








	       Inter-Client Exchange Library

			Version 1.0

		   X Consortium Standard

		 X Version 11, Release 6.4

			 Ralph Mor
			X Consortium



	Copyright (C) 1993, 1994, 1996 X Consortium







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1.  Overview of ICE

There are numerous  possible  inter-client  protocols,	with
many similarities and common needs - authentication, version
negotiation, byte order negotiation, and so on.  The  Inter-
Client	Exchange  (ICE)  protocol  is  intended to provide a
framework for building such protocols, allowing them to make
use  of  common negotiation mechanisms and to be multiplexed
over a single transport connection.

2.  The ICE Library - C Language Interface to ICE

A client that wishes to utilize ICE must first register  the
protocols  it understands with the ICE library.  Each proto-
col is dynamically assigned  a	major  opcode  ranging	from
1-255  (two  clients can use different major opcodes for the
same protocol).  The next step for the client is  either  to
open a connection with another client or to wait for connec-
tions  made  by  other	clients.   Authentication   may   be
required.  A client can both initiate connections with other
clients and be waiting for clients to connect to  itself  (a
nested	session manager is an example).  Once an ICE connec-
tion is established between the  two  clients,	one  of  the
clients needs to initiate a ProtocolSetup in order to "acti-
vate" a given protocol.  Once the other client	accepts  the
ProtocolSetup  (once again, authentication may be required),
the two clients are ready to start passing messages specific
to  that  protocol to each other.  Multiple protocols may be
active on a single ICE connection.  Clients are  responsible
for  notifying	the ICE library when a protocol is no longer
active on an ICE connection, although ICE  does  not  define
how each subprotocol triggers a protocol shutdown.

The  ICE library utilizes callbacks to process incoming mes-
sages.	Using callbacks allows	ProtocolSetup  messages  and
authentication	to  happen behind the scenes.  An additional
benefit is that messages never need to be buffered up by the
library when the client blocks waiting for a particular mes-
sage.

3.  Intended Audience

This document is intended primarily for implementors of pro-
tocol  libraries layered on top of ICE.  Typically, applica-
tions that wish to utilize ICE will make calls into individ-
ual  protocol libraries rather than directly make calls into
the ICE library.  However, some applications  will  have  to
make  some  initial  calls  into the ICE library in order to
accept ICE  connections  (for  example,  a  session  manager
accepting connections from clients).  But in general, proto-
col libraries should be designed to hide the  inner  details
of ICE from applications.





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Inter-Client Exchange Library		    X11, Release 6.4


4.  Header Files and Library Name

The header file <X11/ICE/ICElib.h> defines all of the ICElib
data structures and function prototypes.  ICElib.h  includes
the  header  file  <X11/ICE/ICE.h>, which defines all of the
ICElib constants.  Protocol libraries that need to read  and
write	 messages    should    include	 the   header	file
<X11/ICE/ICEmsg.h>.

Applications should link against ICElib using -lICE.

5.  Note on Prefixes

The following name prefixes are used in the library to	dis-
tinguish between a client that initiates a ProtocolSetup and
a client that responds with a ProtocolReply:

o    IcePo - Ice Protocol Originator

o    IcePa - Ice Protocol Acceptor

6.  Protocol Registration

In order for two clients to exchange messages  for  a  given
protocol,  each side must register the protocol with the ICE
library.  The purpose of registration is for  each  side  to
obtain	a major opcode for the protocol and to provide call-
backs for processing messages and  handling  authentication.
There are two separate registration functions:

o    One to handle the side that does a ProtocolSetup

o    One to handle the side that responds with a ProtocolRe-
     ply

It is recommended that protocol  registration  occur  before
the  two  clients  establish an ICE connection.  If protocol
registration occurs after  an  ICE  connection	is  created,
there  can  be	a  brief  interval of time in which a Proto-
colSetup is received, but the protocol	is  not  registered.
If it is not possible to register a protocol before the cre-
ation of an ICE connection,  proper  precautions  should  be
taken to avoid the above race condition.


The  IceRegisterForProtocolSetup  function  should be called
for the client that initiates a ProtocolSetup.
__
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Inter-Client Exchange Library		    X11, Release 6.4


int IceRegisterForProtocolSetup(protocol_name, vendor, release, version_count, version_recs,
		 auth_count, auth_names, auth_procs, io_error_proc)
     char *protocol_name;
     char *vendor;
     char *release;
     int version_count;
     IcePoVersionRec *version_recs;
     int auth_count;
     char **auth_names;
     IcePoAuthProc *auth_procs;
     IceIOErrorProc io_error_proc;


protocol_name
	  A string specifying the name of  the	protocol  to
	  register.

vendor	  A  vendor  string  with semantics specified by the
	  protocol.

release   A release string with semantics specified  by  the
	  protocol.

version_count
	  The  number  of different versions of the protocol
	  supported.

version_recs
	  List of versions and associated callbacks.

auth_count
	  The number of authentication methods supported.

auth_names
	  The list of authentication methods supported.

auth_procs
	  The list of authentication callbacks, one for each
	  authentication method.

io_error_proc
	  IO error handler, or NULL.
|__

IceRegisterForProtocolSetup   returns	the   major   opcode
reserved or -1 if an error occurred.  In order	to  actually
activate  the  protocol, the IceProtocolSetup function needs
to be called with this major opcode.  Once the	protocol  is
activated,  all  messages  for	the  protocol should be sent
using this major opcode.

A protocol library may support multiple versions of the same
protocol.   The  version_recs  argument  specifies a list of
supported versions of the protocol, which are prioritized in



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Inter-Client Exchange Library		    X11, Release 6.4


decreasing  order  of  preference.  Each version record con-
sists of a major and minor version of the protocol  as	well
as a callback to be used for processing incoming messages.

__
|
typedef struct {
     int major_version;
     int minor_version;
     IcePoProcessMsgProc process_msg_proc;
} IcePoVersionRec;

|__

The IcePoProcessMsgProc callback is responsible for process-
ing the set of messages that can be received by  the  client
that  initiated the ProtocolSetup.  For further information,
see section 6.1, ``Callbacks for Processing Messages.''

Authentication may  be	required  before  the  protocol  can
become	active.   The  protocol  library  must	register the
authentication	methods  that  it  supports  with  the	 ICE
library.  The auth_names and auth_procs arguments are a list
of authentication names and callbacks that are	 prioritized
in  decreasing	order of preference.  For information on the
IcePoAuthProc callback, see  section  6.2,  ``Authentication
Methods.''

The IceIOErrorProc callback is invoked if the ICE connection
unexpectedly breaks.  You should pass NULL for io_error_proc
if  not  interested in being notified.	For further informa-
tion, see section 13, ``Error Handling.''


The IceRegisterForProtocolReply function  should  be  called
for  the  client  that	responds  to  a ProtocolSetup with a
ProtocolReply.
__
|


















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Inter-Client Exchange Library		    X11, Release 6.4


int IceRegisterForProtocolReply(protocol_name, vendor, release, version_count, version_recs,
		    auth_count, auth_names, auth_procs, host_based_auth_proc, protocol_setup_proc,
		     protocol_activate_proc, io_error_proc)
     char *protocol_name;
     char *vendor;
     char *release;
     int version_count;
     IcePaVersionRec *version_recs;
     int auth_count;
     char **auth_names;
     IcePaAuthProc *auth_procs;
     IceHostBasedAuthProc host_based_auth_proc;
     IceProtocolSetupProc protocol_setup_proc;
     IceProtocolActivateProc protocol_activate_proc;
     IceIOErrorProc io_error_proc;


protocol_name
	  A string specifying the name of  the	protocol  to
	  register.

vendor	  A  vendor  string  with semantics specified by the
	  protocol.

release   A release string with semantics specified  by  the
	  protocol.

version_count
	  The  number  of different versions of the protocol
	  supported.

version_recs
	  List of versions and associated callbacks.

auth_count
	  The number of authentication methods supported.

auth_names
	  The list of authentication methods supported.

auth_procs
	  The list of authentication callbacks, one for each
	  authentication method.

host_based_auth_proc
	  Host based authentication callback.

protocol_setup_proc
	  A  callback  to be invoked when authentication has
	  succeeded for a ProtocolSetup but before the	Pro-
	  tocolReply is sent.

protocol_activate_proc
	  A  callback  to be invoked after the ProtocolReply



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Inter-Client Exchange Library		    X11, Release 6.4


	  is sent.

io_error_proc
	  IO error handler, or NULL.
|__

IceRegisterForProtocolReply   returns	the   major   opcode
reserved  or  -1  if  an  error  occurred.  The major opcode
should be used in all subsequent messages sent for this pro-
tocol.

A protocol library may support multiple versions of the same
protocol.  The version_recs argument  specifies  a  list  of
supported versions of the protocol, which are prioritized in
decreasing order of preference.  Each  version	record	con-
sists  of  a major and minor version of the protocol as well
as a callback to be used for processing incoming messages.

__
|
typedef struct {
     int major_version;
     int minor_version;
     IcePaProcessMsgProc process_msg_proc;
} IcePaVersionRec;

|__

The IcePaProcessMsgProc callback is responsible for process-
ing  the  set of messages that can be received by the client
that accepted the ProtocolSetup.  For  further	information,
see section 6.1, ``Callbacks for Processing Messages.''

Authentication	may  be  required  before  the	protocol can
become active.	 The  protocol	library  must  register  the
authentication	 methods  that	it  supports  with  the  ICE
library.  The auth_names and auth_procs arguments are a list
of  authentication  names and callbacks that are prioritized
in decreasing order of preference.  For information  on  the
IcePaAuthProc  callback,  see  section 6.2, ``Authentication
Methods.''

If authentication fails and the client attempting to  initi-
ate  the  ProtocolSetup has not required authentication, the
IceHostBasedAuthProc callback is invoked with the host	name
of  the  originating  client.  If the callback returns True,
the ProtocolSetup will succeed,  even  though  the  original
authentication	failed.  Note that authentication can effec-
tively be disabled by registering  an  IceHostBasedAuthProc,
which  always returns True.  If no host based authentication
is allowed, you should pass NULL for host_based_auth_proc.






