Apache Tomcat 9 (9.0.102) - SSI How To
Author: Glenn L. Nielsen

## SSI How To

### Table of Contents

- Introduction
- Installation
- Servlet Configuration
- Filter Configuration
- Directives
- Variables

### Introduction

SSI (Server Side Includes) are directives that are placed in HTML pages, and evaluated on the server while the pages are being served. They let you add dynamically generated content to an existing HTML page, without having to serve the entire page via a CGI program, or other dynamic technology.

Within Tomcat SSI support can be added when using Tomcat as your HTTP server and you require SSI support. Typically this is done during development when you don't want to run a web server like Apache.

Tomcat SSI support implements the same SSI directives as Apache. See the Apache Introduction to SSI for information on using SSI directives.

SSI support is available as a servlet and as a filter. You should use one or the other to provide SSI support but not both.

Servlet based SSI support is implemented using the class `org.apache.catalina.ssi.SSIServlet`. Traditionally, this servlet is mapped to the URL pattern "*.shtml".

Filter based SSI support is implemented using the class `org.apache.catalina.ssi.SSIFilter`. Traditionally, this filter is mapped to the URL pattern "*.shtml", though it can be mapped to "*" as it will selectively enable/disable SSI processing based on mime types. The contentType init param allows you to apply SSI processing to JSP pages, JavaScript, or any other content you wish.

By default SSI support is disabled in Tomcat.

### Installation

CAUTION - SSI directives can be used to execute programs external to the Tomcat JVM. If you are using the Java SecurityManager this will bypass your security policy configuration in `catalina.policy.`

To use the SSI servlet, remove the XML comments from around the SSI servlet and servlet-mapping configuration in `$CATALINA_BASE/conf/web.xml`.

To use the SSI filter, remove the XML comments from around the SSI filter and filter-mapping configuration in `$CATALINA_BASE/conf/web.xml`.

Only Contexts which are marked as privileged may use SSI features (see the privileged property of the Context element).

### Servlet Configuration

There are several servlet init parameters which can be used to configure the behaviour of the SSI servlet.

- buffered - Should output from this servlet be buffered? (0=false, 1=true) Default 0 (false).
- debug - Debugging detail level for messages logged by this servlet. Default 0.
- expires - The number of seconds before a page with SSI directives will expire. Default behaviour is for all SSI directives to be evaluated for every request.
- isVirtualWebappRelative - Should "virtual" SSI directive paths be interpreted as relative to the context root, instead of the server root? Default false.
- inputEncoding - The encoding to be assumed for SSI resources if one cannot be determined from the resource itself. Default is the default platform encoding.
- outputEncoding - The encoding to be used for the result of the SSI processing. Default is UTF-8.
- allowExec - Is the exec command enabled? Default is false.

### Filter Configuration

There are several filter init parameters which can be used to configure the behaviour of the SSI filter.

- contentType - A regex pattern that must be matched before SSI processing is applied. When crafting your own pattern, don't forget that a mime content type may be followed by an optional character set in the form "mime/type; charset=set" that you must take into account. Default is "text/x-server-parsed-html(;.*)?".
- debug - Debugging detail level for messages logged by this servlet. Default 0.
- expires - The number of seconds before a page with SSI directives will expire. Default behaviour is for all SSI directives to be evaluated for every request.
- isVirtualWebappRelative - Should "virtual" SSI directive paths be interpreted as relative to the context root, instead of the server root? Default false.
- allowExec - Is the exec command enabled? Default is false.

### Directives

Server Side Includes are invoked by embedding SSI directives in an HTML document whose type will be processed by the SSI servlet. The directives take the form of an HTML comment. The directive is replaced by the results of interpreting it before sending the page to the client. The general form of a directive is:

`<!--#directive [param=value] -->`

The directives are:

- config - `<!--#config errmsg="Error occurred" sizefmt="abbrev" timefmt="%B %Y" -->` Used to set SSI error message, the format of dates and file sizes processed by SSI.
  All are optional but at least one must be used. The available options are as follows:
  errmsg - error message used for SSI errors
  sizefmt - format used for sizes in the fsize directive
  timefmt - format used for timestamps in the flastmod directive
- echo - `<!--#echo var="VARIABLE_NAME" encoding="entity" -->` will be replaced by the value of the variable.
  The optional encoding parameter specifies the type of encoding to use. Valid values are entity (default), url or none. NOTE: Using an encoding other than entity can lead to security issues.
- exec - `<!--#exec cmd="file-name" -->` Used to run commands on the host system.
- exec - `<!--#exec cgi="file-name" -->` This acts the same as the include virtual directive, and doesn't actually execute any commands.
- include - `<!--#include file="file-name" -->` inserts the contents. The path is interpreted relative to the document where this directive is being used, and IS NOT a "virtual" path relative to either the context root or the server root.
- include - `<!--#include virtual="file-name" -->` inserts the contents. The path is interpreted as a "virtual" path which is relative to either the context root or the server root (depending on the isVirtualWebappRelative parameter).
- flastmod - `<!--#flastmod file="filename.shtml" -->` Returns the time that a file was last modified. The path is interpreted relative to the document where this directive is being used, and IS NOT a "virtual" path relative to either the context root or the server root.
- flastmod - `<!--#flastmod virtual="filename.shtml" -->` Returns the time that a file was last modified. The path is interpreted as a "virtual" path which is relative to either the context root or the server root (depending on the isVirtualWebappRelative parameter).
- fsize - `<!--#fsize file="filename.shtml" -->` Returns the size of a file. The path is interpreted relative to the document where this directive is being used, and IS NOT a "virtual" path relative to either the context root or the server root.
- fsize - `<!--#fsize virtual="filename.shtml" -->` Returns the size of a file. The path is interpreted as a "virtual" path which is relative to either the context root or the server root (depending on the isVirtualWebappRelative parameter).
- printenv - `<!--#printenv -->` Returns the list of all the defined variables.
- set - `<!--#set var="foo" value="Bar" -->` is used to assign a value to a user-defined variable.
- if elif endif else - Used to create conditional sections. For example:

      <!--#config timefmt="%A" -->
      <!--#if expr="$DATE_LOCAL = /Monday/" -->
      <p>Meeting at 10:00 on Mondays</p>
      <!--#elif expr="$DATE_LOCAL = /Friday/" -->
      <p>Turn in your time card</p>
      <!--#else -->
      <p>Yoga class at noon.</p>
      <!--#endif -->

See the Apache Introduction to SSI for more information on using SSI directives.

### Variables

SSI variables are implemented via request attributes on the javax.servlet.ServletRequest object and are not limited to the SSI servlet. Variables starting with the names "java.", "javax.", "sun" or "org.apache.catalina.ssi.SSIMediator." are reserved and cannot be used.

The SSI servlet currently implements the following variables:

Variable Name | Description
--- | ---
AUTH_TYPE | The type of authentication used for this user: BASIC, FORM, etc.
CONTENT_LENGTH | The length of the data (in bytes or the number of characters) passed from a form.
CONTENT_TYPE | The MIME type of the query data, such as "text/html".
DATE_GMT | Current date and time in GMT
DATE_LOCAL | Current date and time in the local time zone
DOCUMENT_NAME | The current file
DOCUMENT_URI | Virtual path to the file
GATEWAY_INTERFACE | The revision of the Common Gateway Interface that the server uses if enabled: "CGI/1.1".
HTTP_ACCEPT | A list of the MIME types that the client can accept.
HTTP_ACCEPT_ENCODING | A list of the compression types that the client can accept.
HTTP_ACCEPT_LANGUAGE | A list of the languages that the client can accept.
HTTP_CONNECTION | The way that the connection from the client is being managed: "Close" or "Keep-Alive".
HTTP_HOST | The web site that the client requested.
HTTP_REFERER | The URL of the document that the client linked from.
HTTP_USER_AGENT | The browser the client is using to issue the request.
LAST_MODIFIED | Last modification date and time for current file
PATH_INFO | Extra path information passed to a servlet.
PATH_TRANSLATED | The translated version of the path given by the variable PATH_INFO.
QUERY_STRING | The query string that follows the "?" in the URL.
QUERY_STRING_UNESCAPED | Undecoded query string with all shell metacharacters escaped with "\"
REMOTE_ADDR | The remote IP address of the user making the request.
REMOTE_HOST | The remote hostname of the user making the request.
REMOTE_PORT | The port number at remote IP address of the user making the request.
REMOTE_USER | The authenticated name of the user.
REQUEST_METHOD | The method with which the information request was issued: "GET", "POST" etc.
REQUEST_URI | The web page originally requested by the client.
SCRIPT_FILENAME | The location of the current web page on the server.
SCRIPT_NAME | The name of the web page.
SERVER_ADDR | The server's IP address.
SERVER_NAME | The server's hostname or IP address.
SERVER_PORT | The port on which the server received the request.
SERVER_PROTOCOL | The protocol used by the server. E.g. "HTTP/1.1".
SERVER_SOFTWARE | The name and version of the server software that is answering the client request.
UNIQUE_ID | A token used to identify the current session if one has been established.