Chapter 14. Web Application Development

The [HTTPServer] section of the Virtuoso INI file contains parameters that directly affect the HTTP server upon server startup. After the server has been started further configuration can be performed using the Visual Server Administration Interface. Here is an example of the section in the INI file:

[HTTPServer]
  ServerPort = 8890
  ServerRoot = ../vsp
  ServerThreads = 2
  MaxKeepAlives = 10
  KeepAliveTimeout = 10
  DavRoot = DAV

The meanings of these parameters are briefly explained here as a quick reference for the most frequently used parameters:

	See Also:
	The Server Administration chapter contains a complete list of the Virtuoso INI file parameters. In particular, the [HTTPServer] section .

A Virtuoso virtual directory maps logical paths to physical resource locations accompanied by rules and/or parameters that govern how the mappings respond to user-agent (e.g. Web browser) requests. This mechanism allows physical locations to be obscured or simply reorganized. Some resource types require authentication challenges, such as the Visual Server Administration Interface, and/or special headers such as SOAP, which is another HTTP endpoint.

Virtual directories are useful when one server has to provide access to several Web sites. Redirects are not a universal solution to this, it is far better to define virtual directories that point to the other sites. Suppose that we have two companies, "a" and "b", that are to share a Virtuoso server but want to represented on the Web by www.a.com and www.b.com respectively. Their pages could be stored in directories "/a" and "/b" on the server, whilst virtual directories map requests appropriately:

  http://www.a.com/  -->

 /a
  http://www.b.com/  -->

 /b

Hence, user-agent requests for www.a.com receive pages from /a, and likewise for "b". Requests under these domains are mapped back to their physical location such as the request for the URI http://www.a.com/images/picture.jpg retrieves the file /a/images/picture.jpg .

Virtual directory definitions are held within the system table DB.DBA.HTTP_PATH. Virtual directories can be administered in three basic ways:

	See Also:
	Virtual Directory Administration UI vhost_define() , vhost_remove() HTTP_PATH system table

Virtuoso matches user-agent requests against a logical path using the longest entry that matches the path extracted from the URI. Suppose we have two entries '/a/b ' and '/a ' and a request is made of: 'http://foo.bar/a/b/c.html ', will match the entry for '/a/b '.

First, Virtuoso will attempt to locate the physical path that has been mapped to a virtual host, interface and logical path. The virtual host corresponds to the 'Host' header field value from HTTP/1.1 requests. If the first step does not succeed then the server will try resolving the interface and logical path. Failing that, the default step will attempt to resolve the path directly to a physical location.

Figure 14.2. HTTP Virtual Directory Matching

	Note:
	HTTP 1.0 does not use the HOST header. Virtuoso will have little choice but to send HTTP 1.0 user-agents the contents of the default virtual host definition for the interface.

Thus if the following mappings are in effect:

/	->  /DAV
/doc	->  http://docs.biz.com:/
/admin	->  /admin

The following translations would be made:

/doc/howto/intro.html	   -> http://docs.biz.com:/howto/intro.html
/admin/help.vsp		   -> /admin/help.vsp
/gizmo/doc.xml		   -> /DAV/gizmo/doc.xml

Thus, the longest match is selected and the matching substring is replaced by the right hand side of the mapping. Note that this is also how automatic proxying takes place, since a physical path beginning with http:// will be passed forward to a remote server.

www.a.com

'/' mapped to '/a'

http://www.a.com/

WS.WS.host_meta_add ([app-name], [xrd-xml-fragment])

WS.WS.host_meta_add
  (
    'dbpedia.page-descriptor',
    '<Link rel="http://dbpedia.org/resource-descriptor" template="http://dbpedia.org/page/{uri}"/>'
  )
  ;

¶

Virtuoso As A Proxy

The Virtuoso HTTP server can act as a proxy server on the same port as the HTTP port. You can put the host and port that the Virtuoso HTTP server is listening on, into your browser proxy settings and all requests will be processed by it. Also this can be used to retrieve a page inside VSP.

The physical path setting of a virtual directory definition can be URL to another HTTP server. In which case Virtuoso will act as a proxy to that site when the logical path for it is requested.

	See Also:
	Virtuoso also provides VSP functions for proxying. http_proxy() .

The nature of Virtuoso's Web Proxying ability makes it easy and seamless to bind multiple websites under one roof. Existing sites do not have to move or change to be integrated under the Virtuoso Proxy. Simply map them under a logical path name. They can be mapped multiple times or from multiple ports.

