









	       X Session Management Protocol

		   X Consortium Standard

		 X Version 11, Release 6.4

			Mike Wexler
	       Kubota Pacific Computer, Inc.


			  ABSTRACT

     This document specifies a protocol that facili-
     tates the management of groups of client applica-
     tions by a session manager.  The session manager
     can cause clients to save their state, to shut
     down, and to be restarted into a previously saved
     state.  This protocol is layered on top of the X
     Consortium's ICE protocol.






















































    X Window System is a trademark of X Consortium, Inc.

	Copyright (C) 1992, 1993, 1994 X Consortium





Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documenta-
tion files (the ``Software''), to deal in the Software with-
out restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense,
and/or sell copies of the Software, and to permit persons to
whom the Software is furnished to do so, subject to the fol-
lowing conditions:

The above copyright notice and this permission notice shall
be included in all copies or substantial portions of the
Software.

THE SOFTWARE IS PROVIDED ``AS IS'', WITHOUT WARRANTY OF ANY
KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PUR-
POSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE X CONSOR-
TIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE
OR OTHER DEALINGS IN THE SOFTWARE.

















			     ii








1.  Acknowledgements

First I would like to thank the entire ICCCM and Intrinsics
working groups for the comments and suggestions. I would
like to make special thanks to the following people (in
alphabetical order), Jordan Brown, Ellis Cohen, Donna Con-
verse, Vania Joloboff, Stuart Marks, Ralph Mor and Bob
Scheifler.

2.  Definitions and Goals

The purpose of the X Session Management Protocol (XSMP) is
to provide a uniform mechanism for users to save and restore
their sessions.  A session is a group of clients, each of
which has a particular state.  The session is controlled by
a network service called the session manager.  The session
manager issues commands to its clients on behalf of the
user.  These commands may cause clients to save their state
or to terminate.  It is expected that the client will save
its state in such a way that the client can be restarted at
a later time and resume its operation as if it had never
been terminated.  A client's state might include information
about the file currently being edited, the current position
of the insertion point within the file, or the start of an
uncommitted transaction.  The means by which clients are
restarted is unspecified by this protocol.

For purposes of this protocol, a client of the session man-
ager is defined as a connection to the session manager.  A
client is typically, though not necessarily, a process run-
ning an application program connected to an X Window System
display.  However, a client may be connected to more than
one X display or not be connected to any X displays at all.

This protocol is layered on top of the X Consortium's ICE
protocol and relies on the ICE protocol to handle connection
management and authentication.


3.  Overview of the Protocol

Clients use XSMP to register themselves with the session
manager (SM).  When a client starts up, it should connect to
the SM.  The client should remain connected for as long as
it runs.  A client may resign from the session by issuing
the proper protocol messages before disconnecting.  Termina-
tion of the connection without notice will be taken as an
indication that the client died unexpectedly.

Clients are expected to save their state in such a way as to
allow multiple instantiations of themselves to be managed
independently.	A unique value called a client-ID is pro-
vided by the protocol for the purpose of disambiguating mul-
tiple instantiations of clients.  Clients may use this ID,



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X Session Management Protocol		    X11, Release 6.4


for example, as part of a filename in which to store the
state for a particular instantiation.  The client-ID should
be saved as part of the command used to restart this client
(the RestartCommand) so that the client will retain the same
ID after it is restarted.  Certain small pieces of state
might also be stored in the RestartCommand.   For example,
an X11 client might place a `-twoWindow' option in its
RestartCommand to indicate that it should start up in two
window mode when it is restarted.

The client finds the network address of the SM in a system-
dependent way.	On POSIX systems an environment variable
called SESSION_MANAGER will contain a list of network IDs.
Each id will contain the transport name followed by a slash
and the (transport-specific) address.  A TCP/IP address
would look like this:

	  tcp/hostname:portnumber

where the hostname is a fully qualified domain name.  A Unix
Domain address looks like this:

	  local/hostname:path

A DECnet address would look like this:

	  decnet/nodename::objname

If multiple network IDs are specified, they should be sepa-
rated by commas.

			 Rationale

     There was much discussion over whether the XSMP
     protocol should use X as the transport protocol or
     whether it should use its own independent trans-
     port.  It was decided that it would use an inde-
     pendent protocol for several reasons.  First, the
     Session Manager should be able to manage programs
     that do not maintain an X connection.  Second, the
     X protocol is not appropriate to use as a general-
     purpose transport protocol.  Third, a session
     might span multiple displays.

     The protocol is connection based, because there is
     no other way for the SM to determine reliably when
     clients terminate.

     It should be noted that this protocol introduces
     another single point of failure into the system.
     Although it is possible for clients to continue
     running after the SM has exited, this will proba-
     bly not be the case in normal practice.  Normally
     the program that starts the SM will consider the



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X Session Management Protocol		    X11, Release 6.4


     session to be terminated when the SM exits (either
     normally or abnormally).

