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RECVMSG
Section: POSIX Programmer's Manual (3P)Updated: 2013
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PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.NAME
recvmsg --- receive a message from a socketSYNOPSIS
#include <sys/socket.h> ssize_t recvmsg(int socket, struct msghdr *message, int flags);
DESCRIPTION
The recvmsg() function shall receive a message from a connection-mode or connectionless-mode socket. It is normally used with connectionless-mode sockets because it permits the application to retrieve the source address of received data. The recvmsg() function takes the following arguments:- socket
- Specifies the socket file descriptor.
- message
- Points to a msghdr structure, containing both the buffer to store the source address and the buffers for the incoming message. The length and format of the address depend on the address family of the socket. The msg_flags member is ignored on input, but may contain meaningful values on output.
- flags
-
Specifies the type of message reception. Values of this argument are
formed by logically OR'ing zero or more of the following values:
-
- MSG_OOB
- Requests out-of-band data. The significance and semantics of out-of-band data are protocol-specific.
- MSG_PEEK
- Peeks at the incoming message.
- MSG_WAITALL
- On SOCK_STREAM sockets this requests that the function block until the full amount of data can be returned. The function may return the smaller amount of data if the socket is a message-based socket, if a signal is caught, if the connection is terminated, if MSG_PEEK was specified, or if an error is pending for the socket.
-
- MSG_EOR
- End-of-record was received (if supported by the protocol).
- MSG_OOB
- Out-of-band data was received.
- MSG_TRUNC
- Normal data was truncated.
- MSG_CTRUNC
- Control data was truncated.
RETURN VALUE
Upon successful completion, recvmsg() shall return the length of the message in bytes. If no messages are available to be received and the peer has performed an orderly shutdown, recvmsg() shall return 0. Otherwise, -1 shall be returned and errno set to indicate the error.ERRORS
The recvmsg() function shall fail if:- EAGAIN or EWOULDBLOCK
-
The socket's file descriptor is marked O_NONBLOCK and no data is waiting to be received; or MSG_OOB is set and no out-of-band data is available and either the socket's file descriptor is marked O_NONBLOCK or the socket does not support blocking to await out-of-band data. - EBADF
- The socket argument is not a valid open file descriptor.
- ECONNRESET
- A connection was forcibly closed by a peer.
- EINTR
- This function was interrupted by a signal before any data was available.
- EINVAL
- The sum of the iov_len values overflows a ssize_t, or the MSG_OOB flag is set and no out-of-band data is available.
- EMSGSIZE
- The msg_iovlen member of the msghdr structure pointed to by message is less than or equal to 0, or is greater than {IOV_MAX}.
- ENOTCONN
- A receive is attempted on a connection-mode socket that is not connected.
- ENOTSOCK
- The socket argument does not refer to a socket.
- EOPNOTSUPP
- The specified flags are not supported for this socket type.
- ETIMEDOUT
- The connection timed out during connection establishment, or due to a transmission timeout on active connection. The recvmsg() function may fail if:
- EIO
- An I/O error occurred while reading from or writing to the file system.
- ENOBUFS
- Insufficient resources were available in the system to perform the operation.
- ENOMEM
- Insufficient memory was available to fulfill the request.
The following sections are informative.
EXAMPLES
None.APPLICATION USAGE
The select() and poll() functions can be used to determine when data is available to be received.RATIONALE
None.FUTURE DIRECTIONS
None.SEE ALSO
poll(), pselect(), recv(), recvfrom(), send(), sendmsg(), sendto(), shutdown(), socket() The Base Definitions volume of POSIX.1-2008, <sys_socket.h>COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .