xref: /xsrc/external/mit/xtrans/dist/doc/xtrans.xml

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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
                      "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd"
[
<!ENTITY % defs SYSTEM "defs.ent"> %defs;
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<!-- lifted from troff+ms+XMan by doclifter -->
<book id="xtrans">

<bookinfo>
   <title>X Transport Interface</title>
   <subtitle>X Consortium Standard</subtitle>
   <authorgroup>
     <author>
       <firstname>Stuart</firstname><surname>Anderson</surname>
       <affiliation><orgname>NCR Corporation</orgname></affiliation>
     </author>
     <othercredit><firstname>Ralph</firstname><surname>Mor</surname>
       <affiliation><orgname>X Consortium</orgname></affiliation>
     </othercredit>
     <othercredit><firstname>Alan</firstname><surname>Coopersmith</surname>
       <affiliation><orgname>Oracle Corp.</orgname></affiliation>
     </othercredit>
   </authorgroup>
   <releaseinfo>X Version 11, Release &fullrelvers;</releaseinfo>
   <releaseinfo>Version 0.7</releaseinfo>
   <copyright><year>1993</year><year>1994</year>
     <holder>NCR Corporation - Dayton, Ohio, USA</holder>
   </copyright>

<legalnotice>
<para>
All Rights Reserved
</para>
<para>
Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted, provided
that the above copyright notice appear in all copies and that both that
copyright notice and this permission notice appear in supporting
documentation, and that the name NCR not be used in advertising
or publicity pertaining to distribution of the software without specific,
written prior permission.  NCR makes no representations about the
suitability of this software for any purpose.  It is provided "as is"
without express or implied warranty.
</para>
<para>
NCR DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
NO EVENT SHALL NCR BE LIABLE FOR ANY SPECIAL, INDIRECT OR
CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
</para>
</legalnotice>

<legalnotice>
<para role="multiLicensing">
Copyright &copy; 1993, 1994, 2002 The Open Group
</para>
<para>
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the &ldquo;Software&rdquo;), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
</para>
<para>
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
</para>
<para>
THE SOFTWARE IS PROVIDED &ldquo;AS IS&rdquo;, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
</para>
<para>
Except as contained in this notice, the name of The Open Group shall not be
used in advertising or otherwise to promote the sale, use or other dealings
in this Software without prior written authorization from The Open Group.
</para>
<para>
X Window System is a trademark of The Open Group, Inc.
</para>
</legalnotice>
</bookinfo>

<preface><title>The X Transport Interface</title>
<para>
Designed by Stuart Anderson (NCR) with help from Ralph Mor (X Consortium)
</para>

<note><para>
This documentation does not completely match the implementation in R6
(as a result of some late changes made in the code). Specifically, support
was added for font server cloning, and conditional compliation was introduced
for client vs. server code.
</para></note>
</preface>

<chapter id='Purposes_and_Goals'>
<title>Purposes and Goals</title>

<para>The X Transport Interface is intended to combine all system and
transport specific code into a single place in the source tree. This API
should be used by all libraries, clients and servers of the X Window System.
Use of this API should allow the addition of new types of transports and
support for new platforms without making any changes to the source except
in the X Transport Interface code.</para>
<para>This interface should solve the problem of multiple
<code>#ifdef TRANSPORT</code> and <code>#ifdef PLATFORM</code>
statements scattered throughout the source tree.</para>
<para>This interface should provide enough functionality to support all
types of protocols, including connection oriented protocols such as X11 and
FS, and connection-less oriented protocols such as XDMCP.</para>

</chapter>

<chapter id='Overview_of_the_Interface'>
<title>Overview of the Interface</title>

<para>
The interface provides an API for use by applications. The functions in
this API perform work that is common to all transports and systems, such
as parsing an address into a host and port number. The functions in this
API call transport specific functions that are contained in a table whose
contents are defined at compile time. This table contains an entry for each
type of transport. Each entry is a record containing mostly pointers to
function that implements the interface for the given transport.
</para>
<para>
This API does not provide an abstraction for <function>select()</function>
or <function>poll()</function>.
These functions are themselves transport independent, so an additional
interface is not needed for these functions. It is also unclear how such
an interface would affect performance.
</para>
</chapter>

<chapter id='Definition_of_Address_Specification_Format'>
<title>Definition of Address Specification Format</title>

