# Class SctpMultiChannel

java.lang.Object
java.nio.channels.spi.AbstractInterruptibleChannel
java.nio.channels.SelectableChannel
java.nio.channels.spi.AbstractSelectableChannel
com.sun.nio.sctp.SctpMultiChannel

All Implemented Interfaces:
  `Closeable`, `AutoCloseable`, `Channel`, `InterruptibleChannel`

public abstract class SctpMultiChannel extends AbstractSelectableChannel
A selectable channel for message-oriented SCTP sockets.

An SCTP multi channel supports many associations on a single socket. An `SctpMultiChannel` is created by invoking the `open` method of this class. A newly-created channel is open but not yet bound. An attempt to invoke the `receive` method of an unbound channel will cause the `NotYetBoundException` to be thrown. An attempt to invoke the `send` method of an unbound channel will cause it to first invoke the `bind` method. The address(es) that the channel's socket is bound to can be retrieved by calling `getAllLocalAddresses`.

Messages may be sent and received without explicitly setting up an association with the remote peer. The channel will implicitly setup a new association whenever it sends or receives a message from a remote peer if there is not already an association with that peer. Upon successful association setup, an `association changed` notification will be put to the SCTP stack with its `event` parameter set to `COMM_UP`. This notification can be received by invoking `receive`.

Socket options are configured using the `setOption` method. An `SctpMultiChannel` supports the following options:

> Socket options
> Option Name | Description
> --- | ---
> `SCTP_DISABLE_FRAGMENTS` | Enables or disables message fragmentation
> `SCTP_EXPLICIT_COMPLETE` | Enables or disables explicit message completion
> `SCTP_FRAGMENT_INTERLEAVE` | Controls how the presentation of messages occur for the message receiver
> `SCTP_INIT_MAXSTREAMS` | The maximum number of streams requested by the local endpoint during association initialization
> `SCTP_NODELAY` | Enables or disable a Nagle-like algorithm
> `SCTP_PRIMARY_ADDR` | Requests that the local SCTP stack use the given peer address as the association primary
> `SCTP_SET_PEER_PRIMARY_ADDR` | Requests that the peer mark the enclosed address as the association primary
> `SO_SNDBUF` | The size of the socket send buffer
> `SO_RCVBUF` | The size of the socket receive buffer
> `SO_LINGER` | Linger on close if data is present (when configured in blocking mode only)

Additional (implementation specific) options may also be supported. The list of options supported is obtained by invoking the `supportedOptions` method.

SCTP multi channels are safe for use by multiple concurrent threads. They support concurrent sending and receiving, though at most one thread may be sending and at most one thread may be receiving at any given time.

Since:
  1.7

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `SctpMultiChannel(SelectorProvider provider)`
  Initializes a new instance of this class.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `abstract Set<Association>`
  `associations()`
  Returns the open associations on this channel's socket.
  `final SctpMultiChannel`
  `bind(SocketAddress local)`
  Binds the channel's socket to a local address and configures the socket to listen for connections.
  `abstract SctpMultiChannel`
  `bind(SocketAddress local, int backlog)`
  Binds the channel's socket to a local address and configures the socket to listen for connections.
  `abstract SctpMultiChannel`
  `bindAddress(InetAddress address)`
  Adds the given address to the bound addresses for the channel's socket.
  `abstract SctpChannel`
  `branch(Association association)`
  Branches off an association.
  `abstract Set<SocketAddress>`
  `getAllLocalAddresses()`
  Returns all of the socket addresses to which this channel's socket is bound.
  `abstract <T> T`
  `getOption(SctpSocketOption<T> name, Association association)`
  Returns the value of a socket option.
  `abstract Set<SocketAddress>`
  `getRemoteAddresses(Association association)`
  Returns all of the remote addresses to which the given association on this channel's socket is connected.
  `static SctpMultiChannel`
  `open()`
  Opens an SCTP multi channel.
  `abstract <T> MessageInfo`
  `receive(ByteBuffer buffer, T attachment, NotificationHandler<T> handler)`
  Receives a message and/or handles a notification via this channel.
  `abstract int`
  `send(ByteBuffer buffer, MessageInfo messageInfo)`
  Sends a message via this channel.
  `abstract <T> SctpMultiChannel`
  `setOption(SctpSocketOption<T> name, T value, Association association)`
  Sets the value of a socket option.
  `abstract SctpMultiChannel`
  `shutdown(Association association)`
  Shutdown an association without closing the channel.
  `abstract Set<SctpSocketOption<?>>`
  `supportedOptions()`
  Returns a set of the socket options supported by this channel.
  `abstract SctpMultiChannel`
  `unbindAddress(InetAddress address)`
  Removes the given address from the bound addresses for the channel's socket.
  `final int`
  `validOps()`
  Returns an operation set identifying this channel's supported operations.

