








                  [1mInter-Client Exchange Library[0m

                           [1mVersion 1.0[0m

                      [1mX Consortium Standard[0m

                    [1mX Version 11, Release 6.4[0m


                            [4mRalph[24m [4mMor[0m
                          X Consortium



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[1m1.  Overview of ICE[0m

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

[1m2.  The ICE Library - C Language Interface to ICE[0m

A  client that wishes to utilize ICE must first register the pro-
tocols it understands with the ICE library.  Each protocol is dy-
namically 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 connections made by other clients.  Authen-
tication may be required.  A client can both initiate connections
with  other  clients and be waiting for clients to connect to it-
self (a nested session manager is an example).  Once an ICE  con-
nection  is  established  between  the  two  clients,  one of the
clients needs to initiate a in order to "activate" a given proto-
col.  Once the other client accepts the (once again,  authentica-
tion may be required), the two clients are ready to start passing
messages  specific to that protocol to each other.  Multiple pro-
tocols may be active on a single ICE connection.  Clients are re-
sponsible for notifying the ICE library when  a  protocol  is  no
longer  active on an ICE connection, although ICE does not define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  messages.
Using  callbacks allows messages and authentication to happen be-
hind 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 message.

[1m3.  Intended Audience[0m

This document is intended primarily for implementors of  protocol
libraries  layered  on  top of ICE.  Typically, applications that
wish to utilize ICE will make calls into individual protocol  li-
braries  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 ex-
ample, a session manager  accepting  connections  from  clients).
But in general, protocol libraries should be designed to hide the
inner details of ICE from applications.

[1m4.  Header Files and Library Name[0m

The  header  file  defines  all of the ICElib data structures and
function prototypes.  includes the header file which defines  all
of  the  ICElib  constants.  Protocol libraries that need to read



                              - 1 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


and write messages should include the header file

Applications should link against ICElib using -lICE.

[1m5.  Note on Prefixes[0m

The following name prefixes are used in the  library  to  distin-
guish  between  a  client  that initiates a and a client that re-
sponds with a

+o    - Ice Protocol Originator

+o    - Ice Protocol Acceptor

[1m6.  Protocol Registration[0m

In order for two clients to exchange messages for a given  proto-
col,  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 callbacks for processing
messages and handling authentication.   There  are  two  separate
registration functions:

+o    One to handle the side that does a

+o    One to handle the side that responds with a

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 is received, but the protocol is not
registered.  If it is not possible to register a protocol  before
the  creation  of an ICE connection, proper precautions should be
taken to avoid the above race condition.


The function should be called for the client that initiates a
__
||  int IceRegisterForProtocolSetup([4mprotocol_name[24m,  [4mvendor[24m,  [4mrelease[24m,
[4mversion_count[24m, [4mversion_recs[24m,
                 [4mauth_count[24m,   [4mauth_names[24m,   [4mauth_procs[24m,   [4mio_er-[0m
[4mror_proc[24m)
     char *[4mprotocol_name[24m;
     char *[4mvendor[24m;
     char *[4mrelease[24m;
     int [4mversion_count[24m;
     IcePoVersionRec *[4mversion_recs[24m;
     int [4mauth_count[24m;
     char **[4mauth_names[24m;
     IcePoAuthProc *[4mauth_procs[24m;
     IceIOErrorProc [4mio_error_proc[24m;

[4mprotocol_name[0m
          A  string  specifying  the  name  of  the  protocol  to



                              - 2 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


          register.

[4mvendor[24m    A  vendor string with semantics specified by the proto-
          col.

[4mrelease[24m   A release string with semantics specified by the proto-
          col.

[4mversion_count[0m
          The number of different versions of the  protocol  sup-
          ported.

[4mversion_recs[0m
          List of versions and associated callbacks.

[4mauth_count[0m
          The number of authentication methods supported.

[4mauth_names[0m
          The list of authentication methods supported.

[4mauth_procs[0m
          The  list of authentication callbacks, one for each au-
          thentication method.

[4mio_error_proc[0m
          IO error handler, or NULL.
||__

returns the major opcode reserved or -1 if an error occurred.  In
order to actually activate the protocol, the 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 op-
code.

A protocol library may support multiple versions of the same pro-
tocol.   The  version_recs argument specifies a list of supported
versions of the protocol, which are prioritized in decreasing or-
der of preference.  Each version record consists 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  callback  is  responsible for processing the set of messages
that can be received by the client that initiated the For further
information, see section 6.1,  ``Callbacks  for  Processing  Mes-
sages.''

Authentication may be required before the protocol can become ac-
tive.   The  protocol  library  must  register the authentication



                              - 3 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


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  prefer-
ence.   For  information  on the callback, see section 6.2, ``Au-
thentication Methods.''

The 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  information, see section 13,
``Error Handling.''


The function should be called for the client that responds  to  a
with a
__
||  int  IceRegisterForProtocolReply([4mprotocol_name[24m,  [4mvendor[24m, [4mrelease[24m,
[4mversion_count[24m, [4mversion_recs[24m,
                    [4mauth_count[24m,      [4mauth_names[24m,      [4mauth_procs[24m,
[4mhost_based_auth_proc[24m, [4mprotocol_setup_proc[24m,
                     [4mprotocol_activate_proc[24m, [4mio_error_proc[24m)
     char *[4mprotocol_name[24m;
     char *[4mvendor[24m;
     char *[4mrelease[24m;
     int [4mversion_count[24m;
     IcePaVersionRec *[4mversion_recs[24m;
     int [4mauth_count[24m;
     char **[4mauth_names[24m;
     IcePaAuthProc *[4mauth_procs[24m;
     IceHostBasedAuthProc [4mhost_based_auth_proc[24m;
     IceProtocolSetupProc [4mprotocol_setup_proc[24m;
     IceProtocolActivateProc [4mprotocol_activate_proc[24m;
     IceIOErrorProc [4mio_error_proc[24m;

[4mprotocol_name[0m
          A  string specifying the name of the protocol to regis-
          ter.

[4mvendor[24m    A vendor string with semantics specified by the  proto-
          col.

[4mrelease[24m   A release string with semantics specified by the proto-
          col.

[4mversion_count[0m
          The  number  of different versions of the protocol sup-
          ported.

[4mversion_recs[0m
          List of versions and associated callbacks.

[4mauth_count[0m
          The number of authentication methods supported.





                              - 4 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mauth_names[0m
          The list of authentication methods supported.

[4mauth_procs[0m
          The list of authentication callbacks, one for each  au-
          thentication method.

[4mhost_based_auth_proc[0m
          Host based authentication callback.

[4mprotocol_setup_proc[0m
          A  callback  to be invoked when authentication has suc-
          ceeded for a but before the is sent.

[4mprotocol_activate_proc[0m
          A callback to be invoked after the is sent.

[4mio_error_proc[0m
          IO error handler, or NULL.
||__

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

A protocol library may support multiple versions of the same pro-
tocol.  The version_recs argument specifies a list  of  supported
versions of the protocol, which are prioritized in decreasing or-
der  of  preference.  Each version record consists 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 callback is responsible for processing the  set  of  messages
that  can be received by the client that accepted the For further
information, see section 6.1,  ``Callbacks  for  Processing  Mes-
sages.''