     To get around this would require some sort of ren-
     dezvous server that would also introduce a single
     point of failure.	In the absence of a generally
     available rendezvous server, XSMP is kept simple
     in the hopes of making simple reliable SMs.


Some clients may wish to manage the programs they start.
For example, a mail program could start a text editor for
editing the text of a mail message.  A client that does this
is a session manager itself; it should supply the clients it
starts with the appropriate connection information (i.e.,
the SESSION_MANAGER environment variable) that specifies a
connection to itself instead of to the top level session
manager.

Each client has associated with it a list of properties.  A
property set by one client is not visible to any other
client.  These properties are used for the client to inform
the SM of the client's current state.  When a client ini-
tially connects to the SM, there are no properties set.

4.  Data Types

XSMP messages contain several types of data.  Both the SM
and the client always send messages in their native byte
order.	Thus, both sides may need to byte-swap the messages
received.  The need to do byte-swapping is determined at
run-time by the ICE protocol.

If an invalid value is specified for a field of any of the
enumerated types, a BadValue error message must be sent by
the receiver of the message to the sender of the message.

------------------------------------------------------------------------------------
Type Name	 Description
------------------------------------------------------------------------------------
BOOL		 False or True
INTERACT_STYLE	 None, Errors, or Any
DIALOG_TYPE	 Error or Normal
SAVE_TYPE	 Global, Local, or Both
CARD8		 a one-byte unsigned integer
CARD16		 a two-byte unsigned integer
CARD32		 a four-byte unsigned integer
ARRAY8		 a sequence of CARD8s
LISTofARRAY8	 a sequence of ARRAY8s
PROPERTY	 a property name (an ARRAY8), a type name, and a value of that type
LISTofPROPERTY	 a counted collection of PROPERTYs.
------------------------------------------------------------------------------------





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X Session Management Protocol		    X11, Release 6.4


5.  Protocol Setup and Message Format

To start the XSMP protocol, the client sends the server an
ICE ProtocolSetup message.  All XSMP messages are in the
standard ICE message format.  The message's major opcode is
assigned to XSMP by ICE at run-time.  The different parties
(client and SM) may be assigned different major opcodes for
XSMP.  Once assigned, all XSMP messages issued by this party
will use the same major opcode.  The message's minor opcode
specifies which protocol message this message contains.

6.  Client Identification String

A client ID is a string of XPCS characters encoded in ISO
Latin 1 (ISO 8859-1).  No null characters are allowed in
this string.  The client ID string is used in the Register-
Client and RegisterClientReply messages.

Client IDs consist of the pieces described below.  The ID is
formed by concatenating the pieces in sequence, without sep-
arator characters.  All pieces are padded on the left with
'0' characters so as to fill the specified length.  Decimal
numbers are encoded using the characters `0' through `9',
and hexadecimal numbers using the characters `0' through `9'
and `A' through `F'.

o   Version.  This is currently the character `1'.

o   Address type and address.  The address type will be one
    of

	 `1'  a 4-byte IP address encoded as 8 hexadecimal digits
	 `2'  a 6-byte DECNET address encoded as 12 hexadecimal digits


    The address is the one of the network addresses of the
    machine where the session manager (not the client) is
    running.  For example, the IP address 198.112.45.11
    would be encoded as the string "C6702D0B".

o   Time stamp.  A 13-digit decimal number specifying the
    number of milliseconds since 00:00:00 UTC, January 1,
    1970.

o   Process-ID type and process-ID.  The process-ID type
    will be one of

	 `1'  a POSIX process-ID encoded as a 10-digit decimal number.


    The process-ID is the process-ID of the session manager,
    not of a client.





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X Session Management Protocol		    X11, Release 6.4


o   Sequence number.  This is a four-digit decimal number.
    It is incremented every time the session manager creates
    an ID.  After reaching "9999" it wraps to "0000".

			   Rationale

	 Once a client ID has been assigned to the
	 client, the client keeps this ID indefinitely.
	 If the client is terminated and restarted, it
	 will be reassigned the same ID.  It is desir-
	 able to be able to pass client IDs around from
	 machine to machine, from user to user, and
	 from session manager to session manager, while
	 retaining the identity of the client.	This,
	 combined with the indefinite persistence of
	 client IDs, means that client IDs need to be
	 globally unique.  The construction specified
	 above will ensure that any client ID created
	 by any user, session manager, and machine will
	 be different from any other.


7.  Protocol

The protocol consists of a sequence of messages as described
below.	Each message type is specified by an ICE minor
opcode.  A given message type is sent either from a client
to the session manager or from the session manager to a
client; the appropriate direction is listed with each mes-
sage's description.  For each message type, the set of valid
responses and possible error messages are listed.  The ICE
severity is given in parentheses following each error class.

