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src: refactor require('constants')
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The require('constants') module is currently undocumented and mashes
together unrelated constants. This refactors the require('constants')
in favor of distinct os.constants, fs.constants, and crypto.constants
that are specific to the modules for which they are relevant. The
next step is to document those within the specific modules.

PR-URL: #6534
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Robert Lindstaedt <robert.lindstaedt@gmail.com>
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jasnell committed May 17, 2016
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381 changes: 349 additions & 32 deletions doc/api/crypto.md
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275 changes: 252 additions & 23 deletions doc/api/fs.md
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Original file line number Diff line number Diff line change
Expand Up @@ -266,21 +266,21 @@ optional integer that specifies the accessibility checks to be performed. The
following constants define the possible values of `mode`. It is possible to
create a mask consisting of the bitwise OR of two or more values.

- `fs.F_OK` - File is visible to the calling process. This is useful for
determining if a file exists, but says nothing about `rwx` permissions.
- `fs.constants.F_OK` - File is visible to the calling process. This is useful
for determining if a file exists, but says nothing about `rwx` permissions.
Default if no `mode` is specified.
- `fs.R_OK` - File can be read by the calling process.
- `fs.W_OK` - File can be written by the calling process.
- `fs.X_OK` - File can be executed by the calling process. This has no effect
on Windows (will behave like `fs.F_OK`).
- `fs.constants.R_OK` - File can be read by the calling process.
- `fs.constants.W_OK` - File can be written by the calling process.
- `fs.constants.X_OK` - File can be executed by the calling process. This has no
effect on Windows (will behave like `fs.constants.F_OK`).

The final argument, `callback`, is a callback function that is invoked with
a possible error argument. If any of the accessibility checks fail, the error
argument will be populated. The following example checks if the file
`/etc/passwd` can be read and written by the current process.

```js
fs.access('/etc/passwd', fs.R_OK | fs.W_OK, (err) => {
fs.access('/etc/passwd', fs.constants.R_OK | fs.constants.W_OK, (err) => {
console.log(err ? 'no access!' : 'can read/write');
});
```
Expand All @@ -290,8 +290,8 @@ fs.access('/etc/passwd', fs.R_OK | fs.W_OK, (err) => {
* `path` {String | Buffer}
* `mode` {Integer}

Synchronous version of [`fs.access()`][]. This throws if any accessibility checks
fail, and does nothing otherwise.
Synchronous version of [`fs.access()`][]. This throws if any accessibility
checks fail, and does nothing otherwise.

## fs.appendFile(file, data[, options], callback)

Expand Down Expand Up @@ -384,6 +384,12 @@ to the completion callback.

Synchronous close(2). Returns `undefined`.

## fs.constants

Returns an object containing commonly used constants for file system
operations. The specific constants currently defined are described in
[FS Constants][].

## fs.createReadStream(path[, options])

* `path` {String | Buffer}
Expand Down Expand Up @@ -419,9 +425,9 @@ the file instead of the entire file. Both `start` and `end` are inclusive and
start at 0. The `encoding` can be any one of those accepted by [`Buffer`][].

If `fd` is specified, `ReadStream` will ignore the `path` argument and will use
the specified file descriptor. This means that no `'open'` event will be emitted.
Note that `fd` should be blocking; non-blocking `fd`s should be passed to
[`net.Socket`][].
the specified file descriptor. This means that no `'open'` event will be
emitted. Note that `fd` should be blocking; non-blocking `fd`s should be passed
to [`net.Socket`][].

If `autoClose` is false, then the file descriptor won't be closed, even if
there's an error. It is your responsibility to close it and make sure
Expand Down Expand Up @@ -468,7 +474,8 @@ Returns a new [`WriteStream`][] object. (See [Writable Stream][]).
`options` may also include a `start` option to allow writing data at
some position past the beginning of the file. Modifying a file rather
than replacing it may require a `flags` mode of `r+` rather than the
default mode `w`. The `defaultEncoding` can be any one of those accepted by [`Buffer`][].
default mode `w`. The `defaultEncoding` can be any one of those accepted by
[`Buffer`][].

If `autoClose` is set to true (default behavior) on `error` or `end`
the file descriptor will be closed automatically. If `autoClose` is false,
Expand Down Expand Up @@ -507,7 +514,8 @@ non-existent.

## fs.existsSync(path)

Stability: 0 - Deprecated: Use [`fs.statSync()`][] or [`fs.accessSync()`][] instead.
Stability: 0 - Deprecated: Use [`fs.statSync()`][] or [`fs.accessSync()`][]
instead.

