patch #6763: Global DHCP XID can be redefined to something more unique

CHANGELOG

@@ -20,18 +20,7 @@ HISTORY
   ++ New features:
 
   2009-04-15 Simon Goldschmidt
-  * dhcp.c: patch #6764: DHCP rebind and renew did not send hostnam option;
-    Converted constant OPTION_MAX_MSG_SIZE to netif->mtu, check if netif->mtu
-    is big enough in dhcp_start
-
-  2009-04-15 Simon Goldschmidt
-  * netbuf.c: bug #26027: netbuf_chain resulted in pbuf memory leak
-
-  2009-04-15 Simon Goldschmidt
-  * sockets.c, ppp.c: bug #25763: corrected 4 occurrences of SMEMCPY to MEMCPY
-
-  2009-04-15 Simon Goldschmidt
-  * sockets.c: bug #26121: set_errno can be overridden
+  * dhcp.c: patch #6763: Global DHCP XID can be redefined to something more unique
 
   2009-03-31 Kieran Mansley
   * tcp.c, tcp_out.c, tcp_in.c, sys.h, tcp.h, opts.h: add support for
@@ -93,6 +82,21 @@ HISTORY
 
 
   ++ Bugfixes:
+
+  2009-04-15 Simon Goldschmidt
+  * dhcp.c: patch #6764: DHCP rebind and renew did not send hostnam option;
+    Converted constant OPTION_MAX_MSG_SIZE to netif->mtu, check if netif->mtu
+    is big enough in dhcp_start
+
+  2009-04-15 Simon Goldschmidt
+  * netbuf.c: bug #26027: netbuf_chain resulted in pbuf memory leak
+
+  2009-04-15 Simon Goldschmidt
+  * sockets.c, ppp.c: bug #25763: corrected 4 occurrences of SMEMCPY to MEMCPY
+
+  2009-04-15 Simon Goldschmidt
+  * sockets.c: bug #26121: set_errno can be overridden
+
   2009-04-09 Kieran Mansley (patch from Luca Ceresoli <lucaceresoli>)
   * init.c, opt.h: Patch#6774 TCP_QUEUE_OOSEQ breaks compilation when
     LWIP_TCP==0

src/core/dhcp.c

@@ -86,16 +86,20 @@
 
 #include <string.h>
 
+/** Default for DHCP_GLOBAL_XID is 0xABCD0000
+ * This can be changed by defining DHCP_GLOBAL_XID and DHCP_GLOBAL_XID_HEADER, e.g.
+ *  #define DHCP_GLOBAL_XID_HEADER "stdlib.h"
+ *  #define DHCP_GLOBAL_XID rand()
+ */
+#ifdef DHCP_GLOBAL_XID_HEADER
+#include DHCP_GLOBAL_XID_HEADER /* include optional starting XID generation prototypes */
+#endif
+
 /** DHCP_OPTION_MAX_MSG_SIZE is set to the MTU
  * MTU is checked to be big enough in dhcp_start */
 #define DHCP_MAX_MSG_LEN(netif)        (netif->mtu)
 #define DHCP_MAX_MSG_LEN_MIN_REQUIRED  576
 
-/** global transaction identifier, must be
- *  unique for each DHCP request. We simply increment, starting
- *  with this value (easy to match with a packet analyzer) */
-static u32_t xid = 0xABCD0000;
-
 /* DHCP client state machine functions */
 static void dhcp_handle_ack(struct netif *netif);
 static void dhcp_handle_nak(struct netif *netif);
@@ -1358,6 +1362,20 @@ dhcp_create_request(struct netif *netif)
 {
   struct dhcp *dhcp;
   u16_t i;
+#ifndef DHCP_GLOBAL_XID
+  /** default global transaction identifier starting value (easy to match
+   *  with a packet analyser). We simply increment for each new request.
+   *  Predefine DHCP_GLOBAL_XID to a better value or a function call to generate one
+   *  at runtime, any supporting function prototypes can be defined in DHCP_GLOBAL_XID_HEADER */
+  static u32_t xid = 0xABCD0000;
+#else
+  static u32_t xid;
+  static u8_t xid_initialised = 0;
+  if (!xid_initialised) {
+    xid = DHCP_GLOBAL_XID;
+    xid_initialised = !xid_initialised;
+  }
+#endif
   LWIP_ERROR("dhcp_create_request: netif != NULL", (netif != NULL), return ERR_ARG;);
   dhcp = netif->dhcp;
   LWIP_ERROR("dhcp_create_request: dhcp != NULL", (dhcp != NULL), return ERR_VAL;);