1# graceful-fs 2 3graceful-fs functions as a drop-in replacement for the fs module, 4making various improvements. 5 6The improvements are meant to normalize behavior across different 7platforms and environments, and to make filesystem access more 8resilient to errors. 9 10## Improvements over [fs module](https://nodejs.org/api/fs.html) 11 12* Queues up `open` and `readdir` calls, and retries them once 13 something closes if there is an EMFILE error from too many file 14 descriptors. 15* fixes `lchmod` for Node versions prior to 0.6.2. 16* implements `fs.lutimes` if possible. Otherwise it becomes a noop. 17* ignores `EINVAL` and `EPERM` errors in `chown`, `fchown` or 18 `lchown` if the user isn't root. 19* makes `lchmod` and `lchown` become noops, if not available. 20* retries reading a file if `read` results in EAGAIN error. 21 22On Windows, it retries renaming a file for up to one second if `EACCESS` 23or `EPERM` error occurs, likely because antivirus software has locked 24the directory. 25 26## USAGE 27 28```javascript 29// use just like fs 30var fs = require('graceful-fs') 31 32// now go and do stuff with it... 33fs.readFileSync('some-file-or-whatever') 34``` 35 36## Global Patching 37 38If you want to patch the global fs module (or any other fs-like 39module) you can do this: 40 41```javascript 42// Make sure to read the caveat below. 43var realFs = require('fs') 44var gracefulFs = require('graceful-fs') 45gracefulFs.gracefulify(realFs) 46``` 47 48This should only ever be done at the top-level application layer, in 49order to delay on EMFILE errors from any fs-using dependencies. You 50should **not** do this in a library, because it can cause unexpected 51delays in other parts of the program. 52 53## Changes 54 55This module is fairly stable at this point, and used by a lot of 56things. That being said, because it implements a subtle behavior 57change in a core part of the node API, even modest changes can be 58extremely breaking, and the versioning is thus biased towards 59bumping the major when in doubt. 60 61The main change between major versions has been switching between 62providing a fully-patched `fs` module vs monkey-patching the node core 63builtin, and the approach by which a non-monkey-patched `fs` was 64created. 65 66The goal is to trade `EMFILE` errors for slower fs operations. So, if 67you try to open a zillion files, rather than crashing, `open` 68operations will be queued up and wait for something else to `close`. 69 70There are advantages to each approach. Monkey-patching the fs means 71that no `EMFILE` errors can possibly occur anywhere in your 72application, because everything is using the same core `fs` module, 73which is patched. However, it can also obviously cause undesirable 74side-effects, especially if the module is loaded multiple times. 75 76Implementing a separate-but-identical patched `fs` module is more 77surgical (and doesn't run the risk of patching multiple times), but 78also imposes the challenge of keeping in sync with the core module. 79 80The current approach loads the `fs` module, and then creates a 81lookalike object that has all the same methods, except a few that are 82patched. It is safe to use in all versions of Node from 0.8 through 837.0. 84 85### v4 86 87* Do not monkey-patch the fs module. This module may now be used as a 88 drop-in dep, and users can opt into monkey-patching the fs builtin 89 if their app requires it. 90 91### v3 92 93* Monkey-patch fs, because the eval approach no longer works on recent 94 node. 95* fixed possible type-error throw if rename fails on windows 96* verify that we *never* get EMFILE errors 97* Ignore ENOSYS from chmod/chown 98* clarify that graceful-fs must be used as a drop-in 99 100### v2.1.0 101 102* Use eval rather than monkey-patching fs. 103* readdir: Always sort the results 104* win32: requeue a file if error has an OK status 105 106### v2.0 107 108* A return to monkey patching 109* wrap process.cwd 110 111### v1.1 112 113* wrap readFile 114* Wrap fs.writeFile. 115* readdir protection 116* Don't clobber the fs builtin 117* Handle fs.read EAGAIN errors by trying again 118* Expose the curOpen counter 119* No-op lchown/lchmod if not implemented 120* fs.rename patch only for win32 121* Patch fs.rename to handle AV software on Windows 122* Close #4 Chown should not fail on einval or eperm if non-root 123* Fix isaacs/fstream#1 Only wrap fs one time 124* Fix #3 Start at 1024 max files, then back off on EMFILE 125* lutimes that doens't blow up on Linux 126* A full on-rewrite using a queue instead of just swallowing the EMFILE error 127* Wrap Read/Write streams as well 128 129### 1.0 130 131* Update engines for node 0.6 132* Be lstat-graceful on Windows 133* first 134