12. Handling MIME types

12.1 How Sylpheed-Claws checks for Mime types

When attaching a file to a message (composing a new message), the MIME type of the attached file is choosen based on the file extension from the mapping list defined in the mime.types file(s). Sylpheed-Claws defines its MIME type mapping table by loading the system wide MIME types file, then the user file. The systeme file is /usr/share/mime/globs or, if this doesn't exist, SYSCONFDIR/mime.types (SYSCONFDIR can be defined at compile time), or if it does not exist, /etc/mime.types. 

A mime.types file consist of one MIME type definition per line, each definition line starting with the name of the MIME type, followed by a space separated list of the corresponding file extensions. The file can contain empty lines, and comments start with the # character and close at line's end.

Following is a typical mime.types file (an extract of mine):

# This file controls what Internet media types are sent to the client for
# given file extension(s).  Sending the correct media type to the client
# is important so they know how to handle the content of the file.
# The Internet media type registry is at 
# <ftp://ftp.iana.org/in-notes/iana/assignments/media-types/>.

# MIME type                     Extension
application/mac-binhex40        hqx
application/mac-compactpro      cpt
application/msword              doc
application/pdf                 pdf
application/postscript          ai eps ps
application/rtf                 rtf
application/x-bcpio             bcpio
application/x-bzip2             bz2
application/x-csh               csh
application/x-gtar              gtar
application/x-gzip              gz tgz
application/x-kword             kwd kwt
application/x-kspread           ksp
application/x-kpresenter        kpr kpt
application/x-kchart            chrt
application/x-latex             latex
application/x-sh                sh
application/x-shar              shar
application/x-shockwave-flash   swf
application/x-tar               tar
application/x-tcl               tcl
application/x-tex               tex
application/x-texinfo           texinfo texi
application/x-troff             t tr roff
application/x-troff-man         man
application/zip                 zip
audio/mpeg                      mpga mp2 mp3
audio/x-aiff                    aif aiff aifc
audio/x-wav                     wav
image/gif                       gif
image/ief                       ief
image/jpeg                      jpeg jpg jpe
image/png                       png
image/tiff                      tiff tif
text/plain                      asc txt
text/rtf                        rtf
text/sgml                       sgml sgm
text/xml                        xml
video/mpeg                      mpeg mpg mpe
video/x-msvideo                 avi
text/html                       html htm

If the file can be found or has the wrong format, Sylpheed-Claws will assume the default MIME type for all the attachments: application/octet-stream. In such a case, the recipients mail client may not know what application to use to view the attachment.

12.2 How Sylpheed-Claws handles attachments (reception)

When opening an attachment (select the attachment, right click and select Open) Sylpheed-Claws uses one of the following methods to determine the application to launch:

• The attachment is an image: the application is the one defined by the mime_image_viewer variable of the common preferences configuration file ($HOME/.sylpheed/sylpheedrc). If no application is defined, or if the format of the definition is not valid, the default application command is display (ImageMagick viewer).
• The attachment is a sound file: the application is the one defined by the mime_audio_player variable of the common preferences configuration file ($HOME/.sylpheed/sylpheedrc). If no application is defined, or if the format of the definition is not valid, the default application command is play.
• The attachment is a HTML file: the application is the one defined by the uri_cmd variable of the common preferences configuration file ($HOME/.sylpheed/sylpheedrc). This can also be changed in the Common preferences, by changing the Web browser defined in the Other tab.
• Any other attachment type: Sylpheed-Claws relies on metamail to use the correct application (Sylpheed-Claws starts metamail giving it the attachment file and the MIME type taken from the mail).

The binding of the applications to each MIME type is defined in the mailcap file. The systeme wide file is /etc/mailcap, while the user file is $HOME/.mailcap.

In the mailcap file, there is one definition per line, big lines can be broken by escaping the newline with a \ character, the first element of the line is the MIME type, then a semi-colon, (;), and finally the application to launch. The application part (right side of the semi-colon) can contain several shell commands separated by an escaped semi-colon (\;) and the %s string is replaced by the name of the file when launching the command.

Following is a typical mailcap file (an extract of mine):

image/*; ee %s

video/mpeg; gtv %s
video/*; xanim %s

application/pdf; xpdf %s

text/html; dillo %s