An XProc processor is especially sensitive to the way MIME types are configured. An XProc pipeline can process resources of any type: XML, JSON, ZIP, etc. The content type of a resource accessed through HTTP (or HTTPS) is always identified by the server. But the content type of a resource loaded from the filesystem depends on its filename extension and how your JVM is configured.

When the JVM starts, it looks for a file named “.mime.types” in the users’s home directory^*. If it finds one, it uses it to build a mapping from filename extensions to MIME types. The .mime.types file is a text file where each line consists of a MIME type followed by a space separated list of filename extensions. For example:

 1 |# MIME type mapping (Likes that start with “#” are comments.)
   |application/json json
   |application/nvdl+xml nvdl
   |application/relax-ng-compact-syntax rnc
 5 |application/relax-ng+xml rng
   |application/schematron+xml sch
   |text/plain text txt css
   |application/xml xml xpl fo
   |application/xquery xq xqy
10 |application/xsd+xml xsd
   |application/xslt+xml xsl xslt

For XML Calabash, you can also define them in the configuration file.

If there is no MIME type defined for a particular extension, it will be identified as an “application/octet-stream” resource. That’s binary. It is very explicitly not XML or HTML or JSON or text. Most steps will reject binary resources. This will result in errors that might be very confusing if you’re not aware of the problem. To avoid that, XML Calabash takes a heavy-handed approach.

After the MIME types have been configured, from the system, from the user’s .mime.types file, and from the configuration file, if any of the extensions listed in Table 1.1, “Default MIME type mappings” are identified as “application/octet-stream” resources, XML Calabash defines a pragmatically more useful default.

If these defaults are problematic, use one of the existing configuration mechanisms to define the mapping you prefer.

Also, if you have a different convention, perhaps using the extension “.schematron” for Schematron files or “.xs” for XML Schema documents, you will have to provide that mapping yourself. You will also want to provide mappings for other extensions you use.