pumpnet: Add prinet-proxy application

Sits between the game (client) and pumpnet (server) translating
the game's native protocol to more managable http requests.

Encryption and decryption is also taken care off to remove that
burden from the server side. This makes http requests as generic as
"game version X is sending some data. here, go and figure out what
to do" on the server side.

src/main/pumpnet/prinet-proxy/packet.c

@@ -0,0 +1,43 @@
+#include <sodium.h>
+
+#include "pumpnet/prinet-proxy/packet.h"
+
+#include "util/log.h"
+#include "util/mem.h"
+
+static const size_t HEADER_SIZE = sizeof(uint32_t) + sizeof(uint8_t) * SEC_PRINET_NOUNCE_LEN;
+
+struct pumpnet_prinet_proxy_packet* pumpnet_prinet_proxy_packet_alloc(size_t data_len)
+{
+    struct pumpnet_prinet_proxy_packet* packet;
+
+    packet = util_xmalloc(HEADER_SIZE + data_len);
+
+    packet->length = HEADER_SIZE + data_len;
+
+    return packet;
+}
+
+struct pumpnet_prinet_proxy_packet* pumpnet_prinet_proxy_packet_alloc_response(size_t data_len)
+{
+    // + SEC_PRINET_MACBYTES_LEN expected on response only.
+    // Request does not have this included at the end of the game specific data
+    return pumpnet_prinet_proxy_packet_alloc(data_len + SEC_PRINET_MACBYTES_LEN);
+}
+
+size_t pumpnet_prinet_proxy_packet_get_header_len()
+{
+    return HEADER_SIZE;
+}
+
+size_t pumpnet_prinet_proxy_packet_get_data_len(const struct pumpnet_prinet_proxy_packet* packet)
+{
+    log_assert(packet);
+
+    if (packet->length < HEADER_SIZE) {
+        log_error("Packet with size less than header size");
+        return 0;
+    }
+
+    return packet->length - HEADER_SIZE;
+}