software engineering for best resource management

actually only one packet is managed at a time,
then a packetin+packetout buffer area has been created for IPv6 packets.
Upper layers can then access this data by means of pointer,
avoiding further allocations on the stack.
Obviously, packetin is read-only (eg. upper layers can only read it)

coppino.ino

@@ -4,13 +4,10 @@ namespace coppino {
   ipv6::IPv6Addr address;
 
   void handler() {
-    
-    char buffer[LEN];
     int r;
     
-    while ((r = slip::recv(buffer, LEN)) != -1) {
+    while ((r = slip::recv((char*)&ipv6::packetin, LEN)) != -1) {
-      ipv6::IPv6Packet packet(buffer, r);
+      ipv6::packetin.doAction();
-      packet.doAction();
     }
     
   }

ipv6.h

@@ -35,8 +35,11 @@ namespace ipv6 {
     public:
       IPv6Packet();
       IPv6Packet(const char* buffer, int len);
+      void IPv6Packet::setLen(int len);
       void setSrcAddress(const IPv6Addr* address);
+      const IPv6Addr* getSrcAddress();
       void setDstAddress(const IPv6Addr* address);
+      const IPv6Addr* getDstAddress();
       void setNextHeader(uint8_t next_header);
       void setFlow(const char* flow);
       void setPayload(char* payload, int len);
@@ -44,8 +47,11 @@ namespace ipv6 {
       void doAction();
   };
 
+  extern IPv6Packet packetin;
+  extern IPv6Packet packetout;
+
   /* Note: content of message may be changed */
-  void handleICMP(const IPv6Addr* src, const IPv6Addr* dst, const char* flow, char* message, int len);
+  int handleICMP(char* output_buffer, const char* input_buffer, int len);
 
   /* Compute internet checksum. Actually it is not so straightforward: */
   uint16_t compute_checksum(

ipv6.ino

@@ -5,6 +5,10 @@ namespace ipv6 {
 /******** costants ********/
 const IPv6Addr ALL_NODES_ADDRESS("\xff\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01"); /* ff02::1 */
 
+/******** buffer ********/
+IPv6Packet packetin;
+IPv6Packet packetout;
+
 /******** FUNCTIONS *******/
 uint16_t compute_checksum(const IPv6Addr* src_addr, const IPv6Addr* dst_addr, uint8_t next_header, int upper_len, const char* payload, int len) {
   char buffer[LEN];
@@ -67,6 +71,11 @@ void IPv6Packet::setNextHeader(uint8_t next_header) {
   *(packet + 6) = next_header;
 }
 
+void IPv6Packet::setLen(int len) {
+  *(packet + 4) = len >> 8;
+  *(packet + 5) = len & 0xff;
+}
+
 void IPv6Packet::setSrcAddress(const IPv6Addr* address) {
   memcpy(packet + 8, address, 16);
 }
@@ -74,6 +83,13 @@ void IPv6Packet::setDstAddress(const IPv6Addr* address) {
   memcpy(packet + 24, address, 16);
 }
 
+const IPv6Addr* IPv6Packet::getSrcAddress() {
+  return (const IPv6Addr*) (packet + 8);
+}
+const IPv6Addr* IPv6Packet::getDstAddress() {
+  return (const IPv6Addr*) (packet + 24);
+}
+
 void IPv6Packet::setFlow(const char* flow) {
   /* three bytes
     4 most significant bits are ignored
@@ -91,14 +107,22 @@ void IPv6Packet::setPayload(char* payload, int len) {
 void IPv6Packet::doAction() {
   /* if destination is my address, or destination is "all nodes" address, then... */
   if ((memcmp(&(ALL_NODES_ADDRESS), packet + 24, 16) == 0) || (memcmp(&(coppino::address), packet + 24, 16) == 0)) {
-    int len = ((*(packet + 4)) << 8) + (*(packet + 5));
+    int ilen = ((*(packet + 4)) << 8) + (*(packet + 5));  /* input payload length */
+    int olen;                                             /* output payload length */
     