If you already have pages written and working from other servers via ASP or PHP, then you will be able to run these servers concurrently with Virtuoso so they can share form data and give dynamic content from various sources, consistent with our value proposition of maximum incorporation of new technologies with minimum disruption to existing infrastructure. Whether these servers were hosted on various machines or the same machine there is no need to expose their running ports and services. This makes the end user experience cleaner, and helps maintain some server security and/or anonymity.

	Note:
	Virtuoso provides runtime hosting capabilities and PHP support, therefore ASP.Net and PHP and other applications can be run and hosted directly within the file system or WebDAV.

Suppose that you have two machines running existing web servers that serve various parts of your intranet. One web server may have been constructed for or by your sales department while the other server may have been a built by the support department. These servers could be resolved by http://sales.mycompany.com/ and http://support.mycompany.com/ respectively.

You can place Virtuoso on another server and start integrating your existing sites under this installation. You may use the Visual Server Administration Interface or choose to use the following commands via the isql interface:

DB.DBA.VHOST_DEFINE(lpath=>'/sales', ppath=>'http://sales.mycompany.com/');
DB.DBA.VHOST_DEFINE(lpath=>'/support', ppath=>'http://support.mycompany.com/');

This way your old servers will exist under /sales/ and /support/ of your new server. Now you can start adding virtuoso .vsp pages to your new Virtuoso server and they operate interleaved with your existing pages to add new life and functionality as required.

You may decide that you want to install Virtuoso onto a server where a web server already exists. If you plan to use Virtuoso as your default web server and the proxy to your existing server then you will need to make sure that the servers run on different ports. The default port is 80, you will have to configure Virtuoso to use this port from the virtuoso.ini file and then move your existing web server port to another number. Afterwards the procedure is similar:

DB.DBA.VHOST_DEFINE(lpath=>'/apache', ppath=>'http://example.com:90/');

¶

Proxying Virtuoso via Apache

You may also achieve the same goal as above but in reverse, using another web server as a proxy in front of Virtuoso. If you have an existing Apache server that you want to keep as you default web server then you can set up a proxy within Apache to Virtuoso.

Firstly you will need to make sure that Apache can make use of the mod_proxy module available from most Apache distribution sites. You then have to make sure that it is referenced in your httpd.conf (or apache.conf) file. You should have something like:

...
LoadModule proxy_module       modules/libproxy.so
...
AddModule mod_proxy.c
...

¶

Configuration steps

Below we will use the <Location> directive to simplify the configuration:

<Location /virtuoso/>
   ProxyPass               http://example.com:8890/
   ProxyPassReverse        /
</Location>

1. Set the ProxyPass directive:

   The ProxyPass directive makes Apache to change all incoming URLs and map it to the internal http endpoint.

   So when the browser makes a request for:

   http://example.com/virtuoso/conductor/login.vsp
   

   it is rewritten to use:

   http://example.com:8890/conductor/login.vsp
   

   before sending the request over to the Virtuoso server.

2. Set the ProxyPassReverse directive:

   The ProxyPassReverse directive rewrites the HTTP Headers that come back from Virtuoso to map back to the external URL. This is needed for e.g. 303 Location redirects where Virtuoso will use:

   Location: http://example.com:8890/conductor/pageXXX.vsp
   

   which Apache needs to rewrite to:

   Location: http://example.com/virtuoso/conductor/pageXXX.vsp
   

   before sending the reply back to the browser.

3. If the mapping is / ---> / instead of /virtuoso/ ---> / then the settings should be done, since ProxyPass and ProxyPassReverse only deal with rewriting urls and http headers.

   When however there is a path mapping, there is a third step to take:

   Pages can contain clickable links like:

   <a href="/conductor/mypage.vsp">Click Here</a>
   

   If you click on this link in your browser, it would use:

   http://example.com/conductor/mypage.vsp
   

   which does not map back to your /virtuoso/ vpath in apache.

   As phpBB3 has been written from outset to cater for this situation, it will always need to recalculate fully qualified host/path names everywhere in its pages, which is not always very practical.

   Thus Apache needs to be configured to do page rewriting as well as in:

        ProxyHTMLEnable         On
        ProxyHTMLURLMap         / /virtuoso/
        ProxyHTMLURLMap         http://example.com:8890/ /virtuoso/
   

   This will rewrite the content of every page to make sure that links inside the page are rewritten to use the external mapping of this instance.

