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recv(3c)

Standard C Library Functions                                          recv(3C)



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

SYNOPSIS
       #include <sys/socket.h>

       ssize_t recv(int s, void *buf, size_t len, int flags);


       ssize_t recvfrom(int s, void *restrict buf, size_t len, int flags,
            struct sockaddr *restrict from, socklen_t *restrict fromlen);


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

DESCRIPTION
       The  recv(),  recvfrom(),  and  recvmsg() functions are used to receive
       messages from another socket. The s socket is created with socket(3C).


       If from is a non-NULL pointer, the source address  of  the  message  is
       filled  in.  The  value-result  parameter fromlen is initialized to the
       size of the buffer associated with from and modified on return to indi‐
       cate the actual size of the address stored in the buffer. 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 from which the message is received. See socket(3C).


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


       For processes on the same host, recvmsg() can be used to receive a file
       descriptor  from another process, but it cannot receive ancillary data.
       See libxnet(3LIB).


       If a zero-length buffer is specified for a message,  an  EOF  condition
       results  that  is  indistinguishable  from the successful transfer of a
       file descriptor. For that reason, one or more bytes of data  should  be
       provided when recvmsg() passes a file descriptor.


       The select(3C) call can be used to determine when more data arrives.


       The  flags parameter is formed by an OR operation on one or more of the
       following:

       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  to  allow  a  subsequent
                       receive operation to see the same data.


       MSG_WAITALL     Messages  are  blocked  until  the  full amount of data
                       requested is returned. The recv() function can return a
                       smaller  amount of data if a signal is caught, the con‐
                       nection is terminated, MSG_PEEK is specified, or if  an
                       error is pending for the socket.


       MSG_DONTWAIT    Pending   messages   received  on  the  connection  are
                       returned. If data is unavailable, the function does not
                       block.  This  behavior  is the equivalent to specifying
                       O_NONBLOCK on the file descriptor of a  socket,  except
                       that write requests are unaffected.



       The  recvmsg()  function  call  uses  a  msghdr  structure  defined  in
       <sys/socket.h> to minimize the number of directly supplied parameters.

RETURN VALUES
       Upon successful completion, these functions return the number of  bytes
       received.  Otherwise,  they  return  -1  and  set errno to indicate the
       error.

ERRORS
       The recv(), recvfrom(), and recvmsg() functions return errors under the
       following conditions:

       EBADF           The s file descriptor is invalid.


       EINVAL          The  MSG_OOB  flag  is  set  and no out-of-band data is
                       available.


       EINTR           The operation is interrupted by the delivery of a  sig‐
                       nal before any data is available to be received.


       EIO             An  I/O  error  occurs while reading from or writing to
                       the file system.


       ENOMEM          Insufficient user memory is available to complete oper‐
                       ation.


       ENOSR           Insufficient  STREAMS  resources  are available for the
                       operation to complete.


       ENOTSOCK        s is not a socket.


       ESTALE          A stale NFS file handle exists.


       EWOULDBLOCK     The socket is marked  non-blocking  and  the  requested
                       operation  would  block.  EWOULDBLOCK  is also set when
                       socket option SO_RCVTIMEO  is  set  and  the  requested
                       operation  failed  to  transfer data before the timeout
                       expired. For more information, see  the  getsockopt(3C)
                       man page.


       ECONNREFUSED    The  requested  connection was refused by the peer. For
                       connected IPv4 and IPv6 datagram  sockets,  this  indi‐
                       cates that the system received an ICMP Destination Port
                       Unreachable message from the peer.



       The recv() and recvfrom() functions fail  under  the  following  condi‐
       tions:

       EINVAL    The len argument overflows a ssize_t.



       The recvmsg() function returns errors under the following conditions:

       EINVAL    The  msg_iovlen  member of the msghdr structure pointed to by
                 msg  is less than or equal to 0, or greater  than  [IOV_MAX}.
                 See Intro(2) for a definition of [IOV_MAX}.


       EINVAL    One  of the iov_len values in the msg_iov array member of the
                 msghdr structure pointed to by msg is negative, or the sum of
                 the iov_len values in the msg_iov array overflows a ssize_t.


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i)


       ATTRIBUTE TYPEATTRIBUTE VALUE _ Interface StabilityCommitted _ MT-Leve‐
       lAsync-Signal-Safe _ StandardSee standards(7).


SEE ALSO
       fcntl(2), ioctl(2), read(2), connect(3C), getsockopt(3C), recvmmsg(3C),
       select(3C),   send(3C),   socket(3C),  socket.h(3HEAD),  libxnet(3LIB),
       attributes(7)



Oracle Solaris 11.4               9 Jul 2018                          recv(3C)
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