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Inter-Client Exchange Library		    X11, Release 6.4

__
|
typedef Bool (*IceHostBasedAuthProc) ();

Bool HostBasedAuthProc(host_name)
    char *host_name;


host_name The  host  name  of  the  client  that  sent	 the
	  ProtocolSetup.
|__

The   host_name   argument   is   a   string   of  the	form
protocol/hostname, where protocol is one  of  {tcp,  decnet,
local}.

Because  ProtocolSetup	messages  and  authentication happen
behind the scenes via callbacks, the protocol library  needs
some  way  of being notified when the ProtocolSetup has com-
pleted.  This occurs in two phases.  In the first phase, the
IceProtocolSetupProc  callback	is invoked after authentica-
tion has successfully completed but before the	ICE  library
sends a ProtocolReply.	Any resources required for this pro-
tocol should be allocated at this time.   If  the  IceProto-
colSetupProc  returns  a  successful status, the ICE library
will send the ProtocolReply and then invoke the  IceProtoco-
lActivateProc callback.  Otherwise, an error will be sent to
the other client in response to the ProtocolSetup.

The IceProtocolActivateProc  is  an  optional  callback  and
should be registered only if the protocol library intends to
generate a message immediately following the  ProtocolReply.
You  should  pass  NULL  for  protocol_activate_proc  if not
interested in this callback.
__
|
typedef Status (*IceProtocolSetupProc) ();

Status ProtocolSetupProc(ice_conn, major_version, minor_version, vendor, release,
		    client_data_ret, failure_reason_ret)
     IceConn ice_conn;
     int major_version;
     int minor_version;
     char *vendor;
     char *release;
     IcePointer *client_data_ret;
     char **failure_reason_ret;


ice_conn  The ICE connection object.

major_version
	  The major version of the protocol.





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Inter-Client Exchange Library		    X11, Release 6.4


minor_version
	  The minor version of the protocol.

vendor	  The vendor string registered by the protocol orig-
	  inator.

release   The  release	string	registered  by	the protocol
	  originator.

client_data_ret
	  Client data to be set by callback.

failure_reason_ret
	  Failure reason returned.
|__

The pointer stored in the client_data_ret argument  will  be
passed	to  the IcePaProcessMsgProc callback whenever a mes-
sage has arrived for this protocol on the ICE connection.

The vendor and release strings should  be  freed  with	free
when they are no longer needed.

If  a failure occurs, the IceProtocolSetupProc should return
a zero status as well as allocate and return a failure	rea-
son  string  in failure_reason_ret.  The ICE library will be
responsible for freeing this memory.

The IceProtocolActivateProc callback is defined as follows:
__
|
typedef void (*IceProtocolActivateProc)();

void ProtocolActivateProc(ice_conn, client_data)
    IceConn ice_conn;
    IcePointer client_data;


ice_conn  The ICE connection object.

client_data
	  The client data set  in  the	IceProtocolSetupProc
	  callback.
|__

The IceIOErrorProc callback is invoked if the ICE connection
unexpectedly breaks.  You should pass NULL for io_error_proc
if  not  interested in being notified.	For further informa-
tion, see section 13, ``Error Handling.''

6.1.  Callbacks for Processing Messages

When an application detects that there is new data  to	read
on   an   ICE	connection   (via   select),  it  calls  the



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Inter-Client Exchange Library		    X11, Release 6.4


IceProcessMessages function  (see  section  9,	``Processing
Messages'').   When  IceProcessMessages reads an ICE message
header with a major opcode other than zero (reserved for the
ICE  protocol),  it  needs to call a function that will read
the rest of the message, unpack it, and process  it  accord-
ingly.

If  the  message  arrives  at  the client that initiated the
ProtocolSetup, the IcePoProcessMsgProc callback is  invoked.
__
|
typedef void (*IcePoProcessMsgProc)();

void PoProcessMsgProc(ice_conn, client_data, opcode, length, swap, reply_wait, reply_ready_ret)
    IceConn ice_conn;
    IcePointer client_data;
    int opcode;
    unsigned long length;
    Bool swap;
    IceReplyWaitInfo *reply_wait;
    Bool *reply_ready_ret;


ice_conn  The ICE connection object.

client_data
	  Client  data	associated with this protocol on the
	  ICE connection.

opcode	  The minor opcode of the message.

length	  The length (in 8-byte units) of the message beyond
	  the ICE header.

swap	  A  flag  that indicates if byte swapping is neces-
	  sary.

reply_wait
	  Indicates if the invoking client is waiting for  a
	  reply.

reply_ready_ret
	  If set to True, a reply is ready.
|__

If  the  message  arrives  at  the  client that accepted the
ProtocolSetup, the IcePaProcessMsgProc callback is  invoked.
__
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Inter-Client Exchange Library		    X11, Release 6.4


typedef void (*IcePaProcessMsgProc)();

void PaProcessMsgProc(ice_conn, client_data, opcode, length, swap)
    IceConn ice_conn;
    IcePointer client_data;
    int opcode;
    unsigned long length;
    Bool swap;


ice_conn  The ICE connection object.

client_data
	  Client  data	associated with this protocol on the
	  ICE connection.

opcode	  The minor opcode of the message.

length	  The length (in 8-byte units) of the message beyond
	  the ICE header.

swap	  A  flag  that indicates if byte swapping is neces-
	  sary.
|__

In order to read the message, both of these callbacks should
use  the  macros defined for this purpose (see section 12.2,
``Reading ICE Messages'').  Note that byte swapping  may  be
necessary.   As  a  convenience, the length field in the ICE
header will be swapped by ICElib if necessary.

In both of these callbacks, the client_data  argument  is  a
pointer  to client data that was registered at ProtocolSetup
time.  In the case of IcePoProcessMsgProc, the	client	data
was  set  in  the  call to IceProtocolSetup.  In the case of
IcePaProcessMsgProc, the client data was set in the  IcePro-
tocolSetupProc callback.

The   IcePoProcessMsgProc   callback   needs  to  check  the
reply_wait argument.   If  reply_wait  is  NULL  ,  the  ICE
library  expects  the  function  to  pass the message to the
client via a callback.	For example, if this  is  a  Session
Management  ``Save  Yourself'' message, this function should
notify the client of the ``Save Yourself'' via	a  callback.
The  details  of  how  such  a callback would be defined are
implementation-dependent.

However, if reply_wait is not NULL  ,  then  the  client  is
waiting  for a reply or an error for a message it previously
sent.  The reply_wait is of type IceReplyWaitInfo.
__
|
typedef struct {
     unsigned long sequence_of_request;



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Inter-Client Exchange Library		    X11, Release 6.4


     int major_opcode_of_request;
     int minor_opcode_of_request;
     IcePointer reply;
} IceReplyWaitInfo;

|__

IceReplyWaitInfo  contains  the  major/minor   opcodes	 and
sequence  number  of  the message for which a reply is being
awaited.  It also contains a pointer to the reply message to
be  filled  in	(the  protocol library should cast this Ice-
Pointer to the appropriate reply type).  In most cases,  the
reply will have some fixed-size part, and the client waiting
for the reply will have provided a pointer to a structure to
hold  this  fixed-size	data.	If  there is variable-length
data, it would	be  expected  that  the  IcePoProcessMsgProc
callback  will	have to allocate additional memory and store
pointer(s) to that memory in the fixed-size  structure.   If
the  entire  data is variable length (for example., a single
variable-length string), then the  client  waiting  for  the
reply would probably just pass a pointer to fixed-size space
to hold a  pointer,  and  the  IcePoProcessMsgProc  callback
would allocate the storage and store the pointer.  It is the
responsibility of the client receiving the reply to free any
memory allocated on its behalf.

If  reply_wait	is  not  NULL  and IcePoProcessMsgProc has a
reply or error to return  in  response	to  this  reply_wait
(that	is,   no   callback   was   generated),   then	 the
reply_ready_ret argument should be set to True.   Note	that
an  error  should  only be returned if it corresponds to the
reply being waited for.  Otherwise, the  IcePoProcessMsgProc
should either handle the error internally or invoke an error
handler for its library.

If reply_wait is NULL, then care must be taken not to  store
any  value in reply_ready_ret, because this pointer may also
be NULL.

The IcePaProcessMsgProc callback, on the other hand,  should
always	pass  the message to the client via a callback.  For
example,  if  this  is	a  Session   Management   ``Interact
Request'' message, this function should notify the client of
the ``Interact Request'' via a callback.

The reason the IcePaProcessMsgProc callback does not have  a
reply_wait, like IcePoProcessMsgProc does, is because a pro-
cess that is acting as a server should	never  block  for  a
reply  (infinite blocking can occur if the connecting client
does not act properly, denying access to other clients).







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Inter-Client Exchange Library		    X11, Release 6.4


6.2.  Authentication Methods

As already stated, a  protocol	library  must  register  the
authentication	 methods  that	it  supports  with  the  ICE
library.  For each  authentication  method,  there  are  two
callbacks that may be registered:

o    One to handle the side that initiates a ProtocolSetup

o    One  to  handle  the  side that accepts or rejects this
     request

IcePoAuthProc is the callback invoked for  the	client	that
initiated  the ProtocolSetup.  This callback must be able to
respond to the initial ``Authentication  Required''  message
or subsequent ``Authentication Next Phase'' messages sent by
the other client.
__
|
typedef IcePoAuthStatus (*IcePoAuthProc)();

IcePoAuthStatus PoAuthProc(ice_conn, auth_state_ptr, clean_up, swap, auth_datalen, auth_data,
		    reply_datalen_ret, reply_data_ret, error_string_ret)
    IceConn ice_conn;
    IcePointer *auth_state_ptr;
    Bool clean_up;
    Bool swap;
    int auth_datalen;
    IcePointer auth_data;
    int *reply_datalen_ret;
    IcePointer *reply_data_ret;
    char **error_string_ret;


ice_conn  The ICE connection object.

auth_state_ptr
	  A pointer to state for use by  the  authentication
	  callback procedure.

clean_up  If  True, authentication is over, and the function
	  should clean up any state it was maintaining.  The
	  last 6 arguments should be ignored.

swap	  If True, the auth_data may have to be byte swapped
	  (depending on its contents).

auth_datalen
	  The length (in bytes) of the authenticator data.

auth_data The data from the authenticator.

reply_datalen_ret
	  The length (in bytes) of the reply data  returned.