<para>
Addresses are specified in the following syntax,

<synopsis>
<replaceable>protocol</replaceable>/<replaceable>host</replaceable>:<replaceable>port</replaceable>
</synopsis>

where <replaceable>protocol</replaceable> specifies a protocol family
or an alias for a protocol family. A definition of common protocol
families is given in a later section.
</para>
<para>
The <replaceable>host</replaceable> part specifies the name of a host or other
transport dependent entity that could be interpreted as a Network Service Access Point
(NSAP).
</para>
<para>
The <replaceable>port</replaceable> part specifies the name of a Transport Service
Access Point (TSAP). The format of the TSAP is defined by the underlying transport
implementation, but it is represented using a string format when it is
part of an address.
</para>
</chapter>

<chapter id='Internal_Data_Structures'>
<title>Internal Data Structures</title>
<para>
There are two major data structures associated with the transport
independent portion of this interface.  Additional data structures
may be used internally by each transport.
</para>
<sect1 id='Xtransport'>
<title>Xtransport</title>
<para>
Each transport supported has an entry in the transport table. The transport
table is an array of Xtransport records. Each record contains all the entry
points for a single transport. This record is defined as:
</para>

<synopsis>
typedef struct _Xtransport {

    char *TransName;
    int  flags;

    XtransConnInfo (*OpenCOTSClient)(
    struct _Xtransport *,     /* transport */
    char     *,     /* protocol */
    char     *,     /* host */
    char     *      /* port */
    );

    XtransConnInfo (*OpenCOTSServer)(
    struct _Xtransport *,     /* transport */
    char *,     /* protocol */
    char *,     /* host */
    char *      /* port */
    );

    XtransConnInfo (*OpenCLTSClient)(
    struct _Xtransport *,     /* transport */
    char *,               /* protocol */
    char *,               /* host */
    char *               /* port */
    );

    XtransConnInfo (*OpenCLTSServer)(
     struct _Xtransport *,   /* transport */
     char *,     /* protocol */
     char *,     /* host */
     char *     /* port */
    );

    int     (*SetOption)(
     XtransConnInfo,          /* connection */
     int,               /* option */
     int               /* arg */
    );

    int     (*CreateListener)(
     XtransConnInfo,          /* connection */
     char *,               /* port */
     int               /* flags */
    );

    int     (*ResetListener)(
     XtransConnInfo          /* connection */
    );

    XtransConnInfo (*Accept)(
     XtransConnInfo          /* connection */
    );

    int     (*Connect)(
     XtransConnInfo,          /* connection */
     char *,               /* host */
     char *               /* port */
    );

    int     (*BytesReadable)(
     XtransConnInfo,          /* connection */
     BytesReadable_t *     /* pend */
    );

    int     (*Read)(
     XtransConnInfo,          /* connection */
     char *,               /* buf */
     int               /* size */
    );

    int     (*Write)(
     XtransConnInfo,          /* connection */
     char *,               /* buf */
     int               /* size */
    );

    int     (*Readv)(
     XtransConnInfo,          /* connection */
     struct iovec *,          /* buf */
     int               /* size */
    );

    int     (*Writev)(
     XtransConnInfo,          /* connection */
     struct iovec *,          /* buf */
     int               /* size */
    );

    int     (*Disconnect)(
     XtransConnInfo          /* connection */
    );

    int     (*Close)(
     XtransConnInfo          /* connection */
    );

} Xtransport;
</synopsis>

<para>
The <structfield>flags</structfield> field can contain an OR of
the following masks:
<variablelist>
  <varlistentry>
    <term><symbol>TRANS_ALIAS</symbol></term>
    <listitem><para>
indicates that this record is providing an alias, and should
not be used to create a listener.
      </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><symbol>TRANS_LOCAL</symbol></term>
    <listitem><para>
indicates that this is a <symbol>LOCALCONN</symbol> transport.
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><symbol>TRANS_ABSTRACT</symbol></term>
    <listitem><para>
indicates that a local connection transport uses the abstract socket namespace.
    </para></listitem>
  </varlistentry>
</variablelist>
</para>

<para>
Some additional flags may be set in the <structfield>flags</structfield>
field by the library while it is running:
<variablelist>
  <varlistentry>
    <term><symbol>TRANS_DISABLED</symbol></term>
    <listitem><para>
indicates that this transport has been disabled.
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><symbol>TRANS_NOLISTEN</symbol></term>
    <listitem><para>
indicates that servers should not open new listeners using this transport.
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><symbol>TRANS_NOUNLINK</symbol></term>
    <listitem><para>
set by a transport backend to indicate that the endpoints for its connection
should not be unlinked.
    </para></listitem>
  </varlistentry>
</variablelist>
</para>
</sect1>