Authentication may be required before the protocol can become ac-
tive.   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 callback, see section  6.2,  ``Authentica-
tion Methods.''

If authentication fails and the client attempting to initiate the
has not required authentication, the callback is invoked with the
host name of the originating client.  If the callback returns the
will  succeed,  even  though  the original authentication failed.



                              - 5 -





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Note that authentication can effectively be disabled by register-
ing an which always returns If no host  based  authentication  is
allowed, you should pass NULL for host_based_auth_proc.

__
||  typedef Bool (*IceHostBasedAuthProc) ();

Bool HostBasedAuthProc([4mhost_name[24m)
    char *[4mhost_name[24m;

[4mhost_name[24m The host name of the client that sent the
||__

The host_name argument is a string of the form [4mprotocol[24m/[4mhostname[24m,
where [4mprotocol[24m is one of {tcp, decnet, local}.

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

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

Status ProtocolSetupProc([4mice_conn[24m, [4mmajor_version[24m,  [4mminor_version[24m,
[4mvendor[24m, [4mrelease[24m,
                    [4mclient_data_ret[24m, [4mfailure_reason_ret[24m)
     IceConn [4mice_conn[24m;
     int [4mmajor_version[24m;
     int [4mminor_version[24m;
     char *[4mvendor[24m;
     char *[4mrelease[24m;
     IcePointer *[4mclient_data_ret[24m;
     char **[4mfailure_reason_ret[24m;

[4mice_conn[24m  The ICE connection object.

[4mmajor_version[0m
          The major version of the protocol.

[4mminor_version[0m
          The minor version of the protocol.

[4mvendor[24m    The  vendor  string registered by the protocol origina-
          tor.



                              - 6 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mrelease[24m   The release string registered by the protocol  origina-
          tor.

[4mclient_data_ret[0m
          Client data to be set by callback.

[4mfailure_reason_ret[0m
          Failure reason returned.
||__

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

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

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

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

void ProtocolActivateProc([4mice_conn[24m, [4mclient_data[24m)
    IceConn [4mice_conn[24m;
    IcePointer [4mclient_data[24m;

[4mice_conn[24m  The ICE connection object.

[4mclient_data[0m
          The client data set in the callback.
||__

The  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  information,  see  section  13,
``Error Handling.''

[1m6.1.  Callbacks for Processing Messages[0m

When  an application detects that there is new data to read on an
ICE connection (via it calls the function (see section 9,  ``Pro-
cessing Messages'').  When reads an ICE message header with a ma-
jor  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 accordingly.

If the message arrives at the client that initiated the the call-






                              - 7 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


back is invoked.
__
||  typedef void (*IcePoProcessMsgProc)();

void   PoProcessMsgProc([4mice_conn[24m,  [4mclient_data[24m,  [4mopcode[24m,  [4mlength[24m,
[4mswap[24m, [4mreply_wait[24m, [4mreply_ready_ret[24m)
    IceConn [4mice_conn[24m;
    IcePointer [4mclient_data[24m;
    int [4mopcode[24m;
    unsigned long [4mlength[24m;
    Bool [4mswap[24m;
    IceReplyWaitInfo *[4mreply_wait[24m;
    Bool *[4mreply_ready_ret[24m;

[4mice_conn[24m  The ICE connection object.

[4mclient_data[0m
          Client data associated with this protocol  on  the  ICE
          connection.

[4mopcode[24m    The minor opcode of the message.

[4mlength[24m    The  length (in 8-byte units) of the message beyond the
          ICE header.

[4mswap[24m      A flag that indicates if byte swapping is necessary.

[4mreply_wait[0m
          Indicates if the invoking client is waiting for  a  re-
          ply.

[4mreply_ready_ret[0m
          If set to a reply is ready.
||__

If  the message arrives at the client that accepted the the call-
back is invoked.
__
||  typedef void (*IcePaProcessMsgProc)();

void  PaProcessMsgProc([4mice_conn[24m,  [4mclient_data[24m,  [4mopcode[24m,   [4mlength[24m,
[4mswap[24m)
    IceConn [4mice_conn[24m;
    IcePointer [4mclient_data[24m;
    int [4mopcode[24m;
    unsigned long [4mlength[24m;
    Bool [4mswap[24m;

[4mice_conn[24m  The ICE connection object.

[4mclient_data[0m
          Client  data  associated  with this protocol on the ICE
          connection.




                              - 8 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mopcode[24m    The minor opcode of the message.

[4mlength[24m    The length (in 8-byte units) of the message beyond  the
          ICE header.

[4mswap[24m      A flag that indicates if byte swapping is necessary.
||__

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 time.  In the case  of  the
client data was set in the call to In the case of the client data
was set in the callback.

The  callback  needs  to  check  the reply_wait argument.  If re-
ply_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 implemen-
tation-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
__
||  typedef struct {      unsigned long sequence_of_request;      int
major_opcode_of_request;          int    minor_opcode_of_request;
     IcePointer reply; } IceReplyWaitInfo;
||__

contains the major/minor opcodes and sequence number of the  mes-
sage  for  which  a  reply  is being awaited.  It also contains a
pointer to the reply message to be filled in  (the  protocol  li-
brary  should  cast this 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 callback will have to allocate  ad-
ditional memory and store pointer(s) to that memory in the fixed-
size structure.  If the entire data is variable length (for exam-
ple.,  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 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.





                              - 9 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


If reply_wait is not NULL and 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 Note that an
error should only be returned if it corresponds to the reply  be-
ing  waited  for.   Otherwise, the 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  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 no-
tify the client of the ``Interact Request'' via a callback.

The reason the callback does not have a reply_wait, like does, is
because  a  process 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).

[1m6.2.  Authentication Methods[0m

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

+o    One to handle the side that initiates a

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

is  the  callback  invoked for the client that initiated the 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([4mice_conn[24m,  [4mauth_state_ptr[24m,  [4mclean_up[24m,
[4mswap[24m, [4mauth_datalen[24m, [4mauth_data[24m,
                    [4mreply_datalen_ret[24m,     [4mreply_data_ret[24m,    [4mer-[0m
[4mror_string_ret[24m)
    IceConn [4mice_conn[24m;
    IcePointer *[4mauth_state_ptr[24m;
    Bool [4mclean_up[24m;
    Bool [4mswap[24m;
    int [4mauth_datalen[24m;
    IcePointer [4mauth_data[24m;
    int *[4mreply_datalen_ret[24m;
    IcePointer *[4mreply_data_ret[24m;
    char **[4merror_string_ret[24m;

[4mice_conn[24m  The ICE connection object.




                              - 10 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mauth_state_ptr[0m
          A pointer to state for use by the authentication  call-
          back procedure.

[4mclean_up[24m  If  authentication  is  over,  and  the function should
          clean up any state it was maintaining.  The last 6  ar-
          guments should be ignored.

[4mswap[24m      If the auth_data may have to be byte swapped (depending
          on its contents).