     switch(*(packet + 6)) { /* next header */
       case NH_ICMP:
-        handleICMP((IPv6Addr*)(packet + 8), (IPv6Addr*)(packet + 24), packet + 1, packet + 40, len);
+        if ((olen = handleICMP((char*)&packetout + 40, packet + 40, ilen)) != -1) {
+          packetout.setLen(olen);
+          packetout.setFlow((char*)&packetin + 1);
+          packetout.setSrcAddress(packetin.getDstAddress());
+          packetout.setDstAddress(packetin.getSrcAddress());
+          packetout.setNextHeader(NH_ICMP);
+          slip::send((void*)&packetout, 40 + olen);
+         }
         break;
       case NH_UDP:
-        udp::handleUDP((IPv6Addr*)(packet + 8), (IPv6Addr*)(packet + 24), packet + 1, packet + 40, len);
+        //udp::handleUDP((IPv6Addr*)(packet + 8), (IPv6Addr*)(packet + 24), packet + 1, packet + 40, len);
         break;
       default:
         /* no other protocols are known here, sorry :-) */
@@ -107,38 +131,45 @@ void IPv6Packet::doAction() {
   }
 }
 
-void handleICMP(const IPv6Addr* src_addr, const IPv6Addr* dst_addr, const char* flow, char* packet, int len) {
+int handleICMP(char* output_buffer, const char* input_buffer, int len) { //const IPv6Addr* src_addr, const IPv6Addr* dst_addr, const char* flow, char* packet, int len) {
-  uint8_t type = *(packet);
+  uint8_t type = *(input_buffer);
   
   if (type == ICMP_ECHO_REQUEST_TYPE) {  /* if it is ICMPv6 Echo Request, then... */
       /* compute checksum, and assert validity of incoming message */
       char received_checksum[2];
-      memcpy(received_checksum, packet + 2, 2);
+      memcpy(received_checksum, input_buffer + 2, 2);
 
-      memset(packet + 2, 0, 2); /* zero-checksum */
+      memcpy(output_buffer, input_buffer, len);
-      uint16_t computed_checksum = compute_checksum(src_addr, dst_addr, NH_ICMP, len, packet, len);
+      memset(output_buffer + 2, 0, 2); /* zero-checksum */
+      uint16_t computed_checksum = compute_checksum(
+        packetin.getSrcAddress(),
+        packetin.getDstAddress(),
+        NH_ICMP,
+        len,
+        output_buffer,
+        len);
 
       if (memcmp(&computed_checksum, received_checksum, 2) == 0) {  /* if checksum is valid, then... */
         /*  Build an echo reply:
          *  the reply has the same exact format of the request,
          *  except for Type and Checksum */
-        *(packet) = ICMP_ECHO_REPLY_TYPE;
+        *(output_buffer) = ICMP_ECHO_REPLY_TYPE;
-        memset(packet + 2, 0, 2); /* zero-checksum */
+        memset(output_buffer + 2, 0, 2); /* zero-checksum */
 
-        uint16_t checksum = compute_checksum(src_addr, dst_addr, NH_ICMP, len, packet, len);
+        uint16_t checksum = compute_checksum(
-        memcpy(packet + 2, &checksum, 2);
+          packetin.getDstAddress(),
+          packetin.getSrcAddress(),
+          NH_ICMP,
+          len,
+          output_buffer,
+          len);
+        memcpy(output_buffer + 2, &checksum, 2);
 
-        IPv6Packet reply_packet;
+        return len;
-        reply_packet.setPayload(packet, len);
-        reply_packet.setFlow(flow);
-  
-        reply_packet.setSrcAddress(dst_addr);
-        reply_packet.setDstAddress(src_addr);
-        reply_packet.setNextHeader(NH_ICMP);
-        slip::send((void*)&reply_packet, 40 + len);
       }
   }
-  return;
+
+  return -1;
 }
 
 }