gen_sctp
MODULE
gen_sctp
MODULE SUMMARY
The gen_sctp module provides functions for communicating with sockets using the SCTP protocol.
DESCRIPTION
The gen_sctp module provides functions for communicating with
sockets using the SCTP protocol. The implementation assumes that
the OS kernel supports SCTP
(RFC2960) 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),
and on 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, and later on
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.
Record definitions for the gen_sctp 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.
CONTENTS
DATA TYPES
-
assoc_id()
-
An opaque term returned in for example #sctp_paddr_change{}
that identifies an association for an SCTP socket. The term
is opaque except for the special value 0 that has a
meaning such as "the whole endpoint" or "all future associations".
-
charlist() = [char()]
-
-
iolist() = [char() | binary()]
-
-
ip_address()
-
Represents an address of an SCTP socket.
It is a tuple as explained in
inet(3).
-
port_number() = 0 .. 65535
-
-
posix()
-
See
inet(3); POSIX Error Codes.
-
sctp_option()
-
One of the
SCTP Socket Options.
-
sctp_socket()
-
Socket identifier returned from open/*.
-
timeout() = int() | infinity
-
Timeout used in SCTP connect and receive calls.
EXPORTS
abort(sctp_socket(), Assoc) -> ok | {error, posix()}
Types:
Assoc = #sctp_assoc_change{}
Abnormally terminates the association given by Assoc, without
flushing of unsent data. The socket itself remains open. Other
associations opened on this socket are still valid, and it can be
used in new associations.
close(sctp_socket()) -> ok | {error, posix()}
Completely 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 timeout expires,
the call returns and the data is flushed in the background.
connect(Socket, Addr, Port, Opts) -> {ok,Assoc} | {error, posix()}
Same as connect(Socket, Addr, Port, Opts, infinity).
connect(Socket, Addr, Port, [Opt], Timeout) -> {ok, Assoc} | {error, posix()}
Types:
Socket = sctp_socket()
Addr = ip_address() | Host
Port = port_number()
Opt = sctp_option()
Timeout = timeout()
Host = atom() | string()
Assoc = #sctp_assoc_change{}
Establishes a new association for the socket Socket,
with the peer (SCTP server socket) given by
Addr and Port. The Timeout,
is expressed in milliseconds.
A socket can be associated with multiple peers.
The result of connect/* is an #sctp_assoc_change{}
event which contains, in particular, the new
Association ID:
#sctp_assoc_change{
state = atom(),
error = atom(),
outbound_streams = int(),
inbound_streams = int(),
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 got 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 actual stream numbers on the socket, which may be different
from the requested values (OutStreams and MaxInStreams
respectively) if the peer requires lower values.
The following values of state are possible:
-
comm_up: association successfully established. This
indicates a successful completion of connect.
-
cant_assoc: association cannot be established
(connect/* failure).
All other states do not normally occur in the output from
connect/*. Rather, they may occur in
#sctp_assoc_change{} events received instead of data in
recv/* calls.
All of them indicate losing the association due to various
error conditions, and are listed here for the sake of completeness.
The error field may provide more detailed diagnostics.
-
comm_lost;
-
restart;
-
shutdown_comp.
controlling_process(sctp_socket(), pid()) -> ok
Assigns a new controlling process Pid to Socket. Same implementation
as gen_udp:controlling_process/2.
eof(Socket, Assoc) -> ok | {error, Reason}
Types:
Socket = sctp_socket()
Assoc = #sctp_assoc_change{}
Gracefully terminates the association given by Assoc, with
flushing of all unsent data. The socket itself remains open. Other
associations opened on this socket are still valid, and it can be
used in new associations.
listen(Socket, IsServer) -> ok | {error, Reason}
Types:
Socket = sctp_socket()
IsServer = bool()
Sets up a socket to listen on the IP address and port number
it is bound to. IsServer must be 'true' or 'false'.
In the contrast to TCP, in SCTP there is no listening queue length.
