gen_sctp(3erl) Erlang Module Definition gen_sctp(3erl)
NAME
gen_sctp - Functions for communicating with sockets using the SCTP
protocol.
DESCRIPTION
This module provides functions for communicating with sockets using the
SCTP protocol. The implementation assumes that the OS kernel supports
SCTP (RFC 2960) through the user-level Sockets API Extensions.
During development, this implementation was tested on:
* Linux Fedora Core 5.0 (kernel 2.6.15-2054 or later is needed)
* Solaris 10, 11
During OTP adaptation it was tested on:
* SUSE Linux Enterprise Server 10 (x86_64) kernel 2.6.16.27-0.6-smp,
with lksctp-tools-1.0.6
* Briefly on Solaris 10
* SUSE Linux Enterprise Server 10 Service Pack 1 (x86_64) kernel
2.6.16.54-0.2.3-smp with lksctp-tools-1.0.7
* FreeBSD 8.2
This module was written for one-to-many style sockets (type seqpacket).
With the addition of peeloff/2, one-to-one style sockets (type stream)
were introduced.
Record definitions for this module can be found using:
-include_lib("kernel/include/inet_sctp.hrl").
These record definitions use the "new" spelling 'adaptation', not the
deprecated 'adaption', regardless of which spelling the underlying C
API uses.
DATA TYPES
assoc_id()
An opaque term returned in, for example, #sctp_paddr_change{},
which identifies an association for an SCTP socket. The term is
opaque except for the special value 0, which has a meaning such
as "the whole endpoint" or "all future associations".
option() =
{active, true | false | once | -32768..32767} |
{buffer, integer() >= 0} |
{dontroute, boolean()} |
{high_msgq_watermark, integer() >= 1} |
{linger, {boolean(), integer() >= 0}} |
{low_msgq_watermark, integer() >= 1} |
{mode, list | binary} |
list | binary |
{priority, integer() >= 0} |
{recbuf, integer() >= 0} |
{reuseaddr, boolean()} |
{ipv6_v6only, boolean()} |
{sctp_adaptation_layer, #sctp_setadaptation{}} |
{sctp_associnfo, #sctp_assocparams{}} |
{sctp_autoclose, integer() >= 0} |
{sctp_default_send_param, #sctp_sndrcvinfo{}} |
{sctp_delayed_ack_time, #sctp_assoc_value{}} |
{sctp_disable_fragments, boolean()} |
{sctp_events, #sctp_event_subscribe{}} |
{sctp_get_peer_addr_info, #sctp_paddrinfo{}} |
{sctp_i_want_mapped_v4_addr, boolean()} |
{sctp_initmsg, #sctp_initmsg{}} |
{sctp_maxseg, integer() >= 0} |
{sctp_nodelay, boolean()} |
{sctp_peer_addr_params, #sctp_paddrparams{}} |
{sctp_primary_addr, #sctp_prim{}} |
{sctp_rtoinfo, #sctp_rtoinfo{}} |
{sctp_set_peer_primary_addr, #sctp_setpeerprim{}} |
{sctp_status, #sctp_status{}} |
{sndbuf, integer() >= 0} |
{tos, integer() >= 0} |
{tclass, integer() >= 0} |
{ttl, integer() >= 0} |
{recvtos, boolean()} |
{recvtclass, boolean()} |
{recvttl, boolean()}
One of the SCTP Socket Options.
option_name() =
active | buffer | dontroute | high_msgq_watermark | linger |
low_msgq_watermark | mode | priority | recbuf | reuseaddr |
ipv6_v6only | sctp_adaptation_layer | sctp_associnfo |
sctp_autoclose | sctp_default_send_param |
sctp_delayed_ack_time | sctp_disable_fragments | sctp_events |
sctp_get_peer_addr_info | sctp_i_want_mapped_v4_addr |
sctp_initmsg | sctp_maxseg | sctp_nodelay |
sctp_peer_addr_params | sctp_primary_addr | sctp_rtoinfo |
sctp_set_peer_primary_addr | sctp_status | sndbuf | tos |
tclass | ttl | recvtos | recvtclass | recvttl
sctp_socket()
Socket identifier returned from open/*.
