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NAME ^

nsapi_perl - Integrate Perl with Netscape servers

SYNOPSIS ^

In obj.conf

 Init fn="load-modules"
      shlib="/path/nsapi_perl.so"
      funcs="nsapi_perl_init,nsapi_perl_handler"
 Init fn="nsapi_perl_init"
      init-script="/path/nsapi_perl_init.pl"
      shlib="/path/nsapi_perl.so"
      tracelog="/tmp/nsapi_perl.log"

 <Object ppath="/document/root/path/*">
 Directive fn="nsapi_perl_handler"
      module="Netscape::ModuleName" sub="sub_name"
 </Object>

In nsapi_perl_init.pl

 use Netscape::ModuleName;

DESCRIPTION ^

nsapi_perl is the collective name for a set of Netscape Server API (NSAPI) functions and Perl modules that integrate Perl with the Netscape web server family. This is achieved by embedding within the server executable a Perl interpreter, much as mod_perl does for the Apache web server.

Once the interpreter has been embedded the server can be configured so that at any point during a client session a Perl subroutine can be called. These Perl subroutines are passed as arguments Perl objects that allow direct access to the server's API.

The rest of this document describes how to configure and use nsapi_perl; it also provides a couple of examples. It is hoped that as real-world examples start to roll in this document can evolve into a sort of cookbook illustrating how approach common nsapi_perl tasks.

CONFIGURATION ^

Orientation

nsapi_perl consists of the following components

nsapi_perl.so

This is the shared object containing the NSAPI functions that embed a Perl interpreter in the server and run the Perl subroutines.

nsapi_perl_init.pl

This is a Perl program that is (optionally) executed when the server starts. nsapi_perl_init.pl can be used to load modules containing nsapi_perl subroutines at startup, or to predefine global (Perl) configuration variables.

Netscape::Server

This is a Perl module that provides the basic framework for the Perl interface to the NSAPI.

Netscape::Server::Session, Netscape::Server::Request

These are Perl classes from which objects that are passed as arguments to nsapi_perl subroutines are instantiated. These modules are automatically loaded at start-up.

Netscape::Registry

This module allows you run run CGI scripts unmodified from within the Netscape server httpd process. This provides a large performance boost. Netscape::Registry has its own man page.

Initialization

For the server to embed a Perl interpreter it must be told at startup to link with nsapi_perl.so This is done by adding the following to the Server's obj.conf file.

 Init fn="load-modules" shlib="/path/nsapi_perl.so"
      funcs="nsapi_perl_init,nsapi_perl_handler"

(You can wrap it on to multiple lines so long as the second line starts with whitespace). Here, /path is the full path to where you installed nsapi_perl.so. (For Netscape 1.x servers this should be added to the file magnus.conf and should be on a single line.)

After linking to nsapi_perl.so the server must then be told to run the function nsapi_perl_init, which initializes the Perl interpreter. This is done by adding the following line the the server's obj.conf file.

 Init fn="nsapi_perl_init"

(Again for Netscape 1.x servers this is to be done in magnus.conf.)

nsapi_perl_init optionally accepts the init-script=path key/value pair as an arugment. If this argument is specified, path is the full path to a perl script which will be parsed and executed at server start-up.

Conventionally this script is called nsapi_perl_init.pl, although you're free to choose any name you wish. For example, the following line will run foobar.pl in my home directory at server start-up.

 Init fn="nsapi_perl_init"
      init-script="/home/benjamin/foobar.pl"

Early versions of nsapi_perl mandated that nsapi_perl_init be passed the conf=path key/value pair as an argument. The conf argument is still accepted, if given, but a warning is issued about its deprecated nature. If the conf argument is given, then the file specified by path will be parsed and run exactly as for the init-script argument.

nsapi_perl_init also accepts two additional optional arguments: shlib and tracelog.

shlib will almost certainly prove to be necessary on Unix platforms. Its purpose is to make the symbols defined in the nsapi_perl shared library have global visibility. Without this argument, dynamic loading of extension modules - including the Netscape::* modules - will probably fail on Unix. See "DYNAMIC LOADING OF EXTENSIONS" for details.