If IsServer is 'true' the socket accepts new associations, i.e.
it will become an SCTP server socket.
open() -> {ok, Socket} | {error, posix()}
open(Port) -> {ok, Socket} | {error, posix()}
open([Opt]) -> {ok, Socket} | {error, posix()}
open(Port, [Opt]) -> {ok, Socket} | {error, posix()}
Types:
Opt = {ip,IP} | {ifaddr,IP} | {port,Port} | sctp_option()
IP = ip_address() | any | loopback
Port = port_number()
Creates an SCTP socket and binds it to the local addresses
specified 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
one free port.
A default set of socket options
is used. In particular, the socket is opened in
binary and
passive mode,
and with reasonably large
kernel and driver
buffers.
recv(sctp_socket()) -> {ok, {FromIP, FromPort, AncData, BinMsg}} | {error, Reason}
recv(sctp_socket(), timeout()) -> {ok, {FromIP, FromPort, AncData, Data}} | {error, Reason}
Types:
FromIP = ip_address()
FromPort = port_number()
AncData = [#sctp_sndrcvinfo{}]
Data = binary() | charlist() | #sctp_sndrcvinfo{} |
#sctp_assoc_change{} | #sctp_paddr_change{} |
#sctp_adaptation_event{}
Reason = posix() | #sctp_send_failed{} | #scpt_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 timeout is infinity.
FromIP and FromPort indicate the sender's address.
AncData is a list of Ancillary Data items which
may 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 default, since such ancillary data
provide an easy way of determining the association and stream
over which the message has been received.
(An alternative way would be to get the Association ID from the
FromIP and FromPort using the
sctp_get_peer_addr_info socket option,
but this would still not produce the Stream number).
The actual Data received may be a binary(),
or list() of bytes (integers in the range 0 through 255)
depending on the socket mode, or an SCTP Event.
The following SCTP Events are possible:
-
#sctp_sndrcvinfo{}
-
#sctp_assoc_change{};
-
#sctp_paddr_change{
addr = ip_address(),
state = atom(),
error = int(),
assoc_id = assoc_id()
}
Indicates change of the status of the peer's IP address given by
addr within the association assoc_id.
Possible values of state (mostly self-explanatory) include:
-
addr_unreachable;
-
addr_available;
-
addr_removed;
-
addr_added;
-
addr_made_prim.
In case of an error (e.g. addr_unreachable), the
error field provides additional diagnostics. In such cases,
the #sctp_paddr_change{} Event is automatically
converted into an error term returned by
gen_sctp:recv. The error field value can be
converted into a string using error_string/1.
-
#sctp_send_failed{
flags = true | false,
error = int(),
info = #sctp_sndrcvinfo{},
assoc_id = assoc_id()
data = binary()
}
The sender may receive this event if a send operation fails.
The flags is a Boolean specifying whether the data have
actually been transmitted over the wire; error provides
extended diagnostics, use error_string/1;
info is the original
#sctp_sndrcvinfo{} record used in the failed
send/*, and data
is 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
returned by recv/*.
-
#sctp_adaptation_event{
adaptation_ind = int(),
assoc_id = assoc_id()
}
Delivered when a peer sends an Adaptation Layer Indication
parameter (configured through the option
sctp_adaptation_layer).
Note that with the current implementation of
the Erlang/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()
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 identification.
However, such a fine level of user control is rarely required.
The send/4 function 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()
Sends Data message over an existing association and given
stream.
error_string(integer()) -> ok | string() | undefined
Translates an SCTP error number from for example
#sctp_remote_error{} or #sctp_send_failed{} into
an explanatory string, or one of the atoms ok for no
error and undefined for an unrecognized error.
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 those options which are explicitly listed below are allowed
for SCTP sockets. Options can be set on the socket using
gen_sctp:open/1,2 or inet:setopts/2,
retrieved using inet:getopts/2, and when calling
gen_sctp:connect/4,5 options can be changed.
-
{mode, list|binary}or just list or binary.
-
Determines the type of data returned from gen_sctp:recv/1,2.
-
{active, true|false|once}
-
-
If false (passive mode, the default),
the caller needs to do an explicit gen_sctp:recv call
in order to retrieve the available data from the socket.
-
If true (full active mode), the pending data or events are
sent to the owning process.
NB: This can cause the message queue to overflow,
as there is no way to throttle the sender in this case
(no flow control!).