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Inter-Client Exchange Library		    X11, Release 6.4


reply_data_ret
	  The reply data returned.

error_string_ret
	  If  the  authentication  procedure  encounters  an
	  error during authentication,	it  should  allocate
	  and return an error string.
|__

Authentication	may require several phases, depending on the
authentication method.	As a result, the  IcePoAuthProc  may
be  called  more than once when authenticating a client, and
some state will have to be maintained between  each  invoca-
tion.	At  the start of each ProtocolSetup, *auth_state_ptr
is NULL, and the function should initialize  its  state  and
set  this  pointer.   In subsequent invocations of the call-
back, the pointer should be used to get at any state  previ-
ously stored by the callback.

If needed, the network ID of the client accepting the Proto-
colSetup can be obtained by calling the  IceConnectionString
function.

ICElib	will  be  responsible for freeing the reply_data_ret
and error_string_ret pointers with free.

The auth_data pointer may point to a volatile block of	mem-
ory.  If the data must be kept beyond this invocation of the
callback, be sure to make a copy of it.

The IcePoAuthProc should return one of four values:

o    IcePoAuthHaveReply - a reply is available.

o    IcePoAuthRejected - authentication rejected.

o    IcePoAuthFailed - authentication failed.

o    IcePoAuthDoneCleanup - done cleaning up.

IcePaAuthProc is the callback invoked for  the	client	that
received the ProtocolSetup.
__
|













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Inter-Client Exchange Library		    X11, Release 6.4


typedef IcePaAuthStatus (*IcePaAuthProc) ();

IcePaAuthStatus PaAuthProc(ice_conn, auth_state_ptr, swap, auth_datalen, auth_data,
		    reply_datalen_ret, reply_data_ret, error_string_ret)
    IceConn ice_conn;
    IcePointer *auth_state_ptr;
    Bool swap;
    int auth_datalen;
    IcePointer auth_data;
    int *reply_datalen_ret;
    IcePointer *reply_data_ret;
    char **error_string_ret;


ice_conn  The ICE connection object.

auth_state_ptr
	  A  pointer  to state for use by the authentication
	  callback procedure.

swap	  If True, auth_data may have  to  be  byte  swapped
	  (depending on its contents).

auth_datalen
	  The  length  (in bytes) of the protocol originator
	  authentication data.

auth_data The authentication data from the protocol origina-
	  tor.

reply_datalen_ret
	  The length of the authentication data returned.

reply_data_ret
	  The authentication data returned.

error_string_ret
	  If  authentication  is rejected or fails, an error
	  string is returned.
|__


Authentication may require several phases, depending on  the
authentication	method.   As a result, the IcePaAuthProc may
be called more than once when authenticating a	client,  and
some  state  will have to be maintained between each invoca-
tion.  At the start of each ProtocolSetup,  auth_datalen  is
zero,  *auth_state_ptr is NULL, and the function should ini-
tialize its state and set this pointer.  In subsequent invo-
cations  of  the callback, the pointer should be used to get
at any state previously stored by the callback.

If needed, the network ID of the client accepting the Proto-
colSetup  can be obtained by calling the IceConnectionString



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Inter-Client Exchange Library		    X11, Release 6.4


function.

The auth_data pointer may point to a volatile block of	mem-
ory.  If the data must be kept beyond this invocation of the
callback, be sure to make a copy of it.

ICElib will be responsible for transmitting and freeing  the
reply_data_ret and error_string_ret pointers with free.

The IcePaAuthProc should return one of four values:

o    IcePaAuthContinue - continue (or start) authentication.

o    IcePaAuthAccepted - authentication accepted.

o    IcePaAuthRejected - authentication rejected.

o    IcePaAuthFailed - authentication failed.

7.  ICE Connections

In order for two clients to establish an ICE connection, one
client	has  to  be  waiting  for connections, and the other
client has to initiate the connection.	 Most  clients	will
initiate connections, so we discuss that first.

7.1.  Opening an ICE Connection

To  open  an  ICE  connection  with another client (that is,
waiting for connections), use IceOpenConnection.
__
|
IceConn IceOpenConnection(network_ids_list, context, must_authenticate, major_opcode_check,
		    error_length, error_string_ret)
     char *network_ids_list;
     IcePointer context;
     Bool must_authenticate;
     int major_opcode_check;
     int  error_length;
     char *error_string_ret;


network_ids_list
	  Specifies the network ID(s) of the other client.

context   A pointer to an opaque object or  NULL.   Used  to
	  determine  if an ICE connection can be shared (see
	  below).

must_authenticate
	  If True, the other client may not bypass authenti-
	  cation.





			   - 15 -





Inter-Client Exchange Library		    X11, Release 6.4


major_opcode_check
	  Used	to  force a new ICE connection to be created
	  (see below).

error_length
	  Length of the error_string_ret argument passed in.

error_string_ret
	  Returns  a  null-terminated error message, if any.
	  The error_string_ret argument points to user	sup-
	  plied memory.  No more than error_length bytes are
	  used.
|__

IceOpenConnection returns an opaque ICE connection object if
it succeeds; otherwise, it returns NULL.

The network_ids_list argument contains a list of network IDs
separated by commas.  An attempt will be  made	to  use  the
first  network	ID.   If that fails, an attempt will be made
using the second network ID, and so on.  Each network ID has
the following format:

     tcp/<hostname>:<portnumber>    or
     decnet/<hostname>::<objname>   or
     local/<hostname>:<path>


Most protocol libraries will have some sort of open function
that should internally make a call  into  IceOpenConnection.
When  IceOpenConnection is called, it may be possible to use
a previously opened ICE connection (if the target client  is
the  same).   However,	there  are cases in which shared ICE
connections are not desired.

The context argument is used to determine if an ICE  connec-
tion  can be shared.  If context is NULL, then the caller is
always willing to share the connection.  If context  is  not
NULL,  then  the  caller  is not willing to use a previously
opened ICE connection that has a different non-NULL  context
associated with it.

In  addition, if major_opcode_check contains a nonzero major
opcode value, a previously created ICE	connection  will  be
used  only  if the major opcode is not active on the connec-
tion.  This can be used to force  multiple  ICE  connections
between two clients for the same protocol.

Any  authentication  requirements  are handled internally by
the ICE library.  The method  by  which  the  authentication
data is obtained is implementation-dependent.
-----------
   The	X  Consortium's ICElib implementation uses
an .ICEauthority file (see Appendix A).



			   - 16 -





Inter-Client Exchange Library		    X11, Release 6.4


After IceOpenConnection is called, the client  is  ready  to
send  a  ProtocolSetup	(provided  that IceRegisterForProto-
colSetup was called) or receive  a  ProtocolSetup  (provided
that IceRegisterForProtocolReply was called).

7.2.  Listening for ICE Connections

Clients  wishing  to  accept ICE connections must first call
IceListenForConnections or  IceListenForWellKnownConnections
so  that  they can listen for connections.  A list of opaque
"listen" objects are returned, one for each type  of  trans-
port  method  that  is	available (for example, Unix Domain,
TCP, DECnet, and so on).

Normally clients will let ICElib allocate an available	name
in  each transport and return listen objects.  Such a client
will then use IceComposeNetworkIdList to extract the  chosen
names  and  make them available to other clients for opening
the connection.  In certain cases it may be necessary for  a
client	to  listen for connections on pre-arranged transport
object names.  Such a client may use  IceListenForWellKnown-
Connections to specify the names for the listen objects.
__
|
Status IceListenForConnections(count_ret, listen_objs_ret, error_length, error_string_ret)
     int  *count_ret;
     IceListenObj **listen_objs_ret;
     int  error_length;
     char *error_string_ret;


count_ret Returns the number of listen objects created.

listen_objs_ret
	  Returns  a  list  of	pointers  to  opaque  listen
	  objects.

error_length
	  The length of the error_string_ret argument passed
	  in.

error_string_ret
	  Returns  a  null-terminated error message, if any.
	  The error_string_ret points to user supplied	mem-
	  ory.	No more than error_length bytes are used.
|__

The  return  value  of	IceListenForConnections  is zero for
failure and a positive value for success.

__
|





			   - 17 -





Inter-Client Exchange Library		    X11, Release 6.4


Status IceListenForWellKnownConnections(port_id, count_ret, listen_objs_ret, error_length, error_string_ret)
     char *port_id;
     int  *count_ret;
     IceListenObj **listen_objs_ret;
     int  error_length;
     char *error_string_ret;


port_id   Specifies  the   port   identification   for	 the
	  address(es) to be opened.  The value must not con-
	  tain the slash (``/'') or comma (``,'') character;
	  these are reserved for future use.

count_ret Returns the number of listen objects created.

listen_objs_ret
	  Returns  a  list  of	pointers  to  opaque  listen
	  objects.

error_length
	  The length of the error_string_ret argument passed
	  in.

error_string_ret
	  Returns  a  null-terminated error message, if any.
	  The error_string_ret points to user supplied	mem-
	  ory.	No more than error_length bytes are used.
|__

IceListenForWellKnownConnections  constructs  a list of net-
work IDs by prepending each known transport to	port_id  and
then  attempts	to  create  listen  objects  for the result.
Port_id is the portnumber, objname, or path portion  of  the
ICE  network ID. If a listen object for a particular network
ID cannot be created the network ID is ignored.  If no	lis-
ten  objects  are  created  IceListenForWellKnownConnections
returns failure.

The return value of IceListenForWellKnownConnections is zero
for failure and a positive value for success.


To close and free the listen objects, use IceFreeListenObjs.

__
|
void IceFreeListenObjs(count, listen_objs)
    int count;
    IceListenObj *listen_objs;


count	  The number of listen objects.





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Inter-Client Exchange Library		    X11, Release 6.4


listen_objs
	  The listen objects.
|__


To detect a new connection on a listen object, use select on
the descriptor associated with the listen object.


To  obtain the descriptor, use IceGetListenConnectionNumber.

__
|
int IceGetListenConnectionNumber(listen_obj)
    IceListenObj listen_obj;


listen_obj
	  The listen object.
|__


To obtain the network ID string  associated  with  a  listen
object, use IceGetListenConnectionString.
__
|
char *IceGetListenConnectionString(listen_obj)
    IceListenObj listen_obj;


listen_obj
	  The listen object.
|__


A network ID has the following format:

     tcp/<hostname>:<portnumber>    or
     decnet/<hostname>::<objname>   or
     local/<hostname>:<path>


To  compose  a string containing a list of network IDs sepa-
rated	 by    commas	 (the	 format    recognized	  by
IceOpenConnection), use IceComposeNetworkIdList.