__
|    RegisterClient [Client -> SM]

     previous-ID: ARRAY8

     Valid Responses: RegisterClientReply

|__	  Possible Errors: BadValue (CanContinue)


The client must send this message to the SM to register the
client's existence.  If a client is being restarted from a
previous session, the previous-ID field must contain the
client ID from the previous session.  For new clients, pre-
vious-ID should be of zero length.

If previous-ID is not valid, the SM will send a BadValue
error message to the client.  At this point the SM reverts
to the register state and waits for another RegisterClient.
The client should then send a RegisterClient with a null
previous-ID field.



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X Session Management Protocol		    X11, Release 6.4

__
|    RegisterClientReply [Client <- SM]

|__	  client-ID: ARRAY8


The client-ID specifies a unique identification for this
client.  If the client had specified an ID in the previous-
ID field of the RegisterClient message, client-ID will be
identical to the previously specified ID.  If previous-ID
was null, client-ID will be a unique ID freshly generated by
the SM.  The client-ID format is specified in section 6.

If the client didn't supply a previous-ID field to the
RegisterClient message, the SM must send a SaveYourself mes-
sage with type = Local, shutdown = False, interact-style =
None, and fast = False immediately after the RegisterClien-
tReply.  The client should respond to this like any other
SaveYourself message.

__
|    SaveYourself [Client <- SM]

     type: SAVE_TYPE
     shutdown: BOOL
     interact-style: INTERACT_STYLE
     fast: BOOL

     Valid Responses: SetProperties, DeleteProperties, Get-
     Properties, SaveYourselfDone, SaveYourself-
|__	  Phase2Request, InteractRequest


The SM sends this message to a client to ask it to save its
state.	The client writes a state file, if necessary, and,
if necessary, uses SetProperties to inform the SM of how to
restart it and how to discard the saved state.	During this
process it can, if allowed by interact-style, request per-
mission to interact with the user by sending an InteractRe-
quest message.	After the state has been saved, or if it
cannot be successfully saved, and the properties are appro-
priately set, the client sends a SaveYourselfDone message.
If the client wants to save additional information after all
the other clients have finished changing their own state,
the client should send SaveYourselfPhase2Request instead of
SaveYourselfDone.  The client must then freeze interaction
with the user and wait until it receives a SaveComplete,
Die, or a ShutdownCancelled message.

If interact-style is None, the client must not interact with
the user while saving state.  If the interact-style is
Errors, the client may interact with the user only if an
error condition arises.  If interact-style is Any, then the
client may interact with the user for any purpose.  This is
done by sending an InteractRequest message.  The SM will



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send an Interact message to each client that sent an
InteractRequest.  The client must postpone all interaction
until it gets the Interact message.  When the client is done
interacting it should send the SM an InteractDone message.
The InteractRequest message can be sent any time after a
SaveYourself and before a SaveYourselfDone.

Unusual circumstances may dictate multiple interactions.
The client may initiate as many InteractRequest - Interact -
InteractDone sequences as it needs before it sends SaveYour-
selfDone.

When a client receives SaveYourself and has not yet
responded SaveYourselfDone to a previous SaveYourself, it
must send a SaveYourselfDone and may then begin responding
as appropriate to the newly received SaveYourself.

The type field specifies the type of information that should
be saved: Global, Local, or Both.  The Local type indicates
that the application must update the properties to reflect
its current state, send a SaveYourselfDone and continue.
Specifically it should save enough information to restore
the state as seen by the user of this client.  It should not
affect the state as seen by other users.  The Global type
indicates that the user wants the client to commit all of
its data to permanent, globally-accessible storage.  Both
indicates that the client should do both of these.  If Both
is specified, the client should first commit the data to
permanent storage before updating its SM properties.

			  Examples

     If a word processor was sent a SaveYourself with a
     type of Local, it could create a temporary file
     that included the current contents of the file,
     the location of the cursor, and other aspects of
     the current editing session.  It would then update
     its RestartCommand property with enough informa-
     tion to find the temporary file, and its Discard-
     Command with enough information to remove it.

     If a word processor was sent a SaveYourself with a
     type of Global, it would simply save the currently
     edited file.

     If a word processor was sent a SaveYourself with a
     type of Both, it would first save the currently
     edited file.  It would then create a temporary
     file with information such as the current position
     of the cursor and what file is being edited.  It
     would then update its RestartCommand property with
     enough information to find the temporary file, and
     its DiscardCommand with enough information to
     remove it.



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     Once the SM has send SaveYourself to a client, it
     can't send another SaveYourself to that client
     until the client either responds with a SaveYour-
     selfDone or the SM sends a ShutdownCancelled.


