144 lines
4.6 KiB
Markdown
144 lines
4.6 KiB
Markdown
# graceful-fs
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graceful-fs functions as a drop-in replacement for the fs module,
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making various improvements.
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The improvements are meant to normalize behavior across different
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platforms and environments, and to make filesystem access more
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resilient to errors.
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## Improvements over [fs module](https://nodejs.org/api/fs.html)
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* Queues up `open` and `readdir` calls, and retries them once
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something closes if there is an EMFILE error from too many file
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descriptors.
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* fixes `lchmod` for Node versions prior to 0.6.2.
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* implements `fs.lutimes` if possible. Otherwise it becomes a noop.
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* ignores `EINVAL` and `EPERM` errors in `chown`, `fchown` or
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`lchown` if the user isn't root.
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* makes `lchmod` and `lchown` become noops, if not available.
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* retries reading a file if `read` results in EAGAIN error.
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On Windows, it retries renaming a file for up to one second if `EACCESS`
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or `EPERM` error occurs, likely because antivirus software has locked
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the directory.
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## USAGE
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```javascript
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// use just like fs
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var fs = require('graceful-fs')
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// now go and do stuff with it...
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fs.readFile('some-file-or-whatever', (err, data) => {
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// Do stuff here.
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})
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```
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## Sync methods
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This module cannot intercept or handle `EMFILE` or `ENFILE` errors from sync
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methods. If you use sync methods which open file descriptors then you are
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responsible for dealing with any errors.
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This is a known limitation, not a bug.
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## Global Patching
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If you want to patch the global fs module (or any other fs-like
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module) you can do this:
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```javascript
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// Make sure to read the caveat below.
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var realFs = require('fs')
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var gracefulFs = require('graceful-fs')
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gracefulFs.gracefulify(realFs)
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```
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This should only ever be done at the top-level application layer, in
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order to delay on EMFILE errors from any fs-using dependencies. You
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should **not** do this in a library, because it can cause unexpected
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delays in other parts of the program.
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## Changes
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This module is fairly stable at this point, and used by a lot of
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things. That being said, because it implements a subtle behavior
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change in a core part of the node API, even modest changes can be
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extremely breaking, and the versioning is thus biased towards
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bumping the major when in doubt.
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The main change between major versions has been switching between
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providing a fully-patched `fs` module vs monkey-patching the node core
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builtin, and the approach by which a non-monkey-patched `fs` was
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created.
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The goal is to trade `EMFILE` errors for slower fs operations. So, if
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you try to open a zillion files, rather than crashing, `open`
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operations will be queued up and wait for something else to `close`.
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There are advantages to each approach. Monkey-patching the fs means
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that no `EMFILE` errors can possibly occur anywhere in your
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application, because everything is using the same core `fs` module,
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which is patched. However, it can also obviously cause undesirable
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side-effects, especially if the module is loaded multiple times.
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Implementing a separate-but-identical patched `fs` module is more
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surgical (and doesn't run the risk of patching multiple times), but
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also imposes the challenge of keeping in sync with the core module.
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The current approach loads the `fs` module, and then creates a
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lookalike object that has all the same methods, except a few that are
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patched. It is safe to use in all versions of Node from 0.8 through
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7.0.
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### v4
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* Do not monkey-patch the fs module. This module may now be used as a
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drop-in dep, and users can opt into monkey-patching the fs builtin
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if their app requires it.
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### v3
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* Monkey-patch fs, because the eval approach no longer works on recent
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node.
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* fixed possible type-error throw if rename fails on windows
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* verify that we *never* get EMFILE errors
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* Ignore ENOSYS from chmod/chown
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* clarify that graceful-fs must be used as a drop-in
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### v2.1.0
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* Use eval rather than monkey-patching fs.
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* readdir: Always sort the results
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* win32: requeue a file if error has an OK status
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### v2.0
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* A return to monkey patching
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* wrap process.cwd
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### v1.1
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* wrap readFile
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* Wrap fs.writeFile.
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* readdir protection
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* Don't clobber the fs builtin
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* Handle fs.read EAGAIN errors by trying again
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* Expose the curOpen counter
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* No-op lchown/lchmod if not implemented
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* fs.rename patch only for win32
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* Patch fs.rename to handle AV software on Windows
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* Close #4 Chown should not fail on einval or eperm if non-root
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* Fix isaacs/fstream#1 Only wrap fs one time
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* Fix #3 Start at 1024 max files, then back off on EMFILE
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* lutimes that doens't blow up on Linux
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* A full on-rewrite using a queue instead of just swallowing the EMFILE error
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* Wrap Read/Write streams as well
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### 1.0
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* Update engines for node 0.6
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* Be lstat-graceful on Windows
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* first
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