The tracelog argument may be used to enable nsapi_perl tracing; see "DIAGNOSTICS" for full details.

nsapi_perl_init.pl may load the Perl code you wish to have executed by the server. For instance, if you wish to use the Netscape::Registry module, add you can add line like this to nsapi_perl_init.pl.

 use Netscape::Registry;

The module's subroutines will then be pre-compiled when it comes time for the server to run them.

Since nsapi_perl_init.pl is a Perl program that is executed when the server starts, you can use it to perform a multitude of initialization tasks like opening log files, defining global configuration variables, and so on.

If you choose not to use() any modules in nsapi_perl_init.pl, they will be automatically loaded for you when they are needed. However, relying on this method may not be as effiecient in terms of memory for multi-process servers. Auto-loading of modules also implies a small performance penalty when responding to the first request that causes a module to be loaded, since that module has to be compiled before the request can be answered.

In general, therefore, it is probably better to use() all of your modules from nsapi_perl_init.pl.

With the above lines inserted into obj.conf you should see a message like this when starting your server:

 [11/Feb/1998:16:22:00] info: nsapi_perl_init reports: \
 loaded a perl version 5.00401 interpreter

(This message may go to your server's error log, your screen, or both, depending upong your setup.)

At this point Perl is primed and the server is ready to run. Cool.

USAGE ^

How Netscape Serves

To know how to tell the server when to run a subroutine, it helps to know a little of how Netscape servers process requests from clients. Netscape, like Apache, breaks the processing of requests into discrete steps.

1. AuthTrans

During this stage authorization information from the client is checked.

2. NameTrans

The virtual path sent by the client as part of its URL is mapped to physical path on the server's file system.

3. PathCheck

Given the authorization and path information, the server checks whether the client is allowed access or not.

4. ObjectType

The mime type of the file requested is determined.

5. Service

The client's request is processed, usually by sending them the requested file but sometimes by doing something more fun such as running a CGI program.

6. AddLog

The request is logged.

If at any of these stages an error occurs, such as failed authentication or a file not being found, the sequence is aborted and error processing occurs.

Normally obj.conf is set up in such a way that the server's built-in functions handle each stage of the request. However, you can modify obj.conf so that for certain paths special processing occurs. For instance, adding the following to obj.conf overrides the normal list of Service functions for files within the /document/root/foo directory

 <Object ppath="/document/root/foo/*">
 Service fn="special_function" argument="value"
 </Object>

This would cause all client requests of the form http://my.server.domain/foo/* to be serviced by special_function.

Basically each part of the web site that needs special processing is declared as an object. For each object you can then specify one or more directives. A directive is the name of one of 6 processing steps listed above, such as AuthTrans, NameTrans, etc. In the example above, the directive is Service. After each directive comes a sequence like fn="special_function" indicating the name of the function to fulfill that stage of the request for that object. Following this is a sequence of zero or more name=value pairs that will be passed to the function when it executes.

There are other ways to define an object that are beyond the scope of this document; for full details on how to specify special processing for certain parts of your web site I refer you to your Netscape documentation. From here on, I will assume you have at least a rough idea of how to do it.

Calling Your Perl Subroutines

To call Perl subroutines from the server, you need to create an object and have that object call the nsapi_perl function nsapi_perl_handler passing the module and subroutine names as arguments. For example, the sequence

 <Object ppath="/document/root/perl/*">
 Service fn="nsapi_perl_handler" module="Netscape::PerlService
     sub="send_stuff"
 </Object>

would call the Perl subroutine &Netscape::PerlService::send_stuff for all requests that have a URI beginning with /perl.