[4mauth_datalen[0m
          The length (in bytes) of the authenticator data.

[4mauth_data[24m The data from the authenticator.

[4mreply_datalen_ret[0m
          The length (in bytes) of the reply data returned.

[4mreply_data_ret[0m
          The reply data returned.

[4merror_string_ret[0m
          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  au-
thentication  method.   As  a result, the may be called more than
once when authenticating a client, and some state will have to be
maintained  between  each  invocation.   At  the  start  of  each
*auth_state_ptr  is  NULL, and the function should initialize its
state and set this pointer.  In  subsequent  invocations  of  the
callback,  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 can be  ob-
tained by calling the function.

ICElib will be responsible for freeing the reply_data_ret and er-
ror_string_ret pointers with

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

The should return one of four values:

+o    - a reply is available.

+o    - authentication rejected.





                              - 11 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


+o    - authentication failed.

+o    - done cleaning up.

is the callback invoked for the client that received the
__
||  typedef IcePaAuthStatus (*IcePaAuthProc) ();

IcePaAuthStatus    PaAuthProc([4mice_conn[24m,   [4mauth_state_ptr[24m,   [4mswap[24m,
[4mauth_datalen[24m, [4mauth_data[24m,
                    [4mreply_datalen_ret[24m,    [4mreply_data_ret[24m,     [4mer-[0m
[4mror_string_ret[24m)
    IceConn [4mice_conn[24m;
    IcePointer *[4mauth_state_ptr[24m;
    Bool [4mswap[24m;
    int [4mauth_datalen[24m;
    IcePointer [4mauth_data[24m;
    int *[4mreply_datalen_ret[24m;
    IcePointer *[4mreply_data_ret[24m;
    char **[4merror_string_ret[24m;

[4mice_conn[24m  The ICE connection object.

[4mauth_state_ptr[0m
          A  pointer to state for use by the authentication call-
          back procedure.

[4mswap[24m      If auth_data may have to be byte swapped (depending  on
          its contents).

[4mauth_datalen[0m
          The  length  (in  bytes) of the protocol originator au-
          thentication data.

[4mauth_data[24m The authentication data from the protocol originator.

[4mreply_datalen_ret[0m
          The length of the authentication data returned.

[4mreply_data_ret[0m
          The authentication data returned.

[4merror_string_ret[0m
          If authentication is rejected or fails, an error string
          is returned.
||__


Authentication may require several phases, depending on  the  au-
thentication  method.   As  a result, the may be called more than
once when authenticating a client, and some state will have to be
maintained  between  each  invocation.   At  the  start  of  each
auth_datalen  is  zero, *auth_state_ptr is NULL, and the function
should initialize its state and set this pointer.  In  subsequent



                              - 12 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


invocations 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 can be ob-
tained by calling the function.

The auth_data pointer may point to a volatile  block  of  memory.
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  re-
ply_data_ret and error_string_ret pointers with

The should return one of four values:

+o    - continue (or start) authentication.

+o    - authentication accepted.

+o    - authentication rejected.

+o    - authentication failed.

[1m7.  ICE Connections[0m

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 con-
nections, so we discuss that first.

[1m7.1.  Opening an ICE Connection[0m

To open an ICE connection with another client (that  is,  waiting
for connections), use
__
||  IceConn IceOpenConnection([4mnetwork_ids_list[24m, [4mcontext[24m, [4mmust_authen-[0m
[4mticate[24m, [4mmajor_opcode_check[24m,
                    [4merror_length[24m, [4merror_string_ret[24m)
     char *[4mnetwork_ids_list[24m;
     IcePointer [4mcontext[24m;
     Bool [4mmust_authenticate[24m;
     int [4mmajor_opcode_check[24m;
     int  [4merror_length[24m;
     char *[4merror_string_ret[24m;

[4mnetwork_ids_list[0m
          Specifies the network ID(s) of the other client.

[4mcontext[24m   A  pointer to an opaque object or NULL.  Used to deter-
          mine if an ICE connection can be shared (see below).

[4mmust_authenticate[0m
          If the other client may not bypass authentication.




                              - 13 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mmajor_opcode_check[0m
          Used to force a new ICE connection to be  created  (see
          below).

[4merror_length[0m
          Length of the error_string_ret argument passed in.

[4merror_string_ret[0m
          Returns  a  null-terminated error message, if any.  The
          error_string_ret argument points to user supplied  mem-
          ory.  No more than error_length bytes are used.
||__

returns  an  opaque  ICE connection object if it succeeds; other-
wise, it returns NULL.

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

lw(0.25i) lw(2.5i) lw(1i).       tcp/<hostname>:<portnumber>   or
     decnet/<hostname>::<objname>  or                local/<host-
name>:<path>

Most protocol libraries will have some sort of open function that
should internally make a call into When is called, it may be pos-
sible 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  connection
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 connec-
tion that has a different non-NULL context associated with it.

In addition, if major_opcode_check contains a nonzero  major  op-
code value, a previously created ICE connection will be used only
if the major opcode is not active on the connection.  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.

After is called, the client is ready to send a (provided that was
called) or receive a (provided that was called).


-----------
   The X Consortium's ICElib implementation uses an  .ICEau-
thority file (see Appendix A).



                              - 14 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[1m7.2.  Listening for ICE Connections[0m

Clients  wishing  to accept ICE connections must first call or so
that they can listen for connections.  A list of opaque  "listen"
objects  are returned, one for each type of transport 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 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 to spec-
ify the names for the listen objects.
__
||  Status  IceListenForConnections([4mcount_ret[24m,  [4mlisten_objs_ret[24m,  [4mer-[0m
[4mror_length[24m, [4merror_string_ret[24m)
     int  *[4mcount_ret[24m;
     IceListenObj **[4mlisten_objs_ret[24m;
     int  [4merror_length[24m;
     char *[4merror_string_ret[24m;

[4mcount_ret[24m Returns the number of listen objects created.

[4mlisten_objs_ret[0m
          Returns a list of pointers to opaque listen objects.

[4merror_length[0m
          The length of the error_string_ret argument passed in.

[4merror_string_ret[0m
          Returns  a  null-terminated error message, if any.  The
          error_string_ret points to user  supplied  memory.   No
          more than error_length bytes are used.
||__

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

__
||  Status IceListenForWellKnownConnections([4mport_id[24m, [4mcount_ret[24m,  [4mlis-[0m
[4mten_objs_ret[24m, [4merror_length[24m, [4merror_string_ret[24m)
     char *[4mport_id[24m;
     int  *[4mcount_ret[24m;
     IceListenObj **[4mlisten_objs_ret[24m;
     int  [4merror_length[24m;
     char *[4merror_string_ret[24m;

[4mport_id[24m   Specifies  the  port identification for the address(es)
          to be opened.  The value must  not  contain  the  slash
          (``/'')  or comma (``,'') character; these are reserved
          for future use.





                              - 15 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mcount_ret[24m Returns the number of listen objects created.

[4mlisten_objs_ret[0m
          Returns a list of pointers to opaque listen objects.

[4merror_length[0m
          The length of the error_string_ret argument passed in.

