ChannelDispatchOperation — Telepathy D-Bus Interface Specification

# Interface ChannelDispatchOperation

Interface Index (Compact) | Summary | Description | Methods | Signals | Properties

### Methods

HandleWith | (s: Handler) | → | nothing |
Claim | () | → | nothing |
HandleWithTime | (s: Handler, x: UserActionTime) | → | nothing |

### Signals

ChannelLost | (o: Channel, s: Error, s: Message) |
Finished | () |

### Properties

Interfaces | as (DBus_Interface_List) | Read only |  |
Connection | o | Read only |  |
Account | o | Read only |  |
Channels | a(oa{sv}) (Channel_Details_List) | Read only |  |
PossibleHandlers | as (DBus_Well_Known_Name_List) | Read only |  |

Added in 0.17.26. (as a stable interface)

### Description

A channel dispatch operation is an object in the ChannelDispatcher representing a batch of unrequested channels being announced to client Approver processes.

These objects can result from new incoming channels or channels which are automatically created for some reason, but cannot result from outgoing requests for channels.

More specifically, whenever the Connection.Interface.Requests.NewChannels signal contains channels whose Requested property is false, or whenever the Connection.NewChannel signal contains a channel with suppress_handler false, one or more ChannelDispatchOperation objects are created for those channels.

(If some channels in a NewChannels signal are in different bundles, this is an error. The channel dispatcher SHOULD recover by treating the NewChannels signal as if it had been several NewChannels signals each containing one channel.)

First, the channel dispatcher SHOULD construct a list of all the Handlers that could handle all the channels (based on their HandlerChannelFilter property), ordered by priority in some implementation-dependent way. If there are handlers which could handle all the channels, one channel dispatch operation SHOULD be created for all the channels. If there are not, one channel dispatch operation SHOULD be created for each channel, each with a list of channel handlers that could handle that channel.

If no handler at all can handle a channel, the channel dispatcher SHOULD terminate that channel instead of creating a channel dispatcher for it. It is RECOMMENDED that the channel dispatcher closes the channels using Channel.Interface.Destroyable.Destroy if supported, or Channel.Close otherwise. As a special case, the channel dispatcher SHOULD NOT close ContactList channels, and if Close fails, the channel dispatcher SHOULD ignore that channel.

##### Rationale:

ContactList channels are strange. We hope to replace them with something better, such as an interface on the Connection, in a future version of this specification.

When listing channel handlers, priority SHOULD be given to channel handlers that are already handling channels from the same bundle.

If a handler with BypassApproval `= True` could handle all of the channels in the dispatch operation, then the channel dispatcher SHOULD call HandleChannels on that handler, and (assuming the call succeeds) emit Finished and stop processing those channels without involving any approvers.

##### Rationale:

Some channel types can be picked up "quietly" by an existing channel handler. If a Text channel is added to an existing bundle containing a StreamedMedia channel, there shouldn't be any approvers, flashing icons or notification bubbles, if the the UI for the StreamedMedia channel can just add a text box and display the message.

Otherwise, the channel dispatcher SHOULD send the channel dispatch operation to all relevant approvers (in parallel) and wait for an approver to claim the channels or request that they are handled. See AddDispatchOperation for more details on this.

Finally, if the approver requested it, the channel dispatcher SHOULD send the channels to a handler.

# Methods

(Permalink)

## HandleWith (s: Handler) → nothing

### Parameters

- Handler — s (DBus_Bus_Name)

The well-known bus name (starting with `org.freedesktop.Telepathy.Client.`) of the channel handler that should handle the channel, or the empty string if the client has no preferred channel handler.

Called by an approver to accept a channel bundle and request that the given handler be used to handle it.

If successful, this method will cause the ChannelDispatchOperation object to disappear, emitting Finished.

However, this method may fail because the dispatch has already been completed and the object has already gone. If this occurs, it indicates that another approver has asked for the bundle to be handled by a particular handler. The approver MUST NOT attempt to interact with the channels further in this case, unless it is separately invoked as the handler.

Approvers which are also channel handlers SHOULD use Claim instead of HandleWith to request that they can handle a channel bundle themselves.

(FIXME: list some possible errors)

If the channel handler raises an error from HandleChannels, this method MAY respond by raising that same error, even if it is not specifically documented here.

### Possible Errors

- Invalid Argument
The selected handler is non-empty, but is not a syntactically correct DBus_Bus_Name or does not start with "`org.freedesktop.Telepathy.Client.`".
- Not Available
The selected handler is temporarily unable to handle these channels.
- Not Implemented
The selected handler is syntactically correct, but will never be able to handle these channels (for instance because the channels do not match its HandlerChannelFilter, or because HandleChannels raised NotImplemented).
- Not Yours
At the time that HandleWith was called, this dispatch operation was processing an earlier call to HandleWith. The earlier call has now succeeded, so some Handler nominated by another approver is now responsible for the channels. In this situation, the second call to HandleWith MUST NOT return until the first one has returned successfully or unsuccessfully, and if the first call to HandleChannels fails, the channel dispatcher SHOULD try to obey the choice of Handler made by the second call to HandleWith.

(Permalink)

## Claim () → nothing

Called by an approver to claim channels for handling internally. If this method is called successfully, the process calling this method becomes the handler for the channel, but does not have the HandleChannels method called on it.

Clients that call Claim on channels but do not immediately close them SHOULD implement the Handler interface and its HandledChannels property.

Approvers wishing to reject channels MUST call this method to claim ownership of them, and MUST NOT call Close on the channels unless/until this method returns successfully.

##### Rationale:

The channel dispatcher can't know how best to close arbitrary channel types, so it leaves it up to the approver to do so. For instance, for Text channels it is necessary to acknowledge any messages that have already been displayed to the user first - ideally, the approver would display and then acknowledge the messages - or to call Channel.Interface.Destroyable.Destroy if the destructive behaviour of that method is desired.

