Add TCP zero copy example to the TCP echo client demo - IPv6 WinSim (#1138)

* Add TCP zero copy example to the TCP echo client demo - IPv6 WinSim

* Uncrustify: triggered by comment.

* Uncrustify: triggered by comment

* Uncrustify fix formatting

---------

Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: Rahul Kar <118818625+kar-rahul-aws@users.noreply.github.com>
Co-authored-by: Gaurav-Aggarwal-AWS <33462878+aggarg@users.noreply.github.com>

FreeRTOS-Plus/Demo/FreeRTOS_Plus_TCP_IPv6_Demo/IPv6_Multi_WinSim_demo/TCPEchoClient_SingleTasks.c

@@ -70,6 +70,9 @@
 /* The number of instances of the echo client task to create. */
     #define echoNUM_ECHO_CLIENTS          ( 1 )
 
+/* To enable the use of zero copy interface of the TCP sockets */
+    #define USE_TCP_ZERO_COPY             ( 0 )
+
 /*-----------------------------------------------------------*/
 
 /*
@@ -151,6 +154,68 @@
 
         return xReturn;
     }
+/*-----------------------------------------------------------*/
+
+    static BaseType_t vTCPCreateAndSendData( Socket_t xSocket,
+                                             char * pcTransmitBuffer,
+                                             volatile uint32_t * pulTxCount,
+                                             uint32_t ulBufferLength )
+    {
+        BaseType_t lStringLength;
+        BaseType_t lTransmitted;
+        char * pcDstBuffer;
+
+        #if USE_TCP_ZERO_COPY
+            BaseType_t xStreamBufferLength;
+            char * pcBuffer;
+        #endif /* USE_TCP_ZERO_COPY */
+
+        pcDstBuffer = pcTransmitBuffer;
+
+        #if USE_TCP_ZERO_COPY
+            /* Get a direct pointer to the TX head of the circular transmit buffer */
+            pcBuffer = ( char * ) FreeRTOS_get_tx_head( xSocket, &xStreamBufferLength );
+
+            /* Check if sufficient space is there in the stream buffer. If there
+             * isn't enough size use application provided buffer */
+            if( xStreamBufferLength >= ulBufferLength )
+            {
+                /* Use the TCP stream buffer to directly create the TX data */
+                pcDstBuffer = pcBuffer;
+            }
+        #endif /* USE_TCP_ZERO_COPY */
+
+        lStringLength = prvCreateTxData( pcDstBuffer, ulBufferLength );
+
+        /* Add in some unique text at the front of the string. */
+        sprintf( pcDstBuffer, "TxRx message number %u", ( unsigned ) *pulTxCount );
+        ( *pulTxCount )++;
+
+        #if USE_TCP_ZERO_COPY
+            /* Check to see if zero copy is used */
+            if( pcDstBuffer != pcTransmitBuffer )
+            {
+                /* Save a copy of the data in pcTransmitBuffer
+                 * which can be used to verify the echoed back data */
+                memcpy( pcTransmitBuffer, pcDstBuffer, lStringLength );
+
+                /* Set the buffer pointer as NULL to let the stack know
+                 * that its a zero copy */
+                pcDstBuffer = NULL;
+            }
+        #endif /* USE_TCP_ZERO_COPY */
+
+        /* Send the string to the socket. */
+        lTransmitted = FreeRTOS_send( xSocket,                /* The socket being sent to. */
+                                      ( void * ) pcDstBuffer, /* The data being sent. */
+                                      lStringLength,          /* The length of the data being sent. */
+                                      0 );                    /* No flags. */
+
+        configPRINTF( ( "FreeRTOS_send: %u/%u\n", ( unsigned ) lTransmitted, ( unsigned ) lStringLength ) );
+
+        return lTransmitted;
+    }
+
 /*-----------------------------------------------------------*/
 