To make mod_perl enthusiasts feel at home, if the name of the subroutine is omitted the name handler is assumed. Therefore, the following is an equivalent declaration to the one above:

 <Object ppath="/document/root/perl/*">
 Service fn="nsapi_perl_handler" module="Netscape::Service"
 </Object>

You can have more than one directive for an object including more than one directive of a single type. The following would all requests to /perl be handled entirely by Perl:

 <Object ppath="/document/root/perl/*">
 AuthTrans fn="nsapi_perl_handler" module="Netscape::AuthTrans
 NameTrans fn="nsapi_perl_handler" module="Netscape::NameTrans
 PathCheck fn="nsapi_perl_handler" module="Netscape::PathCheck
 ObjectType fn="nsapi_perl_handler" module="Netscape::ObjectType
 Service fn="nsapi_perl_handler" module="Netscape::Service
 AddLog fn="nsapi_perl_handler" module="Netscape::AddLog
 </Object>

Any module name can be chosen to process a request. I recommend, however, that all modules used with nsapi_perl be named somewhere in the Netscape:: hierarchy.

If a module chosen to process a request has not yet been loaded by the server process, it will be compiled by the server at request time. As mentioned in "Initialization", such auto-loading will incur at performance penalty for the first request that causes that module to be used (but not for subequent requests). This auto-loading may also incur a memory-use penalty for multi-process servers. It is therefore recommended that you pre-load modules using a perl start-up script, as described in "Initialization".

SUBROUTINES ^

Arguments passed to subroutines.

When a Perl subroutine is called by nsapi_perl it is passed three arguments:

 sub handler {
     my($pb, $sn, $rq) = @_;
     ...
 }

$pb is a reference to a hash that contains the key=value pairs passed as arguments to nsapi_perl_handler. For instance, if the following was in your obj.conf,

 NameTrans fn="nsapi_perl_handler" module="Netscape::Redirect"
     from="/special" alt="/default/home.html" url="/for_mozilla/home.html"

then the following all would be true:

 $pb->{'fn'} eq 'nsapi_perl_handler';
 $pb->{'module'} eq 'Netscape::Redirect';
 $pb->{'from'} eq '/special';
 $pb->{'alt'} eq '/default/home.html';
 $pb->{'url'} eq '/for_mozilla/home.html';

The contents of %{$pb} should be treated read-only.

$sn is an instance of Netscape::Server::Session which has its own man page. Basically a Session object contains information about the connection to the client host such as its IP address, its socket descriptor and so on. See Netscape::Server::Session for full details, or bear with me here for a while since you'll soon see an example.

$rq is an instance of Netscape::Server::Request which also has its own man page. A Request object contains information derived from the client's http header and is where information constructed by the server in its response is stored. Again, see Netscape::Server::Request or hang on just a little while longer.

The general idea is to use the values in %{$pb} and to implement methods on $sn and $rq to process the request in special ways. The man pages for each of Netscape::Server::Session and Netscape::Server::Request list the available methods.

Anyone whose done NSAPI C programming will recognize the parallel between how nsapi_perl subroutines are called and how NSAPI C functions are called.

Subroutine Return Values

NSAPI C functions are expected to return one of a set of constants indicating success, failure, bewilderment, or whatever. These constants are termed request-response codes. Any nsapi_perl subroutine should also always return one of these constants. The constants are defined in the Netscape::Server module which should therefore always be use()d by your nsapi_perl module.

The following will import the request-response codes from Netscape::Server.

 use Netscape::Server qw/:request_codes/;

The constants are described in detail in Netscape::Server; I will list them here for reference:

 REQ_ABORTED, REQ_EXIT, REQ_NOACTION, REQ_PROCEED

The interpretation of the value returned by the subroutine to the server depends on what stage of the request was being processed, as the following table indicates.

 Request   |            Subroutine returns
 Stage     |REQ_ABORTED|REQ_EXIT|REQ_NOACTION|REQ_PROCEED
 --------------------------------------------------------
 AuthTrans |     x     |   x    |     n      |     s
 NameTrans |     x     |   x    |     n      |     s
 PathCheck |     x     |   x    |     s      |     s
 ObjectType|     x     |   x    |     s      |     s
 Service   |     x     |   x    |     n      |     s
 AddLog    |     ?     |   ?    |     ?      |     ?
 --------------------------------------------------------

 x - request is aborted entirely
 s - request skips to next stage
 n - request goes to next directive in same stage

Basically REQ_ABORTED and REQ_EXIT each indicate an error, but you should only use REQ_EXIT if there was an I/O error when talking to the client. REQ_PROCEED always causes processing to move to the next stage. REQ_NOACTION sometimes causes the next directive in the same stage to be called. This could be used to implement, for instance, a sequence of NameTrans functions each mapping in their own way the request path.

