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<H1 CLASS="chapter"><A NAME="htoc76">Chapter 6</A>  Interoperable Naming Service</H1><P>
<A NAME="chap:ins"></A></P><P>omniORB supports the Interoperable Naming Service (INS). The following
is a summary of its facilities.</P><H2 CLASS="section"><A NAME="toc30"></A><A NAME="htoc77">6.1</A>  Object URIs</H2><P>As well as accepting IOR-format strings, <TT>ORB::string_to_object()</TT>
also supports two Uniform Resource Identifier (URI) [<A HREF="omniORB014.html#rfc2396">BLFIM98</A>]
formats, which can be used to specify objects in a convenient
human-readable form. IOR-format strings are now also considered URIs.</P><H3 CLASS="subsection"><A NAME="htoc78">6.1.1</A>  corbaloc</H3><P><TT>corbaloc</TT> URIs allow you to specify object references which
can be contacted by IIOP, or found through
<TT>ORB::resolve_initial_references()</TT>. To specify an IIOP object
reference, you use a URI of the form:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaloc:iiop:</TT><<I>host</I>><TT>:</TT><<I>port</I>><TT>/</TT><<I>object key</I>>
</BLOCKQUOTE><P>for example:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaloc:iiop:myhost.example.com:1234/MyObjectKey</TT>
</BLOCKQUOTE><P>which specifies an object with key ‘MyObjectKey’ within a
process running on myhost.example.com listening on port 1234. Object
keys containing non-ASCII characters can use the standard URI %
escapes:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaloc:iiop:myhost.example.com:1234/My</TT><TT>%</TT><TT>efObjectKey</TT>
</BLOCKQUOTE><P>denotes an object key with the value 239 (hex ef) in the
third octet.</P><P>The protocol name ‘<TT>iiop</TT>’ can be abbreviated to the empty
string, so the original URI can be written:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaloc::myhost.example.com:1234/MyObjectKey</TT>
</BLOCKQUOTE><P>The IANA has assigned port number 2809<SUP><A NAME="text15" HREF="#note15">1</A></SUP> for use by <TT>corbaloc</TT>, so if
the server is listening on that port, you can leave the port number
out. The following two URIs refer to the same object:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaloc::myhost.example.com:2809/MyObjectKey</TT><BR>
<TT>corbaloc::myhost.example.com/MyObjectKey</TT>
</BLOCKQUOTE><P>You can specify an object which is available at more than
one location by separating the locations with commas:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaloc::myhost.example.com,:localhost:1234/MyObjectKey</TT>
</BLOCKQUOTE><P>Note that you must restate the protocol for each address,
hence the ‘<TT>:</TT>’ before ‘<TT>localhost</TT>’. It could
equally have been written ‘<TT>iiop:localhost</TT>’.</P><P>You can also specify an IIOP version number:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaloc::1.2@myhost.example.com/MyObjectKey</TT>
</BLOCKQUOTE><P>Specifying IIOP versions above 1.0 is slightly risky since higher
versions make use of various information stored in IORs that is not
present in a corbaloc URI. It is generally best to contact initial
corbaloc objects with IIOP 1.0, and rely on higher versions for all
other object references.</P><P>Alternatively, to use <TT>resolve_initial_references()</TT>, you
use a URI of the form:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaloc:rir:/NameService</TT>
</BLOCKQUOTE><H3 CLASS="subsection"><A NAME="htoc79">6.1.2</A>  corbaname</H3><P>
<A NAME="sec:corbaname"></A></P><P><TT>corbaname</TT> URIs cause <TT>string_to_object()</TT> to look-up a
name in a CORBA Naming service. They are an extension of the
<TT>corbaloc</TT> syntax:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaname:</TT><<I>corbaloc location</I>><TT>/</TT><<I>object key</I>><TT>#</TT><<I>stringified name</I>>
</BLOCKQUOTE><P>for example:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaname::myhost/NameService#project/example/echo.obj</TT><BR>
<TT>corbaname:rir:/NameService#project/example/echo.obj</TT>
</BLOCKQUOTE><P>The object found with the <TT>corbaloc</TT>-style portion
must be of type <TT>CosNaming::NamingContext</TT>, or something
derived from it. If the object key (or <TT>rir</TT> name) is
‘<TT>NameService</TT>’, it can be left out:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaname::myhost#project/example/echo.obj</TT><BR>
<TT>corbaname:rir:#project/example/echo.obj</TT>
</BLOCKQUOTE><P>The stringified name portion can also be left out, in which
case the URI denotes the <TT>CosNaming::NamingContext</TT> which would