   If you have set Virtuoso to use EnabledGzipContent=1 , then you need to tell apache it may need to gunzip the content before doing this rewrite with the following line:

        SetOutputFilter         INFLATE;DEFLATE
   

   Although this takes a bit extra CPU power etc, it is still practical to setup a virtual path on user's own system that points to some external system.

   For example, add this to your httpd.conf to get a mapping to dbpedia-live instance:

   <Location /dbp/>
        ProxyPass               http://dbpedia-live.openlinksw.com/
        ProxyPassReverse        /
        ProxyHTMLURLMap         / /dbp/
        ProxyHTMLURLMap         http://dbpedia-live.openlinksw.com/ /dbp/
        SetOutputFilter         INFLATE;DEFLATE
   </Location>
   

   Now you should be able to use for ex.:

   http://example.com/dbp/page/London
   

¶

Usage Example

NameVirtualHost 82.191.21.32

<VirtualHost 82.191.21.32>
ServerName www.mysite.net <http://www.mysite.net>
...

     #  Disable global proxy
     ProxyRequests       Off

     #  Pass original host to Virtuoso
     ProxyPreserveHost   On

     #  Timeout waiting for Virtuoso
     ProxyTimeout        300

     #  Set permission
     <Proxy *>
         Order deny,allow
         Allow from all
     </Proxy>

     #
     #  Map /virtuoso/ to a local Virtuoso instance.
     #
     #  Since ProxyPass and ProxyPassReverse only fix the Headers
     #  of the request, we need to use ProxyHTMLURLMap to rewrite
     #  content.
     #
     <Location /virtuoso/>
         ProxyPass               http://example.com:8890/
         ProxyPassReverse        /

         #  Enable rewrite rules
         ProxyHTMLEnable         On
         ProxyHTMLURLMap         / /virtuoso/
         ProxyHTMLURLMap         http://example.com:8890/ /virtuoso/

# Uncomment this when EnabledGzipContent=1 in virtuoso.ini
         #SetOutputFilter         INFLATE;DEFLATE
     </Location>
</VirtualHost>

If we map the virtual host straight through to Virtuoso, we only need header rewriting and save the time/cpu power to rewrite the content:

     #
     #  Map / to a local Virtuoso instance
     #
     #  Since paths are mapped straight through, we do not have to
     #  rewrite the content.
     #
     <Location />
         ProxyPass               http://example.com:8890/
         ProxyPassReverse        /
     </Location>

	See Also:
	Apache Online Documentation

If a Virtuoso/PL procedure is specified to perform authentication for this mapping then it will be executed. The procedure can take one (varchar) parameter, the 'Realm' value. The result from the procedure must be 1 if authentication successful otherwise must be zero (0). If the procedure returns 0 this causes the processing to terminate and whatever output the hook generated to be sent to the client. Typically this will be an authentication challenge.

The Virtuoso HTTP session management consists of functions for session variables manipulation and an ability to define a pre- and post-processing function. The pre and post-processing functions are used to save and restore session data between HTTP posts, usually to and from a session table.

Session management must be enable by settings the flag for persistent session variables in virtual directory mapping. Virtual directory mappings use the persistent_session_variables flag, which when specified, session variables can be used in a post-process function to determine if the session variables content must be stored on to the session table or not.

The post-processing function hook can be any user-defined Virtuoso/PL procedure, it will be executed every time after processing of the active page.

	See Also:
	VSP Session Management and Session Variables

We will explain the following precompiled procedures in Virtuoso used to authenticate three branches of users.

-- Authenticate against names and passwords in SYS_USERS, using HP_SECURITY for level

create procedure
DB.DBA.HP_AUTH_SQL_USER (in realm varchar)
{
  declare _u_name, _u_password varchar;
  declare _u_group, _u_id, allow_basic integer;

  declare auth, sec, lev varchar;
  declare _user varchar;
  declare ses_dta, lines any;

  lines := http_request_header ();         -- got a request header lines
  sec := http_map_get ('security_level');  -- got a security level from http mapping
  if (isstring (sec))
    sec := ucase (sec);
  if (sec = 'DIGEST')
    allow_basic := 0;	-- if security is only digest then allow basic is false
  else
    allow_basic := 1;

  auth :=
    DB.DBA.vsp_auth_vec (lines);	-- parse request header to got authentication credentials
  if (0 <> auth)			-- and if client sent any authentication information try it
    {

     lev := get_keyword ('authtype', auth, '');	-- check if client tried basic but
						-- domain restricted to digest only
     if (allow_basic = 0 and 'basic' = lev)
	goto nf;
      _user := get_keyword ('username', auth, '');

      if ('' = _user) -- if no user name then 'bye'
	return 0;

      whenever not found goto nf;  -- if no such user in table - 'bye'

