Differences between version 2 and predecessor to the previous major change of recvmsg(2).
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| Newer page: | version 2 | Last edited on Monday, March 17, 2003 1:24:03 am | by PerryLorier | Revert |
| Older page: | version 1 | Last edited on Tuesday, June 4, 2002 12:23:45 am | by perry | Revert |
@@ -1,390 +1,135 @@
-RECV
-!!!RECV
-NAME
-SYNOPSIS
-DESCRIPTION
-RETURN VALUE
-ERRORS
-CONFORMING TO
-NOTE
-SEE ALSO
-----
!!NAME
+recv, recvfrom, recvmsg - receive a message from a socket
-
-recv, recvfrom, recvmsg - receive a message from a socket
!!SYNOPSIS
+ __#include <sys/types.h>__
+ __#include <sys/socket.h>__
+ __int recv(int__ ''s''__, void *__''buf''__, size_t__ ''len''__, int__ ''flags''__);__
-__#include
__
-#include
__
+
__int recvfrom(int
__ ''s''__, void *__''buf''__, size_t__ ''len''__, int__ ''flags''__, struct sockaddr *__''from''__, socklen_t *__''fromlen''__);
__
+ __int recvmsg(int__ ''s''__, struct msghdr *__''msg''__, int__ ''flags''__);__
-__int recv(int__ ''s''__, void *__''buf''__,
-size_t__ ''len''__, int__
-''flags''__);__
-
-
-__int recvfrom(int__ ''s''__, void
-*__''buf''__, size_t__ ''len''__, int__
-''flags''__, struct sockaddr *__''from''__,
-socklen_t *__''fromlen''__);__
-
-
-__int recvmsg(int__ ''s''__, struct msghdr
-*__''msg''__, int__
-''flags''__);__
!!DESCRIPTION
+The __recvfrom__ and __recvmsg__ calls are used to receive messages from a socket, and may be used to receive data on a socket whether or not it is connection-oriented.
+If ''from'' is not NULL, and the socket is not connection-oriented, the source address of the message is filled in. The argument ''fromlen'' is a value-result parameter, initialized to the size of the buffer associated with ''from'', and modified on return to indicate the actual size of the address stored there.
-The __recvfrom
__ and __recvmsg
__ calls are used to
-receive messages
from a socket, and may be used to receive
-data on a socket whether or not it is
-connection-oriented
.
+The __recv
__ call is normally used only on a ''connected'' socket (see connect(2))
and is identical to
__recvfrom
__ with a NULL ''
from'' parameter
.
+All three routines return the length of the message on successful completion. If a message is too long to fit in the supplied buffer, excess bytes may be discarded depending on the type of socket the message is received from (see socket(2)).
-If ''from'' is not NULL, and
the socket is not
-connection-oriented
, the source address of
the message
is
-filled
in. The argument ''fromlen'' is a
value-result
-parameter, initialized to the size of
the buffer associated
-with
''from
'', and modified on return
to indicate
the
-actual size
of the address stored there
.
+If no messages are available at
the socket, the receive calls wait for a message to arrive, unless
the socket
is nonblocking (see fcntl(2))
in which case the
value -1 is returned and
the external variable
''errno
'' set to [EAGAIN]. The receive calls normally return any data available
, up
to the requested amount, rather than waiting for receipt
of the full amount requested
.
+The select(2) or poll(2) call may be used to determine when more data arrives.
-The __recv__ call is normally used only on a
-connected
'' socket (see connect(2)) and is
-identical
to __recvfrom__ with
a NULL
''from
''
-parameter.
+The ''flags
'' argument
to a recv call is formed by '
'OR
'''ing one or more of the following values:
+;__MSG_OOB__: This flag requests receipt of out-of-band data that would not be received in the normal data stream. Some protocols place expedited data at the head of the normal data queue, and thus this flag cannot be used with such protocols.
-All three routines
return the length
of the message on
-successful completion
. If
a message is too long to fit in
-supplied buffer, excess bytes may be discarded depending
-on the type of socket the message is received from (see
-socket(2))
.
+;__MSG_PEEK__: This flag causes the receive operation to
return data from
the beginning
of the receive queue without removing that data from the queue
. Thus,
a subsequent receive call will return
the same data
.
+;__MSG_WAITALL__: This flag requests that the operation block until the full request is satisfied. However, the call may still return less data than requested if a signal is caught, an error or disconnect occurs, or the next data to be received is of a different type than that returned.
-If no messages are available at the socket, the receive
-calls wait for a message to arrive, unless the socket is
-nonblocking (see fcntl(2)) in which case the value -1
-is returned and the external variable ''errno'' set to
-EAGAIN
__. The receive calls normally return any data
-available, up to the requested amount, rather than waiting
-for receipt
of the full amount requested
.
