Channel — Telepathy D-Bus Interface Specification

# Interface Channel

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

### Methods

Close | () | → | nothing |
GetChannelType | () | → | s: Channel_Type | (deprecated)
GetHandle | () | → | u: Target_Handle_Type, u: Target_Handle | (deprecated)
GetInterfaces | () | → | as: Interfaces | (deprecated)

### Signals

Closed | () |

### Properties

ChannelType | s (DBus_Interface) | Read only |  |
Interfaces | as (DBus_Interface_List) | Read only |  |
TargetHandle | u (Handle) | Read only |  |
TargetID | s | Read only |  |
TargetHandleType | u (Handle_Type) | Read only |  |
Requested | b | Read only |  |
InitiatorHandle | u (Contact_Handle) | Read only |  |
InitiatorID | s | Read only |  |

Changed in 0.17.7. Previously we guaranteed that, for any handle type other than Handle_Type_None, and for any channel type and any handle, there would be no more than one channel with that combination of channel type, handle type and handle. This guarantee has now been removed in order to accommodate features like message threads.
Changed in 0.17.10. Previously we did not explicitly guarantee that Channels' object paths had the Connection's object path as a prefix.

### Description

All communication in the Telepathy framework is carried out via channel objects which are created and managed by connections. This interface must be implemented by all channel objects, along with one single channel type, such as Channel.Type.ContactList which represents a list of people (such as a buddy list) or Channel.Type.Text which represents a channel over which textual messages are sent and received.

Each Channel's object path MUST start with the object path of its associated Connection, followed by '/'. There MAY be any number of additional object-path components, which clients MUST NOT attempt to parse.

##### Rationale:

This ensures that Channel object paths are unique, even between Connections and CMs, because Connection object paths are guaranteed-unique via their link to the well-known bus name.

If all connection managers in use are known to comply with at least spec version 0.17.10, then the Connection's object path can even be determined from the Channel's without any additional information, by taking the first 7 components.

Each channel has a number of immutable properties (which cannot vary after the channel has been announced with NewChannels), provided to clients in the ObserveChannels, AddDispatchOperation and HandleChannels methods to permit immediate identification of the channel. This interface contains immutable properties common to all channels. In brief:

- ChannelType specifies the kind of communication carried out on this channel;
- TargetHandleType, TargetHandle and TargetID specify the entity with which this channel communicates, such as the other party in a 1-1 call, or the name of a multi-user chat room;
- InitiatorHandle and InitiatorID specify who created this channel;
- Requested indicates whether the local user requested this channel, or whether it is an incoming call, a text conversation started by a remote contact, a chatroom invitation, etc.

Other optional Interfaces can be implemented to indicate other available functionality, such as Channel.Interface.Group if the channel contains a number of contacts, Channel.Interface.Password to indicate that a channel may have a password set to require entry, and Channel.Interface.ChatState for typing notifications. The interfaces implemented may not vary after the channel has been created. These other interfaces (along with the interface named by ChannelType) may themselves specify immutable properties to be announced up-front along with the properties on this interface.

Some channels are “anonymous”, with TargetHandleType set to `None`, which indicates that the channel is defined by some other properties. For instance, transient ad-hoc chat rooms may be defined only by their members (as visible through the Group interface), and ContactSearch channels represent a single search attempt for a particular Server.

Specific connection manager implementations may implement channel types and interfaces which are not contained within this specification in order to support further functionality. To aid interoperability between client and connection manager implementations, the interfaces specified here should be used wherever applicable, and new interfaces made protocol-independent wherever possible. Because of the potential for 3rd party interfaces adding methods or signals with conflicting names, the D-Bus interface names should always be used to invoke methods and bind signals.

# Methods

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## Close () → nothing

Request that the channel be closed. This is not the case until the Closed signal has been emitted, and depending on the connection manager this may simply remove you from the channel on the server, rather than causing it to stop existing entirely. Some channels such as contact list channels may not be closed.

### Possible Errors

- Disconnected
The connection is not currently connected and cannot be used. This error may also be raised when operations are performed on a Connection for which StatusChanged has signalled status Disconnected for reason None.

##### Rationale:

The second usage corresponds to None in the Connection_Status_Reason enum; if a better reason is available, the corresponding error should be used instead.
- Network Error
Raised when there is an error reading from or writing to the network.
- Not Implemented
This channel may never be closed, e.g. a contact list
- Not Available
This channel is not currently in a state where it can be closed, e.g. a non-empty user-defined contact group

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## GetChannelType () → s: Channel_Type

Deprecated since 0.17.7. Use the ChannelType property if possible.

### Returns

- Channel_Type — s (DBus_Interface)
The interface name

Returns the interface name for the type of this channel. Clients SHOULD use the ChannelType property instead, falling back to this method only if necessary.