      -- got the password from users table

      select U_NAME, PWD_MAGIC_CALC (U_NAME, U_PASSWORD, 1), U_GROUP, U_ID
	into _u_name, _u_password, _u_group, _u_id from DB.DBA.SYS_USERS
	where u_name = _user;

      -- check credential against user name and password

      if (0 = _u_group and 1 = DB.DBA.vsp_auth_verify_pass (auth, _u_name,
					       get_keyword ('realm', auth, ''),
					       get_keyword ('uri', auth, ''),
					       get_keyword ('nonce', auth, ''),
					       get_keyword ('nc', auth, ''),
					       get_keyword ('cnonce', auth, ''),
					       get_keyword ('qop', auth, ''),
					       _u_password))
	{
	  if (http_map_get ('persist_ses_vars'))
	    {			-- if all is ok check for persistent variables storage
	      declare vars any;
	      declare sid varchar;
            vars := null;
            sid := http_param ('sid');
	        -- got from session table stored variables
            vars := coalesce ((select deserialize (ASES_VARS)
              from DB.DBA.ADMIN_SESSION where ASES_ID = sid), null);
            if (sid is not null and vars is null or isarray (vars))
		connection_vars_set (vars);
	      if (sid is not null and connection_get ('sid') is null)
		{
		  connection_set ('sid', sid);
		}
	    }
	  return 1; -- return authenticated
	}
    }
 nf: 	-- all errors go there, we compose authentication header
	-- and send 401 unauthorized to the client
  DB.DBA.vsp_auth_get (realm, http_path (),
		md5 (datestring (now ())),
		md5 ('eEsSlLAaf'),
		'false', lines, allow_basic);
  return 0; -- return not authenticated
}
;

-- Authenticate against SYS_DAV_USER, using HP_SECURITY for level,
-- in the context of DAV administration pages accessed through regular HTTP
-- The logic is the same but in difference of password retrieval.

create procedure
DB.DBA.HP_AUTH_DAV_ADMIN (in realm varchar)
{
  declare _u_name, _u_pwd varchar;
  declare _u_group, _u_id, allow_basic integer;

  declare auth, sec, lev varchar;
  declare _user varchar;
  declare ses_dta, lines any;

  lines := http_request_header ();
  sec := http_map_get ('security_level');
  if (isstring (sec))
    sec := ucase (sec);
  if (sec = 'DIGEST')
    allow_basic := 0;
  else
    allow_basic := 1;
  auth := DB.DBA.vsp_auth_vec (lines);

  if (0 <> auth)
    {

      lev := get_keyword ('authtype', auth, '');
      if (allow_basic = 0 and 'basic' = lev)
	goto nf;
      _user := get_keyword ('username', auth, '');

      if ('' = _user)
	return 0;

      whenever not found goto nf;

      -- we tried to find out password for enabled valid WebDAV user
      select U_NAME, U_PWD, U_GROUP, U_ID
	into _u_name, _u_pwd, _u_group, _u_id from WS.WS.SYS_DAV_USER
	where u_name = _user and U_ACCOUNT_DISABLED = 0;

      if (DB.DBA.vsp_auth_verify_pass (auth, _u_name,
				get_keyword ('realm', auth, ''),
				get_keyword ('uri', auth, ''),
				get_keyword ('nonce', auth, ''),
				get_keyword ('nc', auth, ''),
				get_keyword ('cnonce', auth, ''),
				get_keyword ('qop', auth, ''),
				_u_pwd))
	{
	  if (http_map_get ('persist_ses_vars'))
	    {
	      declare vars any;
	      declare sid varchar;
            vars := null;
            sid := http_param ('sid');
            vars := coalesce ((select deserialize (ASES_VARS)
              from DB.DBA.ADMIN_SESSION where ASES_ID = sid), null);
            if (vars is null or isarray (vars))
		  connection_vars_set (vars);
	      if (connection_get ('sid') is null)
		{
		  connection_set ('sid', sid);
		}
	    }
	  return (_u_id);
	}
    }
 nf:
  DB.DBA.vsp_auth_get (realm, '/admin/admin_dav',
		md5 (datestring (now ())),
		md5 ('vVAadAnIimMDdaNnimda'),
		'false', lines, allow_basic);
  return 0;
}
;

