=head1 NAME

SWISH-LIBRARY - Interface to the Swish-e C library

=head1 What is the Swish-e C library

It is a C library implementation based on swish-e-2.1-dev, but many of
the functions have been rewritten in order to get a thread safe library.
That's is not to say that it is currently thread safe.


The advantage of the library is that the index file(s) can be opened one time
and many queries made on the open index.  This saves the startup time required
to fork and run the swish-e binary, and the expensive time of opening up the
index file.  Some benchmarks have shown a three fold increase in speed.

The downside is that your program now has more code and data in it (the index tables can
use quite a bit of memory), and if a fatal error happens in swish it will bring down your
program.  These are things to think about, especially if embedding swish into a web server
such as Apache where there are many processes serving requests.

The best way to learn about the library is to look at two files included with
the swish-e distribution that make use of the library.


=over 4

=item src/libtest.c

This file gives a basic overview of linking a C program with the Swish-e library.
Not all available functions are used in that example, but it should give you a good overview
of building a program with swish-e.

To build libtest run and run libtest:

    $ make libtest
    $ ./libtest [optional name of index file(s)]

You will be prompted for the search words.  The default index used is F<index.swish-e>.
This can be overridden by placing a list of index files in a quote-protected string.

    $ ./libtest 'index1 index2 index3'

=item perl/SWISHE.xs

The F<SWISHE.xs> file contains more examples of how to read from the perl library.  It includes
example code for reading additional information from the index files.

=back

Not all available functions are documented here.  That's both do to laziness, and the hope
that a better interface will be created for these functions.  Check the above files for details.

You should check for errors after every call.  See the F<src/libtest.c> file for examples.

=head1 Available Functions


=over 4

=item struct SWISH *SwishInit(char *IndexFiles);

This functions opens and reads the header info of the index files
included in IndexFiles string.  The string should contain a space separated
list of index files.

    SWISH *myhandle;
    myhandle = SwishOpen("file1.idx");

This function will return a swish handle.  You must check for errors, and on
error free the memory used by the handle, or abort.

Here's an example of aborting:

    SWISH *swish_handle;
    swish_handle = SwishInit("file1.idx file2.idx");
    if ( SwishError( swish_handle ) )
        SwishAbortLastError( swish_handle );

And here's an example of catching the error:        

    SWISH *swish_handle;
    swish_handle = SwishInit("file1.idx file2.idx");
    if ( SwishError( swish_handle ) )
    {
        printf("Failed to connect to swish. %s\n", SwishErrorString( swish_handle ) );
        SwishClose( swish_handle );  /* free the memory used */
        return 0;
    }


=item struct SWISH *SwishOpen(char *IndexFiles);  [depreciated]

This functions opens and reads header info of the index files
included in IndexFiles

    myhandle = SwishOpen("file1.idx");

Returns NULL on error.  This function is depreciated since there is no way to
find out what error caused an error.  Use SwishInit() instead.

=item void SwishClose(struct SWISH *handle);

This function closes and frees the memory of a Swish handle

=item int SwishSearch(struct SWISH *handle,char *words,int structure,char *properties,char *sortspec);

This function executes a search for a handle.

Input data:

    handle      : value returned by SwishOpen
    words       : the search string
    structure   : At this moment always one (it will implement the -t option of Swish-e)
    properties  : [Depreciated]  Set as NULL.  See text for comments.
    sortspec    : Sort specs for the results. Use NULL if sort by rank

Returns the number of hits or a negative value on error.

    num_results = SwishSearch(swish_handle, "title=test", 1, NULL, "date desc");

There is a new feature here that it is not included in swish-e-2.0: 
You can specify several sorting properties including a combination
of descending and ascending fields.

    field1 asc field2 desc

Currently, when num_results is zero there is also an error condition set ("Word not found").
Therefore, only check and report errors if num_results is a negative number.

    if ( num_results < 0 && SwishError( swish_handle ) )
        SwishAbortLastError( swish_handle );

The B<properties> parameter:

In general, you will find it easiest to use the functions described below to fetch properties:

    SwishResultPropertyStr()
    SwishResultPropertyULong()

You can also pass in a space-separated list of properties to the SwishSearch() function.
This will parse and cache the list of properites and then the property IDs can be used
to fetch the property values.  This saves the time of converting the property names from
a string to a property ID value for each result.  It's unlikely that the speed-up is
sigificant.  See the perl/SWISHE.xs code for an example how this can be done.