Similarly, an Approver for StreamedMedia channels can close the channel with a reason (e.g. "busy") if desired. The channel dispatcher, which is designed to have no specific knowledge of particular channel types, can't do that.

If successful, this method will cause the ChannelDispatchOperation object to disappear, emitting Finished, in the same way as for HandleWith.

This method may fail because the dispatch operation has already been completed. Again, see HandleWith for more details. The approver MUST NOT attempt to interact with the channels further in this case.

(FIXME: list some other possible errors)

### Possible Errors

- Not Yours
At the time that Claim was called, this dispatch operation was processing a call to HandleWith which has now succeeded, so some Handler nominated by another approver is now responsible for the channel.

(Permalink)

## HandleWithTime (s: Handler, x: UserActionTime) → nothing

Added in 0.19.6. At the time of writing, no released implementation of the Channel Dispatcher implements this method; clients should fall back to calling HandleWith.

### Parameters

- Handler — s (DBus_Bus_Name)

The well-known bus name (starting with `org.freedesktop.Telepathy.Client.`) of the channel handler that should handle the channel, or the empty string if the client has no preferred channel handler.

- UserActionTime — x (User_Action_Timestamp)

The time at which user action occurred.

A variant of HandleWith allowing the approver to pass an user action time. This timestamp will be passed to the Handler when HandleChannels is called.

### Possible Errors

- Invalid Argument
The selected handler is non-empty, but is not a syntactically correct DBus_Bus_Name or does not start with "`org.freedesktop.Telepathy.Client.`".
- Not Available
The selected handler is temporarily unable to handle these channels.
- Not Implemented
The selected handler is syntactically correct, but will never be able to handle these channels (for instance because the channels do not match its HandlerChannelFilter, or because HandleChannels raised NotImplemented).
- Not Yours
At the time that HandleWith was called, this dispatch operation was processing an earlier call to HandleWith. The earlier call has now succeeded, so some Handler nominated by another approver is now responsible for the channels. In this situation, the second call to HandleWith MUST NOT return until the first one has returned successfully or unsuccessfully, and if the first call to HandleChannels fails, the channel dispatcher SHOULD try to obey the choice of Handler made by the second call to HandleWith.

# Signals

(Permalink)

## ChannelLost (o: Channel, s: Error, s: Message)

### Parameters

- Channel — o
The Channel that closed.
- Error — s (DBus_Error_Name)

The name of a D-Bus error indicating why the channel closed. If no better reason can be found, `org.freedesktop.Telepathy.Error.NotAvailable` MAY be used as a fallback; this means that this error SHOULD NOT be given any more specific meaning.

- Message — s
A string associated with the D-Bus error.

A channel has closed before it could be claimed or handled. If this is emitted for the last remaining channel in a channel dispatch operation, it MUST immediately be followed by Finished.

This signal MUST NOT be emitted until all Approvers that were invoked have returned (successfully or with an error) from their AddDispatchOperation method.

##### Rationale:

This means that Approvers can connect to the ChannelLost signal in a race-free way. Non-approver processes that discover a channel dispatch operation in some way (such as observers) will have to follow the usual "connect to signals then recover state" model - first connect to ChannelLost and Finished, then download Channels (and on error, perhaps assume that the operation has already Finished).

(Permalink)

## Finished ()

Emitted when this dispatch operation finishes. The dispatch operation is no longer present and further methods must not be called on it.

Approvers that have a user interface SHOULD stop notifying the user about the channels in response to this signal; they MAY assume that on errors, they would have received ChannelLost first.

Its object path SHOULD NOT be reused for a subsequent dispatch operation; the ChannelDispatcher MUST choose object paths in a way that avoids immediate re-use.

##### Rationale:

Otherwise, clients might accidentally call HandleWith or Claim on a new dispatch operation instead of the one they intended to handle.

This signal MUST NOT be emitted until all Approvers that were invoked have returned (successfully or with an error) from their AddDispatchOperation method.

##### Rationale:

This means that Approvers can connect to the ChannelLost signal in a race-free way. Non-approver processes that discover a channel dispatch operation in some way (such as observers) will have to follow the usual "connect to signals then recover state" model - first connect to ChannelLost and Finished, then download Channels (and on error, perhaps assume that the operation has already Finished).

# Properties

Accessed using the org.freedesktop.DBus.Properties interface.
(Permalink)

## Interfaces — as (DBus_Interface_List)

Read only
A list of the extra interfaces provided by this channel dispatch operation. This property cannot change.
(Permalink)

## Connection — o

Read only
The Connection with which the Channels are associated. The well-known bus name to use can be derived from this object path by removing the leading '/' and replacing all subsequent '/' by '.'. This property cannot change.
(Permalink)

## Account — o

Read only
The Account with which the Connection and Channels are associated. This property cannot change.
(Permalink)

## Channels — a(oa{sv}) (Channel_Details_List)

Read only
The Channels to be dispatched, and their properties. Change notification is via the ChannelLost signal (channels cannot be added to this property, only removed).
(Permalink)

## PossibleHandlers — as (DBus_Well_Known_Name_List)

Read only

The well known bus names (starting with `org.freedesktop.Telepathy.Client.`) of the possible Handlers for these channels. The channel dispatcher MUST place the most preferred handlers first, according to some reasonable heuristic. As a result, approvers SHOULD use the first handler by default.

The heuristic used to prioritize handlers SHOULD give a higher priority to handlers that are already running.

##### Rationale:

If, for instance, Empathy and Kopete have similar functionality, and Empathy is running, we should prefer to send channels to it rather than launching Kopete via service activation.