517 lines
18 KiB
Plaintext
517 lines
18 KiB
Plaintext
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! title Non Session Management API
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! author Jonathan Moore Liles #(email,male@tuxfamily.org)
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! date August 1, 2010
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-- Table Of Contents
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: Non Session Management API version 0.8
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The Non Session Management API is used by the various components of
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the Non audio production suite to allow any number of independent
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programs to be managed together as part of a logical session (i.e. a
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song). Thus, operations such as loading and saving are synchronized.
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The API comprises a simple Open Sound Control (OSC) based protocol,
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along with some behavioral guidelines, which can easily be
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implemented by various applications.
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The Non project contains an program called `nsmd` which is an
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implementation of the server side of the NSM API. `nsmd` is
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controlled by the `non-session-manager` GUI. However, the same
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server-side API can also be implemented by other session managers
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(such as LADISH), although consistency and robustness will likely
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suffer if non-NSM compliant clients are allowed to participate in a
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session.
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The only dependency for client implementations `liblo` (the OSC
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library), which several Linux audio applications already link to or
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plan to link to in the future.
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The aim of this project is to thoroughly define the behavior
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required of clients. This is an area where other attempts at session
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management (LASH and JACK-Session) have failed. Often the difficulty
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with these systems has been not in implementing support for them,
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but in attempting to interpret the confusing, ambiguous, or
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ill-conceived API documentation. For these reasons and more all
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previous attempts at Linux audio session management protocols are
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considered harmful.
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You *WILL* see some unambiguous and emphatic language in this
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document. For the good of the user, these rules are meant to be
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followed and are non-negotiable. If an application does not conform
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to this specification it should be considered broken. Consistency
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across applications under session management is very important for a
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good user experience.
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:: Client Behavior Under Session Management
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Most graphical applications make available to the user a common set
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of file operations, typically presented under a File or Project
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menu.
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These are: New, Open, Save, Save As, Close and Quit or Exit.
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The following sub-sections describe how these options should behave when
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the application is part of an NSM session. These rules only apply
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when session management is active (that is, after the `announce`
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handshake described in the #(ref,NSM OSC Protocol) section).
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In order to provide a consistent and predictable user experience, it
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is critically important for applications to adhere to these
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guidelines.
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::: New
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This option may empty\/reset the current file or project (possibly
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after user confirmation). *UNDER NO CIRCUMSTANCES* should it allow
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the user to create a new project\/file in another location.
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::: Open
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This option *MUST* be disabled.
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The application may, however, elect to implement an option called
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'Import into Session', creates a copy of a file\/project which is
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then saved at the session path provided by NSM.
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::: Save
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This option should behave as normal, saving the current
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file\/project as established by the NSM `open` message.
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*UNDER NO CIRCUMSTANCES* should this option present the user with a
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choice of where to save the file.
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::: Save As
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This option *MUST* be disabled.
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The application may, however, elect to implement an option called
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'Export from Session', which creates a copy of the current
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file\/project which is then saved in a user-specified location
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outside of the session path provided by NSM.
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::: Close (as distinguished from Quit or Exit)
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This option *MUST* be disabled unless its meaning is to disconnect
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the application from session management.
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::: Quit or Exit
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This option may behave as normal (even possibly asking the user to
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confirm exiting).
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:: NSM OSC Protocol
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All message parameters are *REQUIRED*. All messages *MUST* be sent
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from the same socket as the `announce` message, using the
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`lo\_send\_from` method of liblo or its equivalent, as the server uses
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the return addresses to distinguish between clients.
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::: Establishing a Connection
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:::: Announce
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At launch, the client *MUST* check the environment for the value of
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`NSM\_URL`. If present, the client *MUST* send the following message
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to the provided address as soon as it is ready to respond to the
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`\/nsm\/client\/open` event:
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> /nsm/server/announce s:application_name s:capabilities i:api_version_major i:api_version_minor i:pid
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If `NSM\_URL` is undefined, invalid, or unreachable, then the client
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should proceed assuming that session management is unavailable.
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`api\_version\_major` and `api\_version\_minor` must be the two
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parts of the version number of the NSM API as defined by this
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document.
