recvfrom(2)recvfrom(2)NAMErecvfrom - Receive messages from sockets
SYNOPSIS
#include <sys/socket.h>
ssize_t recvfrom(
int socket,
void *buffer,
size_t length,
int flags,
struct sockaddr *address,
socklen_t *address_len );
[XNS4.0] The definition of the recvfrom() function in XNS4.0 uses a
size_t data type for the address_len parameter instead of a socklen_t
data type as specified in XNS5.0 (the previous definition).
[Tru64 UNIX] The following definition of the recvfrom() function does
not conform to current standards and is supported only for backward
compatibility (see standards(5)): int recvfrom(
int socket,
char *buffer,
int length,
int flags,
struct sockaddr *address,
int *address_len );
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
recvfrom(): XNS5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
Specifies the socket file descriptor. Specifies a pointer to the buf‐
fer to which the message should be written. Specifies the length (in
bytes) of the buffer pointed to by the buffer parameter. Points to a
value that controls message reception. The parameter to control message
reception is formed by the logical OR of one or more of the following
values: Peeks at the incoming message. Processes out-of-band data.
Requests that the function block wait 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, MSG_PEEK was
specified, or an error is pending for the socket. Points to a sockaddr
structure, the format of which is determined by the domain and by the
behavior requested for the socket. The sockaddr structure is an overlay
for a sockaddr_in, sockaddr_un, sockaddr_in6, or sockaddr_storage
structure, depending on which of the supported address families is
active.
[Tru64 UNIX] If the compile-time option _SOCKADDR_LEN is
defined before the sys/socket.h header file is included, the
sockaddr structure takes 4.4BSD behavior, with a field for spec‐
ifying the length of the socket address. Otherwise, the default
4.3BSD sockaddr structure is used, with the length of the socket
address assumed to be 14 bytes or less.
If _SOCKADDR_LEN is defined, the 4.3BSD sockaddr structure is
defined with the name osockaddr. Specifies the length of the
sockaddr structure pointed to by the address parameter.
DESCRIPTION
The recvfrom() function permits an application program to receive mes‐
sages from unconnected sockets. It is normally applied to unconnected
sockets because it includes parameters that permit a calling program to
retrieve the source endpoint of received data.
To obtain the source address of the message, specify a nonzero value
for the address parameter. The recvfrom() function is called with the
address_len parameter set to the size of the buffer specified by the
address parameter. On return, this function modifies the address_len
parameter to the actual size in bytes of the address specified by the
address parameter. The recvfrom() function returns the length of the
message written to the buffer pointed to by the buffer parameter. When
a message is too long for the specified buffer, excess bytes may be
truncated depending on the type of socket that issued the message, and
depending on which flags are set with the flags parameter.
When no message is available at the socket specified by the socket
parameter, the recvfrom() function waits for a message to arrive,
unless the socket is nonblocking. When the socket is nonblocking, errno
is set to [EWOULDBLOCK].
Use the select() and poll() functions to determine when more data
arrives.
NOTES
[Tru64 UNIX] When compiled in the X/Open UNIX environment or the
POSIX.1g socket environment, calls to the recvfrom() function are
internally renamed by prepending _E to the function name. When you are
debugging a module that includes the recvfrom() function and for which
_XOPEN_SOURCE_EXTENDED or _POSIX_PII_SOCKET has been defined, use
_Erecvfrom to refer to the recvfrom() call. See standards(5) for fur‐
ther information.
RETURN VALUES
Upon successful completion, the byte length of the written message is
returned. If no messages are available and the peer has closed the con‐
nection, the recv() function returns a value of 0. Otherwise, the func‐
tion returns a value of -1 and sets errno to indicate the error.
ERRORS
If the recvfrom() function fails, errno may be set to one of the fol‐
lowing values: The socket parameter is not a valid file descriptor. A
connection was forcibly closed by a peer. Nonexistent or protected
address space is specified for the message buffer, sending address, or
address length.
[Tru64 UNIX] A valid message buffer was not specified. A sig‐
nal interrupted recvfrom before any data was available. The
MSG-OOB flag is set and no out-of-band data is available. An
I/O error occurred while reading from or writing to the file
system. Insufficient resources are available in the system to
complete the call. The system did not have sufficient memory to
fulfill the request. The available STREAMS resources were
insufficient for the operation to complete. A receive is
attempted on a connection-oriented socket that is not connected.
The socket parameter refers to a file, not a socket. The speci‐
fied flags are not supported this socket type. The connection
timed out during connection establishment, or due to a transmis‐
sion timeout on active connection. The socket is nonblocking;
no data is ready to be received.
The MSG_OOB flag is set, no out-of-band data is available, and
either the socket is nonblocking or does not support blocking to
await out-of-band data.
SEE ALSO
Functions: read(2), recv(2), recvmsg(2), select(2), send(2),
sendmsg(2), sendto(2), shutdown(2), socket(2), write(2).
Standards: standards(5).
Network Programmer's Guide
recvfrom(2)