* `path` {String | Buffer}

Expand Down Expand Up @@ -789,7 +797,7 @@ to a non-existent file. The exclusive flag may or may not work with network file
systems.

`flags` can also be a number as documented by open(2); commonly used constants
are available from `require('constants')`. On Windows, flags are translated to
are available from `fs.constants`. On Windows, flags are translated to
their equivalent ones where applicable, e.g. `O_WRONLY` to `FILE_GENERIC_WRITE`,
or `O_EXCL|O_CREAT` to `CREATE_NEW`, as accepted by CreateFileW.

Expand Down Expand Up @@ -1038,11 +1046,11 @@ Synchronous stat(2). Returns an instance of [`fs.Stats`][].
* `callback` {Function}

Asynchronous symlink(2). No arguments other than a possible exception are given
to the completion callback.
The `type` argument can be set to `'dir'`, `'file'`, or `'junction'` (default
is `'file'`) and is only available on Windows (ignored on other platforms).
Note that Windows junction points require the destination path to be absolute. When using
`'junction'`, the `target` argument will automatically be normalized to absolute path.
to the completion callback. The `type` argument can be set to `'dir'`,
`'file'`, or `'junction'` (default is `'file'`) and is only available on
Windows (ignored on other platforms). Note that Windows junction points require
the destination path to be absolute. When using `'junction'`, the `target`
argument will automatically be normalized to absolute path.

Here is an example below:

Expand Down Expand Up @@ -1255,9 +1263,9 @@ _Note: when an `fs.watchFile` operation results in an `ENOENT` error, it will
of zero. If the file is created later on, the listener will be called again,
with the latest stat objects. This is a change in functionality since v0.10._

_Note: [`fs.watch()`][] is more efficient than `fs.watchFile` and `fs.unwatchFile`.
`fs.watch` should be used instead of `fs.watchFile` and `fs.unwatchFile`
when possible._
_Note: [`fs.watch()`][] is more efficient than `fs.watchFile` and
`fs.unwatchFile`. `fs.watch` should be used instead of `fs.watchFile` and
`fs.unwatchFile` when possible._

## fs.write(fd, buffer, offset, length[, position], callback)

Expand Down Expand Up @@ -1387,6 +1395,226 @@ The synchronous version of [`fs.writeFile()`][]. Returns `undefined`.

Synchronous versions of [`fs.write()`][]. Returns the number of bytes written.

## FS Constants

The following constants are exported by `fs.constants`. **Note:** Not every
constant will be available on every operating system.

### File Access Constants

The following constants are meant for use with [`fs.access()`][].

<table>
<tr>
<th>Constant</th>
<th>Description</th>
</tr>
<tr>
<td><code>F_OK</code></td>
<td>Flag indicating that the file is visible to the calling process.</td>
</tr>
<tr>
<td><code>R_OK</code></td>
<td>Flag indicating that the file can be read by the calling process.</td>
</tr>
<tr>
<td><code>W_OK</code></td>
<td>Flag indicating that the file can be written by the calling
process.</td>
</tr>
<tr>
<td><code>X_OK</code></td>
<td>Flag indicating that the file can be executed by the calling
process.</td>
</tr>
</table>

### File Open Constants

The following constants are meant for use with `fs.open()`.

<table>
<tr>
<th>Constant</th>
<th>Description</th>
</tr>
<tr>
<td><code>O_RDONLY</code></td>
<td>Flag indicating to open a file for read-only access.</td>
</tr>
<tr>
<td><code>O_WRONLY</code></td>
<td>Flag indicating to open a file for write-only access.</td>
</tr>
<tr>
<td><code>O_RDWR</code></td>
<td>Flag indicating to open a file for read-write access.</td>
</tr>
<tr>
<td><code>O_CREAT</code></td>
<td>Flag indicating to create the file if it does not already exist.</td>
</tr>
<tr>
<td><code>O_EXCL</code></td>
<td>Flag indicating that opening a file should fail if the
<code>O_CREAT</code> flag is set and the file already exists.</td>
</tr>
<tr>
<td><code>O_NOCTTY</code></td>
<td>Flag indicating that if path identifies a terminal device, opening the
path shall not cause that terminal to become the controlling terminal for
the process (if the process does not already have one).</td>
</tr>
<tr>
<td><code>O_TRUNC</code></td>
<td>Flag indicating that if the file exists and is a regular file, and the
file is opened successfully for write access, its length shall be truncated
to zero.</td>
</tr>
<tr>
<td><code>O_APPEND</code></td>
<td>Flag indicating that data will be appended to the end of the file.</td>
</tr>
<tr>
<td><code>O_DIRECTORY</code></td>
<td>Flag indicating that the open should fail if the path is not a
directory.</td>
</tr>
<tr>
<td><code>O_NOATIME</code></td>
<td>Flag indicating reading accesses to the file system will no longer
result in an update to the `atime` information associated with the file.
This flag is available on Linux operating systems only.</td>
</tr>
<tr>
<td><code>O_NOFOLLOW</code></td>
<td>Flag indicating that the open should fail if the path is a symbolic
link.</td>
</tr>
<tr>
<td><code>O_SYNC</code></td>
<td>Flag indicating that the file is opened for synchronous I/O.</td>
</tr>
<tr>
<td><code>O_SYMLINK</code></td>
<td>Flag indicating to open the symbolic link itself rather than the
resource it is pointing to.</td>
</tr>
<tr>
<td><code>O_DIRECT</code></td>
<td>When set, an attempt will be made to minimize caching effects of file
I/O.</td>
</tr>
<tr>
<td><code>O_NONBLOCK</code></td>
<td>Flag indicating to open the file in nonblocking mode when possible.</td>
</tr>
</table>

