# path-scurry

Extremely high performant utility for building tools that read
the file system, minimizing filesystem and path string munging
operations to the greatest degree possible.

## Ugh, yet another file traversal thing on npm?

Yes. None of the existing ones gave me exactly what I wanted.

## Well what is it you wanted?

While working on [glob](http://npm.im/glob), I found that I
needed a module to very efficiently manage the traversal over a
folder tree, such that:

1. No `readdir()` or `stat()` would ever be called on the same
   file or directory more than one time.
2. No `readdir()` calls would be made if we can be reasonably
   sure that the path is not a directory. (Ie, a previous
   `readdir()` or `stat()` covered the path, and
   `ent.isDirectory()` is false.)
3. `path.resolve()`, `dirname()`, `basename()`, and other
   string-parsing/munging operations are be minimized. This
   means it has to track "provisional" child nodes that may not
   exist (and if we find that they _don't_ exist, store that
   information as well, so we don't have to ever check again).
4. The API is not limited to use as a stream/iterator/etc. There
   are many cases where an API like node's `fs` is preferrable.
5. It's more important to prevent excess syscalls than to be up
   to date, but it should be smart enough to know what it
   _doesn't_ know, and go get it seamlessly when requested.
6. Do not blow up the JS heap allocation if operating on a
   directory with a huge number of entries.
7. Handle all the weird aspects of Windows paths, like UNC paths
   and drive letters and wrongway slashes, so that the consumer
   can return canonical platform-specific paths without having to
   parse or join or do any error-prone string munging.

## PERFORMANCE

JavaScript people throw around the word "blazing" a lot. I hope
that this module doesn't blaze anyone. But it does go very fast,
in the cases it's optimized for, if used properly.

PathScurry provides ample opportunities to get extremely good
performance, as well as several options to trade performance for
convenience.

Benchmarks can be run by executing `npm run bench`.

As is always the case, doing more means going slower, doing
less means going faster, and there are trade offs between speed
and memory usage.

PathScurry makes heavy use of [LRUCache](http://npm.im/lru-cache)
to efficiently cache whatever it can, and `Path` objects remain
in the graph for the lifetime of the walker, so repeated calls
with a single PathScurry object will be extremely fast. However,
adding items to a cold cache means "doing more", so in those
cases, we pay a price. Nothing is free, but every effort has been
made to reduce costs wherever possible.

Also, note that a "cache as long as possible" approach means that
changes to the filesystem may not be reflected in the results of
repeated PathScurry operations.

For resolving string paths, `PathScurry` ranges from 5-50 times
faster than `path.resolve` on repeated resolutions, but around
100 to 1000 times _slower_ on the first resolution. If your
program is spending a lot of time resolving the _same_ paths
repeatedly (like, thousands or millions of times), then this can
be beneficial. But both implementations are pretty fast, and
speeding up an infrequent operation from 4µs to 400ns is not
going to move the needle on your app's performance.

For walking file system directory trees, a lot depends on how
often a given PathScurry object will be used, and also on the
walk method used.

With default settings on a folder tree of 100,000 items,
consisting of around a 10-to-1 ratio of normal files to
directories, PathScurry performs comparably to
[@nodelib/fs.walk](http://npm.im/@nodelib/fs.walk), which is the
fastest and most reliable file system walker I could find. As
far as I can tell, it's almost impossible to go much faster in a
Node.js program, just based on how fast you can push syscalls out
to the fs thread pool.

On my machine, that is about 1000-1200 completed walks per second
for async or stream walks, and around 500-600 walks per second
synchronously.

In the warm cache state, PathScurry's performance increases
around 4x for async `for await` iteration, 10-15x faster for
streams and synchronous `for of` iteration, and anywhere from 30x
to 80x faster for the rest.

```
# walk 100,000 fs entries, 10/1 file/dir ratio
# operations / ms
 New PathScurry object  |  Reuse PathScurry object
     stream:  1112.589  |  13974.917
sync stream:   492.718  |  15028.343
 async walk:  1095.648  |  32706.395
  sync walk:   527.632  |  46129.772
 async iter:  1288.821  |   5045.510
  sync iter:   498.496  |  17920.746
```

A hand-rolled walk calling `entry.readdir()` and recursing
through the entries can benefit even more from caching, with
greater flexibility and without the overhead of streams or
generators.