[4merror_string_ret[0m
          Returns a null-terminated error message, if  any.   The
          error_string_ret  points  to  user supplied memory.  No
          more than error_length bytes are used.
||__

constructs a list of network IDs by prepending each known  trans-
port  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 net-
work ID cannot be created the network ID is ignored.  If no  lis-
ten objects are created returns failure.

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


To close and free the listen objects, use

__
||  void IceFreeListenObjs([4mcount[24m, [4mlisten_objs[24m)
    int [4mcount[24m;
    IceListenObj *[4mlisten_objs[24m;

[4mcount[24m     The number of listen objects.

[4mlisten_objs[0m
          The listen objects.
||__


To detect a new connection on a listen object,  use  on  the  de-
scriptor associated with the listen object.


To obtain the descriptor, use

__
||  int IceGetListenConnectionNumber([4mlisten_obj[24m)
    IceListenObj [4mlisten_obj[24m;

[4mlisten_obj[0m
          The listen object.
||__





                              - 16 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


To  obtain the network ID string associated with a listen object,
use
__
||  char *IceGetListenConnectionString([4mlisten_obj[24m)
    IceListenObj [4mlisten_obj[24m;

[4mlisten_obj[0m
          The listen object.
||__


A network ID has the following format:

lw(0.25i) lw(2.5i) lw(1i).       tcp/<hostname>:<portnumber>   or
     decnet/<hostname>::<objname>  or                local/<host-
name>:<path>

To compose a string containing a list of network IDs separated by
commas (the format recognized by use

__
||  char *IceComposeNetworkIdList([4mcount[24m, [4mlisten_objs[24m)
    int [4mcount[24m;
    IceListenObj *[4mlisten_objs[24m;

[4mcount[24m     The number of listen objects.

[4mlisten_objs[0m
          The listen objects.
||__


[1m7.3.  Host Based Authentication for ICE Connections[0m

If  authentication  fails  when  a client attempts to open an ICE
connection and the initiating client has not required authentica-
tion, a host based authentication procedure  may  be  invoked  to
provide a last chance for the client to connect.  Each listen ob-
ject has such a callback associated with it, and this callback is
set using the function.
__
||  void IceSetHostBasedAuthProc([4mlisten_obj[24m, [4mhost_based_auth_proc[24m)
    IceListenObj [4mlisten_obj[24m;
    IceHostBasedAuthProc [4mhost_based_auth_proc[24m;

[4mlisten_obj[0m
          The listen object.

[4mhost_based_auth_proc[0m
          The host based authentication procedure.
||__

By  default,  each listen object has no host based authentication
procedure    associated    with    it.     Passing    NULL    for



                              - 17 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


host_based_auth_proc  turns  off  host based authentication if it
was previously set.

__
||  typedef Bool (*IceHostBasedAuthProc) ();

Bool HostBasedAuthProc([4mhost_name[24m)
    char *[4mhost_name[24m;

[4mhost_name[24m The host name of the client that tried to open  an  ICE
          connection.
||__

The host_name argument is a string in the form [4mprotocol[24m/[4mhostname[24m,
where [4mprotocol[24m is one of {tcp, decnet, local}.

If  returns  access will be granted, even though the original au-
thentication failed.  Note that authentication can effectively be
disabled by registering an which always returns

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

[1m7.4.  Accepting ICE Connections[0m

After  a  connection  attempt  is detected on a listen object re-
turned by you should call This returns a new opaque  ICE  connec-
tion object.
__
||  IceConn IceAcceptConnection([4mlisten_obj[24m, [4mstatus_ret[24m)
    IceListenObj [4mlisten_obj[24m;
    IceAcceptStatus *[4mstatus_ret[24m;

[4mlisten_obj[0m
          The  listen  object  on  which a new connection was de-
          tected.

[4mstatus_ret[0m
          Return status information.
||__

The status_ret argument is set to one of the following values:

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

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

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

In  general,  to  detect  new connections, you should call on the
file descriptors associated with the listen objects.  When a  new



                              - 18 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


connection  is  detected, the function should be called.  may re-
turn 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 connection status to become valid.

The  following  pseudo-code  demonstrates how connections are ac-
cepted:

new_ice_conn = IceAcceptConnection (listen_obj,  &accept_status);
if  (accept_status != IceAcceptSuccess) {      close the file de-
scriptor 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); }

After is called and the connection has been validated, the client
is  ready to receive a (provided that was called) or send a (pro-
vided that was called).

[1m7.5.  Closing ICE Connections[0m

To close an ICE connection created with or use
__
||  IceCloseStatus IceCloseConnection([4mice_conn[24m)
    IceConn [4mice_conn[24m;




                              - 19 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mice_conn[24m  The ICE connection to close.
||__

To actually close an ICE  connection,  the  following  conditions
must be met:

+o    The  [4mopen[24m [4mreference[24m [4mcount[24m must have reached zero on this ICE
     connection.  When 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 must be matched with a call to The connection can be
     closed only on the last call to

+o    The [4mactive[24m [4mprotocol[24m [4mcount[24m must have reached zero.  Each time
     a 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 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.

returns one of the following values:

+o    -  the  ICE  connection  was closed at this time.  The watch
     procedures were invoked and the connection was freed.

+o    - an IO error had occurred on the connection, but  is  being
     called  within  a  nested The watch procedures have been in-
     voked at this time, but the connection will be freed as soon
     as possible (when the nesting level reaches zero and returns
     a status of

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

+o    -  the  connection  was not closed at this time and shutdown
     negotiation started with the client on the other side of the
     ICE connection.  When the  connection  is  actually  closed,
     will return a status of


When  it  is  known  that the client on the other side of the ICE
connection has terminated the connection without initiating shut-
down negotiation, the function should be called to turn off shut-
down negotiation.  This will prevent from  writing  to  a  broken
connection.
__
||  void IceSetShutdownNegotiation([4mice_conn[24m, [4mnegotiate[24m)
    IceConn [4mice_conn[24m;
    Bool [4mnegotiate[24m;



                              - 20 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mice_conn[24m  A valid ICE connection object.

[4mnegotiate[24m If shutdown negotiating will be turned off.
||__


To  check  the  shutdown negotiation status of an ICE connection,
use
__
||  Bool IceCheckShutdownNegotiation([4mice_conn[24m)
    IceConn [4mice_conn[24m;

[4mice_conn[24m  A valid ICE connection object.
||__

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

[1m7.6.  Connection Watch Procedures[0m

To add a watch procedure that will be  called  each  time  ICElib
opens a new connection via or or closes a connection via use
__
||  Status IceAddConnectionWatch([4mwatch_proc[24m, [4mclient_data[24m)
    IceWatchProc [4mwatch_proc[24m;
    IcePointer [4mclient_data[24m;

[4mwatch_proc[0m
          The  watch  procedure  to  invoke  when ICElib opens or
          closes a connection.

[4mclient_data[0m
          This pointer will be passed to the watch procedure.
||__

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

Note that several calls to might share the same  ICE  connection.
In such a case, the watch procedure is only invoked when the con-
nection  is first created (after authentication succeeds).  Simi-
larly, because connections might be shared, the  watch  procedure
is  called  only  if 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 dif-
ficult without the watch procedures.