		   Advice to Implementors

     If the client stores local any state in a file or
     similar "external" storage, it must create a dis-
     tinct copy in response to each SaveYourself mes-
     sage.  It must not simply refer to a previous
     copy, because the SM may discard that previous
     saved state using a DiscardCommand without knowing
     that it is needed for the new checkpoint.


The shutdown field specifies whether the system is being
shut down.

			 Rationale

     The interaction may be different depending on
     whether or not shutdown is set.

The client must save and then must prevent interaction until
it receives a SaveComplete, Die, or a ShutdownCancelled,
because anything the user does after the save will be lost.

The fast field specifies whether or not the client should
save its state as quickly as possible.	For example, if the
SM knows that power is about to fail, it should set the fast
field to True.

__
|    SaveYourselfPhase2 [Client <- SM]


     Valid Responses: SetProperties, DeleteProperties, Get-
|__	  Properties, SaveYourselfDone, InteractRequest


The SM sends this message to a client that has previously
sent a SaveYourselfPhase2Request message.  This message
informs the client that all other clients are in a fixed
state and this client can save state that is associated with
other clients.

			 Rationale

     Clients that manager other clients (window man-
     agers, workspace managers, etc) need to know when
     all clients they are managing are idle, so that
     the manager can save state related to each of the



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     clients without being concerned with that state
     changing.

The client writes a state file, if necessary, and, if neces-
sary, uses SetProperties to inform the SM of how to restart
it and how to discard the saved state.	During this process
it can request permission to interact with the user by send-
ing an InteractRequest message.  This should only be done if
an error occurs that requires user interaction to resolve.
After the state has been saved, or if it cannot be success-
fully saved, and the properties are appropriately set, the
client sends a SaveYourselfDone message.


__
|    SaveYourselfRequest [Client -> SM]

     type: SAVE_TYPE
     shutdown: BOOL
     interact-style: INTERACT_STYLE
     fast: BOOL
     global: BOOL

|__	  Valid Responses: SaveYourself


An application sends this to the SM to request a checkpoint.
When the SM receives this request it may generate a SaveY-
ourself message in response and it may leave the fields
intact.

			  Example

     A vendor of a UPS (Uninterruptible Power Supply)
     might include an SM client that would monitor the
     status of the UPS and generate a fast shutdown if
     the power is about to be lost.


If global is set to True, then the resulting SaveYourself
should be sent to all applications.  If global is set to
False, then the resulting SaveYourself should be sent to the
application that sent the SaveYourselfRequest.

__
|    InteractRequest [Client -> SM]

     dialog-type: DIALOG_TYPE

     Valid Responses: Interact, ShutdownCancelled

|__	  Possible Errors: BadState (CanContinue)





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During a checkpoint or session-save operation, only one
client at a time might be granted the privilege of interact-
ing with the user.  The InteractRequest message causes the
SM to emit an Interact message at some later time if the
shutdown is not cancelled by another client first.

The dialog-type field specifies either Errors, indicating
that the client wants to start an error dialog or Normal,
meaning the client wishes to start a non-error dialog.

__
|    Interact [Client <- SM]

     Valid Responses: InteractDone
|__


This message grants the client the privilege of interacting
with the user.	When the client is done interacting with the
user it must send an InteractDone message to the SM unless a
shutdown cancel is received.

		   Advice to Implementors

     If a client receives a ShutdownCancelled after
     receiving an Interact message, but before sending
     a InteractDone, the client should abort the inter-
     action and send a SaveYourselfDone.


__
|    InteractDone [Client -> SM]

     cancel-shutdown: BOOL

     Valid Responses: ShutdownCancelled
|__


This message is used by a client to notify the SM that it is
done interacting.

Setting the cancel-shutdown field to True indicates that the
user has requested that the entire shutdown be cancelled.
Cancel-shutdown may only be True if the corresponding SaveY-
ourself message specified True for the shutdown field and
Any or Errors for the interact-style field.  Otherwise, can-
cel-shutdown must be False.









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__
|    SaveYourselfDone [Client -> SM]

     success: BOOL

     Valid Responses: SaveComplete, Die, ShutdownCancelled
|__


This message is sent by a client to indicate that all of the
properties representing its state have been updated.  After
sending SaveYourselfDone the client must wait for a SaveCom-
plete, ShutdownCancelled, or Die message before changing its
state.	If the SaveYourself operation was successful, then
the client should set the success field to True; otherwise
the client should set it to False.

			  Example

     If a client tries to save its state and runs out
     of disk space, it should return False in the suc-
     cess field of the SaveYourselfDone message.


__
|    SaveYourselfPhase2Request [Client -> SM]

     Valid Responses: ShutdownCancelled, SaveYourselfPhase2
|__


This message is sent by a client to indicate that it needs
to be informed when all the other clients are quiescent, so
it can continue its state.

__
|    Die [Client <- SM]

|__	  Valid Responses: ConnectionClosed


When the SM wants a client to die it sends a Die message.
Before the client dies it responds by sending a Connection-
Closed message and may then close its connection to the SM
at any time.