+;
__MSG
_NOSIGNAL
__: This flag turns off raising
of [SIGPIPE] on stream sockets when
the other end disappears
.
+;__MSG_TRUNC__: Return the real length of the packet, even when it was longer than the passed buffer. Only valid for packet sockets.
-The select(2) or poll(2) call may be used to
-determine when more data arrives.
-
-
-The ''flags'' argument to a recv call is formed by
-''OR'''ing one or more of the following
-values:
-
-
-__MSG_OOB__
-
-
-This flag requests receipt of out-of-band data that would
-not be received in the normal data stream. Some protocols
-place expedited data at the head of the normal data queue,
-and thus this flag cannot be used with such
-protocols.
-
-
-__MSG_PEEK__
-
-
-This flag causes the receive operation to return data from
-the beginning of the receive queue without removing that
-data from the queue. Thus, a subsequent receive call will
-return the same data.
-
-
-__MSG_WAITALL__
-
-
-This flag requests that the operation block until the full
-request is satisfied. However, the call may still return
-less data than requested if a signal is caught, an error or
-disconnect occurs, or the next data to be received is of a
-different type than that returned.
-
-
-__MSG_NOSIGNAL__
-
-
-This flag turns off raising of __SIGPIPE__ on stream
-sockets when the other end disappears.
-
-
-__MSG_TRUNC__
-
-
-Return the real length of the packet, even when it was
-longer than the passed buffer. Only valid for packet
-sockets.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
+;
__MSG_ERRQUEUE__:
This flag specifies that queued errors should be received from the socket error queue. The error is passed in an ancillary message with a type dependent on the protocol (for IPv4 __IP_RECVERR__). The user should supply a buffer of sufficient size. See cmsg(3) and ip(7) for more information. The payload of the original packet that caused the error is passed as normal data via __msg_iovec__. The original destination address of the datagram that caused the error is supplied via
__msg_name__.
+For local errors, no address is passed (this can be checked with the ''cmsg_len'' member of the __cmsghdr__). For error receives, the __MSG_ERRQUEUE__ is set in the
+__msghdr__. After an error has been passed, the pending socket error is regenerated based on the next queued error and will be passed on the next socket operation.
-For local errors, no address
is passed (this can be checked
-with the ''cmsg
_len'' member of the
__cmsghdr
__). For
-error receives, the
__MSG_ERRQUEUE__ is set in the
-__msghdr__. After an error has been passed, the pending
-socket error is regenerated based on the next queued error
-and will be passed on the next socket
-operation.
+The error
is supplied in a
__sock
_extended
_err
__ structure:
+ #define SO_EE_ORIGIN_NONE 0
+ #define SO_EE_ORIGIN_LOCAL 1
+ #define SO_EE_ORIGIN_ICMP 2
+ #define SO_EE_ORIGIN_ICMP6 3
+ struct sock_extended_err
+ {
+ u_int32_t ee_errno; /* error number */
+ u_int8_t ee_origin; /* where the error originated */
+ u_int8_t ee_type; /* type */
+ u_int8_t ee_code; /* code */
+ u_int8_t ee_pad;
+ u_int32_t ee_info; /* additional information */
+ u_int32_t ee_data; /* other data */
+ /* More data may follow */
+ };
+ struct sockaddr *SO_EE_OFFENDER(struct sock_extended_err *);
-The
error is supplied in
a __sock
_extended
_err
__
-structure:
+__ee_errno__ contains the errno number of the queued
error. __ee_origin__
is the origin code of where the error originated. The other fields are protocol specific. The macro __SOCK_EE_OFFENDER__ returns
a pointer to the address of the network object where the error originated from given a pointer to the ancillary message. If this address is not known, the ''sa
_family'' member of the
__sockaddr
__ contains
__AF_UNSPEC__ and the other fields of the __sockaddr__ are undefined. The payload of the packet that caused the error is passed as normal data.
+For local errors, no address is passed (this can be checked with the ''cmsg_len'' member of the __cmsghdr__). For error receives, the __MSG_ERRQUEUE__ is set in the
+__msghdr__. After an error has been passed, the pending socket error is regenerated based on the next queued error and will be passed on the next socket operation.
