[Xapian-discuss] Mime2Text library, derived from omindex

[Olly Betts]

On Wed, Nov 09, 2011 at 12:22:22PM -0800, Liam wrote:
> I've started a branch for a patch. Would love any feedback
> 
> Header
> https://github.com/networkimprov/xapian/blob/liam_mime2text-lib/xapian-applications/omega/mime2text.h

Some thoughts from looking at just the header:

I don't like that this API forces you to have a file on disk.  If you're
unpacking a container format you may well have data in memory, and while
it might be necessary to write it to disk to pass it to some extractors,
we really want to avoid that for extractors with a library API, or where
we can feed data to an external filter on stdin.

The ctor should be marked explicit, since there's a single argument form
of it; we don't want to quietly promote from bool to Mime2Text.

Needs documentation comments.

Why does the public API here take const char * parameters not const
std::string&?  If we really want const char * internally and the overhead
of a conversion to std::string matters for the case where the user has
a const char * to start with, we should provide overloaded forms which
call c_str() for the user.

Why is "command" in Mime2Text::Fields?  It doesn't seem to be a field.

We don't expose members of a class/struct elsewhere in the public C++
APIs we provide, so for consistency perhaps we shouldn't here.  Though
this presumably isn't intended to go in the core API, so perhaps that
isn't such a concern.  It does mean these values can't be lazily
computed though (for example, the sample probably could be in some cases
otherwise).

For consistency with conventions in the other public C++ APIs (and the
whole of the rest of the code) don't use camel case for method names or
parameters (setCommand, setMimeType, iKey, iValue, outFields), only for
class and struct names.

Did you intend to use "protected" rather than "private" for the internal
stuff?  That means that users can subclass to get access to it, and ties
down the details of that...

There's no way to remove an entry from the command or mine maps with
the current API (you could create your own subclass of Mime2Text to do
this, but that's a bit mad, and I'm unconvinced those maps should be
protected rather than private anyway).

Cheers,
    Olly