  ### Methods declared in class java.nio.channels.spi.AbstractSelectableChannel

  `blockingLock, configureBlocking, implCloseChannel, implCloseSelectableChannel, implConfigureBlocking, isBlocking, isRegistered, keyFor, provider, register`

  ### Methods declared in class java.nio.channels.SelectableChannel

  `register`

  ### Methods declared in class java.nio.channels.spi.AbstractInterruptibleChannel

  `begin, close, end, isOpen`

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

  ### Methods declared in interface java.nio.channels.Channel

  `isOpen`

- ## Constructor Details

  - ### SctpMultiChannel

    protected SctpMultiChannel(SelectorProvider provider)
    Initializes a new instance of this class.
    Parameters:
      `provider` - The selector provider for this channel

- ## Method Details

  - ### open

    public static SctpMultiChannel open() throws IOException
    Opens an SCTP multi channel.

    The new channel is unbound.

    Returns:
      A new SCTP multi channel
    Throws:
      `UnsupportedOperationException` - If the SCTP protocol is not supported
      `IOException` - If an I/O error occurs

  - ### associations

    public abstract Set<Association> associations() throws IOException
    Returns the open associations on this channel's socket.

    Only associations whose `COMM_UP` association change event has been received are included in the returned set of associations. Associations for which a `COMM_LOST` or `SHUTDOWN` association change event have been receive are removed from the set of associations.

    The returned set of associations is a snapshot of the open associations at the time that this method is invoked.

    Returns:
      A `Set` containing the open associations, or an empty `Set` if there are none.
    Throws:
      `ClosedChannelException` - If this channel is closed
      `IOException` - If some other I/O error occurs

  - ### bind

    public abstract SctpMultiChannel bind(SocketAddress local, int backlog) throws IOException
    Binds the channel's socket to a local address and configures the socket to listen for connections.

    This method is used to establish a relationship between the socket and the local address. Once a relationship is established then the socket remains bound until the channel is closed. This relationship may not necesssarily be with the address `local` as it may be removed by `unbindAddress`, but there will always be at least one local address bound to the channel's socket once an invocation of this method successfully completes.

    Once the channel's socket has been successfully bound to a specific address, that is not automatically assigned, more addresses may be bound to it using `bindAddress`, or removed using `unbindAddress`.

    The backlog parameter is the maximum number of pending connections on the socket. Its exact semantics are implementation specific. An implementation may impose an implementation specific maximum length or may choose to ignore the parameter. If the backlog parameter has the value `0`, or a negative value, then an implementation specific default is used.

    Parameters:
      `local` - The local address to bind the socket, or `null` to bind the socket to an automatically assigned socket address
      `backlog` - The maximum number of pending connections
    Returns:
      This channel
    Throws:
      `ClosedChannelException` - If this channel is closed
      `AlreadyBoundException` - If this channel is already bound
      `UnsupportedAddressTypeException` - If the type of the given address is not supported
      `IOException` - If some other I/O error occurs

  - ### bind

    public final SctpMultiChannel bind(SocketAddress local) throws IOException
    Binds the channel's socket to a local address and configures the socket to listen for connections.

