From 7c19414c37f8780f5d012d1e0d09b85436c98ee9 Mon Sep 17 00:00:00 2001
From: Daniel Collins <solemnwarning@solemnwarning.net>
Date: Mon, 14 Apr 2014 22:45:38 +0100
Subject: [PATCH] Use appropriate MTU for packet size limits.

---
 src/interface.c |  2 +-
 src/interface.h |  3 +++
 src/winsock.c   | 13 ++++++++++---
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/src/interface.c b/src/interface.c
index 7897ae9..4d0c1f8 100644
--- a/src/interface.c
+++ b/src/interface.c
@@ -414,7 +414,7 @@ static void _init_pcap_interfaces(void)
 		}
 		
 		char errbuf[PCAP_ERRBUF_SIZE];
-		pcap_t *pcap = pcap_open(i->name, 1500 /* TODO */, PCAP_OPENFLAG_MAX_RESPONSIVENESS, 0, NULL, errbuf);
+		pcap_t *pcap = pcap_open(i->name, ETHERNET_MTU, PCAP_OPENFLAG_MAX_RESPONSIVENESS, 0, NULL, errbuf);
 		if(!pcap)
 		{
 			log_printf(LOG_ERROR, "Could not open WinPcap interface '%s': %s", i->name, errbuf);
diff --git a/src/interface.h b/src/interface.h
index d25d583..b2efba3 100644
--- a/src/interface.h
+++ b/src/interface.h
@@ -29,6 +29,9 @@
 extern "C" {
 #endif
 
+/* TODO: Dynamic MTU, per interface. */
+#define ETHERNET_MTU 1500
+
 #define WILDCARD_IFACE_HWADDR addr48_in((unsigned char[]){0x00,0x00,0x00,0x00,0x00,0x00})
 
 typedef struct ipx_interface_ip ipx_interface_ip_t;
diff --git a/src/winsock.c b/src/winsock.c
index a8311be..a15940a 100644
--- a/src/winsock.c
+++ b/src/winsock.c
@@ -72,6 +72,13 @@ static size_t strsize(void *str, bool unicode)
 		: strlen(str) + 1;
 }
 
+static int _max_ipx_payload(void)
+{
+	return ipx_use_pcap
+		? (ETHERNET_MTU - sizeof(real_ipx_packet_t))
+		: MAX_DATA_SIZE;
+}
+
 #define PUSH_NAME(name) \
 { \
 	int i = 0; \
@@ -921,7 +928,7 @@ int WSAAPI getsockopt(SOCKET fd, int level, int optname, char FAR *optval, int F
 			}
 			else if(optname == IPX_MAXSIZE)
 			{
-				RETURN_INT_OPT(MAX_DATA_SIZE);
+				RETURN_INT_OPT(_max_ipx_payload());
 			}
 			else if(optname == IPX_ADDRESS)
 			{
@@ -944,7 +951,7 @@ int WSAAPI getsockopt(SOCKET fd, int level, int optname, char FAR *optval, int F
 				
 				ipxdata->wan       = FALSE;
 				ipxdata->status    = FALSE;
-				ipxdata->maxpkt    = MAX_DATA_SIZE;
+				ipxdata->maxpkt    = _max_ipx_payload();
 				ipxdata->linkspeed = 100000; /* 10MBps */
 				
 				free_ipx_interface(nic);
@@ -1406,7 +1413,7 @@ int WSAAPI sendto(SOCKET fd, const char *buf, int len, int flags, const struct s
 			}
 		}
 		
-		if(len > MAX_DATA_SIZE)
+		if(len > _max_ipx_payload())
 		{
 			WSASetLastError(WSAEMSGSIZE);