Send RTPS header and payload in one stream

This avoids assembling the header and payload on the receiver side

msg/templates/uorb_microcdr/microRTPS_client.cpp.template

@@ -79,6 +79,7 @@ void* send(void* /*unused*/)
     uint64_t sent = 0, total_sent = 0;
     int loop = 0, read = 0;
     uint32_t length = 0;
+    uint16_t header_length = 0;
 
     /* subscribe to topics */
     int fds[@(len(send_topics))] = {};
@@ -91,7 +92,8 @@ void* send(void* /*unused*/)
 
     // microBuffer to serialized using the user defined buffer
     struct microBuffer microBufferWriter;
-    initStaticAlignedBuffer(data_buffer, BUFFER_SIZE, &microBufferWriter);
+    header_length=transport_node->get_header_length();
+    initStaticAlignedBuffer(&data_buffer[header_length], BUFFER_SIZE-header_length, &microBufferWriter);
     // microCDR structs for managing the microBuffer
     struct microCDR microCDRWriter;
     initMicroCDR(&microCDRWriter, &microBufferWriter);
@@ -110,7 +112,9 @@ void* send(void* /*unused*/)
             struct @(topic)_s data;
             // copy raw data into local buffer
             if (orb_copy(ORB_ID(@(topic)), fds[@(idx)], &data) == 0) {
-                serialize_@(topic)(&data, data_buffer, &length, &microCDRWriter);
+                /* payload is shifted by header length to make room for header*/
+                serialize_@(topic)(&data, &data_buffer[header_length], &length, &microCDRWriter);
+
                 if (0 < (read = transport_node->write((char)@(message_id(topic)), data_buffer, length)))
                 {
                     total_sent += read;

msg/templates/urtps/microRTPS_agent.cpp.template

@@ -193,12 +193,14 @@ void t_send(void *data)
         // Send subscribed topics over UART
         while (topics.hasMsg(&topic_ID))
         {
-            eprosima::fastcdr::FastBuffer cdrbuffer(data_buffer, sizeof(data_buffer));
+            uint16_t header_length = get_header_length();
+            /* make room for the header to fill in later */
+            eprosima::fastcdr::FastBuffer cdrbuffer(&data_buffer[header_length], sizeof(data_buffer)-header_length);
             eprosima::fastcdr::Cdr scdr(cdrbuffer);
             if (topics.getMsg(topic_ID, scdr))
             {
                 length = scdr.getSerializedDataLength();
-                if (0 < (length = transport_node->write(topic_ID, scdr.getBufferPointer(), length)))
+                if (0 < (length = transport_node->write(topic_ID, data_buffer, length)))
                 {
                     total_sent += length;
                     ++sent;

msg/templates/urtps/microRTPS_transport.cpp

@@ -35,6 +35,7 @@
 #include <stdio.h>
 #include <errno.h>
 #include <sys/socket.h>
+#include <cstdlib>
 
 #include "microRTPS_transport.h"
 
@@ -193,6 +194,11 @@ ssize_t Transport_node::read(uint8_t *topic_ID, char out_buffer[], size_t buffer
 	return len;
 }
 
+ssize_t Transport_node::get_header_length()
+{
+    return sizeof(struct Header);
+}
+
 ssize_t Transport_node::write(const uint8_t topic_ID, char buffer[], size_t length)
 {
 	if (!fds_OK()) {
@@ -214,7 +220,7 @@ ssize_t Transport_node::write(const uint8_t topic_ID, char buffer[], size_t leng
 
 	// [>,>,>,topic_ID,seq,payload_length,CRCHigh,CRCLow,payload_start, ... ,payload_end]
 
-	uint16_t crc = crc16((uint8_t *)buffer, length);
+	uint16_t crc = crc16((uint8_t *)&buffer[sizeof(header)], length);
 
 	header.topic_ID = topic_ID;
 	header.seq = seq++;
@@ -223,18 +229,13 @@ ssize_t Transport_node::write(const uint8_t topic_ID, char buffer[], size_t leng
 	header.crc_h = (crc >> 8) & 0xff;
 	header.crc_l = crc & 0xff;
 
-	ssize_t len = node_write(&header, sizeof(header));
-
-	if (len != sizeof(header)) {
+	/* Headroom for header is created in client */
+	/*Fill in the header in the same payload buffer to call a single node_write */
+	memcpy(buffer, &header, sizeof(header));
+	ssize_t len = node_write(buffer, length + sizeof(header));
+	if (len != ssize_t(length + sizeof(header))) {
 		goto err;
 	}
-
-	len = node_write(buffer, length);
-
-	if (len != ssize_t(length)) {
-		goto err;
-	}
-
 	return len + sizeof(header);
 
 err:

msg/templates/urtps/microRTPS_transport.h

@@ -46,6 +46,8 @@ public:
 	virtual uint8_t close() {return 0;}
 	ssize_t read(uint8_t *topic_ID, char out_buffer[], size_t buffer_len);
 	ssize_t write(const uint8_t topic_ID, char buffer[], size_t length);
+	/* Get the Length of struct Header to make headroom for the size of struct Header alongwith payload*/
+	ssize_t get_header_length();
 
 protected:
 	virtual ssize_t node_read(void *buffer, size_t len) = 0;