RECV(3N-SVR4)       RISC/os Reference Manual        RECV(3N-SVR4)



NAME
     recv, recvfrom, recvmsg - receive a message from a socket

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>

     int recv(s, buf, len, flags)
     int s;
     char *buf;
     int len, flags;

     int recvfrom(s, buf, len, flags, from, fromlen)
     int s;
     char *buf;
     int len, flags;
     struct sockaddr *from;
     int *fromlen;

     int recvmsg(s, msg, flags)
     int s;
     struct msghdr *msg;
     int flags;

DESCRIPTION
     s is a socket created with socket(3N).  recv(), recvfrom(),
     and recvmsg() are used to receive messages from another
     socket.  recv() may be used only on a connected socket (see
     connect(3N)), while recvfrom() and recvmsg() may be used to
     receive data on a socket whether it is in a connected state
     or not.

     If from is not a NULL pointer, the source address of the
     message is filled in.  fromlen is a value-result parameter,
     initialized to the size of the buffer associated with from,
     and modified on return to indicate the actual size of the
     address stored there.  The length of the message is
     returned.  If a message is too long to fit in the supplied
     buffer, excess bytes may be discarded depending on the type
     of socket the message is received from (see socket(3N)).

     If no messages are available at the socket, the receive call
     waits for a message to arrive, unless the socket is non-
     blocking (see fcntl(2)) in which case -1 is returned with
     the external variable errno set to EWOULDBLOCK.

     The select() call may be used to determine when more data
     arrives.

     The flags parameter is formed by ORing one or more of the
     following:




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RECV(3N-SVR4)       RISC/os Reference Manual        RECV(3N-SVR4)



     MSG_OOB   Read any out-of-band data present on the socket
               rather than the regular in-band data.

     MSG_PEEK  Peek at the data present on the socket; the data
               is returned, but not consumed, so that a subse-
               quent receive operation will see the same data.

     The recvmsg() call uses a msghdr structure to minimize the
     number of directly supplied parameters.  This structure is
     defined in /usr/include/sys/socket.h and includes the fol-
     lowing members:

          caddr_t      msg_name;         /* optional address */
          int          msg_namelen;      /* size of address */
          struct iovec *msg_iov;         /* scatter/gather array */
          int          msg_iovlen;       /* # elements in msg_iov */
          caddr_t      msg_accrights;    /* access rights sent/received */
          int          msg_accrightslen;

     Here msg_name and msg_namelen specify the destination
     address if the socket is unconnected; msg_name may be given
     as a NULL pointer if no names are desired or required.  The
     msg_iov and msg_iovlen describe the scatter-gather loca-
     tions, as described in read(2).  A buffer to receive any
     access rights sent along with the message is specified in
     msg_accrights, which has length msg_accrightslen.

RETURN VALUE
     These calls return the number of bytes received, or -1 if an
     error occurred.

ERRORS
     The calls fail if:

     EBADF               s is an invalid descriptor.

     ENOTSOCK            s is a descriptor for a file, not a
                         socket.

     EINTR               The operation was interrupted by
                         delivery of a signal before any data was
                         available to be received.

     EWOULDBLOCK         The socket is marked non-blocking and
                         the requested operation would block.

     ENOMEM              There was insufficient user memory
                         available for the operation to complete.

     ENOSR               There were insufficient STREAMS
                         resources available for the operation to
                         complete.



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RECV(3N-SVR4)       RISC/os Reference Manual        RECV(3N-SVR4)



SEE ALSO
     connect(3N), fcntl(2), getsockopt(3N), ioctl(2), read(2),
     send(3N), socket(3N).




















































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