-- The same as for DAV admin pages but in the context of DAV protocol requests.
create procedure
DB.DBA.HP_AUTH_DAV_PROTOCOL (in realm varchar)
{
  declare _u_name, _u_password, _perms varchar;
  declare _u_id, _u_group, req_user, req_group, what integer;
  declare auth varchar;
  declare _user varchar;
  declare our_auth_vec, lines, sec, path, req_perms, req_meth, cmp_perms, def_page varchar;
  declare _method, lev, allow_basic, authenticated integer;

  declare c cursor for select 1, COL_OWNER, COL_GROUP, COL_PERMS
      from WS.WS.SYS_DAV_COL where WS.WS.COL_PATH (COL_ID) = path;
  declare r cursor for select 2, RES_OWNER, RES_GROUP, RES_PERMS
      from WS.WS.SYS_DAV_RES where RES_FULL_PATH = path;

  authenticated := 0;

  lines := http_request_header ();
  path := http_physical_path ();

  if (isarray (lines))
    {
      req_meth := aref (lines, 0);
      if (strchr (req_meth, ' ') is not null)
        req_meth := lower (substring (req_meth, 1, strchr (req_meth, ' ')));
    }

  -- there we compose mask for permissions compared against
  -- resource or collection permission
  if (req_meth = 'get' or
      req_meth = 'post' or
      req_meth = 'options' or
      req_meth = 'propfind' or
      req_meth = 'head' or
      req_meth = 'trace' or
      req_meth = 'copy')
    cmp_perms := '1__'; -- in this case only read access needed
  else if (req_meth = 'mkcol' or req_meth = 'put')
    {
      if (length (path) > 1
          and strrchr (substring (path, 1, length(path) - 1), '/') is not null)
        path := substring (path, 1,
	  strrchr (substring (path, 1, length(path) - 1), '/') + 1);
      cmp_perms := '11_';
    }
  else
    cmp_perms := '11_'; -- but in this we needs a read/write access

  what := 0;
  whenever not found goto fr;
  open c (prefetch 1);
  fetch c into what, req_user, req_group, req_perms;
		-- get from collections owner , owner group and permissions

  def_page := http_map_get ('default_page');
  if (isstring (def_page))
    {
      path := concat (path, def_page);
      what := 0;
    }
fr:
  close c;

  if (not what)
    {
      whenever not found goto fe;
      open r (prefetch 1);
      fetch r into what, req_user, req_group, req_perms; -- if not a collection try a resource
fe:
      close r;
    }

  sec := http_map_get ('security_level'); -- see DB user authentication
  if (isstring (sec))
    sec := ucase (sec);
  if (sec = 'DIGEST')
    allow_basic := 0;
  else
    allow_basic := 1;

  auth := DB.DBA.vsp_auth_vec (lines);

  if (0 <> auth)
    {
      lev := get_keyword ('authtype', auth, '');
      if (allow_basic = 0 and 'basic' = lev)
	goto nf;

      _user := get_keyword ('username', auth);

      if (_user = '' or isnull (_user))
	{
	  goto nf;
	}

      whenever not found goto nf;

      select U_NAME, U_PWD, U_GROUP, U_ID, U_METHODS, U_DEF_PERMS
	into _u_name, _u_password, _u_group, _u_id, _method, _perms from WS.WS.SYS_DAV_USER
	where U_NAME = _user and U_ACCOUNT_DISABLED = 0;
      if (_u_password is null)
	goto nf;
      if (DB.DBA.vsp_auth_verify_pass (auth, _u_name,
				coalesce(get_keyword ('realm', auth), ''),
				coalesce(get_keyword ('uri', auth), ''),
				coalesce(get_keyword ('nonce', auth), ''),
				coalesce(get_keyword ('nc', auth),''),
				coalesce(get_keyword ('cnonce', auth), ''),
				coalesce(get_keyword ('qop', auth), ''),
				_u_password))
	{
	  update WS.WS.SYS_DAV_USER set U_LOGIN_TIME = now () where U_NAME = _user;
	  if (http_map_get ('persist_ses_vars'))
	  {
	    declare vars any;
	    declare sid varchar;
	    vars := null;
	    sid := http_param ('sid');
	    vars := coalesce ((select deserialize (ASES_VARS)
            from DB.DBA.ADMIN_SESSION where ASES_ID = sid), null);
          if (vars is null or isarray (vars))
		connection_vars_set (vars);
	    if (connection_get ('sid') is null)
	    {
		connection_set ('sid', sid);
	    }
	  }
	  if (connection_get ('DAVUserID') <> _u_id)
	    connection_set ('DAVUserID', _u_id);
          authenticated := 1;
	}
    }