##### Rationale:

The GetAll method lets clients retrieve all properties in one round-trip.
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## GetHandle () → u: Target_Handle_Type, u: Target_Handle

Deprecated since 0.17.7. Use the TargetHandleType and TargetHandle properties if possible.

### Returns

- Target_Handle_Type — u (Handle_Type)
The same as TargetHandleType.
- Target_Handle — u (Handle)
The same as TargetHandle.

Returns the handle type and number if this channel represents a communication with a particular contact, room or server-stored list, or zero if it is transient and defined only by its contents. Clients SHOULD use the TargetHandle and TargetHandleType properties instead, falling back to this method only if necessary.

##### Rationale:

The GetAll method lets clients retrieve all properties in one round-trip.
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## GetInterfaces () → as: Interfaces

Deprecated since 0.17.7. Use the Interfaces property if possible.

### Returns

- Interfaces — as (DBus_Interface_List)
An array of the D-Bus interface names

Get the optional interfaces implemented by the channel. Clients SHOULD use the Interfaces property instead, falling back to this method only if necessary.

##### Rationale:

The GetAll method lets clients retrieve all properties in one round-trip.

# Signals

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## Closed ()

Emitted when the channel has been closed. Method calls on the channel are no longer valid after this signal has been emitted, and the connection manager may then remove the object from the bus at any point.

# Properties

Accessed using the org.freedesktop.DBus.Properties interface.
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## ChannelType — s (DBus_Interface)

Read only
Added in 0.17.7.

The channel's type. This cannot change once the channel has been created.

For compatibility between older connection managers and newer clients, if this is unavailable or is an empty string, clients MUST use the result of calling GetChannelType.

##### Rationale:

The GetAll method lets clients retrieve all properties in one round-trip, which is desirable.

When requesting a channel, the request MUST specify a channel type, and the request MUST fail if the specified channel type cannot be supplied.

##### Rationale:

Common sense.
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## Interfaces — as (DBus_Interface_List)

Read only
Added in 0.17.7.

Extra interfaces provided by this channel. This SHOULD NOT include the channel type and the Channel interface itself, and cannot change once the channel has been created.

For compatibility between older connection managers and newer clients, if this is unavailable, or if this is an empty list and ChannelType is an empty string, clients MUST use the result of calling GetInterfaces instead. If this is an empty list but ChannelType is non-empty, clients SHOULD NOT call GetInterfaces; this implies that connection managers that implement the ChannelType property MUST also implement the Interfaces property correctly.

##### Rationale:

The GetAll method lets clients retrieve all properties in one round-trip, which is desirable.

When requesting a channel with a particular value for this property, the request must fail without side-effects unless the connection manager expects to be able to provide a channel whose interfaces include at least the interfaces requested.

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## TargetHandle — u (Handle)

Read only
Added in 0.17.7.

The handle (a representation for the identifier) of the contact, chatroom, etc. with which this handle communicates. Its type is given by the TargetHandleType property.

This is fixed for the lifetime of the channel, so channels which could potentially be used to communicate with multiple contacts, and do not have an identity of their own (such as a Handle_Type_Room handle), must have TargetHandleType set to Handle_Type_None and TargetHandle set to 0.

Unlike in the telepathy-spec 0.16 API, there is no particular uniqueness guarantee - there can be many channels with the same (channel type, handle type, handle) tuple. This is necessary to support conversation threads in XMPP and SIP, for example.

If this is present in a channel request, it must be nonzero, TargetHandleType MUST be present and not Handle_Type_None, and TargetID MUST NOT be present. Properties from Addressing1 MUST NOT be present.

The channel that satisfies the request MUST either:

- have the specified TargetHandle property; or
- have TargetHandleType = Handle_Type_None, TargetHandle = 0, and be configured such that it could communicate with the specified handle in some other way (e.g. have the requested contact handle in its Group interface)

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## TargetID — s

Read only
Added in 0.17.9.

The string that would result from inspecting the TargetHandle property (i.e. the identifier in the IM protocol of the contact, room, etc. with which this channel communicates), or the empty string if the TargetHandle is 0.

##### Rationale:

The presence of this property avoids the following race condition:

- New channel C is signalled with target handle T
- Client calls InspectHandles(CONTACT, [T])
- Channel C closes, removing the last reference to handle T
- InspectHandles(CONTACT, [T]) returns an error

If this is present in a channel request, TargetHandleType MUST be present and not Handle_Type_None, and TargetHandle MUST NOT be present. Properties from Addressing1 MUST NOT be present.The request MUST fail with error InvalidHandle, without side-effects, if the requested TargetID would not be accepted by RequestHandles.

The returned channel must be related to the handle corresponding to the given identifier, in the same way as if TargetHandle had been part of the request instead.

