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This chapter is from the book

This chapter is from the book

5.4 The mime.types File

The Multipurpose Internet Mail Extensions (MIME) types file contains mappings between file extensions and MIME types. This file is utilized during request processing to tell the server what type of resource is being requested. It bases this information on the extension of the resource (such as .txt, .html, or .cgi) and associates a type, language, or encoding method based on the extension.

An initial MIME types file is created for each Web Server configuration; the name of the file is simply mime.types. You may create additional MIME types files and associate them to different virtual servers by using the <mime-file> element in the server.xml. Example 5.5 demonstrates the use of the <mime-file> element in the server.xml file.

Example 5.5. Virtual Server Definition for the MIME File

<virtual-server>
  <name>www.example.com</name>
  <http-listener-name>http-listener-1</http-listener-name>
  <host>www.example.com</host>
  <object-file>www.example.com-obj.conf</object-file>
  <mime-file>mymime.types</mime-file>
  <document-root>/export/home/example.com/public_html</document-root>
  <access-log>
     <file>/export/home/example.com/logs/access</file>
  </access-log>
</virtual-server>

Associating different MIME files to each virtual server gives you the flexibility to support different resources at the virtual server level.

5.4.1 File Structure

The mime.types file contains a series of associations that helps the instance identity the request type and subsequently understand how to process the request. Example 5.6 demonstrates the MIME types file for the default Administration Node.

Example 5.6. Sample mime.types File

#--Sun Microsystems Inc. MIME Information
# Do not delete the above line. It is used to identify the file type.
#
# Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
# Use is subject to license terms.
#

type=application/octet-stream                     exts=bin
type=application/astound                          exts=asd,asn
type=application/fastman                          exts=lcc
type=application/java-archive                     exts=jar
type=application/java-serialized-object           exts=ser
type=application/java-vm                          exts=class
type=application/mac-binhex40                     exts=hqx
type=application/x-stuffit                        exts=sit
type=application/mbedlet                          exts=mbd
type=application/msword                           exts=doc,dot,wiz,rtf
type=application/oda                              exts=oda
type=application/pdf                              exts=pdf
type=application/postscript                       exts=ai,eps,ps
type=application/studiom                          exts=smp
type=application/timbuktu                         exts=tbt
type=application/vnd.ms-excel                     exts=xls,xlw,xla,
                                                  xlc,xlm,xlt
type=application/vnd.ms-powerpoint                exts=ppt,pps,pot

[entries deleted]

enc=x-gzip                                        exts=gz
enc=x-compress                                    exts=z
enc=x-uuencode                                    exts=uu,uue

type=magnus-internal/parsed-html                  exts=shtml
type=magnus-internal/cgi                          exts=cgi,exe,bat

type=application/x-x509-ca-cert                   exts=cacert
type=application/x-x509-server-cert               exts=scert
type=application/x-x509-user-cert                 exts=ucert
type=application/x-x509-email-cert                exts=ecert

type=application/vnd.sun.xml.writer               exts=sxw
type=application/vnd.sun.xml.writer.template      exts=stw
type=application/vnd.sun.xml.calc                 exts=sxc
type=application/vnd.sun.xml.calc.template        exts=stc
type=application/vnd.sun.xml.draw                 exts=sxd
type=application/vnd.sun.xml.draw.template        exts=std
type=application/vnd.sun.xml.impress              exts=sxi
type=application/vnd.sun.xml.impress.template     exts=sti
type=application/vnd.sun.xml.writer.global        exts=sxg
type=application/vnd.sun.xml.math                 exts=sxm

type=application/vnd.stardivision.writer          exts=sdw
type=application/vnd.stardivision.writer-global   exts=sgl
type=application/vnd.stardivision.calc            exts=sdc
type=application/vnd.stardivision.draw            exts=sda
type=application/vnd.stardivision.impress         exts=sdd
type=application/vnd.stardivision.impress-packed  exts=sdp
type=application/vnd.stardivision.math            exts=smf,sdf
type=application/vnd.stardivision.chart           exts=sds
type=application/vnd.stardivision.mail            exts=sdm

5.4.2 File Structure

The format is similar to the format of request/response information that is exchanged between a web browser and the Web Server to which it connects. This related format is specified as part of the Hypertext Transfer Protocol (HTTP) and has the following rules:

The first line in the MIME types file identifies the file format:

    #--Sun Microsystems MIME Information

Other uncommented lines have the following format:

    type=type/subtype exts=[file extensions]

where type/subtype refers to the MIME type and subtype and exts refers to the file extensions associated with this type. For example, the MIME types file uses the following mapping to associate the extensions .html and .htm to the type text/html:

    type=text/html exts=htm,html

5.4.3 Processing

The MIME types configuration file determines how your Web Server’s virtual server maps filename extensions to MIME types that are returned to the browser. Your browser then maps these MIME types to “helper” applications or in-line plug-ins.

