Download Network Enabler SDK 2 API Reference

Network Enabler SDK 2 API Reference
recvfrom
API Reference
receive a datagram and store the source
address
Data
Input/Output
Syntax
#include <sdksock.h>
int recvfrom ( int s, char *buf, int len, int flags, SOCKADDR *from,
int *fromlen );
Arguments
s
buf
len
flags
from
fromlen
a descriptor identifying a bound socket
a buffer for the incoming data
the length of buf
specifies the way in which the call is made
an optional pointer to a buffer which will hold the source address
upon return
an optional pointer to the size of the from buffer
Description
This function is used to read incoming data on a (possibly connected) socket and capture the
address from which the data was sent.
For sockets of type SOCK_STREAM, all information currently available up to the size of the
buffer supplied is returned. The from and fromlen parameters are ignored for
SOCK_STREAM sockets.
For datagram sockets, data is extracted from the first enqueued datagram, up to the size of
the buffer supplied. If the datagram is larger than the buffer supplied, the buffer is filled with
the first part of the message, and the excess data is lost.
If from is non-zero, and the socket is of type SOCK_DGRAM, the network address of the peer
which sent the data is copied to the corresponding SOCKADDR. The value pointed to by
fromlen is initialized to the size of this structure, and is modified on return to indicate the
actual size of the address stored there.
If no incoming data is available at the socket, the recvfrom() call waits for data to arrive
unless the socket is non-blocking. In this case a value of -1 is returned with the error code set
to EWOULDBLOCK. The select() calls may be used to determine when more data arrives.
If the socket is of type SOCK_STREAM and the remote side has shut down the connection
gracefully or the connection has been reset, a recvfrom() will complete immediately with
0 bytes received.
flags may be used to influence the behavior of the function invocation beyond the options
specified for the associated socket. That is, the semantics of this function are determined by
the socket options and the flags parameter. The latter is constructed by “or-ing” any of the
following values:
Value
MSG_OOB
Meaning
read out-of-band data (SOCK_STREAM only)
Return Value
If there are no errors, recvfrom() returns the number of bytes received. If the connection
has been closed, it returns 0. Otherwise, it returns -1, and the global variable errno will
contain one of the following values.
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