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iPlanet Web Server, FastTrack Edition Programmer's Guide |
Chapter 3 Server-Parsed HTML Tags
HTML files can contain tags that are executed on the server. In addition to supporting the standard server-side tags, iPlanet Web Server 4.1 allows you to embed servlets and define your own server-side tags.This chapter has the following sections:
Using Server-Side HTML Commands
When you activate parsing, you need to be sure that the following directives are added to your obj.conf file (note that native threads are turned off):Defining Customized Server-Parsed HTML Tags
Init funcs="shtml_init,shtml_send" shlib="install_dir/bin/https/bin/Shtml.dll" NativeThread="no" fn="load-modules" Note that you must set NativeThread="no" for 4.1 iPlanet Web Servers. In addition, these functions now originate from Shtml.dll (or libShtml.so on Unix), which is located in install_dir/bin/https/bin for Windows NT (and install_dir/bin/https/lib for Unix).
Using Server-Side HTML Commands
This section describes the HTML commands for including server-parsed tags in HTML files. These commands are embedded into HTML files, which are processed by the built-in SAF parse-html.The server replaces each command with data determined by the command and its attributes.
<!--#command attribute1 attribute2 <Body>... -->
The format for each attribute is a name-value pair such as:
Commands and attribute names should be in lower case.
The commands are "hidden" within HTML comments so they are ignored if not parsed by the server. The standard server-side commands are:
config
The config command initializes the format for other commands.
The errmsg attribute defines a message sent to the client when an error occurs while parsing the file. This error is also logged in the error log file.
Example:The timefmt attribute determines the format of the date for the flastmod command. It uses the same format characters as the util_strftime function. The default time format is: "%A, %d-%b-%y %T".
The sizefmt attribute determines the format of the file size for the fsize command. It can have one of these values:
- Refer to the Time Formats appendix in the NSAPI Programmer's Guide for iPlanet Web Server for details about time formats.
<!--#config timefmt="%r %a %b %e, %Y" sizefmt="abbrev"-->
This sets the date format to a value such as 08:23:15 AM Wed Apr 15, 1996, and the file size format to the number of KB or MB of characters used by the file.
include
The include command inserts a file into the parsed file. You can nest files by including another parsed file, which then includes another file, and so on. The client requesting the parsed document must also have access to the included file if your server uses access control for the directories where they reside.In iPlanet Web Server 4.1, you can use the include command with the virtual attribute to include a CGI program file. You must also use an exec command to execute the CGI program.
The virtual attribute is the URI of a file on the server.
Example:The file attribute is a relative path name from the current directory. It cannot contain elements such as ../ and it cannot be an absolute path.
<!--#include file="bottle.gif"-->
echo
The echo command inserts the value of an environment variable. The var attribute specifies the environment variable to insert. If the variable is not found, "(none)" is inserted. For a list of environment variables, see the section "Environment Variables in Server-Side HTML Commands."
fsize
The fsize command sends the size of a file. The attributes are the same as those for the include command (virtual and file). The file size format is determined by the sizefmt attribute in the config command.<!--#fsize file="bottle.gif"-->
flastmod
The flastmod command prints the date a file was last modified. The attributes are the same as those for the include command (virtual and file). The date format is determined by the timefmt attribute in the config command.<!--#flastmod file="bottle.gif"-->
exec
The exec command runs a shell command or CGI program.
The cmd attribute (Unix only) runs a command using /bin/sh. You may include any special environment variables in the command.
Example:The cgi attribute runs a CGI program and includes its output in the parsed file.
Environment Variables in Server-Side HTML Commands
In addition to the normal set of environment variables used in CGI, you may include the following variables in your parsed commands:
DOCUMENT_NAME
DOCUMENT_URI
- is the file name of the parsed file.
QUERY_STRING_UNESCAPED
- is the virtual path to the parsed file (for example, /shtml/test.shtml).
DATE_LOCAL
- is the unescaped version of any search query the client sent with all shell-special characters escaped with the \ character.
DATE_GMT
- is the current date and local time.
LAST_MODIFIED
- is the current date and time expressed in Greenwich Mean Time.
- is the date the file was last modified.
Embedding Servlets
iPlanet Web Server 4.1 supports the <SERVLET> tag as defined by Java Web Server. This tag allows you to embed servlet output in an HTML file. No configuration changes are necessary to enable this behavior. If SSI and servlets are both enabled, the server recognizes the <SERVLET> tag.The <SERVLET> tag syntax is slightly different from that of other SSI commands; it resembles the <APPLET> tag syntax:
<servlet name=name code=classfile codebase=path iParam1=v1 iParam2=v2>
<param name=param1 value=v3>
<param name=param2 value=v4>
.