__
|    SaveComplete [Client <- SM]

|__	  Valid Responses:


When the SM is done with a checkpoint, it will send each of
the clients a SaveComplete message.  The client is then free
to change its state.



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__
|__  ShutdownCancelled [Client <- SM]


The shutdown currently in process has been aborted.  The
client can now continue as if the shutdown had never hap-
pened.	If the client has not sent SaveYourselfDone yet, the
client can either abort the save and send SaveYourselfDone
with the success field set to False, or it can continue with
the save and send a SaveYourselfDone with the success field
set to reflect the outcome of the save.

__
|    ConnectionClosed [Client -> SM]

|__	  reason: LISTofARRAY8


Specifies that the client has decided to terminate.  It
should be immediately followed by closing the connection.

The reason field specifies why the client is resigning from
the session.  It is encoded as an array of Compound Text
strings.  If the resignation is expected by the user, there
will typically be zero ARRAY8s here.  But if the client
encountered an unexpected fatal error, the error message
(which might otherwise be printed on stderr on a POSIX sys-
tem) should be forwarded to the SM here, one ARRAY8 per line
of the message.  It is the responsibility of the SM to dis-
play this reason to the user.

After sending this message, the client must not send any
additional XSMP messages to the SM.

		   Advice to Implementors

     If additional messages are received, they should
     be discarded.


			 Rationale

     The reason for sending the ConnectionClosed mes-
     sage before actually closing the connections is
     that some transport protocols will not provide
     immediate notification of connection closure.


__
|    SetProperties [Client -> SM]

|__	  properties: LISTofPROPERTY






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Sets the specified properties to the specified values.
Existing properties not specified in the SetProperties mes-
sage are unaffected.  Some properties have predefined seman-
tics.  See section 11, "Predefined Properties."

The protocol specification recommends that property names
used for properties not defined by the standard should begin
with an underscore.  To prevent conflicts among organiza-
tions, additional prefixes should be chosen (for example,
_KPC_FAST_SAVE_OPTION).  The organizational prefixes should
be registered with the X Registry.  The XSMP reserves all
property names not beginning with an underscore for future
use.

__
|    DeleteProperties [Client -> SM]

|__	  property-names: LISTofARRAY8


Removes the named properties.

__
|    GetProperties [Client -> SM]

|__	  Valid Responses: GetPropertiesReply


Requests that the SM respond with the values of all the
properties for this client.

__
|    GetPropertiesReply [Client <- SM]

|__	  values: LISTofPROPERTY


This message is sent in reply to a GetProperties message and
includes the values of all the properties.

8.  Errors

When the receiver of a message detects an error condition,
the receiver sends an ICE error message to the sender.
There are only two types of errors that are used by the
XSMP: BadValue and BadState.  These are both defined in the
ICE protocol.

Any message received out-of-sequence will generate a Bad-
State error message.







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9.  State Diagrams

These state diagrams are designed to cover all actions of
both the client and the SM.

9.1.  Client State Diagram


start:
     ICE protocol setup complete -> register



register:
     send RegisterClient -> collect-id



collect-id:
     receive RegisterClientReply -> idle



shutdown-cancelled:
     send SaveYourselfDone -> idle



idle: [Undoes any freeze of interaction with user.]
     receive Die -> die
     receive SaveYourself -> freeze-interaction
     send GetProperties -> idle
     receive GetPropertiesReply -> idle
     send SetProperties -> idle
     send DeleteProperties -> idle
     send ConnectionClosed -> connection-closed
     send SaveYourselfRequest -> idle



die:
     send ConnectionClosed -> connection-closed



freeze-interaction:
     freeze interaction with user -> save-yourself










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save-yourself:
     receive ShutdownCancelled -> shutdown-cancelled
     send SetProperties -> save-yourself
     send DeleteProperties -> save-yourself
     send GetProperties -> save-yourself
     receive GetPropertiesReply -> save-yourself
     send InteractRequest -> interact-request
     send SaveYourselfPhase2Request -> waiting-for-phase2
     if shutdown mode:
	  send SaveYourselfDone -> save-yourself-done
     otherwise:
	  send SaveYourselfDone -> idle



waiting-for-phase2:
     receive ShutdownCancelled -> shutdown-cancelled
     receive SaveYourselfPhase2 -> phase2



phase2:
     receive ShutdownCancelled -> shutdown-cancelled
     send SetProperties -> save-yourself
     send DeleteProperties -> save-yourself
     send GetProperties -> save-yourself
     receive GetPropertiesReply -> save-yourself
     send InteractRequest -> interact-request (errors only)
     if shutdown mode:
	  send SaveYourselfDone -> save-yourself-done
     otherwise:
	  send SaveYourselfDone -> idle



interact-request:
     receive Interact -> interact
     receive ShutdownCancelled -> shutdown-cancelled



interact:
     send InteractDone -> save-yourself
     receive ShutdownCancelled -> shutdown-cancelled



save-yourself-done: (changing state is forbidden)
     receive SaveComplete -> idle
     receive Die -> die
     receive ShutdownCancelled -> idle