have been used for a look-up:</P><BLOCKQUOTE CLASS="quote">
<TT>corbaname::myhost.example.com</TT><BR>
<TT>corbaname:rir:</TT>
</BLOCKQUOTE><P>The first of these examples is the easiest way of specifying
the location of a naming service.</P><H2 CLASS="section"><A NAME="toc31"></A><A NAME="htoc80">6.2</A>  Configuring resolve_initial_references</H2><P>
<A NAME="sec:insargs"></A></P><P>The INS specifies two standard command line arguments which provide a
portable way of configuring <TT>ORB::resolve_initial_references()</TT>:</P><H3 CLASS="subsection"><A NAME="htoc81">6.2.1</A>  ORBInitRef</H3><P><TT>-ORBInitRef</TT> takes an argument of the form
<<I>ObjectId</I>><TT>=</TT><<I>ObjectURI</I>>. So, for example,
with command line arguments of:</P><BLOCKQUOTE CLASS="quote">
<TT>-ORBInitRef NameService=corbaname::myhost.example.com</TT>
</BLOCKQUOTE><P><TT>resolve_initial_references("NameService")</TT> will
return a reference to the object with key ‘NameService’ available on
myhost.example.com, port 2809. Since IOR-format strings are considered
URIs, you can also say things like:</P><BLOCKQUOTE CLASS="quote">
<TT>-ORBInitRef NameService=IOR:00ff...</TT>
</BLOCKQUOTE><H3 CLASS="subsection"><A NAME="htoc82">6.2.2</A>  ORBDefaultInitRef</H3><P><TT>-ORBDefaultInitRef</TT> provides a prefix string which is used to
resolve otherwise unknown names. When
<TT>resolve_initial_references()</TT> is unable to resolve a name which
has been specifically configured (with <TT>-ORBInitRef</TT>), it
constructs a string consisting of the default prefix, a ‘<TT>/</TT>’
character, and the name requested. The string is then fed to
<TT>string_to_object()</TT>. So, for example, with a command line of:</P><BLOCKQUOTE CLASS="quote">
<TT>-ORBDefaultInitRef corbaloc::myhost.example.com</TT>
</BLOCKQUOTE><P>a call to <TT>resolve_initial_references("MyService")</TT>
will return the object reference denoted by
‘<TT>corbaloc::myhost.example.com/MyService</TT>’.</P><P>Similarly, a <TT>corbaname</TT> prefix can be used to cause
look-ups in the naming service. Note, however, that since a
‘<TT>/</TT>’ character is always added to the prefix, it is
impossible to specify a look-up in the root context of the naming
service—you have to use a sub-context, like:</P><BLOCKQUOTE CLASS="quote">
<TT>-ORBDefaultInitRef corbaname::myhost.example.com#services</TT>
</BLOCKQUOTE><H2 CLASS="section"><A NAME="toc32"></A><A NAME="htoc83">6.3</A>  omniNames</H2><H3 CLASS="subsection"><A NAME="htoc84">6.3.1</A>  NamingContextExt</H3><P>omniNames supports the extended <TT>CosNaming::NamingContextExt</TT>
interface:</P><DIV CLASS="lstlisting"><B>module</B> CosNaming {
<B>interface</B> NamingContextExt : NamingContext {
<B>typedef</B> <B>string</B> StringName;
<B>typedef</B> <B>string</B> Address;
<B>typedef</B> <B>string</B> URLString;
StringName to_string(<B>in</B> Name n) <B>raises</B>(InvalidName);
Name to_name (<B>in</B> StringName sn) <B>raises</B>(InvalidName);
<B>exception</B> InvalidAddress {};
URLString to_url(<B>in</B> Address addr, <B>in</B> StringName sn)
<B>raises</B>(InvalidAddress, InvalidName);
<B>Object</B> resolve_str(<B>in</B> StringName n)
<B>raises</B>(NotFound, CannotProceed, InvalidName, AlreadyBound);
};
};</DIV><P><TT>to_string()</TT> and <TT>to_name()</TT> convert from <TT>CosNaming::Name</TT>
sequences to flattened strings and vice-versa. Note that calling
these operations involves remote calls to the naming service, so they
are not particularly efficient. You can use the omniORB specific local
<TT>omniURI::nameToString()</TT> and <TT>omniURI::stringToName()</TT>
functions instead.</P><P>A <TT>CosNaming::Name</TT> is stringified by separating name components
with ‘<TT>/</TT>’ characters. The <TT>kind</TT> and <TT>id</TT> fields of
each component are separated by ‘<TT>.</TT>’ characters. If the
<TT>kind</TT> field is empty, the representation has no trailing
‘<TT>.</TT>’; if the <TT>id</TT> is empty, the representation starts
with a ‘<TT>.</TT>’ character; if both <TT>id</TT> and <TT>kind</TT>
are empty, the representation is just a ‘<TT>.</TT>’. The backslash
‘<TT>\</TT>’ is used to escape the meaning of
‘<TT>/</TT>’, ‘<TT>.</TT>’ and ‘<TT>\</TT>’ itself.</P><P><TT>to_url()</TT> takes a <TT>corbaloc</TT> style address and key string
(but without the <TT>corbaloc:</TT> part), and a stringified name,
and returns a <TT>corbaname</TT> URI (incorrectly called a URL)
string, having properly escaped any invalid characters. The
specification does not make it clear whether or not the address string