##### Rationale:

Requesting channels with a string identifier saves a round-trip (the call to RequestHandles). It also allows the channel dispatcher to accept a channel request for an account that is not yet connected (and thus has no valid handles), bring the account online, and pass on the same parameters to the new connection's CreateChannel method.

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## TargetHandleType — u (Handle_Type)

Read only
Added in 0.17.7.

The type of TargetHandle.

If this is omitted from a channel request, connection managers SHOULD treat this as equivalent to Handle_Type_None.

If this is omitted or is Handle_Type_None, TargetHandle and TargetID MUST be omitted from the request.

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## Requested — b

Read only
Added in 0.17.13. (as stable API)

True if this channel was created in response to a local request, such as a call to Connection.RequestChannel or Connection.Interface.Requests.CreateChannel.

##### Rationale:

The idea of this property is to distinguish between "incoming" and "outgoing" channels, in a way that doesn't break down when considering special cases like contact lists that are automatically created on connection to the server, or chatrooms that an IRC proxy/bouncer like irssi-proxy or bip was already in.

The reason we want to make that distinction is that UIs for things that the user explicitly requested should start up automatically, whereas for incoming messages and VoIP calls we should first ask the user whether they want to open the messaging UI or accept the call.

If the channel was not explicitly requested (even if it was created as a side-effect of a call to one of those functions, e.g. because joining a Tube in a MUC context on XMPP implies joining that MUC), then this property is false.

For compatibility with older connection managers, clients SHOULD assume that this property is true if they see a channel announced by the Connection.NewChannel signal with the suppress_handler parameter set to true.

##### Rationale:

In a correct connection manager, the only way to get such a channel is to request it.

Clients MAY additionally assume that this property is false if they see a channel announced by the NewChannel signal with the suppress_handler parameter set to false.

##### Rationale:

This is more controversial, since it's possible to get that parameter set to false by requesting a channel. However, there's no good reason to do so, and we've deprecated this practice.

In the particular case of the channel dispatcher, the only side-effect of wrongly thinking a channel is unrequested is likely to be that the user has to confirm that they want to use it, so it seems fairly harmless to assume in the channel dispatcher that channels with suppress_handler false are indeed unrequested.

It does not make sense for this property to be in channel requests—it will always be true for channels returned by CreateChannel, and callers of EnsureChannel cannot control whether an existing channel was originally requested locally—so it MUST NOT be accepted.

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## InitiatorHandle — u (Contact_Handle)

Read only
Added in 0.17.13. (as stable API)

The contact who initiated the channel; for instance, the contact who invited the local user to a chatroom, or the contact who initiated a call.

This does not necessarily represent the contact who created the underlying protocol-level construct. For instance, if Rob creates a chatroom, Will joins that chatroom, and Will invites Simon to join it, then Simon will see Will as the InitiatorHandle of the channel representing the chatroom.

##### Rationale:

The room creator is generally a less useful piece of information than the inviter, is less likely to be available at invitation time (i.e. can't necessarily be an immutable property), and is less likely to be available at all. The creator of a chatroom is not currently available via Telepathy; if added in future, it is likely to be made available as a property on the Chatroom interface (bug 23151).

For channels requested by the local user, this MUST be the value of Connection.SelfHandle at the time the channel was created (i.e. not a channel-specific handle).

##### Rationale:

On some protocols, the SelfHandle may change (as signalled by Connection.SelfHandleChanged), but this property is immutable. Hence, locally-requested channels' InitiatorHandle and InitiatorID may not match the current SelfHandle; Requested can be used to determine whether the channel was created locally.

For channels requested by a remote user, this MUST be their handle. If unavailable or not applicable, this MUST be 0 (for instance, contact lists are not really initiated by anyone in particular, and it's easy to imagine a protocol where chatroom invitations can be anonymous).

For channels with the Group interface, this SHOULD be the same contact who is signalled as the "Actor" causing the self-handle to be placed in the local-pending set.

This SHOULD NOT be a channel-specific handle, if possible.

It does not make sense for this property to be in channel requests - the initiator will always be the local user - so it MUST NOT be accepted.

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## InitiatorID — s

Read only
Added in 0.17.13. (as stable API)

The string that would result from inspecting the InitiatorHandle property (i.e. the initiator's identifier in the IM protocol).

##### Rationale:

The presence of this property avoids the following race condition:

- New StreamedMedia channel C is signalled with initiator handle I
- Client calls InspectHandles(CONTACT, [I])
- Channel C closes, removing the last reference to handle I
- InspectHandles(CONTACT, [I]) returns an error
- Client can indicate that a call was missed, but not who called!

It does not make sense for this property to be in channel requests - the initiator will always be the local user - so it MUST NOT be accepted.