-#define SO
_EE
_ORIGIN
_NONE
-#define SO
_EE_ORIGIN_LOCAL 1
-#define SO_EE_ORIGIN_ICMP 2
-#define SO_EE_ORIGIN_ICMP6 3
-struct sock_extended_err
-{
-u_int32_t ee_errno; /* error
number */
-u_int8_t ee_origin; /* where
the error originated */
-u_int8_t ee_type;
/* type */
-u_int8_t ee_code; /* code */
-u_int8_t ee_pad;
-u_int32_t ee_info; /* additional information */
-u_int32_t ee_data; /* other data */
-/* More data may follow */
-};
-struct sockaddr *SO_EE_OFFENDER(struct sock_extended_err *);
+The
__recvmsg
__ call uses a ''msghdr'' structure to minimize the
number of directly supplied parameters. This structure has
the following form, as defined in
+''<sys
/socket.h>'':
+ struct msghdr {
+ void * msg_name; /* optional address */
+ socklen_t msg_namelen; /* size of address */
+ struct iovec * msg_iov; /* scatter/gather array */
+ size_t msg_iovlen; /* # elements in msg_iov */
+ void * msg_control; /* ancillary data, see below */
+ socklen_t msg_controllen; /* ancillary data buffer len */
+ int msg_flags; /* flags on received message */
+ };
-__ee_errno__ contains the errno number of the queued
-error. __ee_origin__ is the origin code of where the
-error originated. The other fields are protocol specific.
-The macro __SOCK_EE_OFFENDER__ returns a pointer to the
-address of the network object where the error originated
-from given a pointer to the ancillary message. If this
-address is not known, the ''sa_family'' member of the
-__sockaddr__ contains __AF_UNSPEC__ and the other
-fields of the __sockaddr__ are undefined. The payload of
-the packet that caused the error is passed as normal
-data.
-
-
-For local errors, no address is passed (this can be checked
-with the ''cmsg_len'' member of the __cmsghdr__). For
-error receives, the __MSG_ERRQUEUE__ is set in the
-__msghdr__. After an error has been passed, the pending
-socket error is regenerated based on the next queued error
-and will be passed on the next socket
-operation.
-
-
-The __recvmsg__ call uses a ''msghdr'' structure to
-minimize the number of directly supplied parameters. This
-structure has the following form, as defined in
-'''':
-
-
-struct msghdr {
-void * msg_name; /* optional address */
-socklen_t msg_namelen; /* size of address */
-struct iovec * msg_iov; /* scatter/gather array */
-size_t msg_iovlen; /* # elements in msg_iov */
-void * msg_control; /* ancillary data, see below */
-socklen_t msg_controllen; /* ancillary data buffer len */
-int msg_flags; /* flags on received message */
-};
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
+Here ''msg_name'' and ''msg_namelen'' specify the destination address if the socket is unconnected; ''msg_name'' may be given as a null pointer if no names are desired or required. The fields ''msg_iov'' and ''msg_iovlen'' describe scatter-gather locations, as discussed in readv(2). The field ''msg_control'', which has length
''msg_controllen'', points to a buffer for other protocol control related messages or miscellaneous ancillary data. When __recvmsg__ is called, ''msg_controllen'' should contain the length of the available buffer in ''msg_control''; upon return from a successful call it will contain the length of the control message sequence.
The messages are of the form:
+ struct cmsghdr {
+ socklen_t cmsg_len; /* data byte count, including hdr */
+ int cmsg_level; /* originating protocol */
+ int cmsg_type; /* protocol-specific type */
+ /* followed by
+ u_char cmsg_data[[]; */
+ };
-struct cmsghdr {
-socklen_t cmsg_len; /*
data byte count, including hdr */
-int cmsg_level; /* originating protocol */
-int cmsg_type; /* protocol-specific type */
-/* followed
by
-u_char
cmsg_data[[]; */
-};
+Ancillary
data should only be accessed
by the macros defined in
cmsg(3).
+As an example, Linux uses this auxiliary data mechanism to pass extended errors, IP options or file descriptors over Unix sockets.
-Ancillary data should only be accessed by the macros defined
-cmsg
(3
).
+The ''msg_flags'' field
in the msghdr is set on return of __recvmsg__
(). It can contain several flags:
+;__MSG_EOR__: indicates end-of-record; the data returned completed a record (generally used with sockets of type __SOCK_SEQPACKET__).
-As an example, Linux uses this auxiliary data mechanism to
-pass extended errors, IP options or file descriptors over
-Unix sockets
.
+;__MSG_TRUNC__: indicates that the trailing portion of a datagram was discarded because the datagram was larger than the buffer supplied
.
+;__MSG_CTRUNC__: indicates that some control data were discarded due to lack of space in the buffer for ancillary data.
-The ''msg
_flags'' field in the msghdr is set on return of
-recvmsg
__(). It can contain several flags
:
+;
__MSG
_OOB
__: is returned to indicate that expedited or out-of-band data were received.
+;__MSG_ERRQUEUE__: indicates that no data was received but an extended error from the socket error queue.