-- Check permissions
  if (authenticated and _u_id = 1) -- If user is DAV admin all rights granted
    return 1;
  else if (not authenticated and req_perms like concat ('______', cmp_perms, '%'))
    return -1; 	-- if not authenticated and resource
			-- does have public access return authenticated
  else if (authenticated and
          ((_u_id = req_user and req_perms like concat (cmp_perms, '%')) or
	   (req_group = _u_group and req_perms like concat ('___', cmp_perms, '%')) or
	   (req_perms like concat ('______', cmp_perms, '%'))))
    return (_u_id); 	-- if user is owner or belongs to group
				-- ownership return authenticated
  else if (authenticated) 	-- if authenticated but does not access
					-- return false but set 403 forbidden
    {
      http_request_status ('HTTP/1.1 403 Forbidden');
      http ( concat ('<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">',
             '<HTML><HEAD>',
             '<TITLE>403 Forbidden</TITLE>',
             '</HEAD><BODY><H1>Forbidden</H1>',
             'Access to the resource is forbidden.</BODY></HTML>'));
      return 0;
    }
-- End check permissions

nf: 	-- all error cases go there, we send authentication credentials
	-- and turn status 401 Unauthorized, and return false
  DB.DBA.vsp_auth_get (realm, '/DAV',
      md5 (datestring(now())),
      md5 ('opaakki'),
      'false', lines, allow_basic);
  return 0;
}
;

-- Post-processing function, this will executed after processing
-- the request but before sending result to the client.
create procedure
DB.DBA.HP_SES_VARS_STORE ()
{
  declare vars any;
  declare sid varchar;
  if (http_map_get ('persist_ses_vars') and connection_is_dirty ())
    -- if connection variables changed in request and persistent variables stored
    {
      vars := connection_vars (); -- get all variables
      connection_vars_set (null); -- set immediately to empty vector (prevent changing)
      sid := get_keyword ('sid', vars, null); -- got the session ID
      -- store the variables in session table
      if (sid is not null)
	update DB.DBA.ADMIN_SESSION set ASES_VARS = serialize (vars) where ASES_ID = sid;
    }
}
;

These functions are implemented as part of Virtuoso server by default. The user can freely define their own procedures based on this logic to use for special authentication (different users information table etc.) and session management.

If there are many long-running tasks processing on Virtuoso it is possible to have denial of service. To prevent this we can use status and stop functions. We can retrieve the URL, client IP-address, and process status code for all currently running VSP requests, then use this information to isolated and eliminate a process.

http_pending_req()

	See Also:
	Long HTTP Transactions

The Virtuoso WebRobot (WebCopy) is useful for retrieving Internet web sites and storing them on to a local WebDAV repository. Once retrieved, the local copy in the WebDAV repository can be exported to the local filesystem or another WebDAV enabled server. The common features and usages are demonstrated in the WebCopy User Interface in the Visual Server Administration Interface. This document provides the actual API's and techniques useful for some other implementations.

¶

Creating A New Target

A new web server target is created by inserting a row in to the WS.WS.VFS_SITE table and then a row in to the WS.WS.VFS_QUEUE table.

	See Also:
	Web Robot System Tables for table definitions

Example 14.2. Creating a new target

This example creates a new target pointing to the site http://www.foo.com/help/, with instructions to walk across foreign links, delete a local page if it is detected that it has been removed from the remote, retrieve images, walk on entire site using HTTP GET method. The content will be stored in /DAV/sites/www_foo_com collection in the local WebDAV repository.