### File Type Constants

The following constants are meant for use with the [`fs.Stats`][] object's
`mode` property for determining a file's type.

<table>
<tr>
<th>Constant</th>
<th>Description</th>
</tr>
<tr>
<td><code>S_IFMT</code></td>
<td>Bit mask used to extract the file type code.</td>
</tr>
<tr>
<td><code>S_IFREG</code></td>
<td>File type constant for a regular file.</td>
</tr>
<tr>
<td><code>S_IFDIR</code></td>
<td>File type constant for a directory.</td>
</tr>
<tr>
<td><code>S_IFCHR</code></td>
<td>File type constant for a character-oriented device file.</td>
</tr>
<tr>
<td><code>S_IFBLK</code></td>
<td>File type constant for a block-oriented device file.</td>
</tr>
<tr>
<td><code>S_IFIFO</code></td>
<td>File type constant for a FIFO/pipe.</td>
</tr>
<tr>
<td><code>S_IFLNK</code></td>
<td>File type constant for a symbolic link.</td>
</tr>
<tr>
<td><code>S_IFSOCK</code></td>
<td>File type constant for a socket.</td>
</tr>
</table>

### File Mode Constants

The following constants are meant for use with the [`fs.Stats`][] object's
`mode` property for determining the access permissions for a file.

<table>
<tr>
<th>Constant</th>
<th>Description</th>
</tr>
<tr>
<td><code>S_IRWXU</code></td>
<td>File mode indicating readable, writable and executable by owner.</td>
</tr>
<tr>
<td><code>S_IRUSR</code></td>
<td>File mode indicating readable by owner.</td>
</tr>
<tr>
<td><code>S_IWUSR</code></td>
<td>File mode indicating writable by owner.</td>
</tr>
<tr>
<td><code>S_IXUSR</code></td>
<td>File mode indicating executable by owner.</td>
</tr>
<tr>
<td><code>S_IRWXG</code></td>
<td>File mode indicating readable, writable and executable by group.</td>
</tr>
<tr>
<td><code>S_IRGRP</code></td>
<td>File mode indicating readable by group.</td>
</tr>
<tr>
<td><code>S_IWGRP</code></td>
<td>File mode indicating writable by group.</td>
</tr>
<tr>
<td><code>S_IXGRP</code></td>
<td>File mode indicating executable by group.</td>
</tr>
<tr>
<td><code>S_IRWXO</code></td>
<td>File mode indicating readable, writable and executable by others.</td>
</tr>
<tr>
<td><code>S_IROTH</code></td>
<td>File mode indicating readable by others.</td>
</tr>
<tr>
<td><code>S_IWOTH</code></td>
<td>File mode indicating writable by others.</td>
</tr>
<tr>
<td><code>S_IXOTH</code></td>
<td>File mode indicating executable by others.</td>
</tr>
</table>

[`Buffer.byteLength`]: buffer.html#buffer_class_method_buffer_bytelength_string_encoding
[`Buffer`]: buffer.html#buffer_buffer
[Caveats]: #fs_caveats
Expand Down Expand Up @@ -1418,3 +1646,4 @@ Synchronous versions of [`fs.write()`][]. Returns the number of bytes written.
[Readable Stream]: stream.html#stream_class_stream_readable
[Writable Stream]: stream.html#stream_class_stream_writable
[inode]: http://www.linux.org/threads/intro-to-inodes.4130
[FS Constants]: #fs_fs_constants
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