                              - 21 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


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 connec-
tions (with the opening argument set to

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

void WatchProc([4mice_conn[24m, [4mclient_data[24m, [4mopening[24m, [4mwatch_data[24m)
    IceConn [4mice_conn[24m;
    IcePointer [4mclient_data[24m;
    Bool [4mopening[24m;
    IcePointer *[4mwatch_data[24m;

[4mice_conn[24m  The opened or closed ICE connection.  Call to  get  the
          file descriptor associated with this connection.

[4mclient_data[0m
          Client data specified in the call to

[4mopening[24m   If  the  connection is being opened.  If the connection
          is being closed.

[4mwatch_data[0m
          Can be used to save a pointer to client data.
||__

If opening is 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


To remove a watch procedure, use
__
||  void IceRemoveConnectionWatch([4mwatch_proc[24m, [4mclient_data[24m)
    IceWatchProc [4mwatch_proc[24m;
    IcePointer [4mclient_data[24m;


[4mwatch_proc[0m
          The watch procedure that was passed to

[4mclient_data[0m
          The client_data pointer that was passed to
||__








                              - 22 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[1m8.  Protocol Setup and Shutdown[0m

To activate a protocol on a given ICE connection, use

__
||  IceProtocolSetupStatus   IceProtocolSetup([4mice_conn[24m,    [4mmy_opcode[24m,
[4mclient_data[24m, [4mmust_authenticate[24m,
                    [4mmajor_version_ret[24m,   [4mminor_version_ret[24m,  [4mven-[0m
[4mdor_ret[24m, [4mrelease_ret[24m, [4merror_length[24m, [4merror_string_ret[24m)
    IceConn [4mice_conn[24m;
    int [4mmy_opcode[24m;
    IcePointer [4mclient_data[24m;
    Bool [4mmust_authenticate[24m;
    int *[4mmajor_version_ret[24m;
    int *[4mminor_version_ret[24m;
    char **[4mvendor_ret[24m;
    char **[4mrelease_ret[24m;
    int [4merror_length[24m;
    char *[4merror_string_ret[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mmy_opcode[24m The major opcode of the protocol to be set up,  as  re-
          turned by

[4mclient_data[0m
          The  client  data stored in this pointer will be passed
          to the callback.

[4mmust_authenticate[0m
          If the other client may not bypass authentication.

[4mmajor_version_ret[0m
          The major version of the protocol to  be  used  is  re-
          turned.

[4mminor_version_ret[0m
          The  minor  version  of  the protocol to be used is re-
          turned.

[4mvendor_ret[0m
          The vendor string specified by the protocol acceptor.

[4mrelease_ret[0m
          The release string specified by the protocol acceptor.

[4merror_length[0m
          Specifies the length of the  error_string_ret  argument
          passed in.

[4merror_string_ret[0m
          Returns  a  null-terminated error message, if any.  The
          error_string_ret argument points to user supplied  mem-
          ory.  No more than error_length bytes are used.



                              - 23 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


||__

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

returns one of the following values:

+o    - the major_version_ret, minor_version_ret, vendor_ret,  re-
     lease_ret are set.

+o    or  -  check  error_string_ret  for failure reason.  The ma-
     jor_version_ret, minor_version_ret, vendor_ret,  release_ret
     are not set.

+o    -  this  protocol is already active on this connection.  The
     major_version_ret,   minor_version_ret,   vendor_ret,    re-
     lease_ret are not set.


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

__
||  Status IceProtocolShutdown([4mice_conn[24m, [4mmajor_opcode[24m)
    IceConn [4mice_conn[24m;
    int [4mmajor_opcode[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mmajor_opcode[0m
          The major opcode of the protocol to shut down.
||__

The  return value of 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 con-
nection.  By activated, we mean that a succeeded on  the  connec-
tion.   Note that ICE does not define how each sub-protocol trig-
gers a protocol shutdown.

[1m9.  Processing Messages[0m

To process incoming messages on an ICE connection, use
__
||  IceProcessMessagesStatus IceProcessMessages([4mice_conn[24m, [4mreply_wait[24m,
[4mreply_ready_ret[24m)
    IceConn [4mice_conn[24m;
    IceReplyWaitInfo *[4mreply_wait[24m;
    Bool *[4mreply_ready_ret[24m;

[4mice_conn[24m  A valid ICE connection object.




                              - 24 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mreply_wait[0m
          Indicates if a reply is being waited for.

[4mreply_ready_ret[0m
          If set to on return, a reply is ready.
||__

is used in two ways:

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

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

contains  the major/minor opcodes and sequence number of the mes-
sage for which a reply is being  awaited.   It  also  contains  a
pointer  to  the  reply message to be filled in (the protocol li-
brary should cast this 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 callback will have to allocate ad-
ditional memory and store pointer(s) to that memory in the fixed-
size structure.  If the entire data is variable length (for exam-
ple, 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  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.

__
||  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 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 will be set to

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

returns one of the following values:

+o    - no error occurred.





                              - 25 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


+o    - an IO error occurred, and the caller must explicitly close
     the connection by calling

+o    - the ICE connection has been closed (closing of the connec-
     tion  was  deferred  because of shutdown negotiation, or be-
     cause the nesting level was not zero).  Do  not  attempt  to
     access  the  ICE connection at this point, since it has been
     freed.

[1m10.  Ping[0m

To send a ``Ping'' message to the client on the other side of the
ICE connection, use
__
||  Status IcePing([4mice_conn[24m, [4mping_reply_proc[24m, [4mclient_data[24m)
    IceConn [4mice_conn[24m;
    IcePingReplyProc [4mping_reply_proc[24m;
    IcePointer [4mclient_data[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mping_reply_proc[0m
          The callback to invoke when the Ping reply arrives.

[4mclient_data[0m
          This pointer will be passed to the callback.
||__

returns zero for failure and a positive value for success.

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

void PingReplyProc([4mice_conn[24m, [4mclient_data[24m)
    IceConn [4mice_conn[24m;
    IcePointer [4mclient_data[24m;

[4mice_conn[24m  The ICE connection object.

[4mclient_data[0m
          The client data specified in the call to
||__


[1m11.  Using ICElib Informational Functions[0m

__
||  IceConnectStatus IceConnectionStatus([4mice_conn[24m)
||__    IceConn [4mice_conn[24m;

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




                              - 26 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


+o    -  the  connection is not valid yet (that is, authentication
     is taking place).  This is only relevant to connections cre-
     ated by

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

+o    - the connection had been rejected  (that is, authentication
     failed).  This is only relevant to connections created by

+o    - an IO error has occurred on the connection.

__
||  char *IceVendor([4mice_conn[24m)
||__    IceConn [4mice_conn[24m;

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

__
||  char *IceRelease([4mice_conn[24m)
||__    IceConn [4mice_conn[24m;

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

__
||  int IceProtocolVersion([4mice_conn[24m)
||__    IceConn [4mice_conn[24m;

returns the major version of the ICE protocol on this connection.