EXPORTS
abort(Socket, Assoc) -> ok | {error, inet:posix()}
Types:
Socket = sctp_socket()
Assoc = #sctp_assoc_change{}
Abnormally terminates the association specified by Assoc, with-
out flushing of unsent data. The socket itself remains open.
Other associations opened on this socket are still valid, and
the socket can be used in new associations.
close(Socket) -> ok | {error, inet:posix()}
Types:
Socket = sctp_socket()
Closes the socket and all associations on it. The unsent data is
flushed as in eof/2. The close/1 call is blocking or otherwise
depending of the value of the linger socket option. If close
does not linger or linger time-out expires, the call returns and
the data is flushed in the background.
connect(Socket, Addr, Port, Opts) ->
{ok, #sctp_assoc_change{state = comm_up}} |
{error, #sctp_assoc_change{state = cant_assoc}} |
{error, inet:posix()}
Types:
Socket = sctp_socket()
Addr = inet:ip_address() | inet:hostname()
Port = inet:port_number()
Opts = [Opt :: option()]
Same as connect(Socket, Addr, Port, Opts, infinity).
connect(Socket, Addr, Port, Opts, Timeout) ->
{ok, #sctp_assoc_change{state = comm_up}} |
{error, #sctp_assoc_change{state = cant_assoc}} |
{error, inet:posix()}
Types:
Socket = sctp_socket()
Addr = inet:ip_address() | inet:hostname()
Port = inet:port_number()
Opts = [Opt :: option()]
Timeout = timeout()
Establishes a new association for socket Socket, with the peer
(SCTP server socket) specified by Addr and Port. Timeout, is ex-
pressed in milliseconds. A socket can be associated with multi-
ple peers.
Warning:
Using a value of Timeout less than the maximum time taken by the
OS to establish an association (around 4.5 minutes if the de-
fault values from RFC 4960 are used), can result in inconsistent
or incorrect return values. This is especially relevant for as-
sociations sharing the same Socket (that is, source address and
port), as the controlling process blocks until connect/* re-
turns. connect_init/* provides an alternative without this limi-
tation.
The result of connect/* is an #sctp_assoc_change{} event that
contains, in particular, the new Association ID:
#sctp_assoc_change{
state = atom(),
error = integer(),
outbound_streams = integer(),
inbound_streams = integer(),
assoc_id = assoc_id()
}
The number of outbound and inbound streams can be set by giving
an sctp_initmsg option to connect as in:
connect(Socket, Ip, Port>,
[{sctp_initmsg,#sctp_initmsg{num_ostreams=OutStreams,
max_instreams=MaxInStreams}}])
All options Opt are set on the socket before the association is
attempted. If an option record has undefined field values, the
options record is first read from the socket for those values.
In effect, Opt option records only define field values to change
before connecting.
The returned outbound_streams and inbound_streams are the stream
numbers on the socket. These can be different from the requested
values (OutStreams and MaxInStreams, respectively) if the peer
requires lower values.
state can have the following values:
comm_up:
Association is successfully established. This indicates a
successful completion of connect.
cant_assoc:
The association cannot be established (connect/* failure).
Other states do not normally occur in the output from connect/*.
Rather, they can occur in #sctp_assoc_change{} events received
instead of data in recv/* calls. All of them indicate losing the
association because of various error conditions, and are listed
here for the sake of completeness:
comm_lost:
restart:
shutdown_comp:
Field error can provide more detailed diagnostics. The error
field value can be converted into a string using error_string/1.
connect_init(Socket, Addr, Port, Opts) ->
ok | {error, inet:posix()}
Types:
Socket = sctp_socket()
Addr = inet:ip_address() | inet:hostname()
Port = inet:port_number()
Opts = [option()]
Same as connect_init(Socket, Addr, Port, Opts, infinity).
connect_init(Socket, Addr, Port, Opts, Timeout) ->
ok | {error, inet:posix()}
Types:
Socket = sctp_socket()
Addr = inet:ip_address() | inet:hostname()
Port = inet:port_number()
Opts = [option()]
Timeout = timeout()
Initiates a new association for socket Socket, with the peer
(SCTP server socket) specified by Addr and Port.
The fundamental difference between this API and connect/* is
that the return value is that of the underlying OS connect(2)
system call. If ok is returned, the result of the association
establishment is received by the calling process as an #sctp_as-
soc_change{} event. The calling process must be prepared to re-
ceive this, or poll for it using recv/*, depending on the value
of the active option.