__
|
char *IceComposeNetworkIdList(count, listen_objs)
    int count;
    IceListenObj *listen_objs;






			   - 19 -





Inter-Client Exchange Library		    X11, Release 6.4


count	  The number of listen objects.

listen_objs
	  The listen objects.
|__


7.3.  Host Based Authentication for ICE Connections

If authentication fails when a client attempts	to  open  an
ICE  connection  and  the initiating client has not required
authentication, a host based authentication procedure may be
invoked  to provide a last chance for the client to connect.
Each listen object has such a callback associated  with  it,
and  this  callback is set using the IceSetHostBasedAuthProc
function.
__
|
void IceSetHostBasedAuthProc(listen_obj, host_based_auth_proc)
    IceListenObj listen_obj;
    IceHostBasedAuthProc host_based_auth_proc;


listen_obj
	  The listen object.

host_based_auth_proc
	  The host based authentication procedure.
|__

By default, each listen object has no host based authentica-
tion   procedure  associated  with  it.   Passing  NULL  for
host_based_auth_proc turns off host based authentication  if
it was previously set.

__
|
typedef Bool (*IceHostBasedAuthProc) ();

Bool HostBasedAuthProc(host_name)
    char *host_name;


host_name The  host name of the client that tried to open an
	  ICE connection.
|__

The  host_name	argument   is	a   string   in   the	form
protocol/hostname,  where  protocol  is one of {tcp, decnet,
local}.

If  IceHostBasedAuthProc  returns  True,  access   will   be
granted,  even	though	the  original authentication failed.
Note that authentication  can  effectively  be	disabled  by



			   - 20 -





Inter-Client Exchange Library		    X11, Release 6.4


registering  an  IceHostBasedAuthProc,	which always returns
True.

Host based authentication is also allowed  at  ProtocolSetup
time.  The callback is specified in the IceRegisterForProto-
colReply  function  (see  section  6,  ``Protocol  Registra-
tion'').

7.4.  Accepting ICE Connections

After  a  connection  attempt is detected on a listen object
returned  by  IceListenForConnections,	 you   should	call
IceAcceptConnection.   This returns a new opaque ICE connec-
tion object.
__
|
IceConn IceAcceptConnection(listen_obj, status_ret)
    IceListenObj listen_obj;
    IceAcceptStatus *status_ret;


listen_obj
	  The listen object on which a	new  connection  was
	  detected.

status_ret
	  Return status information.
|__

The  status_ret argument is set to one of the following val-
ues:

o    IceAcceptSuccess - the accept operation succeeded,  and
     the function returns a new connection object.

o    IceAcceptFailure - the accept operation failed, and the
     function returns NULL.

o    IceAcceptBadMalloc - a memory  allocation	failed,  and
     the function returns NULL.

In  general,  to  detect  new  connections,  you should call
select on the file descriptors associated  with  the  listen
objects.   When a new connection is detected, the IceAccept-
Connection function should be  called.	 IceAcceptConnection
may  return a new ICE connection that is in a pending state.
This is because before	the  connection  can  become  valid,
authentication	may  be  necessary.  Because the ICE library
cannot block and wait for the  connection  to  become  valid
(infinite  blocking  can occur if the connecting client does
not act properly), the application must wait for the connec-
tion status to become valid.





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Inter-Client Exchange Library		    X11, Release 6.4


The  following	pseudo-code demonstrates how connections are
accepted:


new_ice_conn = IceAcceptConnection (listen_obj, &accept_status);
if (accept_status != IceAcceptSuccess)
{
     close the file descriptor and return
}

status = IceConnectionStatus (new_ice_conn);
time_start = time_now;

while (status == IceConnectPending)
{
     select() on {new_ice_conn, all open connections}

     for (each ice_conn in the list of open connections)
	  if (data ready on ice_conn)
	  {
	       status = IceProcessMessages (ice_conn, NULL, NULL);
	       if (status == IceProcessMessagesIOError)
		    IceCloseConnection (ice_conn);
	  }

     if (data ready on new_ice_conn)
     {
	  /*
	   * IceProcessMessages is called until the connection
	   * is non-pending.  Doing so handles the connection
	   * setup request and any authentication requirements.
	   */

	  IceProcessMessages (new_ice_conn, NULL, NULL);
	  status = IceConnectionStatus (new_ice_conn);
     }
     else
     {
	  if (time_now - time_start > MAX_WAIT_TIME)
	       status = IceConnectRejected;
     }
}

if (status == IceConnectAccepted)
{
     Add new_ice_conn to the list of open connections
}
else
{
     IceCloseConnection (new_ice_conn);
}






			   - 22 -





Inter-Client Exchange Library		    X11, Release 6.4


After IceAcceptConnection is called and the  connection  has
been  validated,  the  client  is  ready to receive a Proto-
colSetup  (provided  that  IceRegisterForProtocolReply	 was
called)  or send a ProtocolSetup (provided that IceRegister-
ForProtocolSetup was called).

7.5.  Closing ICE Connections

To close an ICE connection created with IceOpenConnection or
IceAcceptConnection, use IceCloseConnection.
__
|
IceCloseStatus IceCloseConnection(ice_conn)
    IceConn ice_conn;


ice_conn  The ICE connection to close.
|__

To  actually  close  an ICE connection, the following condi-
tions must be met:

o    The open reference count must have reached zero on this
     ICE  connection.	When IceOpenConnection is called, it
     tries to use a previously opened ICE connection.  If it
     is  able  to  use an existing connection, it increments
     the open reference count on the connection by one.  So,
     to close an ICE connection, each call to IceOpenConnec-
     tion must be matched with a call to IceCloseConnection.
     The  connection  can be closed only on the last call to
     IceCloseConnection.

o    The active protocol count must have reached zero.	Each
     time  a  ProtocolSetup  succeeds on the connection, the
     active protocol count is incremented by one.  When  the
     client  no  longer  expects  to use the protocol on the
     connection, the IceProtocolShutdown function should  be
     called,  which  decrements the active protocol count by
     one (see section 8, ``Protocol Setup and Shutdown'').

o    If shutdown negotiation is enabled on  the  connection,
     the client on the other side of the ICE connection must
     agree to have the connection closed.

IceCloseConnection returns one of the following values:

o    IceClosedNow - the ICE connection was  closed  at	this
     time.   The  watch procedures were invoked and the con-
     nection was freed.

o    IceClosedASAP - an IO error had occurred on the connec-
     tion,  but  IceCloseConnection is being called within a
     nested IceProcessMessages.  The watch  procedures	have
     been  invoked  at this time, but the connection will be



			   - 23 -





Inter-Client Exchange Library		    X11, Release 6.4


     freed as soon  as	possible  (when  the  nesting  level
     reaches zero and IceProcessMessages returns a status of
     IceProcessMessagesConnectionClosed).

o    IceConnectionInUse - the connection was not  closed  at
     this  time,  because  it  is being used by other active
     protocols.

o    IceStartedShutdownNegotiation - the connection was  not
     closed  at  this  time and shutdown negotiation started
     with the client on the other side of  the	ICE  connec-
     tion.   When the connection is actually closed, IcePro-
     cessMessages    will     return	 a     status	  of
     IceProcessMessagesConnectionClosed.


When  it  is  known that the client on the other side of the
ICE connection has terminated the connection without  initi-
ating  shutdown  negotiation,  the IceSetShutdownNegotiation
function should be called to turn off shutdown	negotiation.
This  will prevent IceCloseConnection from writing to a bro-
ken connection.
__
|
void IceSetShutdownNegotiation(ice_conn, negotiate)
    IceConn ice_conn;
    Bool negotiate;


ice_conn  A valid ICE connection object.

negotiate If False, shutdown negotiating will be turned off.
|__


To  check  the shutdown negotiation status of an ICE connec-
tion, use IceCheckShutdownNegotiation.
__
|
Bool IceCheckShutdownNegotiation(ice_conn)
    IceConn ice_conn;


ice_conn  A valid ICE connection object.
|__

IceCheckShutdownNegotiation returns True if shutdown negoti-
ation  will  take  place  on  the  connection; otherwise, it
returns False.	Negotiation is on by default for  a  connec-
tion.  It can only be changed with the IceSetShutdownNegoti-
ation function.






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Inter-Client Exchange Library		    X11, Release 6.4


7.6.  Connection Watch Procedures

To add a watch procedure  that	will  be  called  each	time
ICElib	opens  a  new  connection  via	IceOpenConnection or
IceAcceptConnection   or    closes    a    connection	 via
IceCloseConnection, use IceAddConnectionWatch.
__
|
Status IceAddConnectionWatch(watch_proc, client_data)
    IceWatchProc watch_proc;
    IcePointer client_data;


watch_proc
	  The watch procedure to invoke when ICElib opens or
	  closes a connection.

client_data
	  This pointer will be passed to  the  watch  proce-
	  dure.
|__

The  return value of IceAddConnectionWatch is zero for fail-
ure, and a positive value for success.

Note that several calls to IceOpenConnection might share the
same ICE connection.  In such a case, the watch procedure is
only invoked when the connection  is  first  created  (after
authentication	succeeds).   Similarly,  because connections
might be shared, the watch procedure is called only if	Ice-
CloseConnection actually closes the connection (right before
the IceConn is freed).

The watch procedures are very useful for  applications	that
need  to  add  a file descriptor to a select mask when a new
connection is created and remove the  file  descriptor	when
the   connection  is  destroyed.   Because  connections  are
shared, knowing when to add and remove the  file  descriptor
from  the  select  mask would be difficult without the watch
procedures.

Multiple watch procedures may be  registered  with  the  ICE
library.  No assumptions should be made about their order of
invocation.

If one or more ICE connections were already created  by  the
ICE  library  at the time the watch procedure is registered,
the watch procedure will instantly be invoked  for  each  of
these  ICE  connections  (with	the  opening argument set to
True).