<sect1 id='XtransConnInfo'>
<title>XtransConnInfo</title>
<para>
Each connection will have an opaque <structname>XtransConnInfo</structname>
transport connection
object allocated for it. This record contains information specific to the
connection. The record is defined as:

<synopsis>
typedef struct _XtransConnInfo *XtransConnInfo;

struct _XtransConnInfo {
    struct _Xtransport     *transptr;
    char     *priv;
    int          flags;
    int          fd;
    int          family;
    char     *addr;
    int          addrlen;
    char     *peeraddr;
    int          peeraddrlen;
};
</synopsis>
</para>
</sect1>
</chapter>

<chapter id='Exposed_Transport_Independent_API'>
<title>Exposed Transport Independent API</title>

<para>
This API is included in each library and server that uses it. The API may
be used by the library, but it is not added to the public API for that
library. This interface is simply an implementation facilitator. This API
contains a low level set of core primitives, and a few utility functions
that are built on top of the primitives.  The utility functions exist to
provide a more familiar interface that can be used to port existing code.
</para>
<para>
A macro is defined in Xtrans.h for TRANS(func) that creates a unique function
name depending on where the code is compiled. For example, when built for
Xlib, TRANS(OpenCOTSClient) becomes <function>_X11TransOpenCOTSClient</function>.
</para>
<para>
All failures are considered fatal, and the connection should be closed
and re-established if desired. In most cases, however, the value of
errno will be available for debugging purposes.
</para>
<sect1 id='Core_Interface_API'>
<title>Core Interface API</title>
<itemizedlist mark='bullet'>
  <listitem>
    <para>
XtransConnInfo TRANS(OpenCOTSClient)(char *address)
    </para>
    <para>
This function creates a Connection-Oriented Transport that is
suitable for use by a client. The parameter <parameter>address</parameter>
contains the full address of the server to which this endpoint will be connected.  This
functions returns an opaque transport connection object on success, or
NULL on failure.
    </para>
  </listitem>
  <listitem>
    <para>
XtransConnInfo TRANS(OpenCOTSServer)(char *address)
    </para>
    <para>
This function creates a Connection-Oriented Transport that is suitable
for use by a server. The parameter <parameter>address</parameter> contains the
full address to which this server will be bound. This functions returns an opaque
transport connection object on success, or NULL on failure.
    </para>
  </listitem>
  <listitem>
    <para>
XtransConnInfo TRANS(OpenCLTSClient)(char *address)
    </para>
    <para>
This function creates a Connection-Less Transport that is suitable for
use by a client. The parameter <parameter>address</parameter> contains the
full address of the server to which this endpoint will be connected. This functions
returns an opaque transport connection object on success, or NULL on failure.
    </para>
  </listitem>
  <listitem>
    <para>
XtransConnInfo TRANS(OpenCLTSServer)(char *address)
    </para>
    <para>
This function creates a Connection-Less Transport that is suitable for
use by a server. The parameter <parameter>address</parameter> contains the
full address to which this server will be bound. This functions returns an opaque
transport connection object on success, or NULL on failure.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(SetOption)(XtransConnInfo connection, int option, int arg)
    </para>
    <para>
This function sets transport options, similar to the way
<function>setsockopt()</function> and <function>ioctl()</function> work.
The parameter <parameter>connection</parameter> is an endpoint
that was obtained from _XTransOpen*() functions. The parameter
<parameter>option</parameter> contains the option that will be set. The actual
values for option are defined in a later section. The parameter
<parameter>arg</parameter> can be used to pass in an additional value that may
be required by some options. This function return 0 on
success and -1 on failure.
    </para>
    <note><para>
Based on current usage, the complimentary function
<function>TRANS(GetOption)</function> is not necessary.
    </para></note>
  </listitem>
  <listitem>
    <para>
int TRANS(CreateListener)(XtransConnInfo connection, char *port, int flags)
    </para>
    <para>
This function sets up the server endpoint for listening. The parameter
<parameter>connection</parameter> is an endpoint that was obtained from
<function>TRANS(OpenCOTSServer)()</function> or
<function>TRANS(OpenCLTSServer)()</function>. The parameter
<parameter>port</parameter> specifies the
port to which this endpoint should be bound for listening. If port is NULL,
then the transport may attempt to allocate any available TSAP for this
connection. If the transport cannot support this, then this function will
return a failure. The <parameter>flags</parameter> parameter can be set
to <symbol>ADDR_IN_USE_ALLOWED</symbol> to allow the call to the underlying
binding function to fail with a <errorname>EADDRINUSE</errorname> error
without causing the <function>TRANS(CreateListener)</function>
function itself to fail. This function return 0 on success and -1 on failure.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(ResetListener)(XtransConnInfo connection)
    </para>
    <para>
When a server is restarted, certain listen ports may need to be reset.
For example, unix domain needs to check that the file used for
communication has not been deleted. If it has, it must be recreated.
The parameter <parameter>connection</parameter> is an opened and bound
endpoint that was obtained from <function>TRANS(OpenCOTSServer)()</function>