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connection-closed:
     client stops participating in session


9.2.  Session Manager State Diagram


start:
     receive ProtocolSetup -> protocol-setup



protocol-setup:
     send ProtocolSetupReply -> register



register:
     receive RegisterClient -> acknowledge-register



acknowledge-register:
     send RegisterClientReply -> idle



idle:
     receive SetProperties -> idle
     receive DeleteProperties -> idle
     receive ConnectionClosed -> start
     receive GetProperties -> get-properties
     receive SaveYourselfRequest -> save-yourself
     send SaveYourself -> saving-yourself



save-yourself:
     send SaveYourself -> saving-yourself



get-properties:
     send GetPropertiesReply -> idle



saving-get-properties:
     send GetPropertiesReply -> saving-yourself








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saving-yourself:
     receive InteractRequest -> saving-yourself
     send Interact -> saving-yourself
     send ShutdownCancelled -> idle
     receive InteractDone -> saving-yourself
     receive SetProperties -> saving-yourself
     receive DeleteProperties -> saving-yourself
     receive GetProperties -> saving-get-properties
     receive SaveYourselfPhase2Request -> start-phase2
     receive SaveYourselfDone -> save-yourself-done



start-phase2:
     If all clients have sent either SaveYourselfPhase2Request or SaveYourselfDone:
	  send SaveYourselfPhase2 -> phase2
     else
	  -> saving-yourself



phase2:
     receive InteractRequest -> saving-yourself
     send Interact -> saving-yourself
     send ShutdownCancelled -> idle
     receive InteractDone -> saving-yourself
     receive SetProperties -> saving-yourself
     receive DeleteProperties -> saving-yourself
     receive GetProperties -> saving-get-properties
     receive SaveYourselfDone -> save-yourself-done



save-yourself-done:
     If all clients are saved:
	  If shutting down:
	       send Die -> die
	  otherwise
	       send SaveComplete -> idle

     If some clients are not saved:
     -> saving-yourself



die:
     SM stops accepting connections


10.  Protocol Encoding







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10.1.  Types

BOOL
  0  False
  1  True

INTERACT_STYLE
  0  None
  1  Errors
  2  Any

DIALOG_TYPE
  0  Error
  1  Normal

SAVE_TYPE
  0  Global
  1  Local
  2  Both

ARRAY8
  4  CARD32	    length
  n  LISTofCARD8    the array
  p		    p = pad (4 + n, 8)

LISTofARRAY8
  4  CARD32	    count
  4		    unused
  a  ARRAY8	    first array
  b  ARRAY8	    second array
  .
  .
  .
  q  ARRAY8	    last array

PROPERTY
  a  ARRAY8	    name
  b  ARRAY8	    type (XPCS encoded in Latin-1, case sensitive)
  c  LISTofARRAY8   values

LISTofPROPERTY
  4	  CARD32    count
  4		    unused
  a	  PROPERTY  first property
  b	  PROPERTY  second property
  .
  .
  .
  q  PROPERTY	    last property

10.2.  Messages

XSMP is a sub-protocol of ICE.	The major opcode is assigned
at run-time by ICE and is represented here by `?'.



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To start the XSMP protocol, the client sends the server an
ICE ProtocolSetup message.  The protocol-name field should
be specified as "XSMP", the major version of the protocol is
1, the minor version is 0.  These values may change if the
protocol is revised.  The minor version number will be
incremented if the change is compatible, otherwise the major
version number will be incremented.

In ProtocolReply message sent by the session manager, the
XSMP protocol defines the vendor parameter as product iden-
tification of the session manager, and defines the release
parameter as the software release identification of the ses-
sion manager.  The session manager should supply this infor-
mation in the ICE ProtocolReply message.

RegisterClient
  1  ?		    XSMP
  1  1		    opcode
  2		    unused
  4  a/8	    length of remaining data in 8-byte units
  a  ARRAY8	    previous-ID

RegisterClientReply
  1  ?		    XSMP
  1  2		    opcode
  2		    unused
  4  a/8	    length of remaining data in 8-byte units
  a  ARRAY8	    client-ID

SaveYourself
  1  ?		    XSMP
  1  3		    opcode
  2		    unused
  4  1		    length of remaining data in 8-byte units
  1  SAVE_TYPE	    type
  1  BOOL	    shutdown
  1  INTERACT_STYLE interact-style
  1  BOOL	    fast
  4		    unused