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Note that if the application intends to register JACK clients,
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`application\_name` *MUST* be the same as the name that would
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normally by passed to `jack\_client\_open`. For example, Non-Mixer
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sends "Non-Mixer" as its `application\_name`. Applications *MUST
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NOT* register their JACK clients until receiving an `open` message;
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the `open` message will provide a unique client name prefix suitable
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for passing to JACK. This is probably the most complex requirement
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of the NSM API, but it isn't difficult to implement, especially if
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the application simply wishes to delay its initialization process
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for up to one second while awaiting the `announce` reply and
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subsequent `open` message.
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`capabilities` *MUST* be a string containing a colon separated list
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of the special capabilities the client
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possesses. e.g. ":dirty:switch:progress:"
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// Available Client Capabilities
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[[ Name, Description
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[[ switch, client is capable of responding to multiple `open` messages without restarting
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[[ dirty, client knows when it has unsaved changes
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[[ progress, client can send progress updates during time-consuming operations
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[[ message, client can send textual status updates
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:::: Response
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The server will respond to the client's `announce` message with the
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following message:
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> /reply "/nsm/server/announce" s:message s:name_of_session_manager s:capabilities
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`message` is a welcome message.
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The value of `name\_of\_session\_manager` will depend on the
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implementation of the NSM server. It might say "Non Session
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Manager", or it might say "LADISH". This is for display to the user.
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`capabilities` will be a string containing a colon separated list of
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special server capabilities.
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Presently, the server `capabilities` are:
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// Available Server Capabilities
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[[ Name, Description
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[[ server_control, client-to-server control
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A client should not consider itself to be under session management
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until it receives this response. For example, the Non applications
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activate their "SM" blinkers at this time.
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If there is an error, a reply of the following form will be sent to
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the client:
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> /error "/nsm/server/announce" i:error_code s:error_message
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The following table defines possible values of `error\_code`:
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// Response codes
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[[ Code, Meaning
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[[ ERR_GENERAL, General Error
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[[ ERR_INCOMPATIBLE_API, Incompatible API version
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[[ ERR_BLACKLISTED, Client has been blacklisted.
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::: Server to Client Control Messages
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Compliant clients *MUST* accept the client control messages
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described in this section. All client control messages *REQUIRE* a
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response. Responses *MUST* be delivered back to the sender (NSM)
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from the same socket used by the client in its `announce` message
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(by using `lo\_send\_from`) *AFTER* the action has been completed or
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if an error is encountered. The required response is described in
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the subsection for each message.
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If there is an error and the action cannot be completed, then
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`error\_code` *MUST* be set to a valid error code (see #(fig,Error Code Definitions))
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and `message` to a string describing the problem (suitable
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for display to the user).
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The reply can take one of the following two forms, where `path` *MUST* be
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the path of the message being replied to (e.g. "/nsm\/client\/save"):
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> /reply s:path s:message
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> /error s:path i:error_code s:message
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:::: Quit
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There is no message for this. Clients will receive the Unix SIGTERM
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signal and *MUST* close cleanly *IMMEDIATELY*, without displaying
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any kind of dialog to the user and regardless of whether or not
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unsaved changes would be lost. When a session is closed the
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application will receive this signal soon after having responded to
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a `save` message.
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:::: Open
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> /nsm/client/open s:path_to_instance_specific_project s:display_name s:client_id
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`path\_to\_instance_specific\_project` is a path name assigned to
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the client for storing its project data.
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The client may append to the path, creating a sub-directory,
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e.g. '/song.foo' or simply append the client's native file extension
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(e.g. '.non' or '.XML'). The same transformation *MUST* be applied
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to the name when opening an existing project, as NSM will only
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provide the instance specific part of the path.
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If a project exists at the path, the client *MUST* immediately open
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it.
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If a project does not exist at the path, then the client *MUST*
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immediately create and open a new one at the specified path or, for
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clients which hold all their state in memory, store the path for
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later use when responding to the `save` message.
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No file or directory will be created at the specified path by the
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server. It is up to the client to create what it needs.
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For clients which *HAVE NOT* specified the `:switch:` capability,
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the `open` message will only be delivered once, immediately
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following the `announce` response.
