[erlang-questions] Re: file operations on zipped files (Re: how to add a module to preLoaded?)

[Ulf Wiger]

On 5 Apr 2011, at 15:43, Håkan Mattsson wrote:

> On Thu, Mar 31, 2011 at 8:04 PM, Ulf Wiger
> <ulf.wiger@REDACTED> wrote:
> 
>> The change in prim_file gives no overhead in the normal case,
>> except for an extra pattern-match on the error value, and - if
>> {error, enotdir}, a scan of the file name to see if there is a
>> .ez file in the path. If so, the corresponding action is mapped
>> on the archive. If the file is to be opened, as with epp,
>> a "read_file()" is done, and the contents moved into a
>> ram_file, which allows the same operations as prim_file.
>> 
>> For this last case, I needed prim_ram_file in preloaded…
> 
> Is erl_prim_loader:get_file(File) too slow for your needs?

Surely not, but how does that help in this case?

I assume you mean that I could have used that function rather than implementing my own read_file_from_archive()? I definitely would if I had known about it. Since it's even documented, I can only blame my own ignorance. (:

So is your suggestion to call erl_prim_loader:get_file/1 instead of the prim_file:try_zip_read_file/2 that I wrote?

(https://github.com/uwiger/otp/blob/uw-prim_file-reads-zip/erts/preloaded/src/prim_file.erl#L577)

or did you have something else in mind? I suspect you are among the few who can claim any depth of knowledge in this area.

> 
>> A minor quirk is that code:lib_dir/1 has been defined to return
>> a path *outside* the zip archive, presumably because you cannot
>> load DLLs from an archive. Epp uses code:lib_dir/1 too, so even
>> with the above changes, epp would fail to find the .hrl
>> files. I solved this by having epp call code:where_is_file(Lib
>> ++ ".app") and then finding the include from there. If that
>> fails, it calls code:lib_dir/1 as before.
> 
> Would it not be better if epp used code:lib_dir(App, include) instead?

That function suffers from the same "problem" as code:lib_dir(App) -
in the case of a zip archive, it actually returns what I assume would be the path of the unpacked archive, whereas code:where_is_file(F) actually points to the location inside the archive.

$ erl -pa run_proper.ez/proper/ebin
Erlang R14B03 (erts-5.8.4) [source] [smp:4:4] [rq:4] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.8.4  (abort with ^G)
1> application:load(proper).
ok
2> code:lib_dir(proper,include).
"./run_proper/include"
3> code:where_is_file("proper.app").
"run_proper.ez/proper/ebin/proper.app"

BR,
Ulf W

Ulf Wiger, CTO, Erlang Solutions, Ltd.
http://erlang-solutions.com



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