The parameters are as described in connect/*, except the Timeout
value.
The timer associated with Timeout only supervises IP resolution
of Addr.
controlling_process(Socket, Pid) -> ok | {error, Reason}
Types:
Socket = sctp_socket()
Pid = pid()
Reason = closed | not_owner | badarg | inet:posix()
Assigns a new controlling process Pid to Socket. Same implemen-
tation as gen_udp:controlling_process/2.
eof(Socket, Assoc) -> ok | {error, Reason}
Types:
Socket = sctp_socket()
Assoc = #sctp_assoc_change{}
Reason = term()
Gracefully terminates the association specified by Assoc, with
flushing of all unsent data. The socket itself remains open.
Other associations opened on this socket are still valid. The
socket can be used in new associations.
error_string(ErrorNumber) -> ok | string() | unknown_error
Types:
ErrorNumber = integer()
Translates an SCTP error number from, for example, #sctp_re-
mote_error{} or #sctp_send_failed{} into an explanatory string,
or one of the atoms ok for no error or undefined for an unrecog-
nized error.
listen(Socket, IsServer) -> ok | {error, Reason}
listen(Socket, Backlog) -> ok | {error, Reason}
Types:
Socket = sctp_socket()
Backlog = integer()
Reason = term()
Sets up a socket to listen on the IP address and port number it
is bound to.
For type seqpacket, sockets (the default) IsServer must be true
or false. In contrast to TCP, there is no listening queue length
in SCTP. If IsServer is true, the socket accepts new associa-
tions, that is, it becomes an SCTP server socket.
For type stream, sockets Backlog define the backlog queue length
just like in TCP.
open() -> {ok, Socket} | {error, inet:posix()}
open(Port) -> {ok, Socket} | {error, inet:posix()}
open(Opts) -> {ok, Socket} | {error, inet:posix()}
open(Port, Opts) -> {ok, Socket} | {error, inet:posix()}
Types:
Opts = [Opt]
Opt =
{ip, IP} |
{ifaddr, IP} |
inet:address_family() |
{port, Port} |
{type, SockType} |
option()
IP = inet:ip_address() | any | loopback
Port = inet:port_number()
SockType = seqpacket | stream
Socket = sctp_socket()
Creates an SCTP socket and binds it to the local addresses spec-
ified by all {ip,IP} (or synonymously {ifaddr,IP}) options (this
feature is called SCTP multi-homing). The default IP and Port
are any and 0, meaning bind to all local addresses on any free
port.
Other options:
inet6:
Sets up the socket for IPv6.
inet:
Sets up the socket for IPv4. This is the default.
A default set of socket options is used. In particular, the
socket is opened in binary and passive mode, with SockType seq-
packet, and with reasonably large kernel and driver buffers.
If the socket is in passive mode data can be received through
the recv/1,2 calls.
If the socket is in active mode data received data is delivered
to the controlling process as messages:
{sctp, Socket, FromIP, FromPort, {AncData, Data}}
See recv/1,2 for a description of the message fields.
Note:
This message format unfortunately differs slightly from the
gen_udp message format with ancillary data, and from the
recv/1,2 return tuple format.
peeloff(Socket, Assoc) -> {ok, NewSocket} | {error, Reason}
Types:
Socket = sctp_socket()
Assoc = #sctp_assoc_change{} | assoc_id()
NewSocket = sctp_socket()
Reason = term()
Branches off an existing association Assoc in a socket Socket of
type seqpacket (one-to-many style) into a new socket NewSocket
of type stream (one-to-one style).