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For clients which *HAVE* specified the `:switch:` capability, the
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client *MUST* immediately switch to the specified project or create
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a new one if it doesn't exist.
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Clients which are incapable of switching projects or are prone to
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crashing upon switching *MUST NOT* include `:switch:` in their
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capability string.
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If the user the is allowed to run two or more instances of the
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application simultaneously (that is to say, there is no technical
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limitation preventing them from doing so, even if it doesn't make
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sense to the author), then such an application *MUST PRE-PEND* the
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provided `client\_id` string to any names it registers with common
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subsystems (e.g. JACK client names). This ensures that multiple
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instances of the same application can be restored in any order
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without scrambling the JACK connections or causing other
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conflicts. The provided `client\_id` will be a concatenation of the
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value of `application\_name` sent by the client in its `announce`
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message and a unique identifier. Therefore, applications which
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create single JACK clients can use the value of `client\_id` directly
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as their JACK client name. Applications which register multiple JACK
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clients (e.g. Non-Mixer) *MUST PRE-PEND* `client\_id` value to the
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client names they register with JACK and the application determined
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part *MUST* be unique for that (JACK) client.
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For example, a suitable JACK client name would be:
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> $CLIENT_ID/track-1
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Note that this means that the application *MUST NOT* register with
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JACK (or any other subsystem requiring unique names) until it
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receives an `open` message from NSM. Likewise, applications with the
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`:switch:` capability should close their JACK clients and re-create
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them with using the new `client\_id`. Re-registering is necessary
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because the JACK API does currently support renaming existing
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clients, although this is a sorely needed addition.
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A response is *REQUIRED* *AFTER* the open operation has been
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completed. Ongoing progress may be indicated by sending messages to
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`\/nsm\/client\/progress`.
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::::: Response
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The client *MUST* respond to the 'open' message with:
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> /reply "/nsm/client/open" s:message
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Or
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> /error "/nsm/client/open" i:error_code s:message
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// Response Codes
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[[ Code, Meaning
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[[ ERR, General Error
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[[ ERR_BAD_PROJECT, An existing project file was found to be corrupt
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[[ ERR_CREATE_FAILED, A new project could not be created
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[[ ERR_UNSAVED_CHANGES, Unsaved changes would be lost
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[[ ERR_NOT_NOW, Operation cannot be completed at this time
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:::: Save
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> /nsm/client/save
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The client *MUST* immediately save the current application specific
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project data to the project path previously established in the
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'open' message. *UNDER NO CIRCUMSTANCES* should a dialog be
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displayed to the user (giving a choice of where to save, etc.)
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This message will only be delivered after a previous `open` message,
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and may be sent any number of times within the course of a session
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(including zero, if the user aborts the session).
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::::: Response
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The client *MUST* respond to the 'save' message with:
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> /reply "/nsm/client/save" s:message
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Or
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> /error "/nsm/client/save" i:error_code s:message
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// Response Codes
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[[ Code, Meaning
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[[ ERR, General Error
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[[ ERR_SAVE_FAILED, Project could not be saved
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[[ ERR_NOT_NOW, Operation cannot be completed at this time
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::: Server to Client Informational Messages
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:::: Session is Loaded
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Accepting this message is optional. The intent is to signal to
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clients which may have some interdependence (say, peer to peer OSC
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connections) that the session is fully loaded and all their peers
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are available.
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> /nsm/client/session_is_loaded
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This message does not require a response.
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::: Client to Server Informational Messages
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These are optional messages which a client can send to the NSM
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server to inform it about the client's status. The client should not
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expect any reply to these messages. If a client intends to send a
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message described in this section, then it *MUST* add the
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appropriate value to its `capabilities` string when composing the
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`announce` message.
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:::: Progress
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> /nsm/client/progress f:progress
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For potentially time-consuming operations, such as `save` and
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`open`, progress updates may be indicated throughout the duration by
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sending a floating point value between 0.0 and 1.0, 1.0 indicating
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completion, to the NSM server.
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The server will not send a response to these messages, but will
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relay the information to the user.
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Note that even when using the `progress` feature, the final
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response to the `save` or `open` message is still *REQUIRED*.
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Clients which intend to send `progress` messages should include
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`:progress:` in their `announce` capability string.