I have never seen any documentation about how the server interprets values returned by AddLog functions. I suppose since it is the last step anyway, it may not really matter.

Netscape::Server also provides other constants that can be used to set the http status of the request or the severity of errors; see Netscape::Server for full details.

DYNAMIC LOADING OF EXTENSIONS ^

When you put a statement in a module that causes automatic loading of a Perl extension, such as

 use Socket;

you may get error messages from the run-time loader that look like:

 Can't load '/path/lib/perl5/arch/auto/Foo/Foo.so' for module Foo:
 ld.so.1: ./ns-httpd: fatal: relocation error: symbol not found:
 Perl_sv_undef: referenced in '/path/lib/perl5/arch/auto/Foo/Foo.so'
 at /path/lib/perl5/arch/5.00404/DynaLoader.pm line 166.

This is because the Perl library is loaded into the Netscape server by dlopen(3) (or its equivalent). On many platforms symbols contained in objects loaded in by dlopen are not visibile to other objects loaded in by dlopen (such as Foo.so in the above example).

On some operating systems, this restriction may be worked around by adding the shlib argument to the nsapi_perl_init() function call in obj.conf, like this:

 Init fn="nsapi_perl_init"
      init-script="/home/benjamin/foobar.pl"
      shlib="/path/to/nsapi_perl.so"

Here, /path/to/nsapi_perl.so should be the full path to the nsapi_perl shared object. This location was determined during the installation of nsapi_perl.

The presence of a shlib argument in the call to nsapi_perl_init causes nsapi_perl to call dlopen(3) on /path/to/nsapi_perl.so, passing dlopen a flag (RTLD_GLOBAL) that tells the runtime linker symbols within this object are to be visible to other objects acquired at a later time via dlopen.

Obviously this workaround only works on those systems that define RTLD_GLOBAL. Currently this includes at least Solaris and IRIX; there may be others too that I am not aware of. A shlib argument on a system that does not support RTLD_GLOBAL is silently ignored.

(Earlier versions of nsapi_perl used a libperl argument to nsapi_perl init instead of shlib. libperl was expected to point to a (shared) perl library, like libperl.so. It is now recommended that you use the shlib argument instead of the libperl argument, and that you point to the nsapi_perl shared object itself, rather than the shared Perl library.)

Incidently, extension modules on Win32 are reported to work just fine "out of the box".

EXAMPLES ^

Hello World

In obj.conf:

 <Object ppath="/document/root/greetings/*">
 ObjectType fn="nsapi_perl_handler" module="Netscape::HelloWorld"
     sub="content_type" type="text/html"
 Service fn="nsapi_perl_handler" module="Netscape::HelloWorld"
 </Object>

In nsapi_perl_init.pl: use Netscape::HelloWorld;

In HelloWorld.pm:

 package Netscape::HelloWorld;
 use strict;
 use Netscape::Server qw/:all/;

 sub content_type {
     my($pb, $sn, $rq) = @_;
  
     # --- Set the content type as configured   
     my $type = $pb->{'type'};
     defined $type or
         return REQ_ABORTED;
     $rq->srvhdrs('content-type', $type);
     return REQ_PROCEED;
 }

 sub handler {
     my($pb, $sn, $rq) = @_;
     my($proceed);

     # --- Set status to 200 OK
     $sn->protocol_status($rq, PROTOCOL_OK);

     # --- Initiate response
     $proceed = $sn->protocol_start_response($rq);
     if ($proceed == REQ_PROCEED) {
         $sn->net_write("<h1>Hello World</h1>\n");
         return REQ_PROCEED;
     } elsif ($proceed == REQ_NOACTION) {
         # --- Client probably did an if-modified request
         return REQ_PROCEED;
     } else {
         # --- Yikes! Something bad has happened
         return $proceed;
     }
 }

 1;

Redirect

Here's a Perl equivalent to the https_redirect function listed on page 143 of the Enterprise 2.0 Unix Programmer Guide. Note that I don't particularly care for the logic of this subroutine, or the original C function from which it was derived. It is presented here merely to illustrate the potential advantages of nsapi_perl.

