,0 +1,21 @@
+#include "VpnPacket.hpp"
+
+const size_t VpnPacket::VPN_HEADER_SIZE = 0;
+
+static const size_t OUTER_HEADERS_SIZE =
+    40 /* IPv6 header */ + 8 /* UDP header */;
+    // We use a TUN device, hence we don't have a layer 2 header.
+
+VpnPacket::VpnPacket(size_t mtu)
+    : _data_space(mtu-OUTER_HEADERS_SIZE), _data_size(0)
+{
+    _data = new char[mtu - OUTER_HEADERS_SIZE];
+}
+
+VpnPacket::~VpnPacket() {
+    delete[] _data;
+}
+
+bool VpnPacket::parse_as_ipv6() {
+    return parse_ipv6_header(get_payload(), get_payload_size(), _ipv6_header);
+}

VpnPacket.hpp

@@ -0,0 +1,42 @@
+#pragma once
+
+/** A packet to be transmitted or received over the VPN socket */
+
+#include <cstdlib>
+
+#include "ip_header.hpp"
+
+class VpnPacket {
+    public:
+        static const size_t VPN_HEADER_SIZE;
+
+        VpnPacket(size_t mtu);
+        ~VpnPacket();
+
+        /// Try to parse the packet as IPv6, return `false` upon failure.
+        bool parse_as_ipv6();
+        bool ipv6_parsed() const { return _ipv6_parsed; }
+        const IPv6Header& get_ipv6_header() const { return _ipv6_header; }
+
+        const char* get_payload() const { return _data + VPN_HEADER_SIZE; }
+        char* get_payload() { return _data + VPN_HEADER_SIZE; }
+        size_t get_payload_space() const {
+            return _data_space - VPN_HEADER_SIZE; }
+        size_t get_payload_size() const {
+            return _data_size - VPN_HEADER_SIZE; }
+        void set_payload_size(size_t payload_size) {
+            _data_size = payload_size + VPN_HEADER_SIZE; }
+
+        const char* get_data() const { return _data; }
+        char* get_data() { return _data; }
+        size_t get_data_space() const { return _data_space; }
+        size_t get_data_size() const { return _data_size; }
+        void set_data_size(size_t data_size) { _data_size = data_size; }
+
+    private:
+        char* _data;
+        size_t _data_space, _data_size;
+
+        bool _ipv6_parsed;
+        IPv6Header _ipv6_header;
+};