use static buffers for CoAP PDUs

pdu.c

@@ -16,22 +16,41 @@
 #endif
 
 #include "debug.h"
-#include "mem.h"
 #include "pdu.h"
 #include "option.h"
 #include "encode.h"
 
+#ifdef WITH_CONTIKI
+#include "memb.h"
+
+typedef unsigned char _pdu[COAP_MAX_PDU_SIZE];
+
+MEMB(pdu_storage, _pdu, COAP_PDU_MAXCNT);
+
+void
+coap_pdu_resources_init() {
+  memb_init(&pdu_storage);
+}
+#else /* WITH_CONTIKI */
+#include "mem.h"
+#endif /* WITH_CONTIKI */
+
 coap_pdu_t *
 coap_pdu_init(unsigned char type, unsigned char code, 
 	      unsigned short id, size_t size) {
   coap_pdu_t *pdu;
 
+  assert(size <= COAP_MAX_PDU_SIZE);
   /* Size must be large enough to fit the header. */
-  if (size < sizeof(coap_hdr_t)) 
+  if (size < sizeof(coap_hdr_t) || size > COAP_MAX_PDU_SIZE)
     return NULL;
 
-  //size must be large enough for hdr
+  /* size must be large enough for hdr */
+#ifndef WITH_CONTIKI
   pdu = coap_malloc(sizeof(coap_pdu_t) + size);
+#else /* WITH_CONTIKI */
+  pdu = (coap_pdu_t *)memb_alloc(&pdu_storage);
+#endif /* WITH_CONTIKI */
   if (pdu) {
     memset(pdu, 0, sizeof(coap_pdu_t) + size);
     pdu->max_size = size;
@@ -45,7 +64,7 @@ coap_pdu_init(unsigned char type, unsigned char code,
        pointer is moved to the back */
     pdu->length = sizeof(coap_hdr_t);
     pdu->data = (unsigned char *)pdu->hdr + pdu->length;
-  }
+  } 
   return pdu;
 }
 
@@ -64,7 +83,11 @@ coap_new_pdu() {
 
 void
 coap_delete_pdu(coap_pdu_t *pdu) {
+#ifndef WITH_CONTIKI
   coap_free( pdu );
+#else /* WITH_CONTIKI */
+  memb_free(&pdu_storage, pdu);
+#endif /* WITH_CONTIKI */
 }
 
 int