			   - 25 -





Inter-Client Exchange Library		    X11, Release 6.4


The watch procedure is of type IceWatchProc.
__
|
typedef void (*IceWatchProc)();

void WatchProc(ice_conn, client_data, opening, watch_data)
    IceConn ice_conn;
    IcePointer client_data;
    Bool opening;
    IcePointer *watch_data;


ice_conn  The opened or closed ICE connection.	Call IceCon-
	  nectionNumber  to  get the file descriptor associ-
	  ated with this connection.

client_data
	  Client   data   specified   in   the	  call	  to
	  IceAddConnectionWatch.

opening   If  True,  the  connection  is  being  opened.  If
	  False, the connection is being closed.

watch_data
	  Can be used to save a pointer to client data.
|__

If opening is True, the client should  set  the  *watch_data
pointer to any data it may need to save until the connection
is closed and the watch  procedure  is	invoked  again	with
opening set to False.


To remove a watch procedure, use IceRemoveConnectionWatch.
__
|
void IceRemoveConnectionWatch(watch_proc, client_data)
    IceWatchProc watch_proc;
    IcePointer client_data;



watch_proc
	  The	watch	procedure   that   was	 passed   to
	  IceAddConnectionWatch.

client_data
	  The  client_data  pointer  that  was	 passed   to
	  IceAddConnectionWatch.
|__







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Inter-Client Exchange Library		    X11, Release 6.4


8.  Protocol Setup and Shutdown

To  activate  a  protocol  on  a  given  ICE connection, use
IceProtocolSetup.

__
|
IceProtocolSetupStatus IceProtocolSetup(ice_conn, my_opcode, client_data, must_authenticate,
		    major_version_ret, minor_version_ret, vendor_ret, release_ret, error_length, error_string_ret)
    IceConn ice_conn;
    int my_opcode;
    IcePointer client_data;
    Bool must_authenticate;
    int *major_version_ret;
    int *minor_version_ret;
    char **vendor_ret;
    char **release_ret;
    int error_length;
    char *error_string_ret;


ice_conn  A valid ICE connection object.

my_opcode The major opcode of the protocol to be set up,  as
	  returned by IceRegisterForProtocolSetup.

client_data
	  The  client  data  stored  in this pointer will be
	  passed to the IcePoProcessMsgProc callback.

must_authenticate
	  If True, the other client may not bypass authenti-
	  cation.

major_version_ret
	  The  major  version  of the protocol to be used is
	  returned.

minor_version_ret
	  The minor version of the protocol to	be  used  is
	  returned.

vendor_ret
	  The vendor string specified by the protocol accep-
	  tor.

release_ret
	  The  release	string	specified  by  the  protocol
	  acceptor.

error_length
	  Specifies the length of the error_string_ret argu-
	  ment passed in.




			   - 27 -





Inter-Client Exchange Library		    X11, Release 6.4


error_string_ret
	  Returns a null-terminated error message,  if	any.
	  The  error_string_ret argument points to user sup-
	  plied memory.  No more than error_length bytes are
	  used.
|__

The  vendor_ret and release_ret strings should be freed with
free when no longer needed.

IceProtocolSetup returns one of the following values:

o    IceProtocolSetupSuccess   -   the	  major_version_ret,
     minor_version_ret, vendor_ret, release_ret are set.

o    IceProtocolSetupFailure  or  IceProtocolSetupIOError  -
     check  error_string_ret  for   failure   reason.	 The
     major_version_ret,    minor_version_ret,	 vendor_ret,
     release_ret are not set.

o    IceProtocolAlreadyActive -  this  protocol  is  already
     active  on  this  connection.   The  major_version_ret,
     minor_version_ret, vendor_ret, release_ret are not set.


To  notify  the  ICE  library  when a given protocol will no
longer	 be    used    on    an    ICE	  connection,	 use
IceProtocolShutdown.

__
|
Status IceProtocolShutdown(ice_conn, major_opcode)
    IceConn ice_conn;
    int major_opcode;


ice_conn  A valid ICE connection object.

major_opcode
	  The major opcode of the protocol to shut down.
|__

The  return value of IceProtocolShutdown is zero for failure
and a positive value for success.

Failure will occur if the major opcode was never  registered
OR  the  protocol of the major opcode was never activated on
the connection.  By activated, we mean that a  ProtocolSetup
succeeded  on the connection.  Note that ICE does not define
how each sub-protocol triggers a protocol shutdown.







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Inter-Client Exchange Library		    X11, Release 6.4


9.  Processing Messages

To process incoming  messages  on  an  ICE  connection,  use
IceProcessMessages.
__
|
IceProcessMessagesStatus IceProcessMessages(ice_conn, reply_wait, reply_ready_ret)
    IceConn ice_conn;
    IceReplyWaitInfo *reply_wait;
    Bool *reply_ready_ret;


ice_conn  A valid ICE connection object.

reply_wait
	  Indicates if a reply is being waited for.

reply_ready_ret
	  If set to True on return, a reply is ready.
|__

IceProcessMessages is used in two ways:

o    In the first, a client may generate a message and block
     by calling IceProcessMessages repeatedly until it	gets
     its reply.

o    In  the  second, a client calls IceProcessMessages with
     reply_wait set to NULL in response  to  select  showing
     that  there is data to read on the ICE connection.  The
     ICE library may process zero or more complete messages.
     Note  that messages that are not blocked for are always
     processed by invoking callbacks.

IceReplyWaitInfo  contains  the  major/minor   opcodes	 and
sequence  number  of  the message for which a reply is being
awaited.  It also contains a pointer to the reply message to
be  filled  in	(the  protocol library should cast this Ice-
Pointer to the appropriate reply type).  In most cases,  the
reply will have some fixed-size part, and the client waiting
for the reply will have provided a pointer to a structure to
hold  this  fixed-size	data.	If  there is variable-length
data, it would	be  expected  that  the  IcePoProcessMsgProc
callback  will	have to allocate additional memory and store
pointer(s) to that memory in the fixed-size  structure.   If
the  entire  data  is variable length (for example, a single
variable-length string), then the  client  waiting  for  the
reply would probably just pass a pointer to fixed-size space
to hold a  pointer,  and  the  IcePoProcessMsgProc  callback
would allocate the storage and store the pointer.  It is the
responsibility of the client receiving the reply to free  up
any memory allocated on its behalf.





			   - 29 -





Inter-Client Exchange Library		    X11, Release 6.4

__
|
typedef struct {
     unsigned long sequence_of_request;
     int major_opcode_of_request;
     int minor_opcode_of_request;
     IcePointer reply;
} IceReplyWaitInfo;

|__

If reply_wait is not NULL and IceProcessMessages has a reply
or error to return in response to this reply_wait (that  is,
no  callback  was generated), then the reply_ready_ret argu-
ment will be set to True.

If reply_wait is NULL, then the caller may  also  pass	NULL
for  reply_ready_ret and be guaranteed that no value will be
stored in this pointer.

IceProcessMessages returns one of the following values:

o    IceProcessMessagesSuccess - no error occurred.

o    IceProcessMessagesIOError - an IO error  occurred,  and
     the  caller  must	explicitly  close  the connection by
     calling IceCloseConnection.

o    IceProcessMessagesConnectionClosed - the ICE connection
     has been closed (closing of the connection was deferred
     because of shutdown negotiation, or because the IcePro-
     cessMessages  nesting  level  was	not  zero).   Do not
     attempt to access the ICE	connection  at	this  point,
     since it has been freed.

10.  Ping

To  send  a ``Ping'' message to the client on the other side
of the ICE connection, use IcePing.
__
|
Status IcePing(ice_conn, ping_reply_proc, client_data)
    IceConn ice_conn;
    IcePingReplyProc ping_reply_proc;
    IcePointer client_data;


ice_conn  A valid ICE connection object.

ping_reply_proc
	  The  callback  to  invoke  when  the	Ping   reply
	  arrives.

client_data
	  This	  pointer    will    be    passed   to	 the



			   - 30 -





Inter-Client Exchange Library		    X11, Release 6.4


	  IcePingReplyProc callback.
|__

IcePing returns zero for failure and a	positive  value  for
success.

When  IceProcessMessages  processes  the Ping reply, it will
invoke the IcePingReplyProc callback.
__
|
typedef void (*IcePingReplyProc)();

void PingReplyProc(ice_conn, client_data)
    IceConn ice_conn;
    IcePointer client_data;


ice_conn  The ICE connection object.

client_data
	  The client data specified in the call to  IcePing.
|__


11.  Using ICElib Informational Functions

__
|
IceConnectStatus IceConnectionStatus(ice_conn)
    IceConn ice_conn;
|__

IceConnectionStatus returns the status of an ICE connection.
The possible return values are:

o    IceConnectPending - the connection  is  not  valid  yet
     (that  is,  authentication  is  taking place).  This is
     only    relevant	 to    connections    created	  by
     IceAcceptConnection.

o    IceConnectAccepted  - the connection has been accepted.
     This  is  only  relevant  to  connections	created   by
     IceAcceptConnection.

o    IceConnectRejected  -  the connection had been rejected
     (that is, authentication failed).	This is  only  rele-
     vant to connections created by IceAcceptConnection.

o    IceConnectIOError	-  an  IO  error has occurred on the
     connection.







			   - 31 -





Inter-Client Exchange Library		    X11, Release 6.4

__
|
char *IceVendor(ice_conn)
    IceConn ice_conn;
|__

IceVendor returns the ICE library vendor identification  for
the  other  side  of  the  connection.	The string should be
freed with a call to free when no longer needed.

__
|
char *IceRelease(ice_conn)
    IceConn ice_conn;
|__

IceRelease returns the release	identification	of  the  ICE
library  on  the  other  side of the connection.  The string
should be freed with a call to free when no longer needed.

__
|
int IceProtocolVersion(ice_conn)
    IceConn ice_conn;
|__

IceProtocolVersion returns the major version of the ICE pro-
tocol on this connection.

__
|
int IceProtocolRevision(ice_conn)
    IceConn ice_conn;
|__

IceProtocolRevision  returns  the  minor  version of the ICE
protocol on this connection.

__
|
int IceConnectionNumber(ice_conn)
    IceConn ice_conn;
|__

IceConnectionNumber returns the file descriptor of this  ICE
connection.

__
|
char *IceConnectionString(ice_conn)
    IceConn ice_conn;
|__

IceConnectionString  returns  the  network  ID of the client
that accepted this connection.	The string should  be  freed



			   - 32 -





Inter-Client Exchange Library		    X11, Release 6.4


with a call to free when no longer needed.

__
|
unsigned long IceLastSentSequenceNumber(ice_conn)
    IceConn ice_conn;
|__

IceLastSentSequenceNumber returns the sequence number of the
last message sent on this ICE connection.

