recvfrom

#include <rtl.h>

int recv (
    int sock,          /* Socket descriptor */
    char *buf,         /* Pointer to a buffer for data */
    int len,           /* Size of data buffer in bytes */
    int flags,         /* Message flags */
    SOCKADDR *from,    /* Pointer to address structure */
    int *fromlen);     /* Length of address structure */

The recvfrom function is used to receive data that has been queued for a socket. It is normally used to receive messages on SOCK_DGRAM socket type, but can also be used to receive a reliable, ordered stream of data on a connected SOCK_STREAM socket type. It reads as much information as currently available up to the size of the buffer specified.

In blocking mode, which is enabled if the system detects RTX environment, this functions waits for received data. In non blocking mode, you must call the recvfrom function again if the error code SCK_EWOULDBLOCK is returned.

The argument sock specifies a socket descriptor returned from a previous call to socket.

The argument buf is a pointer to the application data buffer for storing the data to. If the available data is too large to fit in the supplied application buffer buf, excess bytes are discarded in case of SOCK_DGRAM sockets. For socket types SOCK_STREAM, the data is buffered internally so the application can retrieve all data by multiple calls of recvfrom function.

The argument len specifies the size of the application data buffer.

The argument flags specifies the message flags:

The argument from is a pointer to the SOCKADDR structure. If from is not NULL, the source IP address and port number of the datagram is filled in.

The argument fromlen is a pointer to the address length. It should initially contain the amount of space pointed to by from. On return it contains the actual length of the address returned in bytes.

The recvfrom function is in the RL-TCPnet library. The prototype is defined in rtl.h.

note

• You must call the socket function before any other function calls to the BSD socket.
• If a negative number is returned, it represents an error code.
• The number of bytes actually read can be less than len.

The recvfrom function returns the following result:

• numbytes
  The number of bytes copied to application buffer buf (a positive number).
• SCK_EINVALID
  The socket identified with sock is invalid, or in invalid state.
• SCK_ECLOSED
  Remote end point has closed the connection.
• SCK_EWOULDBLOCK
  The function would block, and the socket is set to non blocking mode.
• SCK_ETIMEOUT
  The function wait for data timeout has expired in blocking mode.
• SCK_ELOCKED
  The socket is locked by another task in RTX environment.

ioctlsocket, recv, send, sendto

#include <rtl.h>

__task void server (void) {
  SOCKADDR_IN addr;
  int sock, res, addrlen;
  char dbuf[4];

  while (1) {
    sock = socket (AF_INET, SOCK_DGRAM, IPPROTO_UDP);

    addr.sin_port        = htons(1001);
    addr.sin_family      = PF_INET;
    addr.sin_addr.s_addr = INADDR_ANY;

    bind (sock, (SOCKADDR *)&addr, sizeof (addr));

    while (1) {
      addrlen = sizeof (addr);
      res = recvfrom (sock, dbuf, sizeof (dbuf), 0, addr, &addrlen);
      if (res <= 0) {
        break;
      }
      procrec ((U8 *)dbuf);
      printf ("Remote IP: %d.%d.%d.%d\n",addr.sin_addr.s_b1,
                                         addr.sin_addr.s_b2,
                                         addr.sin_addr.s_b3,
                                         addr.sin_addr.s_b4);
      printf ("Remote port: %d\n",ntohs (addr.sin_port));
    }
    closesocket (sock);
  }
}