The cold cache state is still limited by the costs of file system
operations, but with a warm cache, the only bottleneck is CPU
speed and VM optimizations. Of course, in that case, some care
must be taken to ensure that you don't lose performance as a
result of silly mistakes, like calling `readdir()` on entries
that you know are not directories.

```
# manual recursive iteration functions
      cold cache  |  warm cache
async:  1164.901  |  17923.320
   cb:  1101.127  |  40999.344
zalgo:  1082.240  |  66689.936
 sync:   526.935  |  87097.591
```

In this case, the speed improves by around 10-20x in the async
case, 40x in the case of using `entry.readdirCB` with protections
against synchronous callbacks, and 50-100x with callback
deferrals disabled, and _several hundred times faster_ for
synchronous iteration.

If you can think of a case that is not covered in these
benchmarks, or an implementation that performs significantly
better than PathScurry, please [let me
know](https://github.com/isaacs/path-scurry/issues).

## USAGE

```ts
// hybrid module, load with either method
import { PathScurry, Path } from 'path-scurry'
// or:
const { PathScurry, Path } = require('path-scurry')

// very simple example, say we want to find and
// delete all the .DS_Store files in a given path
// note that the API is very similar to just a
// naive walk with fs.readdir()
import { unlink } from 'fs/promises'

// easy way, iterate over the directory and do the thing
const pw = new PathScurry(process.cwd())
for await (const entry of pw) {
  if (entry.isFile() && entry.name === '.DS_Store') {
    unlink(entry.fullpath())
  }
}

// here it is as a manual recursive method
const walk = async (entry: Path) => {
  const promises: Promise<any> = []
  // readdir doesn't throw on non-directories, it just doesn't
  // return any entries, to save stack trace costs.
  // Items are returned in arbitrary unsorted order
  for (const child of await pw.readdir(entry)) {
    // each child is a Path object
    if (child.name === '.DS_Store' && child.isFile()) {
      // could also do pw.resolve(entry, child.name),
      // just like fs.readdir walking, but .fullpath is
      // a *slightly* more efficient shorthand.
      promises.push(unlink(child.fullpath()))
    } else if (child.isDirectory()) {
      promises.push(walk(child))
    }
  }
  return Promise.all(promises)
}

walk(pw.cwd).then(() => {
  console.log('all .DS_Store files removed')
})

const pw2 = new PathScurry('/a/b/c') // pw2.cwd is the Path for /a/b/c
const relativeDir = pw2.cwd.resolve('../x') // Path entry for '/a/b/x'
const relative2 = pw2.cwd.resolve('/a/b/d/../x') // same path, same entry
assert.equal(relativeDir, relative2)
```

## API

[Full TypeDoc API](https://isaacs.github.io/path-scurry)

There are platform-specific classes exported, but for the most
part, the default `PathScurry` and `Path` exports are what you
most likely need, unless you are testing behavior for other
platforms.

Intended public API is documented here, but the full
documentation does include internal types, which should not be
accessed directly.

### Interface `PathScurryOpts`

The type of the `options` argument passed to the `PathScurry`
constructor.

- `nocase`: Boolean indicating that file names should be compared
  case-insensitively. Defaults to `true` on darwin and win32
  implementations, `false` elsewhere.

  **Warning** Performing case-insensitive matching on a
  case-sensitive filesystem will result in occasionally very
  bizarre behavior. Performing case-sensitive matching on a
  case-insensitive filesystem may negatively impact performance.

- `childrenCacheSize`: Number of child entries to cache, in order
  to speed up `resolve()` and `readdir()` calls. Defaults to
  `16 * 1024` (ie, `16384`).

  Setting it to a higher value will run the risk of JS heap
  allocation errors on large directory trees. Setting it to `256`
  or smaller will significantly reduce the construction time and
  data consumption overhead, but with the downside of operations
  being slower on large directory trees. Setting it to `0` will
  mean that effectively no operations are cached, and this module
  will be roughly the same speed as `fs` for file system
  operations, and _much_ slower than `path.resolve()` for
  repeated path resolution.

- `fs` An object that will be used to override the default `fs`
  methods.  Any methods that are not overridden will use Node's
  built-in implementations.

  - lstatSync
  - readdir (callback `withFileTypes` Dirent variant, used for
    readdirCB and most walks)
  - readdirSync
  - readlinkSync
  - realpathSync
  - promises: Object containing the following async methods:
    - lstat
    - readdir (Dirent variant only)
    - readlink
    - realpath

### Interface `WalkOptions`

The options object that may be passed to all walk methods.