    This method works as if invoking it were equivalent to evaluating the expression:

    >      bind(local, 0);

    Parameters:
      `local` - The local address to bind the socket, or `null` to bind the socket to an automatically assigned socket address
    Returns:
      This channel
    Throws:
      `ClosedChannelException` - If this channel is closed
      `AlreadyBoundException` - If this channel is already bound
      `UnsupportedAddressTypeException` - If the type of the given address is not supported
      `IOException` - If some other I/O error occurs

  - ### bindAddress

    public abstract SctpMultiChannel bindAddress(InetAddress address) throws IOException
    Adds the given address to the bound addresses for the channel's socket.

    The given address must not be the `wildcard` address. The channel must be first bound using `bind` before invoking this method, otherwise `NotYetBoundException` is thrown. The `bind` method takes a `SocketAddress` as its argument which typically contains a port number as well as an address. Addresses subquently bound using this method are simply addresses as the SCTP port number remains the same for the lifetime of the channel.

    New associations setup after this method successfully completes will be associated with the given address. Adding addresses to existing associations is optional functionality. If the endpoint supports dynamic address reconfiguration then it may send the appropriate message to the peer to change the peers address lists.

    Parameters:
      `address` - The address to add to the bound addresses for the socket
    Returns:
      This channel
    Throws:
      `ClosedChannelException` - If this channel is closed
      `NotYetBoundException` - If this channel is not yet bound
      `AlreadyBoundException` - If this channel is already bound to the given address
      `IllegalArgumentException` - If address is `null` or the `wildcard` address
      `IOException` - If some other I/O error occurs

  - ### unbindAddress

    public abstract SctpMultiChannel unbindAddress(InetAddress address) throws IOException
    Removes the given address from the bound addresses for the channel's socket.

    The given address must not be the `wildcard` address. The channel must be first bound using `bind` before invoking this method, otherwise `NotYetBoundException` is thrown.

    If this method is invoked on a channel that does not have `address` as one of its bound addresses, or that has only one local address bound to it, then this method throws `IllegalUnbindException`.

    The initial address that the channel's socket is bound to using `bind` may be removed from the bound addresses for the channel's socket.

    New associations setup after this method successfully completes will not be associated with the given address. Removing addresses from existing associations is optional functionality. If the endpoint supports dynamic address reconfiguration then it may send the appropriate message to the peer to change the peers address lists.

    Parameters:
      `address` - The address to remove from the bound addresses for the socket
    Returns:
      This channel
    Throws:
      `ClosedChannelException` - If this channel is closed
      `NotYetBoundException` - If this channel is not yet bound
      `IllegalUnbindException` - `address` is not bound to the channel's socket, or the channel has only one address bound to it
      `IllegalArgumentException` - If address is `null` or the `wildcard` address
      `IOException` - If some other I/O error occurs

  - ### getAllLocalAddresses

    public abstract Set<SocketAddress> getAllLocalAddresses() throws IOException
    Returns all of the socket addresses to which this channel's socket is bound.
    Returns:
      All the socket addresses that this channel's socket is bound to, or an empty `Set` if the channel's socket is not bound
    Throws:
      `ClosedChannelException` - If the channel is closed
      `IOException` - If an I/O error occurs

  - ### getRemoteAddresses

    public abstract Set<SocketAddress> getRemoteAddresses(Association association) throws IOException
    Returns all of the remote addresses to which the given association on this channel's socket is connected.
    Parameters:
      `association` - The association
    Returns:
      All of the remote addresses for the given association, or an empty `Set` if the association has been shutdown
    Throws:
      `ClosedChannelException` - If the channel is closed
      `IOException` - If an I/O error occurs

  - ### shutdown

    public abstract SctpMultiChannel shutdown(Association association) throws IOException
    Shutdown an association without closing the channel.
    Parameters:
      `association` - The association to shutdown
    Returns:
      This channel
    Throws:
      `ClosedChannelException` - If this channel is closed
      `IOException` - If some other I/O error occurs

  - ### getOption

    public abstract <T> T getOption(SctpSocketOption<T> name, Association association) throws IOException
    Returns the value of a socket option.