and passed to <function>TRANS(CreateListener)()</function>.
This function will return one of the following values:
<symbol>TRANS_RESET_NOOP</symbol>,
<symbol>TRANS_RESET_NEW_FD</symbol>, or
<symbol>TRANS_RESET_FAILURE</symbol>.
    </para>
  </listitem>
  <listitem>
    <para>
XtransConnInfo TRANS(Accept)(XtransConnInfo connection)
    </para>
    <para>
Once a connection indication is received, this function can be called to
accept the connection. The parameter <parameter>connection</parameter> is
an opened and bound endpoint that was obtained from
<function>TRANS(OpenCOTSServer)()</function> and passed to
<function>TRANS(CreateListener)()</function>. This function will return a
new opaque transport connection object upon success, NULL otherwise.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(Connect)(XtransConnInfo connection, char *address)
    </para>
    <para>
This function creates a connection to a server. The parameter
<parameter>connection</parameter> is an endpoint that was obtained
from <function>TRANS(OpenCOTSClient)()</function>. The parameter
<parameter>address</parameter> specifies the TSAP to which this endpoint
should connect. If the
protocol is included in the address, it will be ignored. This function
return 0 on success and -1 on failure.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(BytesReadable)(XtransConnInfo connection, BytesReadable_t *pend);
    </para>
    <para>
This function provides the same functionality as the BytesReadable macro.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(Read)(XtransConnInfo connection, char *buf, int size)
    </para>
    <para>
This function will return the number of bytes requested on a COTS
connection, and will return the minimum of the number bytes requested or
the size of the incoming packet on a CLTS connection.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(Write)(XtransConnInfo connection, char *buf, int size)
    </para>
    <para>
This function will write the requested number of bytes on a COTS
connection, and will send a packet of the requested size on a CLTS connection.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(Readv)(XtransConnInfo connection, struct iovec *buf, int size)
    </para>
    <para>
Similar to <function>TRANS(Read)()</function>.
    </para>
  </listitem>
  <listitem>
    <para>
  int TRANS(Writev)(XtransConnInfo connection, struct iovec *buf, int size)
    </para>
    <para>
Similar to <function>TRANS(Write)()</function>.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(Disconnect)(XtransConnInfo connection)
    </para>
    <para>
This function is used when an orderly disconnect is desired. This function
breaks the connection on the transport. It is similar to the socket function
<function>shutdown()</function>.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(Close)(XtransConnInfo connection)
    </para>
    <para>
This function closes the transport, unbinds it, and frees all resources that
was associated with the transport. If a <function>TRANS(Disconnect)</function>
call was not made on the connection, a disorderly disconnect may occur.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(IsLocal)(XtransConnInfo connection)
    </para>
    <para>
Returns TRUE if it is a local transport.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(GetMyAddr)(XtransConnInfo connection, int *familyp, int *addrlenp,
Xtransaddr **addrp)
    </para>
    <para>
This function is similar to
<function>getsockname()</function>.
This function will allocate space for the address, so it must be freed by
the caller. Not all transports will have a valid address until a connection
is established.  This function should not be used until the connection is
established with
<function>Connect()</function> or
<function>Accept()</function>.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(GetPeerAddr)(XtransConnInfo connection, int *familyp, int *addrlenp,
Xtransaddr **addrp)
    </para>
    <para>
This function is similar to
<function>getpeername()</function>.
This function will allocate space for the address, so it must be freed by
the caller. Not all transports will have a valid address until a connection
is established.  This function should not be used until the connection is
established with
<function>Connect()</function> or
<function>Accept()</function>.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(GetConnectionNumber)(XtransConnInfo connection)
    </para>
    <para>
Returns the file descriptor associated with this transport.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(MakeAllCOTSServerListeners)(char *port, int *partial_ret,
int *count_ret, XtransConnInfo **connections_ret)
    </para>
    <para>
This function should be used by most servers. It will try to establish
a COTS server endpoint for each transport listed in the transport table.
<parameter>partial_ret</parameter> will be set to <symbol>True</symbol> if
only a partial network could be created. <parameter>count_ret</parameter> is
the number of transports returned, and <parameter>connections_ret</parameter>
is the list of transports.
    </para>
  </listitem>
  <listitem>
    <para>
int TRANS(MakeAllCLTSServerListeners)( char *port, int *partial_ret,
int *count_ret, XtransConnInfo **connections_ret)
    </para>
    <para>
This function should be used by most servers. It will try to establish a
CLTS server endpoint for each transport listed in the transport table.
<parameter>partial_ret</parameter> will be set to <symbol>True</symbol> if
only a partial network could be created. <parameter>count_ret</parameter> is
the number of transports returned, and <parameter>connections_ret</parameter>
is the list of transports.
    </para>
  </listitem>
</itemizedlist>
</sect1>

