recv(3N)                                                           recv(3N)

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

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

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

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

     int recvmsg(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 sup-
     plied buffer, excess bytes may be discarded depending on the type of
     socket (SOCKSTREAM and SOCKRAW) from which the message is received
     [see socket(3N)].

     If no messages are available at the socket, the receive call waits for
     a message to arrive, unless the socket is nonblocking [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:

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

     MSGPEEK        "Peek" at the data present on the socket; the data is
                     returned, but not consumed, so that a subsequent
                     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 following members:

     caddrt        msgname;          /* optional address */
     int            msgnamelen;       /* size of address */



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recv(3N)                                                           recv(3N)

     struct iovec   *msgiov;          /* scatter/gather array */
     int            msgiovlen;        /* # elements in msgiov */
     caddrt        msgaccrights;     /* access rights sent/received */
     int            msgaccrightslen;

     Here msgname and msgnamelen specify the destination address if the
     socket is unconnected; msgname may be given as a NULL pointer if no
     names are desired or required. The msgiov and msgiovlen describe the
     scatter-gather locations, as described in read(2). A buffer to receive
     any access rights sent along with the message is specified in
     msgaccrights, which has length msgaccrightslen. Not all protocol
     families support the receipt of access rights.

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

DIAGNOSTICS
     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.

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















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