.
</servlet>The code parameter, which specifies the .class file for the servlet, is always required. The .class extension is optional. The codebase parameter is required if the servlet is not defined in the servlets.properties file and the .class file is not in the same directory as the HTML file containing the <SERVLET> tag. The name parameter is required if the servlet is defined in the servlets.properties file, and must match the servlet name defined in that file.
For more information about creating servlets, see the Programmer's Guide to Servlets in iPlanet Web Server.
Defining Customized Server-Parsed HTML Tags
The parsing of server-side tags in .shtml files in iPlanet Web Server 4.1 has been substantially improved over previous releases of iPlanet Web Server. First, the performance of handling server-side tags has been significantly sped up. Secondly, users can now define their own server-side tags.For example, you could define the tag <PRICE> to invokes a function that calculates and displays the price of a product. Then in your .shtml file you could have code such as:
<H2>Product Prices</H2>
<UL>
<LI>Oak Table: <PRICE product="oaktable">
<LI>Pine Bench: <PRICE product="pinebench">
<LI>Patio Chair: <PRICE product="patiochair">
</UL>When the browser displays this code, each occurrence of the <PRICE> tag calls the function that is associated with that tag, and returns the price of the relevant product. The result in the browser might look like this:
The Mechanics
The steps for defining a customized server-parsed tag are:
Define the Functions that Implement the Tag.
Write an Initialization Function to Register the New Tag.
- You must define the tag execution function, and you can optionally also define other functions that are called on tag loading and unloading and on page loading and unloading.
Load the New Tag into the Server.
- Write an initialization function that registers the tag using the shtml_add_tag function.
Define the Functions that Implement the Tag
Define the functions that implement the tags in C, using NSAPI.
Include the header shtml_public.h, which is in the directory install_dir/plugins/include/shtml.
ShtmlTagExecuteFunc is the actual tag handler. It gets called with the usual NSAPI pblock, Session, and Request variables. In addition, it also gets passed the TagUserData created from the result of executing the tag loading and page loading functions (if defined) for that tag.Link against the shtml shared library. On Windows NT, shtml.dll is in install_dir/bin/https/bin. On Unix platforms, libshtml.so or .sl is in install_dir/bin/https/lib.
The signature for the tag execution function is:
typedef int (*ShtmlTagExecuteFunc)(pblock*, Session*, Request*, TagUserData, TagUserData);
Write the body of the tag execution function to generate the output to replace the tag in the .shtml page. Do this in the usual NSAPI way, using the net_write NSAPI function, which writes a specified number of bytes to a specified socket from a specified buffer.
For more information about writing NSAPI plugins, see Chapter 4, "Creating Custom SAFs," in the NSAPI Programmer's Guide for iPlanet Web Server.
For more information about net_write and other NSAPI functions, see Chapter 5, "NSAPI Function Reference," of the NSAPI Programmer's Guide for iPlanet Web Server.
The tag execution function must return an int that indicates whether the server should proceed to the next instruction in obj.conf or not, which is one of:
REQ_PROCEED -- the execution was successful.
The other functions you can define for your tag are:REQ_NOACTION -- nothing happened.
ShtmlTagInstanceLoad
The signatures for these functions are:
ShtmlTagInstanceUnload
- This is called when a page containing the tag is parsed. It is not called if the page is retrieved from the browser's cache. It basically serves as a constructor, the result of which is cached and is passed into ShtmlTagExecuteFunc whenever the execution function is called.
ShtmlTagPageLoadFunc
- This is basically a destructor for cleaning up whatever was created in the ShtmlTagInstanceLoad function. It gets passed the result that was originally returned from the ShtmlTagInstanceLoad function.
ShtmlTagPageUnLoadFn
- This is called when a page containing the tag is executed, regardless of whether the page is still in the browser's cache or not. This provides a way to make information persistent between occurrences of the same tag on the same page.
- This is called after a page containing the tag has executed. It provides a way to clean up any allocations done in a ShtmlTagPageLoadFunc and hence gets passed the result returned from the ShtmlTagPageLoadFunc.
Write an Initialization Function to Register the New Tag
In the initialization function for the shared library that defines the new tag, register the tag using the function shtml_add_tag. The signature is:
Any of these arguments can be NULL except for the tag and execFn.
Load the New Tag into the Server
After creating the shared library that defines the new tag, you load the library into the iPlanet Web Server in the usual way for NSAPI plugins. That is, add the following directives to the configuration file obj.conf:
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Last Updated July 13, 2000