-<!-- $Id: odr.xml,v 1.7 2001-10-26 20:13:44 adam Exp $ -->
+<!-- $Id: odr.xml,v 1.18 2006-04-25 11:25:08 marc Exp $ -->
<chapter id="odr"><title>The ODR Module</title>
<sect1 id="odr.introduction"><title>Introduction</title>
<para>
If you are only interested in writing a Z39.50 implementation based on
the PDUs that are already provided with &yaz;, you only need to concern
- yourself with the section on managing ODR streams (section
- <link linkend="odr-use">Using ODR</link>). Only if you need to
+ yourself with the section on managing ODR streams
+ (<xref linkend="odr.use"/>). Only if you need to
implement ASN.1 beyond that which has been provided, should you
worry about the second half of the documentation
- (section <link linkend="odr-prog">Programming with ODR</link>).
+ (<xref linkend="odr.programming"/>).
If you use one of the higher-level interfaces, you can skip this
section entirely.
</para>
<para>
This is important, so we'll repeat it for emphasis: <emphasis>You do
- not need to read section <link linkend="odr-prog">Programming with
- ODR</link> to implement Z39.50 with &yaz;.</emphasis>
+ not need to read <xref linkend="odr.programming"/>
+ to implement Z39.50 with &yaz;.</emphasis>
</para>
<para>
</para>
</sect1>
- <sect1 id="odr.use"><title id="odr-use">Using ODR</title>
+ <sect1 id="odr.use"><title>Using ODR</title>
<sect2><title>ODR Streams</title>
<para>
The memory subsystem of &odr; is fairly efficient at allocating and
releasing little bits of memory. Rather than managing the individual,
- small bits of space, the system maintains a freelist of larger chunks
+ small bits of space, the system maintains a free-list of larger chunks
of memory, which are handed out in small bits. This scheme is
generally known as a <emphasis>nibble memory</emphasis> system.
It is very useful for maintaining short-lived constructions such
data you wish to decode (eg, <function>odr_integer()</function> odr
<function>z_APDU()</function>).
</para>
-
- <para>
- Examples of encoding/decoding functions:
- </para>
-
- <synopsis>
- int odr_integer(ODR o, int **p, int optional, const char *name);
-
- int z_APDU(ODR o, Z_APDU **p, int optional, const char *name);
- </synopsis>
+
+ <example><title>Encoding and decoding functions</title>
+ <synopsis>
+ int odr_integer(ODR o, int **p, int optional, const char *name);
+
+ int z_APDU(ODR o, Z_APDU **p, int optional, const char *name);
+ </synopsis>
+ </example>
<para>
If the data is absent (or doesn't match the tag corresponding to
last call to <function>odr_reset()</function> will be released.
</para>
- <para>
- The use of the double indirection can be a little confusing at first
- (its purpose will become clear later on, hopefully),
- so an example is in order. We'll encode an integer value, and
- immediately decode it again using a different stream. A useless, but
- informative operation.
- </para>
-
- <programlisting>
-
+ <example><title>Encoding and decoding of an integer</title>
+ <para>
+ The use of the double indirection can be a little confusing at first
+ (its purpose will become clear later on, hopefully),
+ so an example is in order. We'll encode an integer value, and
+ immediately decode it again using a different stream. A useless, but
+ informative operation.
+ </para>
+ <programlisting><![CDATA[
void do_nothing_useful(int value)
{
ODR encode, decode;
odr_destroy(encode);
odr_destroy(decode);
}
- </programlisting>
+]]>
+ </programlisting>
+ <para>
+ This looks like a lot of work, offhand. In practice, the &odr; streams
+ will typically be allocated once, in the beginning of your program
+ (or at the beginning of a new network session), and the encoding
+ and decoding will only take place in a few, isolated places in your
+ program, so the overhead is quite manageable.
+ </para>
+ </example>
+
+ </sect2>
+ <sect2><title>Printing</title>
<para>
- This looks like a lot of work, offhand. In practice, the &odr; streams
- will typically be allocated once, in the beginning of your program
- (or at the beginning of a new network session), and the encoding
- and decoding will only take place in a few, isolated places in your
- program, so the overhead is quite manageable.
+ When an ODR stream is created of type <literal>ODR_PRINT</literal>
+ the ODR module will print the contents of a PDU in a readable format.
+ By default output is written to the <literal>stderr</literal> stream.
+ This behavior can be changed, however, by calling the function
+ <synopsis>
+ odr_setprint(ODR o, FILE *file);
+ </synopsis>
+ before encoders or decoders are being invoked.
+ It is also possible to direct the output to a buffer (of indeed
+ another file), by using the more generic mechanism:
+ <synopsis>
+ void odr_set_stream(ODR o, void *handle,
+ void (*stream_write)(ODR o, void *handle, int type,
+ const char *buf, int len),
+ void (*stream_close)(void *handle));
+ </synopsis>
+ Here the user provides an opaque handle and two handlers,
+ <replaceable>stream_write</replaceable> for writing,
+ and <replaceable>stream_close</replaceable> which is supposed
+ to close/free resources associated with handle.
+ The <replaceable>stream_close</replaceable> handler is optional and
+ if NULL for the function is provided, it will not be invoked.
+ The <replaceable>stream_write</replaceable> takes the ODR handle
+ as parameter, the user defined handle, a type
+ <literal>ODR_OCTETSTRING</literal>, <literal>ODR_VISIBLESTRING</literal>
+ which indicates the type of contents is being written.