The existing association argument Assoc can be either a
#sctp_assoc_change{} record as returned from, for example,
recv/*, connect/*, or from a listening socket in active mode. It
can also be just the field assoc_id integer from such a record.
recv(Socket) ->
{ok, {FromIP, FromPort, AncData, Data}} | {error, Reason}
recv(Socket, Timeout) ->
{ok, {FromIP, FromPort, AncData, Data}} | {error, Reason}
Types:
Socket = sctp_socket()
Timeout = timeout()
FromIP = inet:ip_address()
FromPort = inet:port_number()
AncData = [#sctp_sndrcvinfo{} | inet:ancillary_data()]
Data =
binary() |
string() |
#sctp_sndrcvinfo{} |
#sctp_assoc_change{} |
#sctp_paddr_change{} |
#sctp_adaptation_event{}
Reason =
inet:posix() |
#sctp_send_failed{} |
#sctp_paddr_change{} |
#sctp_pdapi_event{} |
#sctp_remote_error{} |
#sctp_shutdown_event{}
Receives the Data message from any association of the socket. If
the receive times out, {error,timeout} is returned. The default
time-out is infinity. FromIP and FromPort indicate the address
of the sender.
AncData is a list of ancillary data items that can be received
along with the main Data. This list can be empty, or contain a
single #sctp_sndrcvinfo{} record if receiving of such ancillary
data is enabled (see option sctp_events). It is enabled by de-
fault, as such ancillary data provides an easy way of determin-
ing the association and stream over which the message is re-
ceived. (An alternative way is to get the association ID from
FromIP and FromPort using socket option sctp_get_peer_addr_info,
but this does still not produce the stream number).
AncData may also contain ancillary data from the socket op-
tions recvtos, recvtclass or recvttl, if that is supported by
the platform for the socket.
The Data received can be a binary() or a list() of bytes (inte-
gers in the range 0 through 255) depending on the socket mode,
or an SCTP event.
Possible SCTP events:
* #sctp_sndrcvinfo{}
* #sctp_assoc_change{}
*
#sctp_paddr_change{
addr = {ip_address(),port()},
state = atom(),
error = integer(),
assoc_id = assoc_id()
}
Indicates change of the status of the IP address of the peer
specified by addr within association assoc_id. Possible val-
ues of state (mostly self-explanatory) include:
addr_unreachable:
addr_available:
addr_removed:
addr_added:
addr_made_prim:
addr_confirmed:
In case of an error (for example, addr_unreachable), field
error provides more diagnostics. In such cases, event
#sctp_paddr_change{} is automatically converted into an er-
ror term returned by recv. The error field value can be con-
verted into a string using error_string/1.
*
#sctp_send_failed{
flags = true | false,
error = integer(),
info = #sctp_sndrcvinfo{},
assoc_id = assoc_id()
data = binary()
}
The sender can receive this event if a send operation fails.
flags:
A Boolean specifying if the data has been transmitted over
the wire.
error:
Provides extended diagnostics, use error_string/1.
info:
The original #sctp_sndrcvinfo{} record used in the failed
send/*.
data:
The whole original data chunk attempted to be sent.
In the current implementation of the Erlang/SCTP binding,
this event is internally converted into an error term re-
turned by recv/*.
*
#sctp_adaptation_event{
adaptation_ind = integer(),
assoc_id = assoc_id()
}
Delivered when a peer sends an adaptation layer indication
parameter (configured through option sctp_adaptation_layer).
Notice that with the current implementation of the Er-
lang/SCTP binding, this event is disabled by default.
*
#sctp_pdapi_event{
indication = sctp_partial_delivery_aborted,
assoc_id = assoc_id()
}
A partial delivery failure. In the current implementation of
the Erlang/SCTP binding, this event is internally converted
into an error term returned by recv/*.
send(Socket, SndRcvInfo, Data) -> ok | {error, Reason}
Types:
Socket = sctp_socket()
SndRcvInfo = #sctp_sndrcvinfo{}
Data = binary() | iolist()
Reason = term()
Sends the Data message with all sending parameters from a
#sctp_sndrcvinfo{} record. This way, the user can specify the
PPID (passed to the remote end) and context (passed to the local
SCTP layer), which can be used, for example, for error identifi-
cation. However, such a fine level of user control is rarely re-
quired. The function send/4 is sufficient for most applications.
send(Socket, Assoc, Stream, Data) -> ok | {error, Reason}
Types:
Socket = sctp_socket()
Assoc = #sctp_assoc_change{} | assoc_id()
Stream = integer()
Data = binary() | iolist()
Reason = term()
Sends a Data message over an existing association and specified
stream.
SCTP SOCKET OPTIONS
The set of admissible SCTP socket options is by construction orthogonal
to the sets of TCP, UDP, and generic inet options. Only options listed
here are allowed for SCTP sockets. Options can be set on the socket us-
ing open/1,2 or inet:setopts/2, retrieved using inet:getopts/2. Options
can be changed when calling connect/4,5.
