| 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 9.4 |