-__MSG_EOR
__
+;
__MSG_DONTWAIT
__: Enables non-blocking operation; if the operation would block, __EAGAIN__ is returned (this can also be enabled using the __O_NONBLOCK__ with the __F_SETFL__ fcntl(2)).
-
-indicates end-of-record; the data returned completed a
-record (generally used with sockets of type
-__SOCK_SEQPACKET__).
-
-
-__MSG_TRUNC__
-
-
-indicates that the trailing portion of a datagram was
-discarded because the datagram was larger than the buffer
-supplied.
-
-
-__MSG_CTRUNC__
-
-
-indicates that some control data were discarded due to lack
-of space in the buffer for ancillary data.
-
-
-__MSG_OOB__
-
-
-is returned to indicate that expedited or out-of-band data
-were received.
-
-
-__MSG_ERRQUEUE__
-
-
-indicates that no data was received but an extended error
-from the socket error queue.
-
-
-__MSG_DONTWAIT__
-
-
-Enables non-blocking operation; if the operation would
-block, __EAGAIN__ is returned (this can also be enabled
-using the __O_NONBLOCK__ with the __F_SETFL
-fcntl__(2)).
!!RETURN VALUE
+These calls return the number of bytes received, or -1 if an error occurred.
-
-These calls return the number of bytes received, or -1 if an
-error occurred.
!!ERRORS
-
-
-
-
-
+These are some standard errors generated by the socket layer. Additional errors may be generated and returned from the underlying protocol modules; see their manual
pages.
+;[EBADF]: The argument ''s'' is an invalid descriptor.
+;[ECONNREFUSED]: A remote host refused to allow the network connection (typically because it is not running the requested service).
+;[ENOTCONN]: The socket is associated with a connection-oriented protocol and has not been connected (see connect(2) and accept(2)).
+;[ENOTSOCK]: The argument ''s'' does not refer to a socket.
+;[EAGAIN]: The socket is marked non-blocking and the receive operation would block, or a receive timeout had been set and the timeout expired before data was received.
+;[EINTR]: The receive was interrupted by delivery of a signal before any data were available.
+;[EFAULT]: The receive buffer pointer(s) point outside the process's address space.
+;[EINVAL]: Invalid argument passed.
-__EBADF__
-
-
-The argument ''s'' is an invalid descriptor.
-
-
-__ECONNREFUSED__
-
-
-A remote host refused to allow the network connection
-(typically because it is not running the requested
-service).
-
-
-__ENOTCONN__
-
-
-The socket is associated with a connection-oriented protocol
-and has not been connected (see connect(2) and
-accept(2)).
-
-
-__ENOTSOCK__
-
-
-The argument ''s'' does not refer to a
-socket.
-
-
-__EAGAIN__
-
-
-The socket is marked non-blocking and the receive operation
-would block, or a receive timeout had been set and the
-timeout expired before data was received.
-
-
-__EINTR__
-
-
-The receive was interrupted by delivery of a signal before
-any data were available.
-
-
-__EFAULT__
-
-
-The receive buffer pointer(s) point outside the process's
-address space.
-
-
-__EINVAL__
-
-
-Invalid argument passed.
!!CONFORMING TO
+4.4BSD (these function calls first appeared in 4.2BSD).
-
-4.4BSD (these function calls first appeared in
-4.2BSD).
!!NOTE
+The prototypes given above follow glibc2. The Single Unix Specification agrees, except that it has return values of type `ssize_t' (while BSD 4.* and libc4 and libc5 all have `int'). The ''flags'' argument is `int' in BSD 4.*, but `unsigned int' in libc4 and libc5. The ''len'' argument is `int' in BSD 4.*, but `size_t' in libc4 and libc5. The ''fromlen'' argument is `int *' in BSD 4.*, libc4 and libc5. The present `socklen_t *' was invented by POSIX. See also accept(2).
-
-The prototypes given above follow glibc2. The Single Unix
-Specification agrees, except that it has return values of
-type `ssize_t' (while BSD 4.* and libc4 and libc5 all have
-`int'). The ''flags'' argument is `int' in BSD 4.*, but
-`unsigned int' in libc4 and libc5. The ''len'' argument
-is `int' in BSD 4.*, but `size_t' in libc4 and libc5. The
-''fromlen'' argument is `int *' in BSD 4.*, libc4 and
-libc5. The present `socklen_t *' was invented by POSIX. See
-also accept(2).
!!SEE ALSO
-
-
-
-
-
-----
+fcntl(2), read(2), select(2), getsockopt(2), socket(2), cmsg(3)