- `withFileTypes`: Boolean, default true. Indicates that `Path`
  objects should be returned. Set to `false` to get string paths
  instead.
- `follow`: Boolean, default false. Attempt to read directory
  entries from symbolic links. Otherwise, only actual directories
  are traversed. Regardless of this setting, a given target path
  will only ever be walked once, meaning that a symbolic link to
  a previously traversed directory will never be followed.

  Setting this imposes a slight performance penalty, because
  `readlink` must be called on all symbolic links encountered, in
  order to avoid infinite cycles.

- `filter`: Function `(entry: Path) => boolean`. If provided,
  will prevent the inclusion of any entry for which it returns a
  falsey value. This will not prevent directories from being
  traversed if they do not pass the filter, though it will
  prevent the directories themselves from being included in the
  results. By default, if no filter is provided, then all
  entries are included in the results.
- `walkFilter`: Function `(entry: Path) => boolean`. If
  provided, will prevent the traversal of any directory (or in
  the case of `follow:true` symbolic links to directories) for
  which the function returns false. This will not prevent the
  directories themselves from being included in the result set.
  Use `filter` for that.

Note that TypeScript return types will only be inferred properly
from static analysis if the `withFileTypes` option is omitted, or
a constant `true` or `false` value.

### Class `PathScurry`

The main interface. Defaults to an appropriate class based on
the current platform.

Use `PathScurryWin32`, `PathScurryDarwin`, or `PathScurryPosix`
if implementation-specific behavior is desired.

All walk methods may be called with a `WalkOptions` argument to
walk over the object's current working directory with the
supplied options.

#### `async pw.walk(entry?: string | Path | WalkOptions, opts?: WalkOptions)`

Walk the directory tree according to the options provided,
resolving to an array of all entries found.

#### `pw.walkSync(entry?: string | Path | WalkOptions, opts?: WalkOptions)`

Walk the directory tree according to the options provided,
returning an array of all entries found.

#### `pw.iterate(entry?: string | Path | WalkOptions, opts?: WalkOptions)`

Iterate over the directory asynchronously, for use with `for
await of`. This is also the default async iterator method.

#### `pw.iterateSync(entry?: string | Path | WalkOptions, opts?: WalkOptions)`

Iterate over the directory synchronously, for use with `for of`.
This is also the default sync iterator method.

#### `pw.stream(entry?: string | Path | WalkOptions, opts?: WalkOptions)`

Return a [Minipass](http://npm.im/minipass) stream that emits
each entry or path string in the walk. Results are made
available asynchronously.

#### `pw.streamSync(entry?: string | Path | WalkOptions, opts?: WalkOptions)`

Return a [Minipass](http://npm.im/minipass) stream that emits
each entry or path string in the walk. Results are made
available synchronously, meaning that the walk will complete in a
single tick if the stream is fully consumed.

#### `pw.cwd`

Path object representing the current working directory for the
PathScurry.

#### `pw.depth(path?: Path | string): number`

Return the depth of the specified path (or the PathScurry cwd)
within the directory tree.

Root entries have a depth of `0`.

#### `pw.resolve(...paths: string[])`

Caching `path.resolve()`.

Significantly faster than `path.resolve()` if called repeatedly
with the same paths. Significantly slower otherwise, as it
builds out the cached Path entries.

To get a `Path` object resolved from the `PathScurry`, use
`pw.cwd.resolve(path)`. Note that `Path.resolve` only takes a
single string argument, not multiple.

#### `pw.relative(path: string | Path): string`

Return the relative path from the PathWalker cwd to the supplied
path string or entry.

If the nearest common ancestor is the root, then an absolute path
is returned.

#### `pw.basename(path: string | Path): string`

Return the basename of the provided string or Path.

#### `pw.dirname(path: string | Path): string`

Return the parent directory of the supplied string or Path.

#### `async pw.readdir(dir = pw.cwd, opts = { withFileTypes: true })`

Read the directory and resolve to an array of strings if
`withFileTypes` is explicitly set to `false` or Path objects
otherwise.

Can be called as `pw.readdir({ withFileTypes: boolean })` as
well.

Returns `[]` if no entries are found, or if any error occurs.

Note that TypeScript return types will only be inferred properly
from static analysis if the `withFileTypes` option is omitted, or
a constant `true` or `false` value.

#### `pw.readdirSync(dir = pw.cwd, opts = { withFileTypes: true })`

Synchronous `pw.readdir()`

#### `async pw.readlink(link = pw.cwd, opts = { withFileTypes: false })`

Call `fs.readlink` on the supplied string or Path object, and
return the result.

