use lwip pbufs for pdu allocation

so far, this only replaces the allocator; it is not used yet for
zero-copy operations.

pdu.c

@@ -56,6 +56,9 @@ coap_pdu_t *
 coap_pdu_init(unsigned char type, unsigned char code, 
 	      unsigned short id, size_t size) {
   coap_pdu_t *pdu;
+#ifdef WITH_LWIP
+    struct pbuf *p;
+#endif
 
   assert(size <= COAP_MAX_PDU_SIZE);
   /* Size must be large enough to fit the header. */
@@ -63,16 +66,27 @@ coap_pdu_init(unsigned char type, unsigned char code,
     return NULL;
 
   /* size must be large enough for hdr */
-#ifndef WITH_CONTIKI
+#ifdef WITH_POSIX
   pdu = coap_malloc(sizeof(coap_pdu_t) + size);
-#else /* WITH_CONTIKI */
+#endif
+#ifdef WITH_CONTIKI
   pdu = (coap_pdu_t *)memb_alloc(&pdu_storage);
-#endif /* WITH_CONTIKI */
+#endif
+#ifdef WITH_LWIP
+  p = pbuf_alloc(PBUF_TRANSPORT, sizeof(coap_pdu_t) + size, PBUF_RAM);
+  if (p != NULL)
+    pdu = p->payload;
+  else
+    pdu = NULL;
+#endif
   if (pdu) {
     coap_pdu_clear(pdu, size);
     pdu->hdr->id = id;
     pdu->hdr->type = type;
     pdu->hdr->code = code;
+#ifdef WITH_LWIP
+    pdu->pbuf = p;
+#endif
   } 
   return pdu;
 }
@@ -96,11 +110,16 @@ coap_new_pdu() {
 
 void
 coap_delete_pdu(coap_pdu_t *pdu) {
-#ifndef WITH_CONTIKI
+#ifdef WITH_POSIX
   coap_free( pdu );
-#else /* WITH_CONTIKI */
+#endif
+#ifdef WITH_LWIP
+  if (pdu != NULL) /* accepting double free as the other implementation accept that too */
+    pbuf_free(pdu->pbuf);
+#endif
+#ifdef WITH_CONTIKI
   memb_free(&pdu_storage, pdu);
-#endif /* WITH_CONTIKI */
+#endif
 }
 
 int

pdu.h

@@ -13,6 +13,10 @@
 #include "coap_list.h"
 #include "uri.h"
 
+#ifdef WITH_LWIP
+#include <lwip/pbuf.h>
+#endif
+
 /* pre-defined constants that reflect defaults for CoAP */
 
 #define COAP_DEFAULT_RESPONSE_TIMEOUT  2 /* response timeout in seconds */
@@ -206,6 +210,11 @@ typedef struct {
   unsigned short max_delta;	/**< highest option number */
   unsigned short length;	/**< PDU length (including header, options, data)  */
   unsigned char *data;		/**< payload */
+
+#ifdef WITH_LWIP
+  struct pbuf *pbuf; /**< lwIP PBUF. The allocated coap_pdu_t will always reside inside the pbuf's payload, but the pointer has to be kept because no exact offset can be given. */
+#endif
+
 } coap_pdu_t;
 
 /** Options in coap_pdu_t are accessed with the macro COAP_OPTION. */