__
||  int IceProtocolRevision([4mice_conn[24m)
||__    IceConn [4mice_conn[24m;

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

__
||  int IceConnectionNumber([4mice_conn[24m)
||__    IceConn [4mice_conn[24m;

returns the file descriptor of this ICE connection.

__
||  char *IceConnectionString([4mice_conn[24m)
||__    IceConn [4mice_conn[24m;

returns  the  network ID of the client that accepted this connec-
tion.  The string should be freed with a call to when  no  longer
needed.




                              - 27 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m

__
||  unsigned long IceLastSentSequenceNumber([4mice_conn[24m)
||__    IceConn [4mice_conn[24m;

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

__
||  unsigned long IceLastReceivedSequenceNumber([4mice_conn[24m)
||__    IceConn [4mice_conn[24m;

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

__
||  Bool IceSwapping([4mice_conn[24m)
||__    IceConn [4mice_conn[24m;

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

__
||  IcePointer IceGetContext([4mice_conn[24m)
||__    IceConn [4mice_conn[24m;

returns the context associated with a connection created by

[1m12.  ICE Messages[0m

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.

[1m12.1.  Sending ICE Messages[0m

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

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


To get the size of the ICE output buffer, use
__
||  int IceGetOutBufSize([4mice_conn[24m)
     IceConn [4mice_conn[24m;



                              - 28 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mice_conn[24m  A valid ICE connection object.
||__


To flush the ICE output buffer, use
__
||  IceFlush([4mice_conn[24m)
     IceConn [4mice_conn[24m;

[4mice_conn[24m  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([4mice_conn[24m, [4mmajor_opcode[24m,  [4mminor_opcode[24m,  [4mheader_size[24m,
[4m<C_data_type>[24m, [4mpmsg[24m)
     IceConn [4mice_conn[24m;
     int [4mmajor_opcode[24m;
     int [4mminor_opcode[24m;
     int [4mheader_size[24m;
     <C_data_type> *[4mpmsg[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mmajor_opcode[0m
          The major opcode of the message.

[4mminor_opcode[0m
          The minor opcode of the message.

[4mheader_size[0m
          The size of the message header (in bytes).

[4m<C_data_type>[0m
          The actual C data type of the message header.

[4mpmsg[24m      The  message  header  pointer.   After  this  macro  is
          called, the library  can  store  data  in  the  message
          header.
||__

is used to set up a message header on an ICE connection.  It sets
the  major  and minor opcodes of the message, 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.







                              - 29 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m

__
||  IceGetHeaderExtra([4mice_conn[24m,      [4mmajor_opcode[24m,      [4mminor_opcode[24m,
[4mheader_size[24m, [4mextra[24m, [4m<C_data_type>[24m, [4mpmsg[24m, [4mpdata[24m)
     IceConn [4mice_conn[24m;
     int [4mmajor_opcode[24m;
     int [4mminor_opcode[24m;
     int [4mheader_size[24m;
     int [4mextra[24m;
     <C_data_type> *[4mpmsg[24m;
     char *[4mpdata[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mmajor_opcode[0m
          The major opcode of the message.

[4mminor_opcode[0m
          The minor opcode of the message.

[4mheader_size[0m
          The size of the message header (in bytes).

[4mextra[24m     The size of the extra data beyond the header (in 8-byte
          units).

[4m<C_data_type>[0m
          The actual C data type of the message header.

[4mpmsg[24m      The  message  header  pointer.   After  this  macro  is
          called, the library  can  store  data  in  the  message
          header.

[4mpdata[24m     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.
||__

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([4mice_conn[24m, [4mmajor_opcode[24m, [4mminor_opcode[24m)
     IceConn [4mice_conn[24m;
     int [4mmajor_opcode[24m;
     int [4mminor_opcode[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mmajor_opcode[0m
          The major opcode of the message.




                              - 30 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mminor_opcode[0m
          The minor opcode of the message.
||__

is  used  to  generate a message that is identical in size to the
ICE header message, and has no additional data.


__
||  IceErrorHeader([4mice_conn[24m,  [4moffending_major_opcode[24m,   [4moffending_mi-[0m
[4mnor_opcode[24m, [4moffending_sequence_num[24m,
                    [4mseverity[24m, [4merror_class[24m, [4mdata_length[24m)
     IceConn [4mice_conn[24m;
     int [4moffending_major_opcode[24m;
     int [4moffending_minor_opcode[24m;
     int [4moffending_sequence_num[24m;
     int [4mseverity[24m;
     int [4merror_class[24m;
     int [4mdata_length[24m;

[4mice_conn[24m  A valid ICE connection object.

[4moffending_major_opcode[0m
          The  major opcode of the protocol in which an error was
          detected.

[4moffending_minor_opcode[0m
          The minor opcode of the protocol in which an error  was
          detected.

[4moffending_sequence_num[0m
          The  sequence number of the message that caused the er-
          ror.

[4mseverity[24m  or

[4merror_class[0m
          The error class.

[4mdata_length[0m
          Length of data (in 8-byte units) to  be  written  after
          the header.
||__

sets up an error message header.

Note that the two clients connected by ICE may be using different
major  opcodes  for a given protocol.  The offending_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 [4mInter-Client[24m [4mExchange[24m  [4mPro-[0m
[4mtocol[24m standard for more details.



                              - 31 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


lw(1i) lw(1i).  T{ T}   T{ 0x8000 T}
T{ T}   T{ 0x8001 T}
T{ T}   T{ 0x8002 T}
T{ T}   T{ 0x8003 T}

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


To  write  data to an ICE connection, use the 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 and


__
||  IceWriteData([4mice_conn[24m, [4mbytes[24m, [4mdata[24m)
     IceConn [4mice_conn[24m;
     int [4mbytes[24m;
     char *[4mdata[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mbytes[24m     The number of bytes to write.

[4mdata[24m      The data to write.
||__


To write data as 16-bit quantities, use
__
||  IceWriteData16([4mice_conn[24m, [4mbytes[24m, [4mdata[24m)
     IceConn [4mice_conn[24m;
     int [4mbytes[24m;
     short *[4mdata[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mbytes[24m     The number of bytes to write.

[4mdata[24m      The data to write.
||__


To write data as 32-bit quantities, use
__
||  IceWriteData32([4mice_conn[24m, [4mbytes[24m, [4mdata[24m)
     IceConn [4mice_conn[24m;
     int [4mbytes[24m;
     long *[4mdata[24m;

[4mice_conn[24m  A valid ICE connection object.





                              - 32 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mbytes[24m     The number of bytes to write.

[4mdata[24m      The data to write.
||__


To  bypass copying data to the ICE output buffer, use to directly
send data over the network connection.   If  necessary,  the  ICE
output buffer is first flushed.
__
||  IceSendData([4mice_conn[24m, [4mbytes[24m, [4m(char[24m [4m*)[24m [4mdata[24m)
     IceConn [4mice_conn[24m;
     int [4mbytes[24m;
     char *[4mdata[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mbytes[24m     The number of bytes to send.