Can be called as `pw.readlink({ withFileTypes: boolean })` as
well.

Returns `undefined` if any error occurs (for example, if the
argument is not a symbolic link), or a `Path` object if
`withFileTypes` is explicitly set to `true`, or a string
otherwise.

Note that TypeScript return types will only be inferred properly
from static analysis if the `withFileTypes` option is omitted, or
a constant `true` or `false` value.

#### `pw.readlinkSync(link = pw.cwd, opts = { withFileTypes: false })`

Synchronous `pw.readlink()`

#### `async pw.lstat(entry = pw.cwd)`

Call `fs.lstat` on the supplied string or Path object, and fill
in as much information as possible, returning the updated `Path`
object.

Returns `undefined` if the entry does not exist, or if any error
is encountered.

Note that some `Stats` data (such as `ino`, `dev`, and `mode`) will
not be supplied. For those things, you'll need to call
`fs.lstat` yourself.

#### `pw.lstatSync(entry = pw.cwd)`

Synchronous `pw.lstat()`

#### `pw.realpath(entry = pw.cwd, opts = { withFileTypes: false })`

Call `fs.realpath` on the supplied string or Path object, and
return the realpath if available.

Returns `undefined` if any error occurs.

May be called as `pw.realpath({ withFileTypes: boolean })` to run
on `pw.cwd`.

#### `pw.realpathSync(entry = pw.cwd, opts = { withFileTypes: false })`

Synchronous `pw.realpath()`

### Class `Path` implements [fs.Dirent](https://nodejs.org/docs/latest/api/fs.html#class-fsdirent)

Object representing a given path on the filesystem, which may or
may not exist.

Note that the actual class in use will be either `PathWin32` or
`PathPosix`, depending on the implementation of `PathScurry` in
use. They differ in the separators used to split and join path
strings, and the handling of root paths.

In `PathPosix` implementations, paths are split and joined using
the `'/'` character, and `'/'` is the only root path ever in use.

In `PathWin32` implementations, paths are split using either
`'/'` or `'\\'` and joined using `'\\'`, and multiple roots may
be in use based on the drives and UNC paths encountered. UNC
paths such as `//?/C:/` that identify a drive letter, will be
treated as an alias for the same root entry as their associated
drive letter (in this case `'C:\\'`).

#### `path.name`

Name of this file system entry.

**Important**: *always* test the path name against any test
string using the `isNamed` method, and not by directly comparing
this string.  Otherwise, unicode path strings that the system
sees as identical will not be properly treated as the same path,
leading to incorrect behavior and possible security issues.

#### `path.isNamed(s: string)`

Return true if the path is a match for the given path name.  This
handles case sensitivity and unicode normalization.

Note: even on case-sensitive systems, it is **not** safe to test
the equality of the `.name` property to determine whether a given
pathname matches, due to unicode normalization mismatches.

Always use this method instead of testing the `path.name`
property directly.

#### `path.depth()`

Return the depth of the Path entry within the directory tree.
Root paths have a depth of `0`.

#### `path.fullpath()`

The fully resolved path to the entry.

#### `path.isFile()`, `path.isDirectory()`, etc.

Same as the identical `fs.Dirent.isX()` methods.

#### `path.isUnknown()`

Returns true if the path's type is unknown. Always returns true
when the path is known to not exist.

#### `path.resolve(p: string)`

Return a `Path` object associated with the provided path string
as resolved from the current Path object.

#### `path.relative(): string`

Return the relative path from the PathWalker cwd to the supplied
path string or entry.

If the nearest common ancestor is the root, then an absolute path
is returned.

#### `async path.readdir()`

Return an array of `Path` objects found by reading the associated
path entry.

If path is not a directory, or if any error occurs, returns `[]`,
and marks all children as provisional and non-existent.

#### `path.readdirSync()`

Synchronous `path.readdir()`

#### `async path.readlink()`

Return the `Path` object referenced by the `path` as a symbolic
link.

If the `path` is not a symbolic link, or any error occurs,
returns `undefined`.

#### `path.readlinkSync()`

Synchronous `path.readlink()`

#### `async path.lstat()`

Call `lstat` on the path object, and fill it in with details
determined.

If path does not exist, or any other error occurs, returns
`undefined`, and marks the path as "unknown" type.

#### `path.lstatSync()`

Synchronous `path.lstat()`

#### `async path.realpath()`

Call `realpath` on the path, and return a Path object
corresponding to the result, or `undefined` if any error occurs.

#### `path.realpathSync()`

Synchornous `path.realpath()`