     static void prvEchoClientTask( void * pvParameters )
@@ -161,7 +226,7 @@
         const int32_t lMaxLoopCount = 1;
         volatile uint32_t ulTxCount = 0UL;
         BaseType_t xReceivedBytes, xReturned = 0, xInstance;
-        BaseType_t lTransmitted, lStringLength;
+        BaseType_t lTransmitted;
         char * pcTransmittedString, * pcReceivedString;
         WinProperties_t xWinProps;
         TickType_t xTimeOnEntering;
@@ -252,19 +317,7 @@
                 /* Send a number of echo requests. */
                 for( lLoopCount = 0; lLoopCount < lMaxLoopCount; lLoopCount++ )
                 {
-                    /* Create the string that is sent to the echo server. */
+                    lTransmitted = vTCPCreateAndSendData( xSocket, pcTransmittedString, &ulTxCount, echoBUFFER_SIZES );
-                    lStringLength = prvCreateTxData( pcTransmittedString, echoBUFFER_SIZES );
-
-                    /* Add in some unique text at the front of the string. */
-                    sprintf( pcTransmittedString, "TxRx message number %u", ( unsigned ) ulTxCount );
-                    ulTxCount++;
-
-                    /* Send the string to the socket. */
-                    lTransmitted = FreeRTOS_send( xSocket,                        /* The socket being sent to. */
-                                                  ( void * ) pcTransmittedString, /* The data being sent. */
-                                                  lStringLength,                  /* The length of the data being sent. */
-                                                  0 );                            /* No flags. */
-                    configPRINTF( ( "FreeRTOS_send: %u/%u\n", ( unsigned ) lTransmitted, ( unsigned ) lStringLength ) );
 
                     if( xIsFatalError( lTransmitted ) )
                     {
@@ -282,10 +335,27 @@
                     /* Receive data echoed back to the socket. */
                     while( xReceivedBytes < lTransmitted )
                     {
-                        xReturned = FreeRTOS_recv( xSocket,                                 /* The socket being received from. */
+                        #if USE_TCP_ZERO_COPY
-                                                   &( pcReceivedString[ xReceivedBytes ] ), /* The buffer into which the received data will be written. */
+                            uint8_t * pucZeroCopyRxBuffPtr = NULL;
-                                                   lStringLength - xReceivedBytes,          /* The size of the buffer provided to receive the data. */
+                            xReturned = FreeRTOS_recv( xSocket,               /* The socket being received from. */
-                                                   0 );                                     /* No flags. */
+                                                       &pucZeroCopyRxBuffPtr, /* While using FREERTOS_ZERO_COPY flag, pvBuffer is taken as a double pointer which will be updated with pointer to TCP RX stream buffer. */
+                                                       ipconfigTCP_MSS,       /* The size of the buffer provided to receive the data. */
+                                                       FREERTOS_ZERO_COPY );  /* Use FREERTOS_ZERO_COPY flag to enable zero copy. */
+
+                            if( pucZeroCopyRxBuffPtr != NULL )
+                            {
+                                memcpy( &( pcReceivedString[ xReceivedBytes ] ), pucZeroCopyRxBuffPtr, xReturned );
+
+                                /* Release the memory that was previously obtained by calling FreeRTOS_recv()
+                                 * with the flag 'FREERTOS_ZERO_COPY' */
+                                FreeRTOS_ReleaseTCPPayloadBuffer( xSocket, pucZeroCopyRxBuffPtr, xReturned );
+                            }
+                        #else /* if USE_TCP_ZERO_COPY */
+                            xReturned = FreeRTOS_recv( xSocket,                                 /* The socket being received from. */
+                                                       &( pcReceivedString[ xReceivedBytes ] ), /* The buffer into which the received data will be written. */
+                                                       lTransmitted - xReceivedBytes,           /* The size of the buffer provided to receive the data. */
+                                                       0 );                                     /* No flags. */
+                        #endif /* USE_TCP_ZERO_COPY */
 
                         if( xIsFatalError( xReturned ) )
                         {