SaveYourselfRequest
  1  ?		    XSMP
  1  4		    opcode
  2		    unused
  4  1		    length of remaining data in 8-byte units
  1  SAVE_TYPE	    type
  1  BOOL	    shutdown
  1  INTERACT_STYLE interact-style
  1  BOOL	    fast
  1  BOOL	    global
  3		    unused






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InteractRequest
  1  ?		    XSMP
  1  5		    opcode
  1  DIALOG_TYPE    dialog type
  1		    unused
  4  0		    length of remaining data in 8-byte units

Interact
  1  ?		    XSMP
  1  6		    opcode
  2		    unused
  4  0		    length of remaining data in 8-byte units

InteractDone
  1  ?		    XSMP
  1  7		    opcode
  1  BOOL	    cancel-shutdown
  1		    unused
  4  0		    length of remaining data in 8-byte units

SaveYourselfDone
  1  ?		    XSMP
  1  8		    opcode
  1  BOOL	    success
  1		    unused
  4  0		    length of remaining data in 8-byte units

Die
  1  ?		    XSMP
  1  9		    opcode
  2		    unused
  4  0		    length of remaining data in 8-byte units

ShutdownCancelled
  1  ?		    XSMP
  1  10 	    opcode
  2		    unused
  4  0		    length of remaining data in 8-byte units

ConnectionClosed
  1  ?		    XSMP
  1  11 	    opcode
  2		    unused
  4  a/8	    length of remaining data in 8-byte units
  a  LISTofARRAY8   reason

SetProperties
  1  ?		    XSMP
  1  12 	    opcode
  2		    unused
  4  a/8	    length of remaining data in 8-byte units
  a  LISTofPROPERTY properties





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DeleteProperties
  1  ?		    XSMP
  1  13 	    opcode
  2		    unused
  4  a/8	    length of remaining data in 8-byte units
  a  LISTofARRAY8   properties

GetProperties
  1  ?		    XSMP
  1  14 	    opcode
  2		    unused
  4  0		    length of remaining data in 8-byte units

GetPropertiesReply
  1  ?		    XSMP
  1  15 	    opcode
  2		    unused
  4  a/8	    length of remaining data in 8-byte units
  a  LISTofPROPERTY properties

SaveYourselfPhase2Request
  1  ?		    XSMP
  1  16 	    opcode
  2		    unused
  4  0		    length of remaining data in 8-byte units

SaveYourselfPhase2
  1  ?		    XSMP
  1  17 	    opcode
  2		    unused
  4  0		    length of remaining data in 8-byte units


SaveComplete
  1  ?		    XSMP
  1  18 	    opcode
  2		    unused
  4  0		    length of remaining data in 8-byte units


11.  Predefined Properties

All property values are stored in a LISTofARRAY8.  If the
type of the property is CARD8, the value is stored as a
LISTofARRAY8 with one ARRAY8 that is one byte long.  That
single byte contains the CARD8.  If the type of the property
is ARRAY8, the value is stored in the first element of a
single element LISTofARRAY8.

The required properties must be set each time a client con-
nects with the SM.  The properties must be set after the
client sends RegisterClient and before the client sends
SaveYourselfDone.  Otherwise, the behavior of the session
manager is not defined.



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Clients may set, get, and delete nonstandard properties.
The lifetime of stored properties does not extend into sub-
sequent sessions.

----------------------------------------------------------
Name		   Type 	 Posix Type	Required?
----------------------------------------------------------
CloneCommand	   OS-specific	 LISTofARRAY8	   Yes
CurrentDirectory   OS-specific	 ARRAY8 	   No
DiscardCommand	   OS-specific	 LISTofARRAY8	   No*
Environment	   OS-specific	 LISTofARRAY8	   No
ProcessID	   OS-specific	 ARRAY8 	   No
Program 	   OS-specific	 ARRAY8 	   Yes
RestartCommand	   OS-specific	 LISTofARRAY8	   Yes
ResignCommand	   OS-specific	 LISTofARRAY8	   No
RestartStyleHint   CARD8	 CARD8		   No
ShutdownCommand    OS-specific	 LISTofARRAY8	   No
UserID		   ARRAY8	 ARRAY8 	   Yes
----------------------------------------------------------


* Required if any state is stored in an external repository
(e.g., state file).

CloneCommand
   This is like the RestartCommand except it restarts a copy
   of the application.	The only difference is that the
   application doesn't supply its client id at register
   time.  On POSIX systems the type should be a LISTofAR-
   RAY8.

CurrentDirectory
   On POSIX-based systems specifies the value of the current
   directory that needs to be set up prior to starting the
   program and should be of type ARRAY8.

DiscardCommand
   The discard command contains a command that when deliv-
   ered to the host that the client is running on (deter-
   mined from the connection), will cause it to discard any
   information about the current state.  If this command is
   not specified, the SM will assume that all of the
   client's state is encoded in the RestartCommand.  On
   POSIX systems the type should be LISTofARRAY8.