{mode, list|binary} or just list or binary:
Determines the type of data returned from recv/1,2.
{active, true|false|once|N}:
* If false (passive mode, the default), the caller must do an ex-
plicit recv call to retrieve the available data from the socket.
* If true|once|N (active modes) received data or events are sent to
the owning process. See open/0..2 for the message format.
* If true (full active mode) there is no flow control.
Note:
Note that this can cause the message queue to overflow causing for
example the virtual machine to run out of memory and crash.
* If once, only one message is automatically placed in the message
queue, and after that the mode is automatically reset to passive.
This provides flow control and the possibility for the receiver
to listen for its incoming SCTP data interleaved with other in-
ter-process messages.
* If active is specified as an integer N in the range -32768 to
32767 (inclusive), that number is added to the socket's counting
of data messages to be delivered to the controlling process. If
the result of the addition is negative, the count is set to 0.
Once the count reaches 0, either through the delivery of messages
or by being explicitly set with inet:setopts/2, the socket mode
is automatically reset to passive ({active, false}). When a
socket in this active mode transitions to passive mode, the mes-
sage {sctp_passive, Socket} is sent to the controlling process to
notify it that if it wants to receive more data messages from the
socket, it must call inet:setopts/2 to set the socket back into
an active mode.
{tos, integer()}:
Sets the Type-Of-Service field on the IP datagrams that are sent,
to the specified value. This effectively determines a prioritiza-
tion policy for the outbound packets. The acceptable values are
system-dependent.
{priority, integer()}:
A protocol-independent equivalent of tos above. Setting priority
implies setting tos as well.
{dontroute, true|false}:
Defaults to false. If true, the kernel does not send packets
through any gateway, only sends them to directly connected hosts.
{reuseaddr, true|false}:
Defaults to false. If true, the local binding address {IP,Port} of
the socket can be reused immediately. No waiting in state
CLOSE_WAIT is performed (can be required for high-throughput
servers).
{sndbuf, integer()}:
The size, in bytes, of the OS kernel send buffer for this socket.
Sending errors would occur for datagrams larger than val(sndbuf).
Setting this option also adjusts the size of the driver buffer (see
buffer above).
{recbuf, integer()}:
The size, in bytes, of the OS kernel receive buffer for this
socket. Sending errors would occur for datagrams larger than
val(recbuf). Setting this option also adjusts the size of the
driver buffer (see buffer above).
{sctp_module, module()}:
Overrides which callback module is used. Defaults to inet_sctp for
IPv4 and inet6_sctp for IPv6.
{sctp_rtoinfo, #sctp_rtoinfo{}}:
#sctp_rtoinfo{
assoc_id = assoc_id(),
initial = integer(),
max = integer(),
min = integer()
}
Determines retransmission time-out parameters, in milliseconds, for
the association(s) specified by assoc_id.
assoc_id = 0 (default) indicates the whole endpoint. See RFC 2960
and Sockets API Extensions for SCTP for the exact semantics of the
field values.
{sctp_associnfo, #sctp_assocparams{}}:
#sctp_assocparams{
assoc_id = assoc_id(),
asocmaxrxt = integer(),
number_peer_destinations = integer(),
peer_rwnd = integer(),
local_rwnd = integer(),
cookie_life = integer()
}
Determines association parameters for the association(s) specified
by assoc_id.
assoc_id = 0 (default) indicates the whole endpoint. See Sockets
API Extensions for SCTP for the discussion of their semantics.
Rarely used.
{sctp_initmsg, #sctp_initmsg{}}:
#sctp_initmsg{
num_ostreams = integer(),
max_instreams = integer(),
max_attempts = integer(),
max_init_timeo = integer()
}
Determines the default parameters that this socket tries to negoti-
ate with its peer while establishing an association with it. Is to
be set after open/* but before the first connect/*. #sctp_initmsg{}
can also be used as ancillary data with the first call of send/* to
a new peer (when a new association is created).
num_ostreams:
Number of outbound streams
max_instreams:
Maximum number of inbound streams
max_attempts:
Maximum retransmissions while establishing an association
max_init_timeo:
Time-out, in milliseconds, for establishing an association
{sctp_autoclose, integer() >= 0}:
Determines the time, in seconds, after which an idle association is
automatically closed. 0 means that the association is never auto-
matically closed.
