Re: [Monotone-devel] [PATCH] and RFC: binary files merging and hook

[rghetta]

Joel Crisp wrote:

> I'm not against programming, just against making everyone do it. If 
you can provide a framework which allows a registry
> of common file types against the way of handling them and a library 
of shipped code fragments which can be incorporated without the end user 
having to do any coding, then that would be fine.
> Maybe something like:
> monotone types filetype --match=\*.xml --type=text/xml    <--- Setup 
>initial default mappings
I don't like much having a specialized monotone command just for that. 
Besides, this way you can't control the order of matching.
imho, a configuration file is a better solution.

> or
> monotone types filetype --file=foo.xml --type=x-rational-xmi  <---
> Change the type of the file

As I see it, there are three distinct issues to handle:
- mapping file extensions (and/or content) to mime-types
- mapping mime-types to merge/diff tools
- assigning mime-types to files, and handling them in monotone.

The first two tasks can be accomplished by using a bit of lua glue to 
read mappings from configuration files.
These files could be in pure tabular form or, better, use the syntax 
proposed by graydon, i.e. something like
        file_mapping(".xml", "text/xml")
and/or
        content_mapping(offset, bytestring , mime-type)
The same goes for merging:
        merge_tool(mime-type, difftool, mergetool, automerge_allowed)

While the user sees only a collection of mapping directives, these lines 
effectively translate to lua functions calls, making customization both 
powerful and easy.

Storing mime-types in monotone should be done with file attributes, but 
currently this is a bit tricky, because you need a way to resolve 
conflicting mime-types *before* merging.
This could be accomplished by merging .mt-attrs before other files, but 
introducing ordering into merges could be dangerous.
Anyway, there are ongoing developments that should make these things easier.

In the meantime, we could _partially_ resolve the issue by using only 
the mapping tables at merge/diff time, without explicitly assigning a 
mime-type to files.
Per-file mapping is still possible by using the full filename instead of 
the extension
        file_mapping("model.xml", "application/xmi")

Cheers,
Riccardo