__
|
unsigned long IceLastReceivedSequenceNumber(ice_conn)
    IceConn ice_conn;
|__

IceLastReceivedSequenceNumber returns the sequence number of
the last message received on this ICE connection.

__
|
Bool IceSwapping(ice_conn)
    IceConn ice_conn;
|__

IceSwapping  returns True if byte swapping is necessary when
reading messages on the ICE connection.

__
|
IcePointer IceGetContext(ice_conn)
    IceConn ice_conn;
|__

IceGetContext returns the context associated with a  connec-
tion created by IceOpenConnection.

12.  ICE Messages

All  ICE messages have a standard 8-byte header.  The ICElib
macros that read and write messages rely  on  the  following
naming convention for message headers:


     CARD8major_opcode;
     CARD8minor_opcode;
     CARD8data[2];
     CARD32length B32;


The  3rd  and 4th bytes of the message header can be used as
needed.  The length field is specified in units of 8  bytes.




			   - 33 -





Inter-Client Exchange Library		    X11, Release 6.4


12.1.  Sending ICE Messages

The ICE library maintains an output buffer used for generat-
ing messages.  Protocol libraries layered on top of ICE  may
choose	to  batch  messages  together  and  flush the output
buffer at appropriate times.

If an IO error has occurred on an ICE connection, all  write
operations  will  be  ignored.	For further information, see
section 13, ``Error Handling.''


To  get  the  size   of   the	ICE   output   buffer,	 use
IceGetOutBufSize.
__
|
int IceGetOutBufSize(ice_conn)
     IceConn ice_conn;


ice_conn  A valid ICE connection object.
|__


To flush the ICE output buffer, use IceFlush.
__
|
IceFlush(ice_conn)
     IceConn ice_conn;


ice_conn  A valid ICE connection object.
|__

Note  that  the  output  buffer may be implicitly flushed if
there is insufficient space to generate a message.

The following macros can be used to generate ICE messages:

__
|
IceGetHeader(ice_conn, major_opcode, minor_opcode, header_size, <C_data_type>, pmsg)
     IceConn ice_conn;
     int major_opcode;
     int minor_opcode;
     int header_size;
     <C_data_type> *pmsg;


ice_conn  A valid ICE connection object.

major_opcode
	  The major opcode of the message.




			   - 34 -





Inter-Client Exchange Library		    X11, Release 6.4


minor_opcode
	  The minor opcode of the message.

header_size
	  The size of the message header (in bytes).

<C_data_type>
	  The actual C data type of the message header.

pmsg	  The message header pointer.  After this  macro  is
	  called,  the library can store data in the message
	  header.
|__

IceGetHeader is used to set up a message header  on  an  ICE
connection.  It sets the major and minor opcodes of the mes-
sage, and initializes the message's length to the length  of
the header.  If additional variable length data follows, the
message's length field should be updated.


__
|
IceGetHeaderExtra(ice_conn, major_opcode, minor_opcode, header_size, extra, <C_data_type>, pmsg, pdata)
     IceConn ice_conn;
     int major_opcode;
     int minor_opcode;
     int header_size;
     int extra;
     <C_data_type> *pmsg;
     char *pdata;


ice_conn  A valid ICE connection object.

major_opcode
	  The major opcode of the message.

minor_opcode
	  The minor opcode of the message.

header_size
	  The size of the message header (in bytes).

extra	  The size of the extra data beyond the  header  (in
	  8-byte units).

<C_data_type>
	  The actual C data type of the message header.

pmsg	  The  message	header pointer.  After this macro is
	  called, the library can store data in the  message
	  header.




			   - 35 -





Inter-Client Exchange Library		    X11, Release 6.4


pdata	  Returns  a  pointer  to the ICE output buffer that
	  points immediately after the message header.	 The
	  variable  length  data  should be stored here.  If
	  there was  not  enough  room	in  the  ICE  output
	  buffer, pdata is set to NULL.
|__

IceGetHeaderExtra is used to generate a message with a fixed
(and relatively small) amount of variable length data.	 The
complete message must fit in the ICE output buffer.


__
|
IceSimpleMessage(ice_conn, major_opcode, minor_opcode)
     IceConn ice_conn;
     int major_opcode;
     int minor_opcode;


ice_conn  A valid ICE connection object.

major_opcode
	  The major opcode of the message.

minor_opcode
	  The minor opcode of the message.
|__

IceSimpleMessage is used to generate a message that is iden-
tical in size to the ICE header message, and  has  no  addi-
tional data.


__
|
IceErrorHeader(ice_conn, offending_major_opcode, offending_minor_opcode, offending_sequence_num,
		    severity, error_class, data_length)
     IceConn ice_conn;
     int offending_major_opcode;
     int offending_minor_opcode;
     int offending_sequence_num;
     int severity;
     int error_class;
     int data_length;


ice_conn  A valid ICE connection object.

offending_major_opcode
	  The major opcode of the protocol in which an error
	  was detected.





			   - 36 -





Inter-Client Exchange Library		    X11, Release 6.4


offending_minor_opcode
	  The minor opcode of the protocol in which an error
	  was detected.

offending_sequence_num
	  The sequence number of the message that caused the
	  error.

severity  IceCanContinue,	IceFatalToProtocol,	  or
	  IceFatalToConnection.

error_class
	  The error class.

data_length
	  Length  of  data  (in  8-byte units) to be written
	  after the header.
|__

IceErrorHeader sets up an error message header.

Note that the two clients connected by ICE may be using dif-
ferent	major  opcodes	for  a	given protocol.  The offend-
ing_major_opcode passed to this macro is the major opcode of
the protocol for the client sending the error message.

Generic  errors,  which  are  common  to all protocols, have
classes in the range 0x8000..0xFFFF.  See  the	Inter-Client
Exchange Protocol standard for more details.

IceBadMi-    0x8000
nor
IceBad-      0x8001
State
Ice-	     0x8002
BadLength
IceBad-      0x8003
Value


Per-protocol errors have classes in the range 0x0000-0x7fff.


To write data to an ICE  connection,  use  the	IceWriteData
macro.	 If  the data fits into the ICE output buffer, it is
copied there.  Otherwise, the ICE output buffer  is  flushed
and the data is directly sent.

This  macro  is  used  in  conjunction with IceGetHeader and
IceErrorHeader.







			   - 37 -





Inter-Client Exchange Library		    X11, Release 6.4

__
|
IceWriteData(ice_conn, bytes, data)
     IceConn ice_conn;
     int bytes;
     char *data;


ice_conn  A valid ICE connection object.

bytes	  The number of bytes to write.

data	  The data to write.
|__


To write data as 16-bit quantities, use IceWriteData16.
__
|
IceWriteData16(ice_conn, bytes, data)
     IceConn ice_conn;
     int bytes;
     short *data;


ice_conn  A valid ICE connection object.

bytes	  The number of bytes to write.

data	  The data to write.
|__


To write data as 32-bit quantities, use IceWriteData32.
__
|
IceWriteData32(ice_conn, bytes, data)
     IceConn ice_conn;
     int bytes;
     long *data;


ice_conn  A valid ICE connection object.

bytes	  The number of bytes to write.

data	  The data to write.
|__


To bypass copying data to the ICE output  buffer,  use	Ice-
SendData  to directly send data over the network connection.






			   - 38 -





Inter-Client Exchange Library		    X11, Release 6.4


If necessary, the ICE output buffer is first flushed.
__
|
IceSendData(ice_conn, bytes, (char *) data)
     IceConn ice_conn;
     int bytes;
     char *data;


ice_conn  A valid ICE connection object.

bytes	  The number of bytes to send.

data	  The data to send.
|__


To force 32-bit or 64-bit  alignment,  use  IceWritePad.   A
maximum of 7 pad bytes can be specified.
__
|
IceWritePad(ice_conn, bytes)
     IceConn ice_conn;
     int bytes;


ice_conn  A valid ICE connection object.

bytes	  The number of pad bytes.
|__


12.2.  Reading ICE Messages

The  ICE  library maintains an input buffer used for reading
messages.  If the ICE library chooses to perform nonblocking
reads  (this  is  implementation-dependent),  then for every
read operation that it makes, zero or more complete messages
may  be read into the input buffer.  As a result, for all of
the macros described in this section that read messages,  an
actual	read  operation will occur on the connection only if
the data is not already present in the input buffer.


To  get  the   size   of   the	 ICE   input   buffer,	 use
IceGetInBufSize.
__
|
int IceGetInBufSize(ice_conn)
     IceConn ice_conn;


ice_conn  A valid ICE connection object.




			   - 39 -





Inter-Client Exchange Library		    X11, Release 6.4


|__


When  reading  messages,  care must be taken to check for IO
errors.  If any IO error occurs in reading  any  part  of  a
message,  the message should be thrown out.  After using any
of the macros described below for reading messages, the Ice-
ValidIO  macro	can be used to check if an IO error occurred
on the connection.  After an IO error has occurred on an ICE
connection,  all  read operations will be ignored.  For fur-
ther information, see section 13, ``Error Handling.''


__
|
Bool IceValidIO(ice_conn)
    IceConn ice_conn;

|__


The following macros can be used to read ICE messages.
__
|
IceReadSimpleMessage(ice_conn, <C_data_type>, pmsg)
     IceConn ice_conn;
     <C_data_type> *pmsg;


ice_conn  A valid ICE connection object.

<C_data_type>
	  The actual C data type of the message header.

pmsg	  This pointer is set to the message header.
|__

IceReadSimpleMessage is used for messages that are identical
in  size to the 8-byte ICE header, but use the spare 2 bytes
in the header to encode additional data.  Note that the  ICE
library  always  reads	in  these  first  8 bytes, so it can
obtain the major opcode of the	message.   IceReadSimpleMes-
sage  simply returns a pointer to these 8 bytes; it does not
actually read any data into the input buffer.

For a message with variable length data, there are two	ways
of  reading  the  message.   One method involves reading the
complete message in one pass  using  IceReadCompleteMessage.
The  second method involves reading the message header (note
that this may be larger than the 8-byte  ICE  header),	then
reading  the variable length data in chunks (see IceReadMes-
sageHeader and IceReadData).