1. Create target for http://www.foo.com/help/

   insert into WS.WS.VFS_SITE
       (VS_DESCR,VS_HOST,VS_URL,VS_OWN,VS_ROOT,VS_NEWER,VS_DEL,
         VS_FOLLOW,VS_NFOLLOW,VS_SRC,VS_OPTIONS,VS_METHOD,VS_OTHER)
     values
       ('My first test', 'www.foo.com', '/help/', 1, 'sites/www_foo_com', '1990-01-01',
         'checked', '/%;', '', 'checked', null, null, 'checked');
   

2. Create start queue entry

   insert into WS.WS.VFS_QUEUE
       (VQ_HOST,VQ_TS,VQ_URL,VQ_ROOT,VQ_STAT,VQ_OTHER)
     values ('www.foo.com', now(), '/help/', 'sites/www_foo_com', 'waiting', null);
   

¶

Creating A Custom Queue Hook

The custom queue hook can be used to extract the next entry from the robot's queue following a custom algorithm. The following example extracts the oldest entry comparing to the my_data array (this array consists of non-desirable sites) and returns if some are found.

Example 14.3. Creating A Custom Robot Queue Hook

create procedure
  DB.DBA.my_hook (
    in host varchar, in collection varchar, out url varchar, in my_data any
  )
{
  declare next_url varchar;
  whenever not found goto done;

  -- we trying to extract the oldest entry
  declare cr cursor for select VQ_URL from WS.WS.VFS_QUEUE
      where VQ_HOST = host and VQ_ROOT = collection and VQ_STAT = 'waiting'
      order by VQ_HOST, VQ_ROOT, VQ_TS for update;

  open cr;
  while (1)
  {
    fetch cr into next_url;
    if (get_keyword (host, my_data, null) is not null) -- process if host not in black-list
    {
      update WS.WS.VFS_QUEUE set VQ_STAT = 'pending'
	  where VQ_HOST = host and VQ_ROOT = collection and VQ_URL = next_url;
      url := next_url;
      close cr;
      return 1;
    }
    else -- otherwise continue finding
	update WS.WS.VFS_QUEUE set VQ_STAT = 'retrieved'
	  where VQ_HOST = host and VQ_ROOT = collection and VQ_URL = next_url;
    }
done:
  -- if we arrive at the bottom of the queue return false to stop processing
  close cr;
  return 0;
}
;

	Note:
	The default function will return the oldest entry from queue without any restriction. The follow/not-follow restrictions are applied to the path on target before inserting a new queue entry.

¶

Exporting Local Content To Filesystem Or Other Webdav Enabled Server

lfs_exp

dav_exp

	See Also
	Web Robot System tables

The Virtuoso shared object library enables you to create your own custom extensions to the Virtuoso HTTP server and create custom VSEs. Support for PHP page execution was implemented using this functionality. Virtuoso can automatically switch processing mode from VSP to PHP or some other custom extension based on the extension of the files being requested from the HTTP server. To enable Virtuoso to process files of a different extension you have to write a VSE handler where part of the name contains the extension: __http_handler_[extension] . The VSEs for HTTP handling must have the following parameters:

	See Also:
	Virtuoso Server Extensions Interface

Virtuoso supports HTTP 1.1 Chunking Encoding which allows Virtuoso to send the user agent chunks of output as the page is still processing. Chunking is enabled by calling http_flush(1) within the VSP page. Chunks are sent for every 4k worth of output generated. Chunked mode requires the following conditions:

Failing these conditions, http_flush(1) will be a No-Operation.

Chunked mode is not supported for static content.

	See Also:
	http_flush() RFC-2616

In some situations Virtuoso services like WebDAV, JSP, PHP etc. may need to be accessed via an Apache Web Server. All this can be done through apache's mod_proxy to Virtuoso HTTP server and the Virtuoso HTTP server can be configured to take requests coming only from localhost.

The following configuration makes : The Virtuoso server to listen for HTTP requests coming ONLY from localhost. Apache proxies the outside requests to Virtuoso HTTP server.

	line added to the /etc/httpd/conf/httpd.conf
	(999.999.999.999, must be changed with actual IP address of external interface):
	----------------------------------
	Listen 8080
	<VirtualHost 999.999.999.999:8080 127.0.0.1:8080>
	       ServerAdmin webmaster@host.example.domain
	       ProxyPass  / http://example.com/
	</VirtualHost>
	----------------------------------
	

	Then changes in the virtuoso.ini

	[HTTPServer] section)
        ...
	ServerPort = 127.0.0.1:6666
	...
	

The Setting up of the Virtuoso HTTPS Listener can be done by using the file system or using the Virtuoso conductor.

Note that when you want to change from Virtuoso hosted Cert and Public Key to File System and vice versa, first should be stopped the listener for either setup.