{sctp_nodelay, true|false}:
Turns on|off the Nagle algorithm for merging small packets into
larger ones. This improves throughput at the expense of latency.
{sctp_disable_fragments, true|false}:
If true, induces an error on an attempt to send a message larger
than the current PMTU size (which would require fragmentation/re-
assembling). Notice that message fragmentation does not affect the
logical atomicity of its delivery; this option is provided for per-
formance reasons only.
{sctp_i_want_mapped_v4_addr, true|false}:
Turns on|off automatic mapping of IPv4 addresses into IPv6 ones (if
the socket address family is AF_INET6).
{sctp_maxseg, integer()}:
Determines the maximum chunk size if message fragmentation is used.
If 0, the chunk size is limited by the Path MTU only.
{sctp_primary_addr, #sctp_prim{}}:
#sctp_prim{
assoc_id = assoc_id(),
addr = {IP, Port}
}
IP = ip_address()
Port = port_number()
For the association specified by assoc_id, {IP,Port} must be one of
the peer addresses. This option determines that the specified ad-
dress is treated by the local SCTP stack as the primary address of
the peer.
{sctp_set_peer_primary_addr, #sctp_setpeerprim{}}:
#sctp_setpeerprim{
assoc_id = assoc_id(),
addr = {IP, Port}
}
IP = ip_address()
Port = port_number()
When set, informs the peer to use {IP, Port} as the primary address
of the local endpoint for the association specified by assoc_id.
{sctp_adaptation_layer, #sctp_setadaptation{}}:
#sctp_setadaptation{
adaptation_ind = integer()
}
When set, requests that the local endpoint uses the value specified
by adaptation_ind as the Adaptation Indication parameter for estab-
lishing new associations. For details, see RFC 2960 and Sockets API
Extenstions for SCTP.
{sctp_peer_addr_params, #sctp_paddrparams{}}:
#sctp_paddrparams{
assoc_id = assoc_id(),
address = {IP, Port},
hbinterval = integer(),
pathmaxrxt = integer(),
pathmtu = integer(),
sackdelay = integer(),
flags = list()
}
IP = ip_address()
Port = port_number()
Determines various per-address parameters for the association spec-
ified by assoc_id and the peer address address (the SCTP protocol
supports multi-homing, so more than one address can correspond to a
specified association).
hbinterval:
Heartbeat interval, in milliseconds
pathmaxrxt:
Maximum number of retransmissions before this address is consid-
ered unreachable (and an alternative address is selected)
pathmtu:
Fixed Path MTU, if automatic discovery is disabled (see flags be-
low)
sackdelay:
Delay, in milliseconds, for SAC messages (if the delay is en-
abled, see flags below)
flags:
The following flags are available:
hb_enable:
Enables heartbeat
hb_disable:
Disables heartbeat
hb_demand:
Initiates heartbeat immediately
pmtud_enable:
Enables automatic Path MTU discovery
pmtud_disable:
Disables automatic Path MTU discovery
sackdelay_enable:
Enables SAC delay
sackdelay_disable:
Disables SAC delay
{sctp_default_send_param, #sctp_sndrcvinfo{}}:
#sctp_sndrcvinfo{
stream = integer(),
ssn = integer(),
flags = list(),
ppid = integer(),
context = integer(),
timetolive = integer(),
tsn = integer(),
cumtsn = integer(),
assoc_id = assoc_id()
}
#sctp_sndrcvinfo{} is used both in this socket option, and as an-
cillary data while sending or receiving SCTP messages. When set as
an option, it provides default values for subsequent send calls on
the association specified by assoc_id.
assoc_id = 0 (default) indicates the whole endpoint.
The following fields typically must be specified by the sender:
sinfo_stream:
Stream number (0-base) within the association to send the mes-
sages through;
sinfo_flags:
The following flags are recognised:
unordered:
The message is to be sent unordered
addr_over:
The address specified in send overwrites the primary peer ad-
dress
abort:
Aborts the current association without flushing any unsent data
eof:
Gracefully shuts down the current association, with flushing of
unsent data
Other fields are rarely used. For complete information, see RFC
2960 and Sockets API Extensions for SCTP.
