We distinguish two Channel components : ChannelIn and ChannelOut.

• ChannelIn are used to receive messages from other address spaces.
• ChannelOut are used to send messages to other address spaces.

This package contains various Channel implementations. They are based on a socket abstraction. A socket provides an input, an output, and a method to close it (see {@link org.objectweb.dream.channel.SocketState} interface).

Channel components use the {@link org.objectweb.dream.message.codec.MessageCodec} interface to encode and decode messages using the socket's input or output.

Channel components are composite components build as follows:

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PushChannelOut components are made of:

• A GenericPushChannelOut component (implemented by {@link org.objectweb.dream.channel.GenericPushChannelOutImpl}). When this component receives a message on its {@link org.objectweb.dream.Push} interface, it uses a {@link org.objectweb.dream.channel.SocketManager} to retrieve a socket allowing sending the message. Then it uses a {@link org.objectweb.dream.message.codec.MessageCodec} to encode the message. Finally, if the component is bound to a component providing a {@link org.objectweb.dream.channel.WaitByte} interface, it waits for an acknowledgement.
• SocketManager components. These components have an interface allowing the GenericPushChannelOut component to retrieve an appropriate {@link org.objectweb.dream.channel.SocketState} object for each message to be sent. They proceed as follows: they first choose a ChannelIn, then they find a socket allowing sending the message to the chosen ChannelIn.
  These two steps are achieved by different components. The identification of a ChannelIn depends on the socket implementation. For example, TCP Channels use an inet address and a port to identify an ChannelIn. So components responsible for finding a socket provide the {@link org.objectweb.dream.channel.IPSocketManager} interface (see {@link org.objectweb.dream.channel.IPSocketManagerTCPImpl} component).
  The dream library currently provides the following SocketManager components:
  • {@link org.objectweb.dream.channel.SocketManagerIPStaticImpl} statically identifies a ChannelIn using its attribute controller interface ({@link org.objectweb.dream.channel.SocketManagerIPStaticAttributeController}).
  • {@link org.objectweb.dream.channel.SocketManagerIPChunkBasedImpl} identifies a ChannelIn by retrieving a {@link org.objectweb.dream.channel.IPChannelDestinationChunk} chunk in each message. The name of the chunk can be configured using the attribute controller interface ({@link org.objectweb.dream.channel.SocketManagerIPChunkBasedAttributeController}).
  • {@link org.objectweb.dream.channel.IPSocketManagerTCPImpl} creates a socket using given inet address and port. The release method simply closes the socket state.
  • {@link org.objectweb.dream.channel.IPSocketManagerCachingImpl} manages a cache of sockets. If the required socket cannot be found in the cache or is closed, this component delegates to another IPSocketManager. The cache size can be configured using an attribute controller.
    If a socket is required twice without being released, an exception is thrown.
• An optional WaitAck component can be used to wait an acknowledgment on the input of the socket used to send the message. If the received byte is not null, an exception is thrown.

PushChannelIn are made of:

• A GenericPushChannelIn component (implemented by {@link org.objectweb.dream.channel.GeneriquePushChannelIn}). When this component receives a socket on its {@link org.objectweb.dream.channel.OpenedSocket} interface, it uses a {@link org.objectweb.dream.message.codec.MessageCodec} to decode the incoming message. Then, if the component is bound to a component providing a {@link org.objectweb.dream.channel.SendByte} interface, it sends an acknowledgement.
• OpenedSocketManager components. These components are responsible for providing GenericPushChannelIn component with {@link org.objectweb.dream.channel.SocketState} objects allowing reading a message.

The Dream library currently provides the following TCPPushChannelOut components:

• TCPPushChannelOutMonoDestination(inetAdress, port) sends every message to the given inetAdress and port. It uses a persistent connection.
• TCPPushChannelOutIpChunkMonoDestination(chunkName, deleteChunk) sends each message to the destination contained in the chunk whose name is given as argument. If deleteChunk is true the destination chunk is removed before the message is sent. The connection is closed after the message is sent.
• TCPPushChannelOutIPChunkMultiDestination(nbMaxConn, chunkName, deleteChunk), as previous channel, this one uses a chunk to know the destination of each message. It manages a pool of opened socket; the size of this pool is given by the nbMaxConn argument. If the pool is full and a message must be sent using a socket which is not in the pool, the oldest socket is closed.