=item int SwishSeek(struct SWISH *handle, int n)

This function puts the results pointer on the nth result.  The first result is
number zero.  Returns n if operation goes OK or a negative number on error.
After calling SwishSeek() call SwishNext() to fetch the first record at the position
selected by SwishSeek();

Example:

    SwishSeek( swish_handle, 0 );  /* start at the beginning */
    SwishSeek( swish_handle, 5 );  /* start at the sixth record */

If you always read results from the very start you do not need to call SwishSeek().
After a query the position is set to the start of the result list.

=item struct result *SwishNext(struct SWISH *handle)

This function returns next result. It must be executed after SwishSearch.
Returns NULL on error or when no more results are available.  Call SwishError()
to check for errors.

The value returned is used to fetch the various I<properties> for a given file (e.g. rank,
title, path name).  Typically, SwishNext() is called in a loop to fetch and display all the
properties.

=item char *SwishResultPropertyStr (SWISH *handle, RESULT *result, char *property )

Once you have a result returned from SwishNext() you can call this function to fetch
a string value of any property.

    printf("path = %s\n", SwishResultPropertyStr (swish_handle, result, "swishdocpath" ) );

If the property named is not defined (invalid name supplied) swish will return the string "(null)".
If the property does not exist for this result the null string will be returned.

You must not free the memory returned by the call, and you must copy the string to a new
memory location if you wish to keep the string around longer than just while processing the
current result.

Currently, a cache of one result's properties (per index) are stored in memory.

=item unsigned long SwishResultPropertyULong (SWISH *handle, RESULT *result, char *property )

This will return numeric (and date) properties as an unsigned long.

It will return ULONG_MAX on error, which can mean either that the property name specified was
invalid, the property specified was not a numeric or date property, or simply that the no value
exists for the current result.  Check SwishError() to determine if it's a real error vs. just
that the result does not have the property.

=item int SwishError(struct SWISH *handle)

This function returns the last error code.  It's often used as a test to see
if any errors happened on the last operation.

=item char *SwishErrorString(struct SWISH *handle)

Returns the string version of the error code.  See F<src/error.c>
for possible errors.  This is a generic error class.  See
SwishLastErrorMsg() for possible specific messages.


=item char *SwishLastErrorMsg(struct SWISH *handle)

This can return additional (more specific) information about the last error.
For example, SwishErrorString() might return:

    Index file error

But SwishLastErrorMsg might give details like:

    Couldn't open the property file "index1.prop": No such file or directory

=item SwishAbortLastError( SWISH *handle )

This will abort the program, and format and print any error messages.

=item SwishCriticalError( SWISH *handle )

This will return true if the last error was critical.  A critical error means
swish is in an unstable state and you must call SwishClose() on the handle.

=item SwishErrorsToStderr(void)

Call this after calling SwishInit() and any messages or warning will be sent to
stderr (standard error) instead of to stdout.  This might be important when
running swish-e in a web server environment.

=item SetLimitParameter(handle,propertyname,low,hi)

This is used to set the limit ranges on a property (as is done with the -L switch
when running swish from the command line.

=item ClearLimitParameter(handle)

Clears the limits set by SetLimitParameter().  If you use limits you
will need to clear them after each request.

=item Stem(char **inword, int *lenword)

This can be used to convert a word to its stem.  Word is modified in place (or reallocated if
needed.


=back

=head1 Bug-Reports

Please report bug reports to the Swish-e discussion group.
Feel also free to improve or enhance this feature.

=head1 Author
 
Aug 2000
Jose Ruiz
jmruiz@boe.es

Updated: Aug 22, 2002 - Bill Moseley

=head1 Document Info

$Id: SWISH-LIBRARY.pod,v 1.1.1.1 2002/09/20 19:47:29 adcroft Exp $

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