Add support for UNIX / DOS permissions

[dduponchel]

Two new fields on ZipObject, unixPermissions and dosPermissions, hold the
UNIX or DOS permissions of the file. A new option of generate(),
platform (DOS or UNIX) controls the use of the permissions.

The default behavior is to generate DOS archives, without any
permissions, like before.

Bonus side-effect : Finder on mac doesn't use the DOS directory flag,
JSZip didn't properly recognize folders until now.

Fix #194 and #198.

[Stuk]

Fun stuff :)

[Stuk]

Wow, great work.

[dduponchel]

Thanks !

[dduponchel]

I chose simplified permissions (readOnly/executable/etc versus the full unix/dos permissions/mode) for two reasons :

• It's easy to get and set (no need for binary mask, octal is forbidden in strict mode)
• nodejs on windows returns a non executable mode for folders (if generated with platform:"UNIX", this will render it unusable on linux/mac)

Unfortunately, this simplification may hurt too many nodejs users. If they compress a 660 file, JSZip will transform it into a 644 file (it ignores the "group" and "other" part). Same for folders : 750 ? You will get 755.

The best solution may be to replace the *Permissions fields with their numerical representation (from nodejs' stats.mode for example) and using them directly. No more surprises, the user get what is on the disk.
For the first issue (get/set permissions), it may be too much for a zip library to fully parse the file mode (nodejs' fs.Stats don't do that either). To easily set it, we can allow a string ("755", "640" for example) and transform it.
For the second issue, this edge case may be just a documentation issue : something like "Warning : if you set platform in nodejs, be sure to use process.platform as value. <explanation here>".

Does that sounds good to you @Stuk ?

We also lack an options parameter on folder() to set permissions :-)