Re: Simplifying a File reference (Ben Coman)

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Re: Simplifying a File reference (Ben Coman)

Richard A. O'Keefe

Ben Coman <[hidden email]> wrote:
> While 'canonicalize' obviously fits, it seems a bit exotic and a tongue
> twist at five syllables.
> I wonder if 'flatten' might also be suitable.  Is there some concept this
> wouldn't cover?

There are two distinct issues.
(1) Can this file name be put into a form that would have the
     same reference as the original whatever the state of the
     file system?  (That is, whatever the same of the file
     system, the original name and the new form will reference
     to the same thing or neither will refer to anything, as
     long as I don't change directory.)

     For this, it _is_ safe to collapse // to / (except at the
     beginning) and to elide "." entries, but because of
     symbolic links it is *not* safe to elide ".." entries.

(2) Give me an absolute path name that does not contain any
     symbolic links and will refer to the same file as long
     as no directories along the way are renamed or deleted.

There is no POSIX function to do (1).
The POSIX function that does (2) is realpath(2).
If the Smalltalk method is intended to have the same semantics
as the realpath() function, it should have the same name,
possibly spelled #realPath.

There is a Solaris function called resolvepath() which is subtly
different from realpath() and not generally available.

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Re: Simplifying a File reference (Ben Coman)

Ben Coman


On 4 December 2017 at 08:25, Richard A. O'Keefe <[hidden email]> wrote:

Ben Coman <[hidden email]> wrote:
While 'canonicalize' obviously fits, it seems a bit exotic and a tongue
twist at five syllables.
I wonder if 'flatten' might also be suitable.  Is there some concept this
wouldn't cover?

There are two distinct issues.
(1) Can this file name be put into a form that would have the
    same reference as the original whatever the state of the
    file system?  (That is, whatever the same of the file
    system, the original name and the new form will reference
    to the same thing or neither will refer to anything, as
    long as I don't change directory.)

    For this, it _is_ safe to collapse // to / (except at the
    beginning) and to elide "." entries, but because of
    symbolic links it is *not* safe to elide ".." entries.

(2) Give me an absolute path name that does not contain any
    symbolic links and will refer to the same file as long
    as no directories along the way are renamed or deleted.


Thanks for you input.  Thats a nice framework to consider this.
Someone else will have to advise the intent of the method.

 
There is no POSIX function to do (1).
The POSIX function that does (2) is realpath(2).
If the Smalltalk method is intended to have the same semantics
as the realpath() function, it should have the same name,
possibly spelled #realPath.

btw, my personal preference where we echo another api is to use identical capitalization.  
I believe this reduces friction transferring knowledge between domains.
Lucky for me Pharo at least partially follows that convention  e.g. `basename`...

 cheers -ben

There is a Solaris function called resolvepath() which is subtly
different from realpath() and not generally available.


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Re: Simplifying a File reference (Ben Coman)

Alistair Grant
On 4 December 2017 at 01:48, Ben Coman <[hidden email]> wrote:

>
>
> On 4 December 2017 at 08:25, Richard A. O'Keefe <[hidden email]> wrote:
>>
>>
>> Ben Coman <[hidden email]> wrote:
>>>
>>> While 'canonicalize' obviously fits, it seems a bit exotic and a tongue
>>> twist at five syllables.
>>> I wonder if 'flatten' might also be suitable.  Is there some concept this
>>> wouldn't cover?

Just my personal preference, but I think canonicalize is better in
this case.  Flatten to me implies taking all the entries in a
collection and removing the structure.  In this case, we aren't
removing the structure completely, the order of the segments still has
meaning.


>> There are two distinct issues.
>> (1) Can this file name be put into a form that would have the
>>     same reference as the original whatever the state of the
>>     file system?  (That is, whatever the same of the file
>>     system, the original name and the new form will reference
>>     to the same thing or neither will refer to anything, as
>>     long as I don't change directory.)
>>
>>     For this, it _is_ safe to collapse // to / (except at the
>>     beginning) and to elide "." entries, but because of
>>     symbolic links it is *not* safe to elide ".." entries.
>>
>> (2) Give me an absolute path name that does not contain any
>>     symbolic links and will refer to the same file as long
>>     as no directories along the way are renamed or deleted.
>>
>
> Thanks for you input.  Thats a nice framework to consider this.
> Someone else will have to advise the intent of the method.
>
>
>>
>> There is no POSIX function to do (1).
>> The POSIX function that does (2) is realpath(2).
>> If the Smalltalk method is intended to have the same semantics
>> as the realpath() function, it should have the same name,
>> possibly spelled #realPath.

#canonicalize isn't intended to have the same semantics as realpath.
Like it's python and java equivalents, it explicitly ignores symbolic
links.

It should be possible to implement realpath, however the current
stat() / lstat() functionality is broken in Pharo.  I've submitted an
enhancement that fixes this, hopefully it will be merged in soon. :-)
See https://pharo.fogbugz.com/f/cases/18279/isSymlink-seems-to-be-broken-on-Linux


Cheers,
Alistair



> btw, my personal preference where we echo another api is to use identical
> capitalization.
> I believe this reduces friction transferring knowledge between domains.
> Lucky for me Pharo at least partially follows that convention  e.g.
> `basename`...
> https://github.com/pharo-project/pharo/blob/development/src/FileSystem-Core/FileSystemDirectoryEntry.class.st#L75
>
>  cheers -ben
>
>> There is a Solaris function called resolvepath() which is subtly
>> different from realpath() and not generally available.