Add .flag to EACCES errors from the fs module.

[dantman]

fs passes errors that are annotated with .code = 'EACCES' and .path when a file cannot be read or written, it would be useful if the error also had a .flag matching the .flag / flags that the file was attempted to be opened with.

[ghost]

Do u want to have the file access flags(like r w ) in the error object??

[dantman]

Basically. Functions like fs.open{Sync}, fs.readFile{Sync}, fs.writeFile{Sync}, etc... open a file with flags (in the case of ones other than fs.open those flags have defaults). If the user does not have the permission to perform the action then an EACCES error is thrown, and this error is already annotated with the .path of the file that the permissions were denied for. So while you can tell from the error alone what file permissions were denied for, you cannot tell what permissions were denied (which can be a pretty big difference). Hence why I'd like to see the denied .flag (or even .flags) added to the error.

This would allow an error handler further up the stack to identify the difference between the "You do not have permission to read " and "You do not have permission to write ".

[ghost]

I think this feature is not added to the core module because it affects the performance of the entire system since on each error all the permissions must be obtained. But we can have some middleware like thing for our own purpose like this: https://gist.github.com/arjunrp/6169b4d3d18b06007a10

[dantman]

Those aren't the flags I want. I want the flags passed to fs.open/etc... simple 'r', 'w', 'a', 'r+', etc... not something that requires a full stat.

[trevnorris]

I'll happily entertain a PR. :)

[yamadapc]

I'll happily work on this and would like to use the opportunity to understand the node.js core a little better. If someone could point out some details about the fs implementation I'd be stoked.
The fs.open calls for instance, simply forward themselves to binding.open... From what I gather, binding is the js/cpp glue, but I've yet to understand the relationship well.

Could someone point out where the code for the binding module - regardless if it's C or JS - is located in the repo? I know this is somewhat lazy of me to ask, but some pointers are always nice :)

[yamadapc]

Never-mind, I've found it.

[jasnell]

@yamadapc ... any updates on this?