The following subsections describe how MIME mappings are used on both the Web Server and the user agent during request/response processing.

5.4.3.1 Server Processing

When the Web Server receives a request for a resource from a client, it uses the MIME type mappings to determine what kind of resource is being requested.

During the ObjectType stage in the request handling process, the server determines the MIME type attribute of the resource requested by the client. Several different SAFs can be used to determine the MIME type, but the most commonly used one is type-by-extension. This function tells the server to look up the MIME type according to the requested resource’s file extension in the MIME types table (stored in the MIME types file).

MIME types are defined by three attributes: language (lang), encoding (enc), and content-type (type). At least one of these attributes must be present for each type. The most commonly used attribute is type. When the server sends the response to the client, the type, language, and encoding values are transmitted in the Content-Type headers of the response.

If there is more than one ObjectType directive, the server applies all the directives in the order in which they appear. However, after a directive sets an attribute of the MIME type, encoding, or language, further attempts to set the same attribute are ignored.

Figure 5.1 demonstrates a client making a request for a particular file and how the server uses the mime.types file to determine how to process that request.

Figure 5.1

Figure 5.1 MIME File Usage During Request Processing

The following steps indicate a high-level overview of how the server processes this request:

  1. A client makes a URL request of http://www.example.com/index.html.
  2. The server accepts the request and selects the appropriate virtual server (not shown).
  3. The server determines the name of the object configuration file, based on the virtual server’s object-file settings (not shown). This instructs the server on how to process the request (not shown).
  4. The server executes the request-response process, as dictated by the object configuration file.
  5. At the point when the server reaches the ObjectType stage, it reads the MIME types file and searches for an extension that matches the file requested (in this case it is an HTML file).
  6. The server finds a match and sets the type to text/html.
  7. The server selects the appropriate service to process the request (not shown).
  8. The server sends the response to the client with the appropriate Content-type set in the response header.

5.4.3.2 Client Processing

The SAF defined for the appropriate service stage generates the data and sends it back to the client that made the request. When the server sends the data to the client, it also sends headers. These headers include the MIME type attributes that are known (which are usually defined by type attributes).

The client maintains its own MIME types table, as shown in Figure 5.2.

Figure 5.2

Figure 5.2 Client MIME Definitions

When the client receives the header, it uses the information contained in its own MIME types table to determine what to do with the data. For browser clients, the usual action is to display the data in the browser window.

Sometimes the requested resource cannot be displayed in the browser window and needs to be handled by another application. In such cases, the Content-type sent back by the server typically starts with application/; for example, application/x-pdf (for .pdf file extensions) or application/x-maker (for .fm file extensions).

The client has its own set of user-editable mappings that tells the browser which application to use for certain data types. For example, if the type is application/x-pdf, the client usually handles it by opening the Adobe Acrobat Reader application to display the file.

5.4.4 Context

The server.xml file contains definitions for each virtual server contained within the instance, so there is a one-to-many relationship between the server.xml file and virtual servers.

Each virtual server can use a different MIME types file for mapping associations. Therefore, there is a one-to-many relationship between an instance and the MIME types file(s), but there is a one-to-one relationship between the virtual server and its MIME types file.

5.4.5 Modifications

Although the default MIME types file includes a definition of the most commonly known MIME types, you are free to modify the file to add support for any additional MIME types. To add a new MIME type definition, simply append the definition to the existing MIME types in the file in the following format (where type/subtype is the MIME type of the document whose filename ends with one of the extensions listed):

    type=type/subtype exts=extension1,extension2,...,extensionN

The extension list includes any number of comma-separated filename extensions. Examples of MIME type entries can be found in the default MIME types file included with your virtual server.

You can also use the Administration Console or the command line interface to update the MIME types file for the virtual server. After the file is updated, you must deploy the updated configuration before the changes are reflected on the appropriate Administration Node(s).

The MIME types file is read when the instance is started or when a dynamic reconfiguration is performed. The syntax contained in the MIME types file is validated within the start-up or reconfiguration code base. Errors found within the MIME types file or within the server.xml file (as it pertains to the <mime-file> attribute) may prevent the instance from starting.

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