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The channel dispatcher is responsible for responding to new channels and launching client processes to handle them. It also provides functionality for client processes to request that new channels are created.

If a channel dispatcher is running, it is responsible for dispatching new channels on all Connections created by the AccountManager. Connections not created by the AccountManager are outside the scope of the channel dispatcher.

Connections created by standalone Telepathy clients that do not intend to interact with the channel dispatcher should be ignored - otherwise, the channel dispatcher would try to launch handlers for channels that the standalone client was already handling internally.

The current channel dispatcher is defined to be the process that owns the well-known bus name org.freedesktop.Telepathy.ChannelDispatcher on the session bus. This process MUST export an object with this interface at the object path /org/freedesktop/Telepathy/ChannelDispatcher.

Until a mechanism exists for making a reasonable automatic choice of ChannelDispatcher implementation, implementations SHOULD NOT register as an activatable service for the ChannelDispatcher's well-known bus name. Instead, it is RECOMMENDED that some component of the user's session will select and activate a particular implementation, and that other Telepathy-enabled programs can detect whether channel request/dispatch functionality is available by checking whether the ChannelDispatcher's well-known name is in use at runtime.

There are three categories of client process defined by this specification:

Observer: Observers monitor the creation of new channels. This functionality can be used for things like message logging. All observers are notified simultaneously.
Approver: Approvers notify the user that new channels have been created, and also select which channel handler will be used for the channel, either by asking the user or by choosing the most appropriate channel handler.
Handler: Each new channel or set of channels is passed to exactly one handler as its final destination. A typical channel handler is a user interface process handling channels of a particular type.

A list of the extra interfaces provided by this channel dispatcher.

Start a request to create a channel. This initially just creates a ChannelRequest.DRAFT object, which can be used to continue the request and track its success or failure.

The request can take a long time - in the worst case, the channel dispatcher has to ask the account manager to put the account online, the account manager has to ask the operating system to obtain an Internet connection, and the operating system has to ask the user whether to activate an Internet connection using an on-demand mechanism like dialup.

This means that using a single D-Bus method call and response to represent the whole request will tend to lead to that call timing out, which is not the behaviour we want.

If this method is called for an Account that is disabled, invalid or otherwise unusable, no error is signalled until ChannelRequest.DRAFT.Proceed is called, at which point ChannelRequest.DRAFT.Failed is emitted with an appropriate error.

This means there's only one code path for errors, apart from InvalidArgument for "that request makes no sense".

It also means that the request will proceed if the account is enabled after calling CreateChannel, but before calling Proceed.

The Account for which the new channel is to be created.

A dictionary containing desirable properties. This has the same semantics as the corresponding parameter to Connection.Interface.Requests.CreateChannel.

Certain properties will not necessarily make sense in this dictionary: for instance, TargetHandle can only be given if the requester is able to interact with a Connection to the desired account.

The time at which user action occurred, or 0 if this channel request is for some reason not involving user action. The UserActionTime property will be set to this value, and it will eventually be passed as the User_Action_Time parameter of HandleChannels.

Either the well-known bus name (starting with org.freedesktop.Telepathy.Client.) of the preferred handler for this channel, or an empty string to indicate that any handler would be acceptable. The channel dispatcher SHOULD dispatch as many as possible of the resulting channels (ideally, all of them) to that handler, and SHOULD remember the preferred handler so it can try to dispatch subsequent channels in the same bundle to the same handler.

This must be the well-known bus name, not the unique name, to ensure that all handlers do indeed have the Client API, and the Client object on the handler can be located easily.

This is partly so the channel dispatcher can call HandleChannels on it, and partly so the channel dispatcher can recover state if it crashes and is restarted.

If this is a well-known bus name, the channel dispatcher SHOULD call AddRequest on that Handler after this method has returned.

This ordering allows a Handler which calls CreateChannel with itself as the preferred handler to associate the call to AddRequest with that call.

A ChannelRequest.DRAFT object.

The Preferred_Handler is syntactically invalid or does not start with org.freedesktop.Telepathy.Client., the Account does not exist, or one of the Requested_Properties is invalid

Start a request to ensure that a channel exists, creating it if necessary. This initially just creates a ChannelRequest.DRAFT object, which can be used to continue the request and track its success or failure.

The rationale is as for CreateChannel.

The Account for which the new channel is to be created.

A dictionary containing desirable properties. This has the same semantics as the corresponding parameter to Connection.Interface.Requests.EnsureChannel.

Certain properties will not necessarily make sense in this dictionary: for instance, TargetHandle can only be given if the requester is able to interact with a Connection to the desired account.

Either the well-known bus name (starting with org.freedesktop.Telepathy.Client.) of the preferred handler for this channel, or an empty string to indicate that any handler would be acceptable.

This must be the well-known bus name, not the unique name, to ensure that all handlers do indeed have the Client API, and the Client object on the handler can be located easily.

This is partly so the channel dispatcher can call HandleChannels on it, and partly so the channel dispatcher can recover state if it crashes and is restarted.

If this is a well-known bus name, the channel dispatcher SHOULD call AddRequest on that Handler after this method has returned.

This ordering allows a Handler which calls EnsureChannel with itself as the preferred handler to associate the call to AddRequest with that call.

If any new channels are created in response to this request, the channel dispatcher SHOULD dispatch as many as possible of the resulting channels (ideally, all of them) to that handler, and SHOULD remember the preferred handler so it can try to dispatch subsequent channels in the same bundle to the same handler. If the requested channel already exists (that is, Connection.Interface.Requests.EnsureChannel returns Yours=False) then the channel dispatcher SHOULD re-dispatch the channel to its existing handler, and MUST NOT dispatch it to this client (unless it is the existing handler); the request is still deemed to have succeeded in this case.

An address book application, for example, might call EnsureChannel to ensure that a text channel with a particular contact is displayed to the user; it does not care whether a new channel was made. An IM client might call EnsureChannel in response to the user double-clicking an entry in the contact list, with itself as the Preferred_Handler; if the user already has a conversation with that contact in another application, they would expect the existing window to be presented, rather than their double-click leading to an error message. So the request should succeed, even if its Preferred_Handler is not used.

A ChannelRequest.DRAFT object.

The Preferred_Handler is syntactically invalid or does not start with org.freedesktop.Telepathy.Client., the Account does not exist, or one of the Requested_Properties is invalid