</para>
-
+ <para>
+ Another utility useful for diagnostics (error handling) or as
+ part of the printing facilities is:
+ <synopsis>
+ const char **odr_get_element_path(ODR o);
+ </synopsis>
+ which returns a list of current elements that ODR deals with at the
+ moment. For the returned array, say <literal>ar</literal>,
+ <literal>ar[0]</literal> is the top level element,
+ <literal>ar[n]</literal> is the last. The last element has the
+ property that <literal>ar[n+1] == NULL</literal>.
+ </para>
+ <example>
+ <title>Element Path for record</title>
+ <para>
+ For a database record part of a PresentResponse the
+ array returned by <function>odr_get_element</function>
+ is <literal>presentResponse</literal>, <literal>databaseOrSurDiagnostics</literal>, <literal>?</literal>, <literal>record</literal>, <literal>?</literal>, <literal>databaseRecord</literal> . The question mark appears due to
+ unnamed constructions.
+ </para>
+ </example>
</sect2>
-
<sect2><title>Diagnostics</title>
<para>
</sect2>
</sect1>
- <sect1 id="odr.programming"><title id="odr-prog">Programming with ODR</title>
+ <sect1 id="odr.programming"><title>Programming with ODR</title>
<para>
The API of &odr; is designed to reflect the structure of ASN.1, rather
other external forms.
</para>
+ <tip>
+ <para>
+ There is an ASN.1 tutorial available at
+ <ulink url="&url.asn.1.tutorial;">this site</ulink>.
+ This site also has standards for ASN.1 (X.680) and BER (X.690)
+ <ulink url="&url.asn.1.standards;">online</ulink>.
+ </para>
+ </tip>
+
<para>
- The interface is based loosely on that of the Sun Microsystems XDR
- routines.
+ The ODR interface is based loosely on that of the Sun Microsystems
+ XDR routines.
Specifically, each function which corresponds to an ASN.1 primitive
type has a dual function. Depending on the settings of the ODR
stream which is supplied as a parameter, the function may be used
The resulting C source code is quite compact, and is a pretty
straightforward representation of the source ASN.1 specification.
</para>
-
+
<para>
In many cases, the model of the XDR functions works quite well in this
role.
</para>
<synopsis>
-int odr_integer(ODR o, int **p, int optional, const char *name);
+ int odr_integer(ODR o, int **p, int optional, const char *name);
</synopsis>
<para>
(we don't allow values that can't be contained in a C integer.)
</para>
-
+
<para>
This form is typical of the primitive &odr; functions. They are named
after the type of data that they encode or decode. They take an &odr;
</synopsis>
<para>
- The functions are modelled after the manipulation functions that
+ The functions are modeled after the manipulation functions that
accompany the <literal>fd_set</literal> type used by the
<function>select(2)</function> call.
<literal>ODR_MASK_ZERO</literal> should always be called first on a
The C OID representation is simply an array of integers, terminated by
the value -1 (the <literal>Odr_oid</literal> type is synonymous with
the <literal>int</literal> type).
- We suggest that you use the OID database module (see section
- <link linkend="oid">Object Identifiers</link>) to handle object identifiers
+ We suggest that you use the OID database module (see
+ <xref linkend="asn.oid"/>) to handle object identifiers
in your application.
</para>
</sect3>
</sect2>
- <sect2><title id="tag-prim">Tagging Primitive Types</title>
+ <sect2 id="tag.prim"><title>Tagging Primitive Types</title>
<para>
The simplest way of tagging a type is to use the
<para>
The function <function>myInt()</function> can then be used like any of
the primitive functions provided by &odr;. Note that the behavior of
- <function>odr_explicit()</function>
- and <function>odr_implicit()</function> macros
+ <function>odr_explicit_tag()</function>
+ and <function>odr_implicit_tag()</function> macros
act exactly the same as the functions they are applied to - they
respond to error conditions, etc, in the same manner - they
simply have three extra parameters. The class parameter may
Note the 1 in the call to <function>odr_bool()</function>, to mark
that the sequence member is optional.
If either of the member types had been tagged, the macros
- <function>odr_implicit()</function> or <function>odr_explicit()</function>
+ <function>odr_implicit_tag()</function> or
+ <function>odr_explicit_tag()</function>
could have been used.
The new function can be used exactly like the standard functions provided
with &odr;. It will encode, decode or pretty-print a data value of the
<note>
<para>
- See section <link linkend="tag-prim">Tagging Primitive types</link>
- for information on how to tag the primitive types, as well as types
- that are already defined.
+ See <xref linkend="tag.prim"/> for information on how to tag
+ the primitive types, as well as types that are already defined.
</para>
</note>
<para>
which overrides the tag of the type immediately following it. The
- macro <function>odr_implicit()</function> works by calling
+ macro <function>odr_implicit_tag()</function> works by calling
<function>odr_implicit_settag()</function> immediately
before calling the function pointer argument.
Your type function could look like this:
interface) is less than the time that would be required to develop a
better interface. Nevertheless, it is far from satisfying, and it's a
point that will be worked on in the future. One option for you would
- be to simply apply the <function>odr_explicit()</function> macro to
+ be to simply apply the <function>odr_explicit_tag()</function> macro to
the first function, and not
have to worry about <function>odr_constructed_*</function> yourself.
Incidentally, as you might have guessed, the
projects / yaz-moved-to-github.git / blobdiff