    Note that some options are retrieved on the channel's socket, therefore the `association` parameter is not applicable and will be ignored if given. However, if the option is association specific then the association must be given.

    Type Parameters:
      `T` - The type of the socket option value
    Parameters:
      `name` - The socket option
      `association` - The association whose option should be retrieved, or `null` if this option should be retrieved at the channel's socket level.
    Returns:
      The value of the socket option. A value of `null` may be a valid value for some socket options.
    Throws:
      `UnsupportedOperationException` - If the socket option is not supported by this channel
      `ClosedChannelException` - If this channel is closed
      `IOException` - If an I/O error occurs
    See Also:
      - `SctpStandardSocketOptions`

  - ### setOption

    public abstract <T> SctpMultiChannel setOption(SctpSocketOption<T> name, T value, Association association) throws IOException
    Sets the value of a socket option.

    Note that some options are retrieved on the channel's socket, therefore the `association` parameter is not applicable and will be ignored if given. However, if the option is association specific then the association must be given.

    Type Parameters:
      `T` - The type of the socket option value
    Parameters:
      `name` - The socket option
      `value` - The value of the socket option. A value of `null` may be a valid value for some socket options.
      `association` - The association whose option should be set, or `null` if this option should be set at the channel's socket level.
    Returns:
      This channel
    Throws:
      `UnsupportedOperationException` - If the socket option is not supported by this channel
      `IllegalArgumentException` - If the value is not a valid value for this socket option
      `ClosedChannelException` - If this channel is closed
      `IOException` - If an I/O error occurs
    See Also:
      - `SctpStandardSocketOptions`

  - ### supportedOptions

    public abstract Set<SctpSocketOption<?>> supportedOptions()
    Returns a set of the socket options supported by this channel.

    This method will continue to return the set of options even after the channel has been closed.

    Returns:
      A set of the socket options supported by this channel

  - ### validOps

    public final int validOps()
    Returns an operation set identifying this channel's supported operations.

    SCTP multi channels support reading, and writing, so this method returns `(``SelectionKey.OP_READ` `|` `SelectionKey.OP_WRITE``)`.

    Specified by:
      `validOps` in class `SelectableChannel`
    Returns:
      The valid-operation set

  - ### receive

    public abstract <T> MessageInfo receive(ByteBuffer buffer, T attachment, NotificationHandler<T> handler) throws IOException
    Receives a message and/or handles a notification via this channel.

    If a message or notification is immediately available, or if this channel is in blocking mode and one eventually becomes available, then the message or notification is returned or handled, respectively. If this channel is in non-blocking mode and a message or notification is not immediately available then this method immediately returns `null`.

    If this method receives a message it is copied into the given byte buffer and an `MessageInfo` is returned. The message is transferred into the given byte buffer starting at its current position and the buffers position is incremented by the number of bytes read. If there are fewer bytes remaining in the buffer than are required to hold the message, or the underlying input buffer does not contain the complete message, then an invocation of `isComplete` on the returned `MessageInfo` will return `false`, and more invocations of this method will be necessary to completely consume the messgae. Only one message at a time will be partially delivered in any stream. The socket option `SCTP_FRAGMENT_INTERLEAVE` controls various aspects of what interlacing of messages occurs.

    If this method receives a notification then the appropriate method of the given handler, if there is one, is invoked. If the handler returns `CONTINUE` then this method will try to receive another message/notification, otherwise, if `RETURN` is returned this method will return `null`. If an uncaught exception is thrown by the handler it will be propagated up the stack through this method.

    This method may be invoked at any time. If another thread has already initiated a receive operation upon this channel, then an invocation of this method will block until the first operation is complete. The given handler is invoked without holding any locks used to enforce the above synchronization policy, that way handlers will not stall other threads from receiving. A handler should not invoke the `receive` method of this channel, if it does an `IllegalReceiveException` will be thrown.