-
If once, only one message is automatically placed
in the message queue, after that the mode is automatically
re-set to passive. This provides flow control as well as
the possibility for the receiver to listen for its incoming
SCTP data interleaved with other inter-process messages.
-
{buffer, int()}
-
Determines the size of the user-level software buffer used by
the SCTP driver. Not to be confused with sndbuf
and recbuf options which correspond to
the kernel socket buffers. It is recommended
to have val(buffer) >= max(val(sndbuf),val(recbuf)).
In fact, the val(buffer) is automatically set to
the above maximum when sndbuf or recbuf values are set.
-
{tos, int()}
-
Sets the Type-Of-Service field on the IP datagrams being sent,
to the given value, which effectively determines a prioritization
policy for the outbound packets. The acceptable values
are system-dependent. TODO: we do not provide
symbolic names for these values yet.
-
{priority, int()}
-
A protocol-independent equivalent of tos above. Setting
priority implies setting tos as well.
-
{dontroute, true|false}
-
By default false. If true, the kernel does not
send packets via any gateway, only sends them to directly
connected hosts.
-
{reuseaddr, true|false}
-
By default false. If true, the local binding address
{IP,Port} of the socket can be re-used immediately:
no waiting in the CLOSE_WAIT state is performed (may be
required for high-throughput servers).
-
{linger, {true|false, int()}
-
Determines the timeout in seconds for flushing unsent data in the
gen_sctp:close/1 socket call. If the 1st component of the value
tuple is false, the 2nd one is ignored, which means that
gen_sctp:close/1 returns immediately not waiting
for data to be flushed. Otherwise, the 2nd component is
the flushing time-out in seconds.
-
{sndbuf, int()}
-
The size, in bytes, of the *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, int()}
-
The size, in bytes, of the *kernel* recv 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).
-
{sctp_rtoinfo, #sctp_rtoinfo{}}
-
#sctp_rtoinfo{
assoc_id = assoc_id(),
initial = int(),
max = int(),
min = int()
}
Determines re-transmission time-out parameters, in milliseconds,
for the association(s) given by assoc_id.
If assoc_id = 0 (default) indicates the whole endpoint. See
RFC2960 and
Sockets API Extensions for SCTP for the exact semantics of the fields values.
-
{sctp_associnfo, #sctp_assocparams{}}
-
#sctp_assocparams{
assoc_id = assoc_id(),
asocmaxrxt = int(),
number_peer_destinations = int(),
peer_rwnd = int(),
local_rwnd = int(),
cookie_life = int()
}
Determines association parameters for the association(s) given 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 = int(),
max_instreams = int(),
max_attempts = int(),
max_init_timeo = int()
}
Determines the default parameters which this socket attempts
to negotiate with its peer while establishing an association with it.
Should 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: max number of in-bound streams;
-
max_attempts: max re-transmissions while
establishing an association;
-
max_init_timeo: time-out in milliseconds
for establishing an association.
-
{sctp_autoclose, int()|infinity}
-
Determines the time (in seconds) after which an idle association is
automatically closed.
-
{sctp_nodelay, true|false}
-
Turns on|off the Nagle algorithm for merging small packets
into larger ones (which improves throughput at the expense
of latency).
-
{sctp_disable_fragments, true|false}
-
If true, induces an error on an attempt to send
a message which is larger than the current PMTU size
(which would require fragmentation/re-assembling).
Note that message fragmentation does not affect
the logical atomicity of its delivery; this option
is provided for performance 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, int()}
-
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 given by assoc_id,
{IP,Port} must be one of the peer's addresses.
This option determines that the given address is
treated by the local SCTP stack as the peer's primary address.
-
{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 that it should use {IP, Port}
as the primary address of the local endpoint for the association
given by assoc_id.
-
{sctp_adaptation_layer, #sctp_setadaptation{}}
-
#sctp_setadaptation{
adaptation_ind = int()
}
When set, requests that the local endpoint uses the value given by
adaptation_ind as the Adaptation Indication parameter for
establishing new associations. See
RFC2960 and
Sockets API Extenstions for SCTP for more details.