<sect1 id='Utility_API'>
<title>Utility API</title>
<para>
This section describes a few useful functions that have been implemented on
top of the Core Interface API.  These functions are being provided as a
convenience.
</para>
<itemizedlist mark='bullet'>
  <listitem>
    <para>
int TRANS(ConvertAddress)(int *familyp, int *addrlenp, Xtransaddr *addrp)
    </para>
    <para>
This function converts a sockaddr based address to an X authorization based
address (ie AF_INET, AF_UNIX to the X protocol definition (ie FamilyInternet,
FamilyLocal)).
    </para>
  </listitem>
</itemizedlist>
</sect1>
</chapter>

<chapter id='Transport_Option_Definition'>
<title>Transport Option Definition</title>
<para>
The following options are defined for the
<function>TRANS(SetOption)()</function>
 function. If an OS or transport does not support any of these options,
then it will silently ignore the option.
</para>

<itemizedlist mark='bullet'>
  <listitem>
    <para>
<symbol>TRANS_NONBLOCKING</symbol>
    </para>
    <para>
This option controls the blocking mode of the connection. If the argument
is set to 1, then the connection will be set to blocking. If the argument
is set to 0, then the connection will be set to non- blocking.
    </para>
  </listitem>
  <listitem>
    <para>
<symbol>TRANS_CLOSEONEXEC</symbol>
    </para>
    <para>
This option determines what will happen to the connection when an exec is
encountered. If the argument is set to 1, then the connection will be
closed when an exec occurs. If the argument is set to 0, then the
connection will not be closed when an exec occurs.
    </para>
  </listitem>
</itemizedlist>
</chapter>

<chapter id='Hidden_Transport_Dependent_API'>
<title>Hidden Transport Dependent API</title>
<para>
The hidden transport dependent functions are placed in the Xtransport record.
These function are similar to the Exposed Transport Independent API, but
some of the parameters and return values are slightly different.  Stuff like
the <code>#ifdef SUNSYSV</code> should be handled inside these functions.
</para>

