使用 TCP 套接字（零拷贝接口）接收数据
FreeRTOS-Plus-TCP 联网教程的一部分

#define BUFFER_SIZE 512



static void prvEchoClientRxTask( void *pvParameters )

{

    Socket_t xSocket;

    static char cRxedData[ BUFFER_SIZE ];

    BaseType_t lBytesReceived;



    /* It is assumed the socket has already been created and connected before


       being passed into this RTOS task using the RTOS task's parameter. */

    xSocket = ( Socket_t ) pvParameters;



    for( ;; )

    {



        uint8_t *pucZeroCopyRxBuffPtr = NULL;



        /* Receive data from the socket.  xFlags has the zero copy bit set


           (FREERTOS_ZERO_COPY) indicating to the stack that a reference to the


           received data should be passed out to this RTOS task using the second


           parameter to the FreeRTOS_recv() call.  When this is done the


           IP stack is no longer responsible for releasing the buffer, and


           the RTOS task must return the buffer to the stack when it is no longer


           needed using the FreeRTOS_ReleaseTCPPayloadBuffer() API. */

        lBytesReceived =  FreeRTOS_recv( xSocket, /* The socket being received from. */

                          &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 )

        {

            /* Copy the data to application buffer if its required to be processed later */

            memcpy(  &cRxedData, pucZeroCopyRxBuffPtr, lBytesReceived );

            

            /* Release the memory that was previously obtained by calling FreeRTOS_recv()


               with the flag 'FREERTOS_ZERO_COPY' */

            FreeRTOS_ReleaseTCPPayloadBuffer( xSocket, pucZeroCopyRxBuffPtr, lBytesReceived );

        }



        if( lBytesReceived > 0 )

        {

            /* Data was received, process it here. */

            prvProcessData( cRxedData, lBytesReceived );

        }

        else if( lBytesReceived == 0 )

        {

            /* No data was received, but FreeRTOS_recv() did not return an error.


               Timeout? */

        }

        else

        {

            /* Error (maybe the connected socket already shut down the socket?).


               Attempt graceful shutdown. */

            FreeRTOS_shutdown( xSocket, FREERTOS_SHUT_RDWR );

            break;

        }

    }



    /* The RTOS task will get here if an error is received on a read.  Ensure the


       socket has shut down (indicated by FreeRTOS_recv() returning a -pdFREERTOS_ERRNO_EINVAL


       error before closing the socket). */



    while( FreeRTOS_recv( xSocket, pcBufferToTransmit, xTotalLengthToSend, 0 ) >= 0 )

    {

        /* Wait for shutdown to complete.  If a receive block time is used then


           this delay will not be necessary as FreeRTOS_recv() will place the RTOS task


           into the Blocked state anyway. */

        vTaskDelay( pdTICKS_TO_MS( 250 ) );



        /* Note - real applications should implement a timeout here, not just


           loop forever. */

    }



    /* Shutdown is complete and the socket can be safely closed. */

    FreeRTOS_closesocket( xSocket );



    /* Must not drop off the end of the RTOS task - delete the RTOS task. */

    xTaskDelete( NULL );

}