-
{sctp_peer_addr_params, #sctp_paddrparams{}}
-
#sctp_paddrparams{
assoc_id = assoc_id(),
address = {IP, Port},
hbinterval = int(),
pathmaxrxt = int(),
pathmtu = int(),
sackdelay = int(),
flags = list()
}
IP = ip_address()
Port = port_number()
This option determines various per-address parameters for
the association given by assoc_id and the peer address
address (the SCTP protocol supports multi-homing,
so more than 1 address can correspond to a given association).
-
hbinterval: heartbeat interval, in milliseconds;
-
pathmaxrxt: max number of retransmissions
before this address is considered unreachable (and an
alternative address is selected);
-
pathmtu: fixed Path MTU, if automatic discovery is
disabled (see flags below);
-
sackdelay: delay in milliseconds for SAC messages
(if the delay is enabled, see flags below);
-
flags: the following flags are available:
-
hb_enable: enable heartbeat;
-
hb_disable: disable heartbeat;
-
hb_demand: initiate heartbeat immediately;
-
pmtud_enable: enable automatic Path MTU discovery;
-
pmtud_disable: disable automatic Path MTU discovery;
-
sackdelay_enable: enable SAC delay;
-
sackdelay_disable: disable SAC delay.
-
{sctp_default_send_param, #sctp_sndrcvinfo{}}
-
#sctp_sndrcvinfo{
stream = int(),
ssn = int(),
flags = list(),
ppid = int(),
context = int(),
timetolive = int(),
tsn = int(),
cumtsn = int(),
assoc_id = assoc_id()
}
#sctp_sndrcvinfo{} is used both in this socket option, and as
ancillary data while sending or receiving SCTP messages. When
set as an option, it provides a default values for subsequent
gen_sctp:sendcalls on the association given by
assoc_id. assoc_id = 0 (default) indicates
the whole endpoint. The following fields typically need
to be specified by the sender:
-
sinfo_stream: stream number (0-base) within the association
to send the messages through;
-
sinfo_flags: the following flags are recognised:
-
unordered: the message is to be sent unordered;
-
addr_over: the address specified in
gen_sctp:send overwrites the primary peer address;
-
abort: abort the current association without
flushing any unsent data;
-
eof: gracefully shut down the current
association, with flushing of unsent data.
Other fields are rarely used. See
RFC2960 and
Sockets API Extensions for SCTP for full information.
-
{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 (via recv/*)
along with the data. The only
exception is data_io_event which enables or disables
receiving of
#sctp_sndrcvinfo{}
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 = int()
}
Rarely used. Determines the ACK time
(given by assoc_value in milliseconds) for
the given association or the whole endpoint
if assoc_value = 0 (default).
-
{sctp_status, #sctp_status{}}
-
#sctp_status{
assoc_id = assoc_id(),
state = atom(),
rwnd = int(),
unackdata = int(),
penddata = int(),
instrms = int(),
outstrms = int(),
fragmentation_point = int(),
primary = #sctp_paddrinfo{}
}
This option is read-only. It determines the status of
the SCTP association given by assoc_id. Possible values of
state follows. The state designations are mostly
self-explanatory. state_empty is the default which means
that no other state is active:
-
sctp_state_empty
-
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
The semantics of other fields is the following:
-
sstat_rwnd: the association peer's current receiver
window size;
-
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 will occur;
-
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,
cwnd = int(),
srtt = int(),
rto = int(),
mtu = int()
}
IP = ip_address()
Port = port_number()
This option is read-only. It determines the parameters specific to
the peer's address given by address within the association
given by assoc_id. The address field must 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
association ID. This option is rarely used; see
RFC2960 and
Sockets API Extensions for SCTP for the semantics of all fields.
SCTP EXAMPLES
-
Example of an Erlang SCTP Server which 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) orlese IP == any orelse IP == loopback,
is_integer(Port) ->
{ok,S} = gen_sctp:open([{ip,IP},{port,Port}],[{sctp_recbuf,65536}]),
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("Error: ~p~n", [Data])
end,
server_loop(S).
-
Example of an Erlang SCTP Client which interacts with the above Server.
Note that in this example, the Client creates an association with
the Server with 5 outbound streams. For this reason, 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 the corresponding Event being received on
the Server side.
-module(sctp_client).
-export([client/0, client/1, client/2]).
-include("inet.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).
SEE ALSO
kernel 2.13.1
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