npm package: @mojule/mode
Description: Helper functions for dealing with Linux style permissions
Author: Nik Coughlin
Latest version: 0.2.0

# mode

Helper functions for dealing with Linux style permissions

Does not handle sticky bit or set uid/gid on execute - I don't need these - 
happy to accept pull requests, or will add when I need it

`npm install @mojule/mode`

## updateMode

```js
import { updateMode } from '@mojule/mode'

// resource's existing permssions
const modeBefore = 0o0777

// new permissions
const modeAfter = updateMode( modeBefore, 'u+rw,g-rwx,o-rx' )

// 702
console.log( modeAfter.toString( 8 ) )
```

```ts
type UpdateMode = ( mode: number, notation: string | number ) => number
```

## canAccess

```js
import { canAccess, rwx } from '@mojule/mode'

// determine from your environment eg `isRoot = req.user.id === root.id`
const options = { 
  isRoot: true, 
  isGroup: true,
  permissions: 0o0010
}

// root can always read/write
const requestExecute = rwx

// root can execute file because isGroup: true and perms has group x 
const canRootInGroupExecuteFile = canAccess( requestExecute, options )

// true
console.log( canRootInGroupExecuteFile )
```

```ts
type CanAccess = (
  request: number, options?: Partial<AccessOptions>
) => boolean

type AccessOptions = { 
  isDirectory: boolean
  isRoot: boolean
  isOwner: boolean
  isGroup: boolean
  permissions: number
}
```

```js
import { defaultAccessOptions } from '@mojule/mode'

/*
{
  isDirectory: false,
  isRoot: false,
  isGroup: false,
  isOwner: false,
  permissions: 0o0000
}
*/
console.log( defaultAccessOptions )
```

```js
import { canAccess, w } from '@mojule/mode'

// no options returns false for any flag 
console.log( canAccess( w ) )

// no options returns true for empty flags 
console.log( canAccess( 0 ) )
```

## symbolic notation

```js
import { 
  createSymbolicNotation, parseSymbolicNotation 
} from '@mojule/mode'

const note = createSymbolicNotation( 0o0700 )

// rwx------
console.log( note )

const mode = parseSymbolicNotation( 'rw-rw-rw-' )

// 666
console.log( mode.toString( 8 ) )
```

```ts
type CreateSymbolicNotation = ( 
  mode: number 
) => string & SymbolicNotation

type ParseSymbolicNotation = (notation: string) => number

type NullableKey<T extends 'r'|'w'|'x'> = T | '-'

type NullablePerms = 
  `${ NullableKey<'r'> }${ NullableKey<'w'> }${ NullableKey<'x'> }`
)

type SymbolicNotation = (
  `${ NullablePerms }${ NullablePerms }${ NullablePerms }`
)
```

## symbolic update notation

```js
import { 
  parseSymbolicUpdate, applySymbolicUpdateGroup 
} from '@mojule/mode'

const modeBefore = 0o0777

const updates = parseSymbolicUpdate( 'u+rw,g-rwx,o-rx' )

const modeAfter = applySymbolicUpdateGroup( modeBefore, updates )

// 702
console.log( modeAfter.toString( 8 ) )
```

```ts
type ParseSymbolicUpdate = (symbolic: string) => Symbolic[]

type ApplySymbolicUpdateGroup = (
  mode: number, updates: Symbolic[]
) => number

type Symbolic = {
  roleGroup: ( 'u' | 'g' | 'o' )[]
  permsGroup: PermsFlags[]
}

type PermsFlags = {
  operation: '+' | '-' | '='
  perms: ( 'r' | 'w' | 'x' )[]
}
```

## core

```js
import { 
  hasBit, getBit, setBit, clearBit, hasRequestBit,
  r, w, x, wx, rwx
} from '@mojule/mode'

// true
console.log( hasBit( o0710, 'g', 'x' ) )

// false
console.log( hasBit( o0710, 'o', 'x' ) )

// 0o0010
console.log( getBit( o0710, 'g', 'x' ) )

// 0o0000
console.log( getBit( o0710, 'o', 'x' ) )

// 0o0700
console.log( clearBit( o0710, 'g', 'x' ) )

// true
console.log( hasRequestBit( rwx, 'r' ) )

// false
console.log( hasRequestBit( wx, 'r' ) )

// true
console.log( hasRequestBit( r | w | x, 'r' ) )

// false
console.log( hasRequestBit( w | x, 'r' ) )
```

```ts
type RoleKey = 'u' | 'g' | 'o' 
type PermKey = 'r' | 'w' | 'x'

type BitFn<T = number> = ( 
  mode: number, role: RoleKey, perm: PermKey
) => T 

type HasBit = BitFn<boolean>
type GetBit = BitFn
type SetBit = BitFn
type ClearBit = BitFn
type HasRequestBit = (requestMode: number, perm: PermKey) => boolean
```

## license 

MIT License

Copyright (c) 2021 Nik Coughlin

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.