--- name: "sctp_recvv" section: "3" platform: "freebsd" package: "base" version: "16.0-CURRENT-20261027-61c70dc16a79" release: "FreeBSD 16.0-CURRENT (2026-10-27)" platforms: ["linux", "freebsd"] url: "https://new.carta.tech/sctp_recvmsg" --- # sctp\_recvv(3) receive a message from an SCTP socket Part of [sctp\_recvmsg(3)](/sctp_recvmsg/3.md). ## NAME **sctp\_recvmsg**, **sctp\_recvv** – receive a message from an SCTP socket ## LIBRARY Standard C Library (libc, -lc) ## SYNOPSIS **#include \** **#include \** **#include \** *ssize\_t*\ **sctp\_recvmsg**(*int s*, *void \*msg*, *size\_t len*, *struct sockaddr \*from*, *socklen\_t \*fromlen*, *struct sctp\_sndrcvinfo \*sinfo*, *int \*flags*); *ssize\_t*\ **sctp\_recvv**(*int s*, *const struct iovec \*iov*, *int iovlen*, *struct sockaddr \*from*, *socklen\_t \*fromlen*, *void \*info*, *socklen\_t \*infolen*, *unsigned int \*infotype*, *int \*flags*); ## DESCRIPTION The **sctp\_recvmsg**() and **sctp\_recvv**() functions are used to receive a message from another SCTP endpoint. They are 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**() or **sctp\_recvv**() 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\_EOR flag applied. If the message is a complete message then the *flags* argument will have MSG\_EOR 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)](/sctp/4.md) 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)](/select/2.md) 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)](/sctp/4.md)). The *sinfo-\>info\_timetolive* field is not used by **sctp\_recvmsg**(). The **sctp\_recvv**() function works as **sctp\_recvmsg**() with two differences. Firstly, the receive buffer is passed as an array containing *iocnt* objects of type *struct* *iovec*, where the received data will be scattered in the same manner as [readv(2)](/readv/2.md). Secondly, the *sinfo* argument is replaced by the tuple *info*, *infolen*, and *infotype*, which allow different information to be received based on the socket options. To receive an *sctp\_rcvinfo* structure, set the *SCTP\_RECVRCVINFO* socket option, and pass a pointer to a *struct* *sctp\_rcvinfo* structure in *info*. The *sctp\_rcvinfo* structure has the following format: ``` struct sctp_rcvinfo { uint16_t rcv_sid; /* Stream arriving on */ uint16_t rcv_ssn; /* Stream Sequence Number */ uint16_t rcv_flags; /* Flags on the incoming message */ uint32_t rcv_ppid; /* The ppid field */ uint32_t rcv_tsn; /* The transport sequence number */ uint32_t rcv_cumtsn; /* The cumulative TSN */ uint32_t rcv_context; /* Opaque context field */ sctp_assoc_t rcv_assoc_id; /* Peer association id */ }; ``` These fields have the same meaning as the equivalent fields in *struct* *sctp\_sndrcvinfo*, defined above. To receive an *sctp\_nxtinfo* structure, set the *SCTP\_RECVNXTINFO* socket option, and pass a pointer to a *struct* *sctp\_nxtinfo* structure in *info*. The *struct* *sctp\_nxtinfo* structure has the following format: ``` struct sctp_nxtinfo { uint16_t nxt_sid; /* Next message's stream number */ uint16_t nxt_flags; /* Flags (see below) */ uint32_t nxt_ppid; /* The ppid field */ uint32_t nxt_length; /* Length of next message */ sctp_assoc_t nxt_assoc_id; /* Peer association id */ }; ``` The fields *nxt\_sid*, *nxt\_ppid*, and *nxt\_assoc\_id* have the same meaning as in *struct* *sctp\_rcvinfo*, except they refer to the next message rather than the message that was received. The field *nxt\_length* contains the length of the part of the next message currently available in the socket buffer. This may not represent the length of the entire message unless the *SCTP\_COMPLETE* flag is set in *nxt\_flags*. The *nxt\_flags* field is a bitmask which may contain any of the following values: - *SCTP\_UNORDERED*: The next message was sent unordered. - *SCTP\_COMPLETE*: The entirety of the next message has been received in the socket buffer. In this case, the *nxt\_length* field contains the length of the entire message. - *SCTP\_NOTIFICATION*: The next message is a notification, not a user message. If both the *SCTP\_RECVRCVINFO* and *SCTP\_RECVNXTINFO* socket options are set, then pass a pointer to a *struct* *sctp\_recvv\_rn* structure in *info*. This struct has the following format: ``` struct sctp_recvv_rn { struct sctp_rcvinfo recvv_rcvinfo; struct sctp_nxtinfo recvv_nxtinfo; }; ``` The value pointed to by *infolen* should initially contain the length of the structure to which *info* points. When the function returns, it will be set to the length of the returned structure. Additionally, *\*infotype* will be set to one of the following values depending on what type of info was returned: - *SCTP\_RECVV\_NOINFO*: no information was returned. - *SCTP\_RECVV\_RCVINFO*: *\*info* contains an object of type *struct* *sctp\_rcvinfo*. - *SCTP\_RECVV\_NXTINFO*: *\*info* contains an object of type *struct* *sctp\_nxtinfo*. - *SCTP\_RECVV\_RN*: *\*info* contains an object of type *struct* *sctp\_recvv\_rn*. ## RETURN VALUES The call returns the number of bytes received, or -1 if an error occurred. ## ERRORS The **sctp\_recvmsg**() system call fails if: - \[EBADF\] An invalid descriptor was specified. - \[ENOTSOCK\] The argument *s* is not a socket. - \[EFAULT\] An invalid user space address was specified for an argument. - \[EMSGSIZE\] The socket requires that message be sent atomically, and the size of the message to be sent made this impossible. - \[EAGAIN\] The socket is marked non-blocking and the requested operation would block. - \[ENOBUFS\] The system was unable to allocate an internal buffer. The operation may succeed when buffers become available. - \[ENOBUFS\] The output queue for a network interface was full. This generally indicates that the interface has stopped sending, but may be caused by transient congestion. - \[EHOSTUNREACH\] The remote host was unreachable. - \[ENOTCONN\] On a one-to-one style socket no association exists. - \[ECONNRESET\] An abort was received by the stack while the user was attempting to send data to the peer. - \[ENOENT\] On a one to many style socket no address is specified so that the association cannot be located or the SCTP\_ABORT flag was specified on a non-existing association. - \[EPIPE\] The socket is unable to send anymore data (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. ## NOTES The **sctp\_recvmsg**() function is deprecated. New applications should use **sctp\_recvv**(). ## SEE ALSO [getsockopt(2)](/getsockopt/2.md), [recv(2)](/recv/2.md), [select(2)](/select/2.md), [sendmsg(2)](/sendmsg/2.md), [setsockopt(2)](/setsockopt/2.md), [socket(2)](/socket/2.md), [write(2)](/write/2.md), [sctp\_send(3)](/sctp_send/3.md), [sctp\_sendmsg(3)](/sctp_sendmsg/3.md), [sctp(4)](/sctp/4.md) R. Stewart, M. Tuexen, K. Poon, P. Lei, and V. Yasevich, *Sockets API Extensions for the Stream Control Transmission Protocol (SCTP)*, RFC 6458, December 2011. ## STANDARDS The functions described in this document conform to RFC 6458.