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Dear Rusties,
I am currently in the early stages of writing a file system access
library for mozilla-central that might eventually replace some or all
of mozilla-central low-level file access code with something faster
and a little higher level. I also consider porting ? perhaps even
prototyping ? this library to Rust.
For this purpose, I need a little guidance on a few points.
*** #ifdef
My code heavily relies on #ifdefs with macros to compile code
conditionally, depending on both:
- - which platform is targeted (in mozilla-central, that's macros
XP_WIN, XP_UNIX);
- - which primitives are available in libc (through autoconf's
AC_CHECK_FUNS and the macros HAVE_xxxxx that it defines).
What is the best way to achieve this in Rust?
*** Foreign types
- From what I see in the code of unix_os.rs, we can simply define `type
foobar` in a foreign module and use this in the code. Are there any
limitations to this that I should know before employing the technique?
*** Unicode
On Unix platforms, file names are `char*`. On Windows platforms, they
are `wchar*`. In mozilla-central, I use the strings API to make my
life simpler and to handle all conversions for me. How should I do
this with Rust?
As far as I understand, the current win32_os.rs simply assumes that
any `str` passed can be used as a valid `char*`, and relies on Cygwin
to handle any oddity. As most of the features of Win32 are not
available through Cygwin, this is probably something that I cannot use.
*** Garbage-collection / destruction
I am not familiar with Rust resources yet, but chances are that I will
need to interact with them to get destruction and garbage-collection
on file descriptors and directory structures.
- - Do I understand correctly that resources a the right tool for the task?
- - From the documentation, I understand that a failed task will not
call destructors. Do I understand correctly? If so, this seems like a
major issue, as a process with failed tasks will leak file descriptors.
*** Error-handling
For file access, some error conditions are indeed failures, while some
are simply information that should be propagated. As I understand,
Rust will not have ML/C++-style exceptions in any foreseeable future.
I therefore see the following possibilities:
- - Either aggressively `spawn_notify` tasks, `unsupervise` them and
`fail` in case of any error, with some convention to pass `errno`;
- - or have each function return `either::t<Result, Error>` and
propagate error conditions manually, much as is done in current
mozilla-central code;
- - or offer both styles, with some naming convention to differentiate
them ? say submodules `fails` / `dnf`.
Any suggestion on the best policy?
Well, that covers most of my interrogations. Any suggestion or idea?
Thanks,
David
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