should also be escaped by the operation; omniORB does not escape
it. For this reason, it is best to avoid calling <TT>to_url()</TT> if the
address part contains escapable characters. omniORB provides the
equivalent local function <TT>omniURI::addrAndNameToURI()</TT>.</P><P><TT>resolve_str()</TT> is equivalent to calling <TT>to_name()</TT> followed by
the inherited <TT>resolve()</TT> operation. There are no string-based
equivalents of the various bind operations.</P><H3 CLASS="subsection"><A NAME="htoc85">6.3.2</A>  Use with corbaname</H3><P>To make it easy to use omniNames with <TT>corbaname</TT> URIs, it
starts with the default port of 2809, and an object key of
‘<TT>NameService</TT>’ for the root naming context.</P><H2 CLASS="section"><A NAME="toc33"></A><A NAME="htoc86">6.4</A>  omniMapper</H2><P>omniMapper is a simple daemon which listens on port 2809 (or any other
port), and redirects IIOP requests for configured object keys to
associated persistent object references. It can be used to make a
naming service (even an old non-INS aware version of omniNames or
other ORB’s naming service) appear on port 2809 with the object key
‘<TT>NameService</TT>’. The same goes for any other service you may
wish to specify, such as an interface repository. omniMapper is
started with a command line of:</P><BLOCKQUOTE CLASS="quote">
<TT>omniMapper [-port </TT><<I>port</I>><TT>] [-config </TT><<I>config file</I>><TT>] [-v]</TT>
</BLOCKQUOTE><P>The <TT>-port</TT> option allows you to choose a port other
than 2809 to listen on. The <TT>-config</TT> option specifies a
location for the configuration file. The default name is
<TT>/etc/omniMapper.cfg</TT>, or <TT>C:\omniMapper.cfg</TT> on
Windows. omniMapper does not normally print anything; the <TT>-v</TT>
option makes it verbose so it prints configuration information and a
record of the redirections it makes, to standard output.</P><P>The configuration file is very simple. Each line contains a string to
be used as an object key, some white space, and an IOR (or any valid
URI) that it will redirect that object key to. Comments should be
prefixed with a ‘<TT>#</TT>’ character. For example:</P><BLOCKQUOTE CLASS="quote">
<PRE CLASS="verbatim"># Example omniMapper.cfg
NameService IOR:000f...
InterfaceRepository IOR:0100...
</PRE></BLOCKQUOTE><P>omniMapper can either be run on a single machine, in much the same way
as omniNames, or it can be run on <EM>every</EM> machine, with a common
configuration file. That way, each machine’s omniORB configuration
file could contain the line:</P><BLOCKQUOTE CLASS="quote">
<PRE CLASS="verbatim">ORBDefaultInitRef corbaloc::localhost
</PRE></BLOCKQUOTE><H2 CLASS="section"><A NAME="toc34"></A><A NAME="htoc87">6.5</A>  Creating objects with simple object keys</H2><P>In normal use, omniORB creates object keys containing various
information including POA names and various non-ASCII characters.
Since object keys are supposed to be opaque, this is not usually a
problem. The INS breaks this opacity and requires servers to create
objects with human-friendly keys.</P><P>If you wish to make your objects available with human-friendly URIs,
there are two options. The first is to use omniMapper as described
above, in conjunction with a <TT>PERSISTENT</TT> POA. The second is to
create objects with the required keys yourself. You do this with a
special POA with the name ‘<TT>omniINSPOA</TT>’, acquired from
<TT>resolve_initial_references()</TT>. This POA has the <TT>USER_ID</TT>
and <TT>PERSISTENT</TT> policies, and the special property that the
object keys it creates contain only the object ids given to the POA,
and no other data. It is a normal POA in all other respects, so you
can activate/deactivate it, create children, and so on, in the usual
way.</P><P>Children of the omniINSPOA do not inherit its special properties of
creating simple object keys. If the omniINSPOA’s policies are not
suitable for your application, you cannot create a POA with different
policies (such as single threading, for example), and still generate
simple object keys. Instead, you can activate a servant in the
omniINSPOA that uses location forwarding to redirect requests to
objects in a different POA.</P><HR CLASS="footnoterule"><DL CLASS="thefootnotes"><DT CLASS="dt-thefootnotes">
<A NAME="note15" HREF="#text15">1</A></DT><DD CLASS="dd-thefootnotes">Not 2089 as
printed in [<A HREF="omniORB014.html#inschapters">OMG00</A>]!
</DD></DL>
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