Environment
   On POSIX based systems, this will be of type LISTofARRAY8
   where the ARRAY8s alternate between environment variable
   name and environment variable value.

ProcessID
   This specifies an OS-specific identifier for the process.
   On POSIX systems this should of type ARRAY8 and contain
   the return value of getpid() turned into a Latin-1



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   (decimal) string.

Program
   The name of the program that is running.  On POSIX sys-
   tems this should be the first parameter passed to execve
   and should be of type ARRAY8.

RestartCommand
   The restart command contains a command that when deliv-
   ered to the host that the client is running on (deter-
   mined from the connection), will cause the client to
   restart in its current state.  On POSIX-based systems
   this is of type LISTofARRAY8 and each of the elements in
   the array represents an element in the argv array.  This
   restart command should ensure that the client restarts
   with the specified client-ID.

ResignCommand
   A client that sets the RestartStyleHint to RestartAnyway
   uses this property to specify a command that undoes the
   effect of the client and removes any saved state.

			    Example

	A user runs xmodmap.  xmodmap registers with
	the SM, sets RestartStyleHint to RestartAnyway,
	and then terminates.  In order to allow the SM
	(at the user's request) to undo this, xmodmap
	would register a ResignCommand that undoes the
	effects of the xmodmap.


RestartStyleHint

   If the RestartStyleHint property is present, it will con-
   tain the style of restarting the client prefers.  If this
   flag isn't specified, RestartIfRunning is assumed.  The
   possible values are as follows:

   ---------------------------
   Name 		Value
   ---------------------------
   RestartIfRunning	  0
   RestartAnyway	  1
   RestartImmediately	  2
   RestartNever 	  3
   ---------------------------


   The RestartIfRunning style is used in the usual case.
   The client should be restarted in the next session if it
   is connected to the session manager at the end of the
   current session.




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   The RestartAnyway style is used to tell the SM that the
   application should be restarted in the next session even
   if it exits before the current session is terminated.  It
   should be noted that this is only a hint and the SM will
   follow the policies specified by its users in determining
   what applications to restart.


			   Rationale

	This can be specified by a client which sup-
	ports (as MS-Windows clients do) a means for
	the user to indicate while exiting that
	restarting is desired.	It can also be used for
	clients that spawn other clients and then go
	away, but which want to be restarted.


   A client that uses RestartAnyway should also set the
   ResignCommand and ShutdownCommand properties to commands
   that undo the state of the client after it exits.

   The RestartImmediately style is like RestartAnyway, but
   in addition, the client is meant to run continuously.  If
   the client exits, the SM should try to restart it in the
   current session.

		    Advice to Implementors

	It would be wise to sanity-check the frequency
	which which RestartImmediately clients are
	restarted, to avoid a sick client being
	restarted continuously.

   The RestartNever style specifies that the client does not
   wish to be restarted in the next session.

		    Advice To Implementors

	This should be used rarely, if at all.	It will
	cause the client to be silently left out of
	sessions when they are restarted and will prob-
	ably be confusing to users.


ShutdownCommand
   This command is executed at shutdown time to clean up
   after a client that is no longer running but retained its
   state by setting RestartStyleHint to RestartAnyway.	The
   command must not remove any saved state as the client is
   still part of the session.






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			    Example

	A client is run at start up time that turns on
	a camera.  This client then exits.  At session
	shutdown, the user wants the camera turned off.
	This client would set the RestartStyleHint to
	RestartAnyway and would register a Shutdown-
	Command that would turn off the camera.


UserID
   Specifies the user's ID.  On POSIX-based systems this
   will contain the the user's name (the pw_name field of
   struct passwd).











































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		       Table of Contents


   1. Acknowledgements . . . . . . . . . . . . . . . . .   1
   2. Definitions and Goals  . . . . . . . . . . . . . .   1
   3. Overview of the Protocol . . . . . . . . . . . . .   1
   4. Data Types . . . . . . . . . . . . . . . . . . . .   3
   5. Protocol Setup and Message Format  . . . . . . . .   4
   6. Client Identification String . . . . . . . . . . .   4
   7. Protocol . . . . . . . . . . . . . . . . . . . . .   5
   8. Errors . . . . . . . . . . . . . . . . . . . . . .  13
   9. State Diagrams . . . . . . . . . . . . . . . . . .  14
   9.1. Client State Diagram . . . . . . . . . . . . . .  14
   9.2. Session Manager State Diagram  . . . . . . . . .  16
   10. Protocol Encoding . . . . . . . . . . . . . . . .  17
   10.1. Types . . . . . . . . . . . . . . . . . . . . .  18
   10.2. Messages  . . . . . . . . . . . . . . . . . . .  18
   11. Predefined Properties . . . . . . . . . . . . . .  21







































			     iii


