graceful-fs functions as a drop-in replacement for the fs module, making various improvements.
The improvements are meant to normalize behavior across different platforms and environments, and to make filesystem access more resilient to errors.
open and readdir calls, and retries them once
something closes if there is an EMFILE error from too many file
descriptors.lchmod for Node versions prior to 0.6.2.fs.lutimes if possible. Otherwise it becomes a noop.EINVAL and EPERM errors in chown, fchown or
lchown if the user isn't root.lchmod and lchown become noops, if not available.read results in EAGAIN error.On Windows, it retries renaming a file for up to one second if EACCESS
or EPERM error occurs, likely because antivirus software has locked
the directory.
// use just like fs
var fs = require('graceful-fs')
// now go and do stuff with it...
fs.readFile('some-file-or-whatever', (err, data) => {
// Do stuff here.
})This module cannot intercept or handle EMFILE or ENFILE errors from sync
methods. If you use sync methods which open file descriptors then you are
responsible for dealing with any errors.
This is a known limitation, not a bug.
If you want to patch the global fs module (or any other fs-like module) you can do this:
// Make sure to read the caveat below.
var realFs = require('fs')
var gracefulFs = require('graceful-fs')
gracefulFs.gracefulify(realFs)This should only ever be done at the top-level application layer, in order to delay on EMFILE errors from any fs-using dependencies. You should not do this in a library, because it can cause unexpected delays in other parts of the program.
This module is fairly stable at this point, and used by a lot of things. That being said, because it implements a subtle behavior change in a core part of the node API, even modest changes can be extremely breaking, and the versioning is thus biased towards bumping the major when in doubt.
The main change between major versions has been switching between
providing a fully-patched fs module vs monkey-patching the node core
builtin, and the approach by which a non-monkey-patched fs was
created.
The goal is to trade EMFILE errors for slower fs operations. So, if
you try to open a zillion files, rather than crashing, open
operations will be queued up and wait for something else to close.
There are advantages to each approach. Monkey-patching the fs means
that no EMFILE errors can possibly occur anywhere in your
application, because everything is using the same core fs module,
which is patched. However, it can also obviously cause undesirable
side-effects, especially if the module is loaded multiple times.
Implementing a separate-but-identical patched fs module is more
surgical (and doesn't run the risk of patching multiple times), but
also imposes the challenge of keeping in sync with the core module.
The current approach loads the fs module, and then creates a
lookalike object that has all the same methods, except a few that are
patched. It is safe to use in all versions of Node from 0.8 through
7.0.