[4mdata[24m      The data to send.
||__


To force 32-bit or 64-bit alignment, use A maximum of 7 pad bytes
can be specified.
__
||  IceWritePad([4mice_conn[24m, [4mbytes[24m)
     IceConn [4mice_conn[24m;
     int [4mbytes[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mbytes[24m     The number of pad bytes.
||__


[1m12.2.  Reading ICE Messages[0m

The  ICE  library maintains an input buffer used for reading mes-
sages.  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
__
||  int IceGetInBufSize([4mice_conn[24m)
     IceConn [4mice_conn[24m;





                              - 33 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mice_conn[24m  A valid ICE connection object.
||__


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 mes-
sage should be thrown out.  After using any  of  the  macros  de-
scribed  below  for  reading  messages,  the macro can be used to
check if an IO error occurred on the connection.  After an IO er-
ror has occurred on an ICE connection, all read  operations  will
be  ignored.   For  further  information, see section 13, ``Error
Handling.''


__
||  Bool IceValidIO([4mice_conn[24m)
    IceConn [4mice_conn[24m;
||__


The following macros can be used to read ICE messages.
__
||  IceReadSimpleMessage([4mice_conn[24m, [4m<C_data_type>[24m, [4mpmsg[24m)
     IceConn [4mice_conn[24m;
     <C_data_type> *[4mpmsg[24m;

[4mice_conn[24m  A valid ICE connection object.

[4m<C_data_type>[0m
          The actual C data type of the message header.

[4mpmsg[24m      This pointer is set to the message header.
||__

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  addi-
tional  data.   Note  that  the ICE library always reads in these
first 8 bytes, so it can obtain the major opcode of the  message.
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 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 and


__
||  IceReadCompleteMessage([4mice_conn[24m,   [4mheader_size[24m,    [4m<C_data_type>[24m,
[4mpmsg[24m, [4mpdata[24m)
     IceConn [4mice_conn[24m;
     int [4mheader_size[24m;
     <C_data_type> *[4mpmsg[24m;



                              - 34 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


     char *[4mpdata[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mheader_size[0m
          The size of the message header (in bytes).

[4m<C_data_type>[0m
          The actual C data type of the message header.

[4mpmsg[24m      This pointer is set to the message header.

[4mpdata[24m     This  pointer is set to the variable length data of the
          message.
||__

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


After calling and processing the message, should be called.

__
||  IceDisposeCompleteMessage([4mice_conn[24m, [4mpdata[24m)
     IceConn [4mice_conn[24m;
     char *[4mpdata[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mpdata[24m     The pointer to the variable length data returned in
||__

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.


__
||  IceReadMessageHeader([4mice_conn[24m, [4mheader_size[24m, [4m<C_data_type>[24m, [4mpmsg[24m)
     IceConn [4mice_conn[24m;
     int [4mheader_size[24m;
     <C_data_type> *[4mpmsg[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mheader_size[0m
          The size of the message header (in bytes).

[4m<C_data_type>[0m
          The actual C data type of the message header.




                              - 35 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mpmsg[24m      This pointer is set to the message header.
||__

reads just the message header.  The rest of the  data  should  be
read with the 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([4mice_conn[24m, [4mbytes[24m, [4mpdata[24m)
     IceConn [4mice_conn[24m;
     int [4mbytes[24m;
     char *[4mpdata[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mbytes[24m     The number of bytes to read.

[4mpdata[24m     The data is read into this user supplied buffer.
||__


To read data as 16-bit quantities, use
__
||  IceReadData16([4mice_conn[24m, [4mswap[24m, [4mbytes[24m, [4mpdata[24m)
     IceConn [4mice_conn[24m;
     Bool [4mswap[24m;
     int [4mbytes[24m;
     short *[4mpdata[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mswap[24m      If the values will be byte swapped.

[4mbytes[24m     The number of bytes to read.

[4mpdata[24m     The data is read into this user supplied buffer.
||__


To read data as 32-bit quantities, use
__
||  IceReadData32([4mice_conn[24m, [4mswap[24m, [4mbytes[24m, [4mpdata[24m)
     IceConn [4mice_conn[24m;
     Bool [4mswap[24m;
     int [4mbytes[24m;
     long *[4mpdata[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mswap[24m      If the values will be byte swapped.




                              - 36 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mbytes[24m     The number of bytes to read.

[4mpdata[24m     The data is read into this user supplied buffer.
||__


To force 32-bit or 64-bit alignment, use A maximum of 7 pad bytes
can be specified.
__
||  IceReadPad([4mice_conn[24m, [4mbytes[24m)
     IceConn [4mice_conn[24m;
     int [4mbytes[24m;

[4mice_conn[24m  A valid ICE connection object.

[4mbytes[24m     The number of pad bytes.
||__


[1m13.  Error Handling[0m

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 routines if
you prefer your own error handling and can be changed as often as
you like.


To set the ICE error handler, use
__
||  IceErrorHandler IceSetErrorHandler([4mhandler[24m)
    IceErrorHandler [4mhandler[24m;

[4mhandler[24m   The ICE error handler.  You should pass NULL to restore
          the default handler.
||__

returns the previous error handler.

The ICE error handler is invoked when an unexpected ICE  protocol
error (major opcode 0) is encountered.  The action of the default
handler is to print an explanatory message to and if the severity
is  fatal, call 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).




                              - 37 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


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

void ErrorHandler([4mice_conn[24m, [4mswap[24m, [4moffending_minor_opcode[24m, [4moffend-[0m
[4ming_sequence_num[24m, [4merror_class[24m,
                     [4mseverity[24m, [4mvalues[24m)
    IceConn [4mice_conn[24m;
    Bool [4mswap[24m;
    int [4moffending_minor_opcode[24m;
    unsigned long [4moffending_sequence_num[24m;
    int [4merror_class[24m;
    int [4mseverity[24m;
    IcePointer [4mvalues[24m;

[4mice_conn[24m  The ICE connection object.

[4mswap[24m      A flag that indicates if the values need byte swapping.

[4moffending_minor_opcode[0m
          The ICE minor opcode of the offending message.

[4moffending_sequence_num[0m
          The sequence number of the offending message.

[4merror_class[0m
          The error class of the offending message.

[4mseverity[24m  or

[4mvalues[24m    Any  additional  error values specific to the minor op-
          code and class.
||__

The following error classes are defined at the ICE level:


For further information, see the [4mInter-Client[24m  [4mExchange[24m  [4mProtocol[0m
standard.


To handle fatal I/O errors, use

__
||  IceIOErrorHandler IceSetIOErrorHandler([4mhandler[24m)
    IceIOErrorHandler [4mhandler[24m;

[4mhandler[24m   The I/O error handler.  You should pass NULL to restore
          the default handler.
||__

returns the previous IO error handler.





                              - 38 -





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An ICE I/O error handler has the type of

__
||  typedef void (*IceIOErrorHandler)();

void IOErrorHandler([4mice_conn[24m)
    IceConn [4mice_conn[24m;

[4mice_conn[24m  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 neces-
     sary to respond to the IO error and  then  returns,  but  it
     does  not call The ICE connection is given a ``bad IO'' sta-
     tus, and all future reads and writes to the  connection  are
     ignored.  The next time is called it will return a status of
     At that time, the application should call

+o    In  the second, the IO error handler does call and then uses
     the call to get back to the application's main  event  loop.
     The  and  calls  may not work properly on all platforms, and
     special care must be taken to avoid  memory  leaks.   There-
     fore, this second model is less desirable.