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:::: Dirtiness
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> /nsm/client/is_dirty
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> /nsm/client/is_clean
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Some clients may be able to inform the server when they have unsaved
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changes pending. Such clients may optionally send `is\_dirty` and `is\_clean`
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messages.
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Clients which have this capability should include `:dirty:` in their
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`announce` capability string.
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:::: Status Messages
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> /nsm/client/message i:priority s:message
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Clients may send miscellaneous status updates to the server for
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possible display to the user. This may simply be chatter that is
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normally written to the console. `priority` should be a number from
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0 to 3, 3 being the most important.
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Clients which have this capability should include `:message:` in their
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`announce` capability string.
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::: Error Code Definitions
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// Error Code Definitions
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[[ Symbolic Name, Integer Value
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[[ ERR_GENERAL, -1
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[[ ERR_INCOMPATIBLE_API, -2
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[[ ERR_BLACKLISTED, -3
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[[ ERR_LAUNCH_FAILED, -4
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[[ ERR_NO_SUCH_FILE, -5
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[[ ERR_NO_SESSION_OPEN, -6
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[[ ERR_UNSAVED_CHANGES, -7
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[[ ERR_NOT_NOW, -8
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[[ ERR_BAD_PROJECT, -9
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[[ ERR_CREATE_FAILED, -10
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::: Client to Server Control
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If the server publishes the `:server\_control:` capability, then
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clients can also initiate action by the server. For example, a
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client might implement a 'Save All' option which sends a
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`\/nsm\/server\/save` message to the server, rather than requiring
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the user to switch to the session management interface to effect the
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save.
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::: Server Control API
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The session manager not only manages clients via OSC, but it is
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itself controlled via OSC messages. The server responds to the
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following messages.
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All of the following messages will be responded to back to the
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sender's address with one of the two following messages:
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> /reply s:path s:message
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> /error s:path i:error_code s:message
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The first parameter of the reply is the path to the message being
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replied to. The `\/error` reply includes an integer error code
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(non-zero indicates error). `message` will be a description of the
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error.
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The possible errors are:
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// Responses
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[[ Code, Meaning
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[[ ERR_GENERAL, General Error
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[[ ERR_LAUNCH_FAILED, Launch failed
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[[ ERR_NO_SUCH_FILE, No such file
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[[ ERR_NO_SESSION, No session is open
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[[ ERR_UNSAVED_CHANGES, Unsaved changes would be lost
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= /nsm/server/add s:path_to_executable
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Adds a client to the current session.
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= /nsm/server/save
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Saves the current session.
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= /nsm/server/load s:project_name
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Saves the current session and loads a new session.
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= /nsm/server/new s:project_name
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Saves the current session and creates a new session.
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= /nsm/server/close
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Saves and closes the current session.
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= /nsm/server/abort
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Closes the current session *WITHOUT SAVING*
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= /nsm/server/quit
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Saves and closes the current session and terminates the server.
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= /nsm/server/duplicate s:new_project
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Saves and closes the current session, creates a complete copy of
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it as `new_project` and opens it. The existing project should ideally be
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a lightweight template, as copying any audio data could be very time
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consuming.
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= /nsm/server/list
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Lists available projects. One `\/reply` message will be sent for each existing project.
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:::: Client to Client Communication
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If the server includes `:broadcast:` in its capability string, then
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clients may send broadcast messages to each other through the NSM
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server.
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Clients may send messages to the server at the path
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`\/broadcast`.
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The format of this message is as follows:
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> /nsm/server/broadcast [any parameters...]
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The message will then be relayed to all clients in the session at
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the path `\/nsm\/client\/broadcast`.
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For example the message:
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> /nsm/server/broadcast /tempomap/update "0,120,4/4:12351234,240,4/4"
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Would broadcast the following message to all clients in the session
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(except for the sender), some of which might respond to the message
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by updating their own tempo maps. Here the string
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`\/tempomap\/update` is not an OSC path but merely a name-space
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qualifier by which the receivers can filter messages.
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> /nsm/client/broadcast /tempomap/update "0,120,4/4:12351234,240,4/4"
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Clients might use this feature to establish peer to peer OSC
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communication with symbolic names without having to remember the OSC
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ports of peers across sessions.
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