Standards
| Standards / Extensions |
C or C++ |
Dependencies |
|---|
XPG4.2
Single UNIX Specification, Version 3
|
both |
|
Format
X/Open #define _XOPEN_SOURCE_EXTENDED 1
#include <sys/socket.h>
ssize_t recv(int socket, void *buffer, size_t length, int flags);
Berkeley
sockets #define _OE_SOCKETS
#include <sys/socket.h>
int recv(int socket, char *buffer, int length, int flags);
General description
The recv()
function receives data on a socket with descriptor
socket and
stores it in a buffer. The recv() call applies only to connected sockets.
- Parameter
- Description
- socket
- The socket descriptor.
- buf
- The pointer to the buffer that receives the data.
- len
- The length in bytes of the buffer pointed to by the buf parameter.
If the MSG_CONNTERM flag is set, the length of the buffer must be
zero.
- flags
- The flags parameter is set by specifying
one or more of the following flags. If more than one flag is specified,
the logical OR operator ( | ) must be used to separate them. The MSG_CONNTERM flag is mutually exclusive with other
flags.
- MSG_CONNTERM
- Requests that the function completes only when a TCP connection
is terminated. It is valid for TCP sockets only. Other normal receive
requests are also completed. The application must be able to deal
with the fact that a normal receive and this special connection termination
receive might be driven in parallel.
AT-TLS considerations: If AT-TLS is being
used to provide transparent TLS/SSL support for a TCP socket and a
receive request with MSG_CONNTERM is outstanding, AT-TLS will immediately
honor any TLS/SSL close notify alerts sent by the peer and initiate
TLS/SSL session shutdown. For more information about AT-TLS and determining
whether a TCP connection is using AT-TLS, see
z/OS Communications Server: IP Programmer's Guide and Reference.
- MSG_OOB
- Reads any out-of-band data on the socket. Out-of-band data is
sent when the MSG_OOB flag is on for a send(), sendto(), or sendmsg().
The fcntl() command should be used with F_SETOWN to specify the
recipient, either a pid or a gid, of a SIGURG signal that will be
sent when out-of-band data is sent. If no recipient is set, no signal
will be sent. For more information, see the fcntl() command. The recipient
of the data determines whether to receive out-of-band data inline
or not inline by the setting of the SO_OOBINLINE option of setsockopt().
If SO_OOBINLINE is set off and the MSG_OOB flag is set on, the out-of-band
data byte will be read out-of-line. It is invalid for the MSG_OOB
flag to be set on when SO_OOBINLINE is set on. If there is out-of-band
data available, and the MSG_OOB flag is not set (SO_OOBINLINE can
be on or off), then the data up to, but not including, the out-of-band
data will be read. When the read cursor has reached the out-of-band
data byte, then only the out-of-band data will be read on the next
read. The SIOCATMARK option of ioctl() can be used to determine if
the read cursor is currently at the out-of-band data byte. For more
information, refer to the setsockopt() and ioctl() commands.
- MSG_PEEK
- Peeks at the data present on the socket; the data is returned
but not consumed, so that a subsequent receive operation sees the
same data.
- MSG_WAITALL
- Requests that the function block until the full amount of data
requested can be returned. The function may return a smaller amount
of data if a signal is caught, the connection is terminated, an error
is pending, or SO_RCVTIMEO is set and the timer is expired for the
socket.
This call returns the length of the incoming
message or data. If a datagram packet is too long to fit in the supplied
buffer, datagram sockets discard excess bytes. If data is not available
for the socket socket, and socket is
in blocking mode, the recv() call blocks the caller until data arrives.
If data is not available and socket is in
nonblocking mode, recv() returns a -1 and sets the error code to
EWOULDBLOCK. See fcntl() — Control open file descriptors or ioctl() — Control device for a description of how to set nonblocking
mode.
For datagram sockets, this call returns the entire datagram
that was sent, provided that the datagram fits into the specified
buffer. Stream sockets act like streams of information with no boundaries
separating data. For example, if applications A and B are connected
with a stream socket and application A sends 1000 bytes, each call
to this function can return 1 byte, or 10 bytes, or the entire 1000
bytes. Therefore, applications using stream sockets should place this
call in a loop, calling this function until all data has been received.
Special
behavior for C++: To
use this function with C++, you
must use the _XOPEN_SOURCE_EXTENDED 1 feature test macro.
Returned value
If successful, recv() returns
the length of the message or datagram in bytes. The value 0 indicates
the connection is closed.
If unsuccessful, recv() returns -1
and sets errno to one of the following values:
- Error Code
- Description
- EBADF
- socket is not a valid socket descriptor.
- ECONNRESET
- A connection was forcibly closed by a peer.
- EFAULT
- Using the buf and len parameters
would result in an attempt to access storage outside the caller's
address space.
- EINTR
- The recv() call was interrupted by a signal that was caught before
any data was available.
- EINVAL
- The request is invalid or not supported. The MSG_OOB flag is set
and no out-of-band data is available.
- EIO
- There has been a network or transport failure.
- ENOBUFS
- Insufficient system resources are available to complete the call.
- ENOTCONN
- A receive is attempted on a connection-oriented socket that is
not connected.
- ENOTSOCK
- The descriptor is for a file, not for a socket.
- EOPNOTSUPP
- The specified flags are not supported for this socket type or
protocol.
- ETIMEDOUT
- The connection timed out during connection establishment, or due
to a transmission timeout on active connection.
- EWOULDBLOCK
- socket is in nonblocking mode and data
is not available to read. or the SO_RCVTIMEO timeout value was been
reached before data was available.