Before the application I/O error handler is invoked, protocol li-
braries that were interested in being notified of I/O errors will
have  their handlers invoked.  This handler is set up in the pro-
tocol registration functions (see and and could be used to  clean
up state specific to the protocol.


__
||  typedef void (*IceIOErrorProc)();

void IOErrorProc([4mice_conn[24m)
    IceConn [4mice_conn[24m;

[4mice_conn[24m  The ICE connection object.
||__

Note  that  every 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.

[1m14.  Multi-Threading Support[0m

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







                              - 39 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m

__
||  Status IceInitThreads()
||__

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

Protocol  libraries  layered  on  top of ICElib will have to lock
critical sections of code that access an ICE connection (for  ex-
ample, when generating messages).  Two calls, which are generally
implemented as macros, are provided:
__
||  IceLockConn([4mice_conn[24m)
    IceConn [4mice_conn[24m;

IceUnlockConn([4mice_conn[24m)
    IceConn [4mice_conn[24m;

[4mice_conn[24m  The ICE connection.
||__


To keep an ICE connection locked across several ICElib calls, ap-
plications use and
__
||  void IceAppLockConn([4mice_conn[24m)
    IceConn [4mice_conn[24m;

[4mice_conn[24m  The ICE connection to lock.
||__

The function completely locks out other threads using the connec-
tion  until  is  called.   Other threads attempting to use ICElib
calls on the connection will block.  If the program has not  pre-
viously called has no effect.

__
||  void IceAppUnlockConn([4mice_conn[24m)
    IceConn [4mice_conn[24m;

[4mice_conn[24m  The ICE connection to unlock.
||__

The function allows other threads to complete ICElib calls on the
connection  that  were  blocked  by  a previous call to from this
thread.  If the program has not previously called has no effect.

[1m15.  Miscellaneous Functions[0m

To allocate scratch space (for example, when generating  messages
with  variable  data),  use  Each  ICE connection has one scratch



                              - 40 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


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 preserved after any ICElib function is called.

__
||  char *IceAllocScratch([4mice_conn[24m, [4msize[24m)
    IceConn [4mice_conn[24m;
    unsigned long [4msize[24m;

[4mice_conn[24m  A valid ICE connection object.

[4msize[24m      The number of bytes required.
||__

Note that the memory returned by  should  not  be  freed  by  the
caller.   The  ICE library will free the memory when the ICE con-
nection is closed.

[1m16.  Acknowledgements[0m

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.
































                              - 41 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


                           [1mAppendix A[0m

                [1mAuthentication Utility Functions[0m


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

This appendix describes some utility functions that manipulate an
ICE authority file.  The authority file can be used to  pass  au-
thentication 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 header file must be
included.

An entry in the .ICEauthority file is defined  by  the  following
data structure:

__
||  typedef  struct  {       char *protocol_name;      unsigned short
protocol_data_length;      char *protocol_data;       char  *net-
work_id;          char     *auth_name;          unsigned    short
auth_data_length;      char *auth_data; } IceAuthFileEntry;
||__

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 proto-
col_data member.  This can be used to search for old entries that
need to be removed from the file.


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



                              - 42 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


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

lw(0.25i) lw(2.5i) lw(1i).       tcp/<hostname>:<portnumber>   or
     decnet/<hostname>::<objname>  or                local/<host-
name>:<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
__
||  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 This function takes advantage of the fact
that the system call will fail if the name of the  new  link  al-
ready exists.
__
||  int IceLockAuthFile([4mfile_name[24m, [4mretries[24m, [4mtimeout[24m, [4mdead[24m)
    char *[4mfile_name[24m;
    int [4mretries[24m;
    int [4mtimeout[24m;
    long [4mdead[24m;

[4mfile_name[24m The authorization file to lock.

[4mretries[24m   The number of retries.

[4mtimeout[24m   The number of seconds before each retry.

[4mdead[24m      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    - the lock succeeded.

+o    - a system error occurred, and may prove useful.

+o    - the specified number of retries failed.





                              - 43 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


To unlock an authorization file, use
__
||  void IceUnlockAuthFile([4mfile_name[24m)
    char *[4mfile_name[24m;

[4mfile_name[24m The authorization file to unlock.
||__


To read the next entry in an authorization file, use
__
||  IceAuthFileEntry *IceReadAuthFileEntry([4mauth_file[24m)
    FILE *[4mauth_file[24m;

[4mauth_file[24m 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  re-
turned.

Entries should be free with a call to


To write an entry in an authorization file, use
__
||  Status IceWriteAuthFileEntry([4mauth_file[24m, [4mentry[24m)
    FILE *[4mauth_file[24m;
    IceAuthFileEntry *[4mentry[24m;

[4mauth_file[24m The authorization file.

[4mentry[24m     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 re-
turns a nonzero status if the operation was successful.


To search the  default  authorization  file  for  an  entry  that
matches a given protocol_name/network_id/auth_name tuple, use
__
||  IceAuthFileEntry  *IceGetAuthFileEntry([4mprotocol_name[24m, [4mnetwork_id[24m,
[4mauth_name[24m)
    char *[4mprotocol_name[24m;
    char *[4mnetwork_id[24m;
    char *[4mauth_name[24m;

[4mprotocol_name[0m
          The name of the protocol to search on.





                              - 44 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


[4mnetwork_id[0m
          The network ID to search on.

[4mauth_name[24m The authentication method to search on.
||__

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


To free an entry returned by or use
__
||  void IceFreeAuthFileEntry([4mentry[24m)
    IceAuthFileEntry *[4mentry[24m;

[4mentry[24m     The entry to free.
||__









































                              - 45 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


                           [1mAppendix B[0m

                [1mMIT-MAGIC-COOKIE-1 Authentication[0m


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 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  mecha-
nism  should  be  used  to  store  the magic cookie in the user's
.ICEauthority file on a remote machine.

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

__
||  char *IceGenerateMagicCookie([4mlength[24m)
    int [4mlength[24m;

[4mlength[24m    The desired length of the magic cookie.
||__


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


To  store  the authentication data in memory, use Currently, this
function is only used for MIT-MAGIC-COOKIE-1 authentication,  but
it  may  be used for additional authentication methods in the fu-
ture.
__
||  void IceSetPaAuthData([4mnum_entries[24m, [4mentries[24m)
    int [4mnum_entries[24m;
    IceAuthDataEntry *[4mentries[24m;

[4mnum_entries[0m
          The number of authentication data entries.

[4mentries[24m   The list of authentication data entries.
||__

Each entry has associated with it a protocol name  (for  example,
``ICE''  for  ICE  connection  setup authentication, ``XSMP'' for
session  management  authentication),  a  network  ID   for   the



                              - 46 -





[1mInter-Client Exchange Library                    X11, Release 6.4[0m


``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;
||__















































                              - 47 -