<itemizedlist mark='bullet'>
  <listitem>
    <para>
XtransConnInfo *OpenCOTSClient (
struct _Xtransport *thistrans, char *protocol, char *host, char *port)
    </para>
    <para>
This function creates a Connection-Oriented Transport. The parameter
<parameter>thistrans</parameter>
points to an Xtransport entry in the transport table. The parameters
<parameter>protocol</parameter>,
<parameter>host</parameter>,  and
<parameter>port</parameter>, point to strings containing the corresponding
parts of the address that was passed into <function>TRANS(OpenCOTSClient)()</function>.
This function must allocate and initialize the contents of the XtransConnInfo
structure that is returned by this function. This function will open the
transport, and bind it into the transport namespace if applicable. The local
address portion of the XtransConnInfo structure will also be filled in by
this function.
    </para>
  </listitem>
  <listitem>
    <para>
XtransConnInfo *OpenCOTSServer (
struct _Xtransport *thistrans, char *protocol, char *host, char *port)
    </para>
    <para>
This function creates a Connection-Oriented Transport. The parameter
<parameter>thistrans</parameter>
points to an Xtransport entry in the transport table. The
parameters
<parameter>protocol</parameter>,
<parameter>host</parameter>, and
<parameter>port</parameter> point to strings containing the
corresponding parts of the address that was passed into
<function>TRANS(OpenCOTSClient)()</function>.
This function must allocate and initialize the contents of the
XtransConnInfo structure that is returned by this function. This function
will open the transport.
    </para>
  </listitem>
  <listitem>
    <para>
XtransConnInfo *OpenCLTSClient (
struct _Xtransport *thistrans, char *protocol, char *host, char *port)
    </para>
    <para>
This function creates a Connection-Less Transport. The parameter
<parameter>thistrans</parameter>
points to an Xtransport entry in the transport table. The parameters
<parameter>protocol</parameter>,
<parameter>host</parameter>, and
<parameter>port</parameter> point to strings containing the
corresponding parts of the address that was passed into
<function>TRANS(OpenCOTSClient)()</function>.
This function must allocate and initialize the contents of the XtransConnInfo
structure that is returned by this function. This function will open the
transport, and bind it into the transport namespace if applicable. The
local address portion of the XtransConnInfo structure will also be filled
in by this function.
    </para>
  </listitem>
  <listitem>
    <para>
XtransConnInfo *OpenCLTSServer (
struct _Xtransport *thistrans, char *protocol, char *host, char *port)
    </para>
    <para>
This function creates a Connection-Less Transport. The parameter
<parameter>thistrans</parameter>
points to an Xtransport entry in the transport table. The  parameters
<parameter>protocol</parameter>,
<parameter>host</parameter>, and
<parameter>port</parameter> point to strings containing the
corresponding parts of the address that was passed into
<function>TRANS(OpenCOTSClient)()</function>.
This function must allocate and initialize the contents of the
XtransConnInfo structure that is returned by this function. This
function will open the transport.
    </para>
  </listitem>
  <listitem>
    <para>
int SetOption (struct _Xtransport *thistrans, int option, int arg)
    </para>
    <para>
This function provides a transport dependent way of implementing the
options defined by the X Transport Interface. In the current prototype,
this function is not being used, because all of the options defined so far
are transport independent. This function will have to be used if a radically
different transport type is added, or a transport dependent option is defined.
    </para>
  </listitem>
  <listitem>
    <para>
int CreateListener (struct _Xtransport *thistrans, char *port, int flags )
    </para>
    <para>
This function takes a transport endpoint opened for a server, and sets it
up to listen for incoming connection requests. The parameter
<parameter>port</parameter>
contains the port portion of the address that was passed to the Open function.
The parameter <parameter>flags</parameter> should be set to
<symbol>ADDR_IN_USE_ALLOWED</symbol> if the underlying transport endpoint
may be already bound and this should not be considered
as an error. Otherwise flags should be set to 0. This is used by IPv6 code,
where the same socket can be bound to both an IPv6 address and then to a
IPv4 address.  This function will bind the transport into the transport
name space if applicable, and fill in the local address portion of the
XtransConnInfo structure. The transport endpoint will then be set to
listen for incoming connection requests.
    </para>
  </listitem>
  <listitem>
    <para>
int ResetListener (struct _Xtransport *thistrans)
    </para>
    <para>
This function resets the transport for listening.
    </para>
  </listitem>
  <listitem>
    <para>
 XtransConnInfo Accept(struct _Xtransport *thistrans)
    </para>
    <para>
This function creates a new transport endpoint as a result of an
incoming connection request. The parameter
<parameter>thistrans</parameter> is the endpoint
that was opened for listening by the server. The new endpoint is
opened and bound into the transport’s namespace. A XtransConnInfo
structure describing the new endpoint is returned from this function
    </para>
  </listitem>
  <listitem>
    <para>
int Connect(struct _Xtransport *thistrans, char *host, char *port )
    </para>
    <para>
This function establishes a connection to a server. The parameters
<parameter>host</parameter>  and
<parameter>port</parameter>
describe the server to which the connection should be
established. The connection will be established so that
<function>Read()</function> and
<function>Write()</function> call can be made.
    </para>
  </listitem>
  <listitem>
    <para>
int BytesReadable(struct _Xtransport *thistrans, BytesReadable_t *pend )
    </para>
    <para>
This function replaces the
<function>BytesReadable()</function>
macro. This allows each transport to have it’s own mechanism for determining
how much data is ready to be read.
    </para>
  </listitem>
  <listitem>
    <para>
int Read(struct _Xtransport *thistrans, char *buf, int size )
    </para>
    <para>
This function reads size bytes into buf from the connection.
    </para>
  </listitem>
  <listitem>
    <para>
int Write(struct _Xtransport *thistrans, char *buf, int size )
    </para>
    <para>
This function writes size bytes from buf to the connection.
    </para>
  </listitem>
  <listitem>
    <para>
int Readv(struct _Xtransport *thistrans, struct iovec *buf, int size )
    </para>
    <para>
This function performs a <function>readv()</function> on the connection.
    </para>
  </listitem>
  <listitem>
    <para>
int Writev(struct _Xtransport *thistrans, struct iovec *buf, int size )
    </para>
    <para>
This function performs a <function>writev()</function> on the connection.
    </para>
  </listitem>
  <listitem>
    <para>
int Disconnect(struct _Xtransport *thistrans)
    </para>
    <para>
This function initiates an orderly shutdown of a connection. If a
transport does not distinguish between orderly and disorderly
disconnects, then a call to this function will have no affect.
    </para>
  </listitem>
  <listitem>
    <para>
int Close(struct _Xtransport *thistrans)
    </para>
    <para>
This function will break the connection, and close the endpoint.
    </para>
  </listitem>
</itemizedlist>
</chapter>
<chapter id='Configuration'>
<title>Configuration</title>