In obj.conf:

 NameTrans fn="nsapi_perl_handler" module="Netscape::Redirect"
     from="/special" alt="/default/home.html" url="/for_mozilla/home.html"

In nsapi_perl_init.pl:

 use Netscape::Redirect;

In Redirect.pm:

 package Netscape::Redirect;
 use strict;
 use Netscape::Server qw/:all/;

 sub handler {
     my($pb, $sn, $rq) = @_;

     my $ppath = $rq->vars('ppath');
     my $from = $pb->{'from'};
     my $url = $pb->{'url'};
     my $alt = $pb->{'alt'};

     if (not defined $from or not defined $url) {
         log_error(LOG_MISCONFIG, "handler", $sn, $rq,
                   'missing parameter (need from, url)');
         return REQ_ABORTED;
     }

     # --- Here's where the poor sucker using raw NSAPI has to
     # --- resort to the utterly bogus shexp_cmp()
     $ppath =~ /^$from/o or
         return REQ_NOACTION;

     # --- Get the user agent
     defined(my $ua = $rq->headers('user-agent')) or
         return REQ_ABORTED;

     # --- NSAPI has a built-in that looks for Mozilla-like browser,
     # --- but MSIE fools it.  However, now we can use a full Perl
     # --- regular expression here if we want
     if ($ua =~ /Mozilla/ and $ua !~ /MSIE/) {
         $rq->protocol_status($sn, PROTOCOL_REDIRECT);
         $rq->vars('url', $url);
         return REQ_ABORTED;
     }
     
     # --- No match.  Could be MSIE or Lynx or whomever.
     if (defined $alt) {
         # --- Rewrite the request string
         $rq->vars('ppath', $alt);
         return REQ_NOACTION;
     }
     
     # --- Else do nothing
     return REQ_NOACTION;
 }

 1;

DIAGNOSTICS ^

nsapi_perl has a trace facility that can be enabled by providing the tracelog argument to nsapi_perl_init in obj.conf. The value of the tracelog argument is the path to a file where tracing messages will be written. This path is nominally relative to the server's config directory, but that depends on Netscape internals. To be on the safe side, specify a full path. For example, the stanza

 Init fn=nsapi_perl_init
      init-script=/usr/local/suitespot/lib/startup.pl
      tracelog=/usr/local/suitespot/https-foo/logs/nsapi_perl.log

in obj.conf will write the tracelog to /usr/local/suitespot/https-foo/logs/nsapi_perl.log.

If the file specified by the tracelog argument already exists, it will be appended to.

BUGS ^

Send bug reports, comments, or questions to the nsapi_perl mailing list: nsapi_perl@samurai.com.

Here are the major issues at this time:

o

Threading. Although this version contains the first working integration of Perl and Netscape threads, there are still some unresolved issues. Most importantly, Netscape::Registry.pm is not thread-safe at this time.

A mechanism has been identified that will (hopefully) make Netscape::Registry.pm thread-safe, but at the time of writing this mechanism has not been implemented.

o

Early versions of nsapi_perl had problems with Perls that use a static Perl library (such as libperl.a) rather than a dynamic perl library (libperl.so). This seems to be fixed (for me) in version 0.23, but I'm not sure what I did to fix it so YMMV. If are using a static libperl.a and have problems with nsapi_perl, try to recompile Perl so that is uses a dynamic Perl library.

AUTHOR ^

Benjamin Sugars <bsugars@canoe.ca>, with lots of help from Steve Nielsen <Steve.Nielsen@infores.com> and Olivier Dehon <dehon_olivier@jpmorgan.com>.

Please send comments, feature requests, bug reports to the nsapi_perl mailing list: nsapi_perl@samurai.com.

SEE ALSO ^

Netscape::Server, Netscape::Server::Session, Netscape::Server::Request, Netscape::Registry

perl(1)

dlopen(3)

Netscape documentation about their line of web servers and NSAPI.

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