    Type Parameters:
      `T` - The type of the attachment
    Parameters:
      `buffer` - The buffer into which bytes are to be transferred
      `attachment` - The object to attach to the receive operation; can be `null`
      `handler` - A handler to handle notifications from the SCTP stack, or `null` to ignore any notifications.
    Returns:
      The `MessageInfo`, `null` if this channel is in non-blocking mode and no messages are immediately available or the notification handler returns `RETURN` after handling a notification
    Throws:
      `ClosedChannelException` - If this channel is closed
      `AsynchronousCloseException` - If another thread closes this channel while the read operation is in progress
      `ClosedByInterruptException` - If another thread interrupts the current thread while the read operation is in progress, thereby closing the channel and setting the current thread's interrupt status
      `NotYetBoundException` - If this channel is not yet bound
      `IllegalReceiveException` - If the given handler invokes the `receive` method of this channel
      `IOException` - If some other I/O error occurs

  - ### send

    public abstract int send(ByteBuffer buffer, MessageInfo messageInfo) throws IOException
    Sends a message via this channel.

    If this channel is unbound then this method will invoke `bind(null, 0)` before sending any data.

    If there is no association existing between this channel's socket and the intended receiver, identified by the address in the given messageInfo, then one will be automatically setup to the intended receiver. This is considered to be Implicit Association Setup. Upon successful association setup, an `association changed` notification will be put to the SCTP stack with its `event` parameter set to `COMM_UP` . This notification can be received by invoking `receive`.

    If this channel is in blocking mode, there is sufficient room in the underlying output buffer, then the remaining bytes in the given byte buffer are transmitted as a single message. Sending a message is atomic unless explicit message completion `SCTP_EXPLICIT_COMPLETE` socket option is enabled on this channel's socket.

    If this channel is in non-blocking mode, there is sufficient room in the underlying output buffer, and an implicit association setup is required, then the remaining bytes in the given byte buffer are transmitted as a single message, subject to `SCTP_EXPLICIT_COMPLETE`. If for any reason the message cannot be delivered an `association changed` notification is put on the SCTP stack with its `event` parameter set to `CANT_START`.

    The message is transferred from the byte buffer as if by a regular `write` operation.

    This method may be invoked at any time. If another thread has already initiated a send operation upon this channel, then an invocation of this method will block until the first operation is complete.

    Parameters:
      `buffer` - The buffer containing the message to be sent
      `messageInfo` - Ancillary data about the message to be sent
    Returns:
      The number of bytes sent, which will be either the number of bytes that were remaining in the messages buffer when this method was invoked or, if this channel is non-blocking, may be zero if there was insufficient room for the message in the underlying output buffer
    Throws:
      `InvalidStreamException` - If `streamNumber` is negative, or if an association already exists and `streamNumber` is greater than the maximum number of outgoing streams
      `ClosedChannelException` - If this channel is closed
      `AsynchronousCloseException` - If another thread closes this channel while the read operation is in progress
      `ClosedByInterruptException` - If another thread interrupts the current thread while the read operation is in progress, thereby closing the channel and setting the current thread's interrupt status
      `IOException` - If some other I/O error occurs

  - ### branch

    public abstract SctpChannel branch(Association association) throws IOException
    Branches off an association.

    An application can invoke this method to branch off an association into a separate channel. The new bound and connected `SctpChannel` will be created for the association. The branched off association will no longer be part of this channel.

    This is particularly useful when, for instance, the application wishes to have a number of sporadic message senders/receivers remain under the original SCTP multi channel but branch off those associations carrying high volume data traffic into their own separate SCTP channels.

    Parameters:
      `association` - The association to branch off
    Returns:
      The `SctpChannel`
    Throws:
      `ClosedChannelException` - If this channel is closed
      `IOException` - If some other I/O error occurs