<para>
The implementation of each transport can be platform specific. It is expected
that existing connection types such as <symbol>TCPCONN</symbol>,
<symbol>UNIXCONN</symbol>, <symbol>LOCALCONN</symbol>, and
<symbol>STREAMSCONN</symbol> will be replaced with flags for each
possible transport type.
</para>
<para>
In X11R6, the below flags to enable transport types were set in
<symbol>ConnectionFlags</symbol> in the <filename>vendor.cf</filename> or
<filename>site.def</filename> config files.
</para>
<para>
In X11R7 modular releases, these flags are set when running
<filename>configure</filename> scripts which include the
<function>XTRANS_CONNECTION_FLAGS</function> macro from
<filename>xtrans.m4</filename>.
</para>

<informaltable frame='topbot'>
  <tgroup cols='3' align='left' colsep='0' rowsep='0'>
    <colspec colname='define' colwidth='1.0*' />
    <colspec colname='enable' colwidth='2.0*' />
    <colspec colname='desc'   colwidth='2.0*'/>
    <thead>
      <row rowsep='1'>
	<entry><code>#define</code></entry>
	<entry>configure flag</entry>
	<entry>Description</entry>
      </row>
    </thead>
    <tbody>
      <row>
	<entry><symbol>TCPCONN</symbol></entry>
	<entry><option>--enable-tcp-transport</option></entry>
	<entry>
	Enables the INET (IPv4) Domain Socket based transport
	</entry>
      </row>
      <row>
	<entry><symbol>IPv6</symbol></entry>
	<entry><option>--enable-ipv6</option></entry>
	<entry>
	Extends <symbol>TCPCONN</symbol> to enable IPv6 Socket based transport
	</entry>
      </row>
      <row>
	<entry><symbol>UNIXCONN</symbol></entry>
	<entry><option>--enable-unix-transport</option></entry>
	<entry>
	Enables the UNIX Domain Socket based transport
	</entry>
      </row>
      <row>
	<entry><symbol>STREAMSCONN</symbol></entry>
	<entry><emphasis>Not available in X11R7</emphasis></entry>
	<entry>
	Enables the TLI based transports
	</entry>
      </row>
      <row>
	<entry><symbol>LOCALCONN</symbol></entry>
	<entry><option>--enable-local-transport</option></entry>
	<entry>
	Enables the SYSV Local connection transports
	</entry>
      </row>
      <row>
	<entry><symbol>DNETCONN</symbol></entry>
	<entry><emphasis>Not available in X11R7</emphasis></entry>
	<entry>
	Enables the DECnet transports
	</entry>
      </row>
    </tbody>
  </tgroup>
</informaltable>


</chapter>

<chapter id='Transport_Specific_Definitions'>
<title>Transport Specific Definitions</title>