			   - 40 -





Inter-Client Exchange Library		    X11, Release 6.4

__
|
IceReadCompleteMessage(ice_conn, header_size, <C_data_type>, pmsg, pdata)
     IceConn ice_conn;
     int header_size;
     <C_data_type> *pmsg;
     char *pdata;


ice_conn  A valid ICE connection object.

header_size
	  The size of the message header (in bytes).

<C_data_type>
	  The actual C data type of the message header.

pmsg	  This pointer is set to the message header.

pdata	  This pointer is set to the variable length data of
	  the message.
|__

If  the  ICE  input buffer has sufficient space, IceReadCom-
pleteMessage will read the complete  message  into  the  ICE
input buffer.  Otherwise, a buffer will be allocated to hold
the variable length data.  After the call, the	pdata  argu-
ment  should be checked against NULL to make sure that there
was sufficient memory to allocate the buffer.


After calling IceReadCompleteMessage and processing the mes-
sage, IceDisposeCompleteMessage should be called.

__
|
IceDisposeCompleteMessage(ice_conn, pdata)
     IceConn ice_conn;
     char *pdata;


ice_conn  A valid ICE connection object.

pdata	  The  pointer	to the variable length data returned
	  in IceReadCompleteMessage.
|__

If a buffer had to be allocated to hold the variable  length
data (because it did not fit in the ICE input buffer), it is
freed here by ICElib.








			   - 41 -





Inter-Client Exchange Library		    X11, Release 6.4

__
|
IceReadMessageHeader(ice_conn, header_size, <C_data_type>, pmsg)
     IceConn ice_conn;
     int header_size;
     <C_data_type> *pmsg;


ice_conn  A valid ICE connection object.

header_size
	  The size of the message header (in bytes).

<C_data_type>
	  The actual C data type of the message header.

pmsg	  This pointer is set to the message header.
|__

IceReadMessageHeader reads just  the  message  header.	 The
rest  of the data should be read with the IceReadData family
of macros.  This method of reading a message should be	used
when the variable length data must be read in chunks.


To  read  data	directly  into	a  user supplied buffer, use
IceReadData.
__
|
IceReadData(ice_conn, bytes, pdata)
     IceConn ice_conn;
     int bytes;
     char *pdata;


ice_conn  A valid ICE connection object.

bytes	  The number of bytes to read.

pdata	  The data is read into this user supplied buffer.
|__


To read data as 16-bit quantities, use IceReadData16.
__
|
IceReadData16(ice_conn, swap, bytes, pdata)
     IceConn ice_conn;
     Bool swap;
     int bytes;
     short *pdata;


ice_conn  A valid ICE connection object.




			   - 42 -





Inter-Client Exchange Library		    X11, Release 6.4


swap	  If True, the values will be byte swapped.

bytes	  The number of bytes to read.

pdata	  The data is read into this user supplied buffer.
|__


To read data as 32-bit quantities, use IceReadData32.
__
|
IceReadData32(ice_conn, swap, bytes, pdata)
     IceConn ice_conn;
     Bool swap;
     int bytes;
     long *pdata;


ice_conn  A valid ICE connection object.

swap	  If True, the values will be byte swapped.

bytes	  The number of bytes to read.

pdata	  The data is read into this user supplied buffer.
|__


To force 32-bit or 64-bit alignment, use IceReadPad.  A max-
imum of 7 pad bytes can be specified.
__
|
IceReadPad(ice_conn, bytes)
     IceConn ice_conn;
     int bytes;


ice_conn  A valid ICE connection object.

bytes	  The number of pad bytes.
|__


13.  Error Handling

There are two default error handlers in ICElib:

o    One  to handle typically fatal conditions (for example,
     a connection dying because a machine crashed)

o    One to handle ICE-specific protocol errors

These error handlers can be changed  to  user-supplied	rou-
tines  if  you	prefer	your  own  error handling and can be



			   - 43 -





Inter-Client Exchange Library		    X11, Release 6.4


changed as often as you like.


To set the ICE error handler, use IceSetErrorHandler.
__
|
IceErrorHandler IceSetErrorHandler(handler)
    IceErrorHandler handler;


handler   The ICE error handler.  You should  pass  NULL  to
	  restore the default handler.
|__

IceSetErrorHandler returns the previous error handler.

The ICE error handler is invoked when an unexpected ICE pro-
tocol error (major opcode 0) is encountered.  The action  of
the  default  handler  is to print an explanatory message to
stderr and if the  severity  is  fatal,  call  exit  with  a
nonzero  value.   If exiting is undesirable, the application
should register its own error handler.

Note that errors in other protocol domains should be handled
by  their  respective libraries (these libraries should have
their own error handlers).

An ICE error handler has the type of IceErrorHandler.
__
|
typedef void (*IceErrorHandler)();

void ErrorHandler(ice_conn, swap, offending_minor_opcode, offending_sequence_num, error_class,
		     severity, values)
    IceConn ice_conn;
    Bool swap;
    int offending_minor_opcode;
    unsigned long offending_sequence_num;
    int error_class;
    int severity;
    IcePointer values;


ice_conn  The ICE connection object.

swap	  A flag that indicates  if  the  values  need	byte
	  swapping.

offending_minor_opcode
	  The ICE minor opcode of the offending message.

offending_sequence_num
	  The sequence number of the offending message.




			   - 44 -





Inter-Client Exchange Library		    X11, Release 6.4


error_class
	  The error class of the offending message.

severity  IceCanContinue,	IceFatalToProtocol,	  or
	  IceFatalToConnection.

values	  Any additional error values specific to the  minor
	  opcode and class.
|__

The following error classes are defined at the ICE level:


IceBadMinor
IceBadState
IceBadLength
IceBadValue
IceBadMajor
IceNoAuth
IceNoVersion
IceSetupFailed
IceAuthRejected
IceAuthFailed
IceProtocolDuplicate
IceMajorOpcodeDuplicate
IceUnknownProtocol


For  further information, see the Inter-Client Exchange Pro-
tocol standard.


To handle fatal I/O errors, use IceSetIOErrorHandler.

__
|
IceIOErrorHandler IceSetIOErrorHandler(handler)
    IceIOErrorHandler handler;


handler   The I/O error handler.  You should  pass  NULL  to
	  restore the default handler.
|__

IceSetIOErrorHandler  returns the previous IO error handler.

An ICE I/O error handler has the type of  IceIOErrorHandler.

__
|







			   - 45 -





Inter-Client Exchange Library		    X11, Release 6.4


typedef void (*IceIOErrorHandler)();

void IOErrorHandler(ice_conn)
    IceConn ice_conn;


ice_conn  The ICE connection object.
|__

There are two ways of handling IO errors in ICElib:

o    In  the  first,  the  IO error handler does whatever is
     necessary to respond to the IO error and then  returns,
     but  it does not call IceCloseConnection.	The ICE con-
     nection is given a ``bad IO'' status,  and  all  future
     reads  and  writes  to the connection are ignored.  The
     next time IceProcessMessages is called it will return a
     status of IceProcessMessagesIOError.  At that time, the
     application should call IceCloseConnection.

o    In  the  second,  the  IO	error  handler	 does	call
     IceCloseConnection,  and  then uses the longjmp call to
     get back to the application's  main  event  loop.	 The
     setjmp  and  longjmp calls may not work properly on all
     platforms, and special care must be taken to avoid mem-
     ory leaks.  Therefore, this second model is less desir-
     able.

Before the application I/O error handler is invoked,  proto-
col  libraries that were interested in being notified of I/O
errors will  have  their  IceIOErrorProc  handlers  invoked.
This  handler  is  set up in the protocol registration func-
tions	    (see       IceRegisterForProtocolSetup	 and
IceRegisterForProtocolReply)  and  could be used to clean up
state specific to the protocol.


__
|  typedef void (*IceIOErrorProc)();


void IOErrorProc(ice_conn)
    IceConn ice_conn;


ice_conn  The ICE connection object.
|__

Note that every IceIOErrorProc callback must  return.	This
is required because each active protocol must be notified of
the broken connection, and the application IO error  handler
must be invoked afterwards.





			   - 46 -





Inter-Client Exchange Library		    X11, Release 6.4


14.  Multi-Threading Support

To  declare  that multiple threads in an application will be
using the ICE library, use IceInitThreads.

__
|
Status IceInitThreads()

|__

The IceInitThreads function must be the first  ICElib  func-
tion  a  multi-threaded  program  calls.   It  must complete
before	any  other  ICElib  call  is  made.   IceInitThreads
returns  a nonzero status if and only if it was able to ini-
tialize the threads package successfully.   It	is  safe  to
call  IceInitThreads  more  than  once, although the threads
package will only be initialized once.

Protocol libraries layered on top of  ICElib  will  have  to
lock critical sections of code that access an ICE connection
(for example, when generating messages).  Two  calls,  which
are generally implemented as macros, are provided:
__
|
IceLockConn(ice_conn)
    IceConn ice_conn;

IceUnlockConn(ice_conn)
    IceConn ice_conn;


ice_conn  The ICE connection.
|__


To  keep  an  ICE  connection  locked  across several ICElib
calls, applications use IceAppLockConn and IceAppUnlockConn.
__
|
void IceAppLockConn(ice_conn)
    IceConn ice_conn;


ice_conn  The ICE connection to lock.
|__

The  IceAppLockConn  function  completely  locks  out  other
threads  using	the  connection  until	IceAppUnlockConn  is
called.  Other threads attempting to use ICElib calls on the
connection will block.	If the program	has  not  previously
called IceInitThreads, IceAppLockConn has no effect.





			   - 47 -





Inter-Client Exchange Library		    X11, Release 6.4

__
|
void IceAppUnlockConn(ice_conn)
    IceConn ice_conn;


ice_conn  The ICE connection to unlock.
|__

The  IceAppUnlockConn  function allows other threads to com-
plete ICElib calls on the connection that were blocked by  a
previous  call	to  IceAppLockConn from this thread.  If the
program has not previously called IceInitThreads,  IceAppUn-
lockConn has no effect.

15.  Miscellaneous Functions

To allocate scratch space (for example, when generating mes-
sages with variable data), use	IceAllocScratch.   Each  ICE
connection  has  one  scratch space associated with it.  The
scratch space starts off as empty and grows as needed.	 The
contents  of  the scratch space is not guaranteed to be pre-
served after any ICElib function is called.