{sctp_events, #sctp_event_subscribe{}}:
#sctp_event_subscribe{
data_io_event = true | false,
association_event = true | false,
address_event = true | false,
send_failure_event = true | false,
peer_error_event = true | false,
shutdown_event = true | false,
partial_delivery_event = true | false,
adaptation_layer_event = true | false
}
This option determines which SCTP Events are to be received
(through recv/*) along with the data. The only exception is
data_io_event, which enables or disables receiving of #sctp_sndrcv-
info{} ancillary data, not events. By default, all flags except
adaptation_layer_event are enabled, although sctp_data_io_event and
association_event are used by the driver itself and not exported to
the user level.
{sctp_delayed_ack_time, #sctp_assoc_value{}}:
#sctp_assoc_value{
assoc_id = assoc_id(),
assoc_value = integer()
}
Rarely used. Determines the ACK time (specified by assoc_value, in
milliseconds) for the specified association or the whole endpoint
if assoc_value = 0 (default).
{sctp_status, #sctp_status{}}:
#sctp_status{
assoc_id = assoc_id(),
state = atom(),
rwnd = integer(),
unackdata = integer(),
penddata = integer(),
instrms = integer(),
outstrms = integer(),
fragmentation_point = integer(),
primary = #sctp_paddrinfo{}
}
This option is read-only. It determines the status of the SCTP as-
sociation specified by assoc_id. The following are the possible
values of state (the state designations are mostly self-explana-
tory):
sctp_state_empty:
Default. Means that no other state is active.
sctp_state_closed:
sctp_state_cookie_wait:
sctp_state_cookie_echoed:
sctp_state_established:
sctp_state_shutdown_pending:
sctp_state_shutdown_sent:
sctp_state_shutdown_received:
sctp_state_shutdown_ack_sent:
Semantics of the other fields:
sstat_rwnd:
Current receiver window size of the association
sstat_unackdata:
Number of unacked data chunks
sstat_penddata:
Number of data chunks pending receipt
sstat_instrms:
Number of inbound streams
sstat_outstrms:
Number of outbound streams
sstat_fragmentation_point:
Message size at which SCTP fragmentation occurs
sstat_primary:
Information on the current primary peer address (see below for
the format of #sctp_paddrinfo{})
{sctp_get_peer_addr_info, #sctp_paddrinfo{}}:
#sctp_paddrinfo{
assoc_id = assoc_id(),
address = {IP, Port},
state = inactive | active | unconfirmed,
cwnd = integer(),
srtt = integer(),
rto = integer(),
mtu = integer()
}
IP = ip_address()
Port = port_number()
This option is read-only. It determines the parameters specific to
the peer address specified by address within the association speci-
fied by assoc_id. Field address fmust be set by the caller; all
other fields are filled in on return. If assoc_id = 0 (default),
the address is automatically translated into the corresponding as-
sociation ID. This option is rarely used. For the semantics of all
fields, see RFC 2960 and Sockets API Extensions for SCTP.
SCTP EXAMPLES
Example of an Erlang SCTP server that receives SCTP messages and prints
them on the standard output:
-module(sctp_server).
-export([server/0,server/1,server/2]).
-include_lib("kernel/include/inet.hrl").
-include_lib("kernel/include/inet_sctp.hrl").
server() ->
server(any, 2006).
server([Host,Port]) when is_list(Host), is_list(Port) ->
{ok, #hostent{h_addr_list = [IP|_]}} = inet:gethostbyname(Host),
io:format("~w -> ~w~n", [Host, IP]),
server([IP, list_to_integer(Port)]).
server(IP, Port) when is_tuple(IP) orelse IP == any orelse IP == loopback,
is_integer(Port) ->
{ok,S} = gen_sctp:open(Port, [{recbuf,65536}, {ip,IP}]),
io:format("Listening on ~w:~w. ~w~n", [IP,Port,S]),
ok = gen_sctp:listen(S, true),
server_loop(S).
server_loop(S) ->
case gen_sctp:recv(S) of
{error, Error} ->
io:format("SCTP RECV ERROR: ~p~n", [Error]);
Data ->
io:format("Received: ~p~n", [Data])
end,
server_loop(S).