<informaltable frame='all' colsep='1' rowsep='1'>
  <tgroup cols='4' align='center'>
    <colspec colname='c1' colwidth='1.0*'/>
    <colspec colname='c2' colwidth='1.0*'/>
    <colspec colname='c3' colwidth='3.0*'/>
    <colspec colname='c4' colwidth='2.0*'/>
    <thead>
      <row>
        <entry morerows="1">Protocol Family</entry>
        <entry namest="c2" nameend="c4"  align='center'>Address Component</entry>
      </row>
      <row>
        <entry align='center'>protocol</entry>
        <entry align='center'>host</entry>
        <entry align='center'>port</entry>
      </row>
    </thead>
    <tbody>
      <row>
        <entry>Internet</entry>
        <entry>inet inet6 tcp udp</entry>
        <entry>name of an internet addressable host</entry>
        <entry>string containing the name of a service or a valid port number.  Example: "xserver0", "7100"</entry>
      </row>
      <row>
        <entry>DECnet</entry>
        <entry>decnet</entry>
        <entry>name of a DECnet addressable host</entry>
        <entry>string containing the complete name of the object.  Example: "X$X0"</entry>
      </row>
      <row>
        <entry>NETware</entry>
        <entry>ipx</entry>
        <entry>name of a NETware addressable host</entry>
        <entry>Not sure of the specifics yet.</entry>
      </row>
      <row>
        <entry>OSI</entry>
        <entry>osi</entry>
        <entry>name of an OSI adressable host.</entry>
        <entry>Not sure of the specifics yet.</entry>
      </row>
      <row>
        <entry>Local</entry>
        <entry>local pts named sco isc</entry>
        <entry>(ignored)</entry>
        <entry>String containing the port name, ie "xserver0", "fontserver0".</entry>
      </row>
    </tbody>
  </tgroup>
</informaltable>

</chapter>

<chapter id='Implementation_Notes'>
<title>Implementation Notes</title>
<para>
This section refers to the prototype implementation that is being developed
concurrently with this document. This prototype has been able to flush out many
details and problems as the specification was being developed.
</para>
<para>
In X11R6, all of the source code for this interface was located in
<filename>xc/lib/xtrans</filename>.
</para>
<para>
In X11R7, all of the source code for this interface is delivered via
the <systemitem>lib/libxtrans</systemitem> modular package from X.Org,
and is installed under
<filename><replaceable>${prefix}</replaceable>/X11/Xtrans</filename>
so that other modules may find it when they build.
</para>
<para>
All functions names in the source are of the format
<function>TRANS(func)()</function>. The
<function>TRANS()</function>
macro is defined as
<programlisting language="C">
#if (__STDC__ &amp;&amp; !defined(UNIXCPP)) || defined(ANSICPP)
#define TRANS(func) _PROTOCOLTrans##func
#else
#define TRANS(func) _PROTOCOLTrans/**/func
#endif
</programlisting>
</para>

<para>
<symbol>PROTOCOL</symbol> will be uniquely defined in each directory
where this code is compiled.
<symbol>PROTOCOL</symbol> will be defined to be the name of the protocol
that is implemented by the library or server, such as X11, FS, and ICE.
</para>

<para>
All libraries and servers that use the X Transport Interface should have a new
file called <filename><replaceable>TRANSPORT</replaceable>trans.c</filename>.
This file will include the transports based on the configuration flags
provided by the <filename>configure</filename> script. Below is an
example <filename>xfstrans.c</filename> for the font server.
</para>

<programlisting language="C">
#include "config.h"

#define FONT_t 1
#define TRANS_REOPEN 1
#define TRANS_SERVER 1

#include &lt;X11/Xtrans/transport.c&gt;
</programlisting>
<para>
The source files for this interface are listed below.
</para>

<variablelist>
  <varlistentry>
    <term><filename>Xtrans.h</filename></term>
    <listitem><para>
Function prototypes and defines for the Transport Independent API.
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><filename>Xtransint.h</filename></term>
    <listitem><para>
Used by the interface implementation only.
Contains the internal data structures.
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><filename>Xtranssock.c</filename></term>
    <listitem><para>
Socket implementation of the Transport Dependent API.
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><filename>Xtranstli.c</filename></term>
    <listitem><para>
TLI implementation of the Transport Dependent API.
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><filename>Xtransdnet.c</filename></term>
    <listitem><para>
DECnet implementation of the Transport Dependent API.
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><filename>Xtranslocal.c</filename></term>
    <listitem><para>
Implementation of the Transport Dependent API for SYSV Local connections.
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><filename>Xtrans.c</filename></term>
    <listitem><para>
Exposed Transport Independent API Functions.
    </para></listitem>
  </varlistentry>
  <varlistentry>
    <term><filename>Xtransutil.c</filename></term>
    <listitem><para>
Collection of Utility functions that use the X Transport Interface.
    </para></listitem>
  </varlistentry>
</variablelist>


<para>
The file <filename>Xtransint.h</filename> contains much of the transport
related code that was previously in <filename>Xlibint.h</filename> and
<filename>Xlibnet.h</filename>.
This will make the definitions available for all transport users. This
should also obsolete the equivalent code in other libraries.
</para>

</chapter>
</book>