Re: [Monotone-devel] Killing off boost::fs

[Richard Levitte - VMS Whacker]

In message <address@hidden> on Fri, 29 Jul 2005 20:49:33 -0700, Nathaniel Smith 
<address@hidden> said:

njs> Some thoughts on how to do this:
njs>   - right now we have types "file_path" (a versionable path),
njs>     "local_path" (a path within the working dir -- difference
njs>     from file_path is that local_path's can begin "MT/"), and
njs>     fs::path (a generic, points-anywhere path).  All are stored
njs>     as strings, and have constructors that silently normalize, 

Where do I find documentation on fs::path?  All I can find is
boost::filesystem, and I'd like to know what the relationship between
the two is.

Speaking of which, is boost::filesystem interesting to look into?

njs>   - I suggest three slightly different types -- file_path (same as
njs>     now), system_path (same as old fs::path, which is a boost type
njs>     used directly), and bookkeeping_path (which is a path that _does_
njs>     begin with "MT/").  I.e., there is no reason for local_path to be
njs>     a superset of file_paths.

njs>   - one should not be able to instantiate a file_path directly.
njs>     Instead there should be two constructors; one that takes (and
njs>     requires) an already-normalized path, and one that takes an
njs>     unnormalized path and normalizes it.  Doing this allows us to
njs>     be more secure, and probably also faster, when dealing with
njs>     important contexts (e.g., parsing revisions) where we _know_
njs>     that the path should be normalized already.

I assume that in this case, you're not talking about the constructor
methods, but about separate functions.  Otherwise, I don't quite
understand what you mean with "not be able to instantiate a file_path
directly".

Speaking of normalised and not normalised, can't we simply assume that
all paths we get as input aren't normalised?

BTW, I assume that with "normalised", you're talking about removal of
../ when possible, tilde-expansion, compression of a sequence of / to
one /, things like that.

njs>   - it might also make sense to have these constructors take care
njs>     of the prefixing required to deal with calling monotone in a
njs>     subdirectory

So basically, you want the notion of the top of a work directory tree.

njs>   - the bookkeeping_path constructor should require an
njs>     already-normalized path that begins "MT/", since we always
njs>     generate these internally anyway.
njs>   - system_path (maybe needs a better name?) should always be
njs>     absolutified and tilde-expanded, and otherwise do not need to
njs>     be verified.

Do we want any path to be tilde-expanded, or just the system_path?

njs>   - all this code needs to be done very, very carefully, because
njs>     bugs in path normalization/checking can easily lead to
njs>     security exploits.
njs> 
njs> We don't need many actual operations on these:
njs>   - write file
njs>   - read file

Uhm, just a small thing here; there already is iostream, so I'm going
to assume you really mean "open", or possibly even just method that
returns a localised string that represents the path to be used with
normal iostream operations and whatnot.  Actual writing and reading
should be left to iostream, IMHO.

njs>   - file_path: split into components (might be able to optimize
njs>     this if we have our own library, e.g. do it during the
njs>     normalization pass?)

I think it should be done early, yes.

njs> These should probably take care of i18n implicitly (filenames are
njs> represented as UTF-8 when normalized, but may not be when entered
njs> on the command line or in the filesystem).

Cheers,
Richard

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-- 
Richard Levitte                         address@hidden
                                        http://richard.levitte.org/

"When I became a man I put away childish things, including
 the fear of childishness and the desire to be very grown up."
                                                -- C.S. Lewis