SCTP_RECVMSG(3) | Library Functions Manual | SCTP_RECVMSG(3) |
sctp_recvmsg
—
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/sctp.h>
ssize_t
sctp_recvmsg
(int s,
void *msg, size_t len,
struct sockaddr * restrict from,
socklen_t * restrict fromlen, struct
sctp_sndrcvinfo *sinfo, int *flags);
sctp_recvmsg
() system call is used to receive a
message from another SCTP endpoint. The sctp_recvmsg
()
call is used by one-to-one (SOCK_STREAM
) type sockets
after a successful connect
() call or after the
application has performed a listen
() followed by a
successful accept
(). For a one-to-many
(SOCK_SEQPACKET
) type socket, an endpoint may call
sctp_recvmsg
() after having implicitly started an
association via one of the send calls including
sctp_sendmsg
(), sendto
(), and
sendmsg
(). Or, an application may also receive a
message after having called listen
() with a positive
backlog to enable the reception of new associations.
The address of the sender is held in the
from argument with fromlen
specifying its size. At the completion of a successful
sctp_recvmsg
() call from will
hold the address of the peer and fromlen will hold the
length of that address. Note that the address is bounded by the initial
value of fromlen which is used as an in/out
variable.
The length of the message msg to be received
is bounded by len. If the message is too long to fit
in the users receive buffer, then the flags argument
will not have the MSG_EOF
flag
applied. If the message is a complete message then the
flags argument will have
MSG_EOF
set. Locally detected errors are indicated
by a return value of -1 with errno set accordingly.
The flags argument may also hold the value
MSG_NOTIFICATION
. When this occurs it indicates that
the message received is not from the peer endpoint, but
instead is a notification from the SCTP stack (see
sctp(4) for more details). Note
that no notifications are ever given unless the user subscribes to such
notifications using the SCTP_EVENTS
socket
option.
If no messages are available at the socket then
sctp_recvmsg
() normally blocks on the reception of a
message or NOTIFICATION, unless the socket has been placed in non-blocking
I/O mode. The select(2) system
call may be used to determine when it is possible to receive a message.
The sinfo argument is defined as follows.
struct sctp_sndrcvinfo { uint16_t sinfo_stream; /* Stream arriving on */ uint16_t sinfo_ssn; /* Stream Sequence Number */ uint16_t sinfo_flags; /* Flags on the incoming message */ uint32_t sinfo_ppid; /* The ppid field */ uint32_t sinfo_context; /* context field */ uint32_t sinfo_timetolive; /* not used by sctp_recvmsg */ uint32_t sinfo_tsn; /* The transport sequence number */ uint32_t sinfo_cumtsn; /* The cumulative acknowledgment point */ sctp_assoc_t sinfo_assoc_id; /* The association id of the peer */ };
The sinfo->sinfo_ppid field is an opaque 32 bit value that is passed transparently through the stack from the peer endpoint. Note that the stack passes this value without regard to byte order.
The sinfo->sinfo_flags field may include the following:
#define SCTP_UNORDERED 0x0400 /* Message is un-ordered */
The SCTP_UNORDERED
flag is used to specify
that the message arrived with no specific order and was delivered to the
peer application as soon as possible. When this flag is absent the message
was delivered in order within the stream it was received.
The sinfo->sinfo_stream field is the SCTP stream that the message was received on. Streams in SCTP are reliable (or partially reliable) flows of ordered messages.
The sinfo->sinfo_context field is used
only if the local application set an association level context with the
SCTP_CONTEXT
socket option. Optionally a user
process can use this value to index some application specific data structure
for all data coming from a specific association.
The sinfo->sinfo_ssn field will hold the stream sequence number assigned by the peer endpoint if the message is not unordered. For unordered messages this field holds an undefined value.
The sinfo->sinfo_tsn field holds a transport sequence number (TSN) that was assigned to this message by the peer endpoint. For messages that fit in or less than the path MTU this will be the only TSN assigned. Note that for messages that span multiple TSNs this value will be one of the TSNs that was used on the message.
The sinfo->sinfo_cumtsn field holds the current cumulative acknowledgment point of the transport association. Note that this may be larger or smaller than the TSN assigned to the message itself.
The sinfo->sinfo_assoc_id is the unique
association identification that was assigned to the association. For
one-to-many (SOCK_SEQPACKET
) type sockets this value
can be used to send data to the peer without the use of an address field. It
is also quite useful in setting various socket options on the specific
association (see sctp(4)).
The sinfo->info_timetolive field is not
used by sctp_recvmsg
().
sctp_recvmsg
() system call fails if:
EAGAIN
]EBADF
]ECONNRESET
]EFAULT
]EHOSTUNREACH
]EMSGSIZE
]ENOBUFS
]ENOENT
]SCTP_ABORT
flag was specified on a non-existing association.ENOTCONN
]ENOTSOCK
]EPIPE
]SBS_CANTSENDMORE
has been set on the socket).
This typically means that the socket is not connected and is a one-to-one
style socket.Sockets API Extensions for the Stream Control Transmission Protocol (SCTP), RFC, 6458, December 2011.
August 1, 2018 | NetBSD 9.2 |