__
|
char *IceAllocScratch(ice_conn, size)
    IceConn ice_conn;
    unsigned long size;


ice_conn  A valid ICE connection object.

size	  The number of bytes required.
|__

Note that the memory returned by IceAllocScratch should  not
be  freed by the caller.  The ICE library will free the mem-
ory when the ICE connection is closed.

16.  Acknowledgements

Thanks to Bob Scheifler for  his  thoughtful  input  on  the
design	of  the  ICE  library.	Thanks also to Jordan Brown,
Larry Cable, Donna Converse, Clive Feather, Stephen  Gildea,
Vania Joloboff, Kaleb Keithley, Stuart Marks, Hiro Miyamoto,
Ralph Swick, Jim VanGilder, and Mike Wexler.











			   - 48 -





Inter-Client Exchange Library		    X11, Release 6.4


			 Appendix A

	      Authentication Utility Functions


As discussed in this document, the means by which  authenti-
cation	data is obtained by the ICE library (for Connection-
Setup messages or ProtocolSetup messages) is implementation-
dependent.

This appendix describes some utility functions that  manipu-
late  an ICE authority file.  The authority file can be used
to pass authentication data between clients.

The basic operations on the .ICEauthority file are:

o    Get file name

o    Lock

o    Unlock

o    Read entry

o    Write entry

o    Search for entry

These are fairly low-level operations, and  it	is  expected
that  a program, like "iceauth", would exist to add, remove,
and display entries in the file.

In   order   to   use	these	utility    functions,	 the
<X11/ICE/ICEutil.h> header file must be included.

An entry in the .ICEauthority file is defined by the follow-
ing data structure:

__
|
typedef struct {
     char *protocol_name;
     unsigned short protocol_data_length;
     char *protocol_data;
     char *network_id;
     char *auth_name;
     unsigned short auth_data_length;
     char *auth_data;
} IceAuthFileEntry;


-----------
   The	 X   Consortium's   ICElib  implementation
assumes the presence of an ICE authority file.



			   - 49 -





Inter-Client Exchange Library		    X11, Release 6.4


|__

The protocol_name member is either  ``ICE''  for  connection
setup  authentication  or  the	subprotocol  name,  such  as
``XSMP''.  For each entry, protocol  specific  data  can  be
specified  in the protocol_data member.  This can be used to
search for old entries that need  to  be  removed  from  the
file.

The  network_id  member  is  the  network  ID  of the client
accepting authentication (for example, the network ID  of  a
session manager).  A network ID has the following form:

     tcp/<hostname>:<portnumber>    or
     decnet/<hostname>::<objname>   or
     local/<hostname>:<path>


The  auth_name	member	is  the  name  of the authentication
method.  The auth_data member is the  actual  authentication
data, and the auth_data_length member is the number of bytes
in the data.


To  obtain  the  default  authorization   file	 name,	 use
IceAuthFileName.
__
|
char *IceAuthFileName()

|__

If  the ICEAUTHORITY environment variable if set, this value
is returned.  Otherwise, the default authorization file name
is  $HOME/.ICEauthority.   This name is statically allocated
and should not be freed.

To synchronously update the  authorization  file,  the	file
must  be  locked with a call to IceLockAuthFile.  This func-
tion takes advantage of the fact that the link	system	call
will fail if the name of the new link already exists.
__
|
int IceLockAuthFile(file_name, retries, timeout, dead)
    char *file_name;
    int retries;
    int timeout;
    long dead;


file_name The authorization file to lock.

retries   The number of retries.




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Inter-Client Exchange Library		    X11, Release 6.4


timeout   The number of seconds before each retry.

dead	  If  a  lock  already	exists that is the specified
	  dead seconds old, it is broken.  A value  of	zero
	  is used to unconditionally break an old lock.
|__

One of three values is returned:

o    IceAuthLockSuccess - the lock succeeded.

o    IceAuthLockError  -  a system error occurred, and errno
     may prove useful.

o    IceAuthLockTimeout - the specified  number  of  retries
     failed.


To unlock an authorization file, use IceUnlockAuthFile.
__
|
void IceUnlockAuthFile(file_name)
    char *file_name;


file_name The authorization file to unlock.
|__


To  read  the  next  entry  in	an  authorization  file, use
IceReadAuthFileEntry.
__
|
IceAuthFileEntry *IceReadAuthFileEntry(auth_file)
    FILE *auth_file;


auth_file The authorization file.
|__

Note that it is the responsibility  of	the  application  to
open  the file for reading before calling this function.  If
an error is encountered, or there are  no  more  entries  to
read, NULL is returned.

Entries  should be free with a call to IceFreeAuthFileEntry.


To  write  an  entry   in   an	 authorization	 file,	 use
IceWriteAuthFileEntry.
__
|





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Inter-Client Exchange Library		    X11, Release 6.4


Status IceWriteAuthFileEntry(auth_file, entry)
    FILE *auth_file;
    IceAuthFileEntry *entry;


auth_file The authorization file.

entry	  The entry to write.
|__

Note  that  it	is  the responsibility of the application to
open the file for writing before calling this function.  The
function  returns a nonzero status if the operation was suc-
cessful.


To search the default authorization file for an  entry	that
matches  a  given  protocol_name/network_id/auth_name tuple,
use IceGetAuthFileEntry.
__
|
IceAuthFileEntry *IceGetAuthFileEntry(protocol_name, network_id, auth_name)
    char *protocol_name;
    char *network_id;
    char *auth_name;


protocol_name
	  The name of the protocol to search on.

network_id
	  The network ID to search on.

auth_name The authentication method to search on.
|__

If IceGetAuthFileEntry fails to find such an entry, NULL  is
returned.


To   free  an  entry  returned	by  IceReadAuthFileEntry  or
IceGetAuthFileEntry, use IceFreeAuthFileEntry.
__
|
void IceFreeAuthFileEntry(entry)
    IceAuthFileEntry *entry;


entry	  The entry to free.
|__







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Inter-Client Exchange Library		    X11, Release 6.4


			 Appendix B

	     MIT-MAGIC-COOKIE-1 Authentication


The X Consortium's ICElib implementation supports  a  simple
MIT-MAGIC-COOKIE-1 authentication scheme using the authority
file utilities described in Appendix A.

In this model, an application, such as	a  session  manager,
obtains  a  magic  cookie by calling IceGenerateMagicCookie,
and then stores it in the user's local .ICEauthority file so
that  local  clients  can connect.  In order to allow remote
clients to connect, some remote execution  mechanism  should
be  used to store the magic cookie in the user's .ICEauthor-
ity file on a remote machine.

In addition to storing the magic cookie in the .ICEauthority
file,  the  application  needs	to call the IceSetPaAuthData
function in order to store the magic cookie in memory.	When
it comes time for the MIT-MAGIC-COOKIE-1 authentication pro-
cedure to accept or reject the connection, it  will  compare
the  magic  cookie  presented  by the requestor to the magic
cookie in memory.

__
|
char *IceGenerateMagicCookie(length)
    int length;


length	  The desired length of the magic cookie.
|__


The magic cookie returned will be null-terminated.  If	mem-
ory  can not be allocated for the magic cookie, the function
will return NULL.  Otherwise, the  magic  cookie  should  be
freed with a call to free.


To   store   the   authentication   data   in	memory,  use
IceSetPaAuthData.  Currently, this function is only used for
MIT-MAGIC-COOKIE-1  authentication,  but  it may be used for
additional authentication methods in the future.
__
|
void IceSetPaAuthData(num_entries, entries)
    int num_entries;
    IceAuthDataEntry *entries;


num_entries
	  The number of authentication data entries.



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Inter-Client Exchange Library		    X11, Release 6.4


entries   The list of authentication data entries.
|__

Each entry has associated with it a protocol name (for exam-
ple,   ``ICE''	for  ICE  connection  setup  authentication,
``XSMP'' for session management authentication),  a  network
ID for the ``accepting'' client, an authentication name (for
example, MIT-MAGIC-COOKIE-1), and authentication data.	 The
ICE  library  will  merge  these entries with previously set
entries, based on the (protocol_name, network_id, auth_name)
tuple.

__
|
typedef struct {
     char *protocol_name;
     char *network_id;
     char *auth_name;
     unsigned short auth_data_length;
     char *auth_data;
} IceAuthDataEntry;

|__


































			   - 54 -








		     Table of Contents


1. Overview of ICE . . . . . . . . . . . . . . . . . . .   1
2. The ICE Library - C Language Interface to ICE . . . .   1
3. Intended Audience . . . . . . . . . . . . . . . . . .   1
4. Header Files and Library Name . . . . . . . . . . . .   2
5. Note on Prefixes  . . . . . . . . . . . . . . . . . .   2
6. Protocol Registration . . . . . . . . . . . . . . . .   2
6.1. Callbacks for Processing Messages . . . . . . . . .   8
6.2. Authentication Methods  . . . . . . . . . . . . . .  12
7. ICE Connections . . . . . . . . . . . . . . . . . . .  15
7.1. Opening an ICE Connection . . . . . . . . . . . . .  15
7.2. Listening for ICE Connections . . . . . . . . . . .  17
7.3. Host Based Authentication for ICE Connections
 . . . . . . . . . . . . . . . . . . . . . . . . . . . .  20
7.4. Accepting ICE Connections . . . . . . . . . . . . .  21
7.5. Closing ICE Connections . . . . . . . . . . . . . .  23
7.6. Connection Watch Procedures . . . . . . . . . . . .  25
8. Protocol Setup and Shutdown . . . . . . . . . . . . .  27
9. Processing Messages . . . . . . . . . . . . . . . . .  29
10. Ping . . . . . . . . . . . . . . . . . . . . . . . .  30
11. Using ICElib Informational Functions . . . . . . . .  31
12. ICE Messages . . . . . . . . . . . . . . . . . . . .  33
12.1. Sending ICE Messages . . . . . . . . . . . . . . .  34
12.2. Reading ICE Messages . . . . . . . . . . . . . . .  39
13. Error Handling . . . . . . . . . . . . . . . . . . .  43
14. Multi-Threading Support  . . . . . . . . . . . . . .  47
15. Miscellaneous Functions  . . . . . . . . . . . . . .  48
16. Acknowledgements . . . . . . . . . . . . . . . . . .  48
Appendix A - Authentication Utility Functions  . . . . .  49
Appendix B - MIT-MAGIC-COOKIE-1 Authentication . . . . .  53

























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