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NSAPI Programmer's Guide for iPlanet Web Server

Appendix C
MIME Types

This appendix discusses the MIME types file. The sections are:

Introduction

The MIME types file in the config directory contains mappings between MIME (Multipurpose Internet Mail Extensions) types and file extensions. For example, the MIME types file maps the extensions .html and .htm extension to the type text/html:

type=text/html exts=htm,html
When the iPlanet 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.

MIME types can have three attributes: language (lang), encoding (enc), and content-type (type). The most commonly used attribute is type. The server frequently considers the type when deciding how to generate the response to the client. (The enc and lang attributes are rarely used).

By default, the MIME types file is called mime.types. You should not change the name of this file unless you have a particular reason for doing so -- everyone expects it to be called mime.types.

Loading the MIME Types File

When the server is initialized, an Init directive in obj.conf invokes the load-mime-types directive to load the MIME types file: 

Init fn="load-types" mime-types="mime.types"
After loading the MIME types file, the server uses it to create a table of mappings between file extensions and MIME types.

If you make changes to the MIME types file, you will need to restart the server before the changes take effect. The server loads the MIME types file during the initialization step, so it does not notice any changes in the MIME types file until the next time it is initialized.

Determining the MIME Type

During the ObjectType step in the request handling process, the server determines the MIME type attributes of the resource requested by the client. Several different server application functions (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.

The directive in obj.conf that tells the server to look up the MIME type according to the extension is:

ObjectType fn=type-by-extension
If the server uses a different SAF, such as force-type, to determine the type, then the MIME types table is not used for that particular request.

For more details of the ObjectType step, see Chapter 2, "Syntax and Use of obj.conf."

How the Type Affects the Response

The server considers the value of the type attribute when deciding which Service directive in obj.conf to use to generate the response to the client.

By default, if the type does not start with magnus-internal/, the server just sends the requested file to the client. The directive in obj.conf that contains this instruction is:

Service method=(GET|HEAD|POST) type=*~magnus-internal/* fn=send-file
Note here the use of the special characters *~ to mean "does not match." See Appendix D, "Wildcard Patterns," for details of special characters.

By convention, all values of type that require the server to do something other than just send the requested resource to the client start with magnus-internal/.

For example, if the requested resource's file extension is .map, the type is mapped to magnus-internal/imagemap. If the extension is .cgi, .exe, or .bat, the type is set to magnus-internal/cgi:

type=magnus-internal/imagemap       exts=map
type=magnus-internal/cgi            exts=cgi,exe,bat
If the type starts with magnus-internal/, the server executes whichever Service directive in obj.conf matches the specified type. For example, if the type is magnus-internal/imagemap, the server uses the imagemap function to generate the response to the client, as indicated by the following directive:

Service method=(GET|HEAD) type=magnus-internal/imagemap fn=imagemap
If the type is magnus-internal/servlet, the server uses the NSServletService function to generate the response to the client, as indicated by the following directive: 

Service type="magnus-internal/servlet" fn="NSServletService"

What Does the Client Do with the MIME Type?

The Service function generates the data and sends it to the client that made the request. When the server sends the data to the client, it also sends headers. These headers include whichever MIME type attributes are known (which is usually type).

When the client receives the data, it uses the MIME type to decide what to do with the data. For browser clients, the usual thing is to display the data in the browser window.

If the requested resource cannot be displayed in a browser but needs to be handled by another application, its type starts with application/, for example application/octet-stream (for .bin file extensions ) or application/x-maker (for .fm file extensions). The client has its own set of user-editable mappings that tells it which application to use to handle which types of data.

For example, if the type is application/x-maker, the client usually handles it by opening Adobe FrameMaker to display the file.

Syntax of the MIME Types File

The first line in the MIME types file identifies the file format and must read:

#--Netscape Communications Corporation MIME Information
Other non-comment lines have the following format:

type=type/subtype exts=[file extensions] icon=icon

Sample MIME Types File

Here is an example of a MIME types file:

#--Netscape Communications Corporation MIME Information
# Do not delete the above line. It is used to identify the file type.
type=application/octet-stream  exts=bin,exe
type=application/oda           exts=oda
type=application/pdf           exts=pdf
type=application/postscript    exts=ai,eps,ps
type=application/rtf           exts=rtf
type=application/x-mif         exts=mif,fm
type=application/x-gtar        exts=gtar
type=application/x-shar        exts=shar
type=application/x-tar         exts=tar
type=application/mac-binhex40  exts=hqx

type=audio/basic               exts=au,snd
type=audio/x-aiff              exts=aif,aiff,aifc
type=audio/x-wav               exts=wav

type=image/gif                 exts=gif
type=image/ief                 exts=ief
type=image/jpeg                exts=jpeg,jpg,jpe
type=image/tiff                exts=tiff,tif
type=image/x-rgb               exts=rgb
type=image/x-xbitmap           exts=xbm
type=image/x-xpixmap           exts=xpm
type=image/x-xwindowdump       exts=xwd

type=text/html                 exts=htm,html
type=text/plain                exts=txt
type=text/richtext             exts=rtx
type=text/tab-separated-values exts=tsv
type=text/x-setext             exts=etx

type=video/mpeg                exts=mpeg,mpg,mpe
type=video/quicktime           exts=qt,mov
type=video/x-msvideo           exts=avi

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

type=magnus-internal/imagemap  exts=map
type=magnus-internal/parsed-html exts=shtml
type=magnus-internal/cgi       exts=cgi,exe,bat
type=magnus-internal/jsp           exts=jsp
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Last Updated: 03/01/00 09:22:23

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