Example of an Erlang SCTP client interacting with the above server. No-
tice that in this example the client creates an association with the
server with 5 outbound streams. Therefore, sending of "Test 0" over
stream 0 succeeds, but sending of "Test 5" over stream 5 fails. The
client then aborts the association, which results in that the corre-
sponding event is received on the server side.
-module(sctp_client).
-export([client/0, client/1, client/2]).
-include_lib("kernel/include/inet.hrl").
-include_lib("kernel/include/inet_sctp.hrl").
client() ->
client([localhost]).
client([Host]) ->
client(Host, 2006);
client([Host, Port]) when is_list(Host), is_list(Port) ->
client(Host,list_to_integer(Port)),
init:stop().
client(Host, Port) when is_integer(Port) ->
{ok,S} = gen_sctp:open(),
{ok,Assoc} = gen_sctp:connect
(S, Host, Port, [{sctp_initmsg,#sctp_initmsg{num_ostreams=5}}]),
io:format("Connection Successful, Assoc=~p~n", [Assoc]),
io:write(gen_sctp:send(S, Assoc, 0, <<"Test 0">>)),
io:nl(),
timer:sleep(10000),
io:write(gen_sctp:send(S, Assoc, 5, <<"Test 5">>)),
io:nl(),
timer:sleep(10000),
io:write(gen_sctp:abort(S, Assoc)),
io:nl(),
timer:sleep(1000),
gen_sctp:close(S).
A simple Erlang SCTP client that uses the connect_init API:
-module(ex3).
-export([client/4]).
-include_lib("kernel/include/inet.hrl").
-include_lib("kernel/include/inet_sctp.hrl").
client(Peer1, Port1, Peer2, Port2)
when is_tuple(Peer1), is_integer(Port1), is_tuple(Peer2), is_integer(Port2) ->
{ok,S} = gen_sctp:open(),
SctpInitMsgOpt = {sctp_initmsg,#sctp_initmsg{num_ostreams=5}},
ActiveOpt = {active, true},
Opts = [SctpInitMsgOpt, ActiveOpt],
ok = gen_sctp:connect(S, Peer1, Port1, Opts),
ok = gen_sctp:connect(S, Peer2, Port2, Opts),
io:format("Connections initiated~n", []),
client_loop(S, Peer1, Port1, undefined, Peer2, Port2, undefined).
client_loop(S, Peer1, Port1, AssocId1, Peer2, Port2, AssocId2) ->
receive
{sctp, S, Peer1, Port1, {_Anc, SAC}}
when is_record(SAC, sctp_assoc_change), AssocId1 == undefined ->
io:format("Association 1 connect result: ~p. AssocId: ~p~n",
[SAC#sctp_assoc_change.state,
SAC#sctp_assoc_change.assoc_id]),
client_loop(S, Peer1, Port1, SAC#sctp_assoc_change.assoc_id,
Peer2, Port2, AssocId2);
{sctp, S, Peer2, Port2, {_Anc, SAC}}
when is_record(SAC, sctp_assoc_change), AssocId2 == undefined ->
io:format("Association 2 connect result: ~p. AssocId: ~p~n",
[SAC#sctp_assoc_change.state, SAC#sctp_assoc_change.assoc_id]),
client_loop(S, Peer1, Port1, AssocId1, Peer2, Port2,
SAC#sctp_assoc_change.assoc_id);
{sctp, S, Peer1, Port1, Data} ->
io:format("Association 1: received ~p~n", [Data]),
client_loop(S, Peer1, Port1, AssocId1,
Peer2, Port2, AssocId2);
{sctp, S, Peer2, Port2, Data} ->
io:format("Association 2: received ~p~n", [Data]),
client_loop(S, Peer1, Port1, AssocId1,
Peer2, Port2, AssocId2);
Other ->
io:format("Other ~p~n", [Other]),
client_loop(S, Peer1, Port1, AssocId1,
Peer2, Port2, AssocId2)
after 5000 ->
ok
end.
SEE ALSO
gen_tcp(3erl), gen_udp(3erl), inet(3erl), RFC 2960 (Stream Control
Transmission Protocol), Sockets API Extensions for SCTP
Ericsson AB kernel 7.0 gen_sctp(3erl)