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https://github.com/dotnetcarpenter/express-mime-sniff

express-mime-sniff is a package for setting HTTP `Content-Type` headers for files by utilizing a *nix `file` program available on your system.
https://github.com/dotnetcarpenter/express-mime-sniff

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express-mime-sniff is a package for setting HTTP `Content-Type` headers for files by utilizing a *nix `file` program available on your system.

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README 

        
# express-mime-sniff



![Github CI](https://github.com/dotnetCarpenter/express-mime-sniff/actions/workflows/node.js.yml/badge.svg)



**express-mime-sniff** is an [express](http://expressjs.com/) middleware for

setting HTTP `Content-Type` headers for files by utilizing a *nix `file`

program available on your system. **express-mime-sniff** is meant to be used

together and before [`express.static`][express.static].



This approach is independent of file extension, unlike the default logic used

by [`express.static`][express.static] and should therefore yield better results.



```

$ npm install express-mime-sniff --production --save

```



> **express-mime-sniff** should be considered **alpha** at this point.



**express-mime-sniff** uses [sanctuary][sanctuary], which by default does type

checking. To disable type checking, and gain performance, you must set

the environment variable: `NODE_ENV=production`.



# Benchmark



Currently, version `0.4.0` is 77% slower than using [`express.static`][express.static].



Requests/sec: 302.4 vs Requests/sec: 68.7 ~ 77% slower.



```

(68.7 - 302.4) / 302.4 * 100 = -77.28

```



`npm run benchmark`



OR



1. `cd benchmark`

2. `./server.mjs`

3. In another terminal run

   1. `./benchmark-express-static`

   2. `./benchmark-mime-sniff`



# API



- [middleware](#middleware)

  - [serving content from another directory](#serving-content-from-another-directory)

  - [options.filters](#optionsfilters)

  - [options.fallthrough](#optionsfallthrough)

  - [options.silent](#optionssilent)

- [sniffer](#sniffer)

  - [wrap sniffer in Promise](#wrap-sniffer-in-promise)

- [\*nix file program](#nix-file-program)



-------------------------------------------------------------------------------



## middleware



The `middleware` will add `Content-Type` and `'X-Content-Type-Options': 'nosniff'`

HTTP headers to all requests if successful. If an error occur, `middleware` will

write to `stderr` and do nothing with the request but forward it to the next

middleware function. If HTTP-headers are already sent to the client in a

previous middleware function, **express-mime-sniff** will do nothing but burn

CPU cycles.



Remember to use `middleware` before [`express.static`][express.static].



```js

import express        from 'express'

import { middleware } from 'express-mime-sniff'



const app = express ()

app.use (middleware ()) // important to use middleware before express.static

app.use (express.static('.'))

app.listen (8080)

```



### serving content from another directory



If you configure [`express.static`][express.static] to serve content from

another directory than your current working directory, you need to tell the

`middleware`. That is done in the exact same way as with

[`express.static`][express.static].



```js

const ROOT_PATH = 'specify/the/root/directory/from/which/to/serve/static/assets'

const app = express ()



app.use (middleware (ROOT_PATH))

app.use (express.static (ROOT_PATH))

app.listen (8080)

```



### options.filters



```js

middleware (ROOT_PATH, { filters })

```



Add an array of regular expressions to

filter which files **express-mime-sniff** should handle. The RegExp will be

tested against [`request.path`](http://expressjs.com/en/4x/api.html#req.path).



```js

const ROOT_PATH = 'spec/fixtures/'

const OPTIONS = { filters: [/\.txt$/, /\.png$/] }



app = express ()

app.use (middleware (ROOT_PATH, OPTIONS))

app.use (express.static (ROOT_PATH))

app.listen (8080)

```



Or you can use the built-in

[path filter in express](http://expressjs.com/en/4x/api.html#app.use). Notice

that express requires that the RegExp matches the entire path to the file or

the wrong path will be sent to **express-mime-sniff**.



```js

const ROOT_PATH = 'spec/fixtures/'



app = express ()

app.use ([/.*\.txt$/, /.*\.png$/], middleware (ROOT_PATH))

app.use (express.static (ROOT_PATH))

app.listen (8080)

```



### options.fallthrough



```js

middleware (ROOT_PATH, { fallthrough: false })

```



The default value is `true`.



The `fallthrough` option is modeled after serve-static's `fallthrough` option,

and tells the middleware to forward any error to express (like file not found),

if it is set to `false`.



_From the serve-static documentation:_

> Set the middleware to have client errors fall-through as just unhandled

> requests, otherwise forward a client error. The difference is that client

> errors like a bad request or a request to a non-existent file will cause

> this middleware to simply `next()` to your next middleware when this value

> is `true`. When this value is `false`, these errors (even 404s), will invoke

> `next(err)`.

>

> Typically `true` is desired such that multiple physical directories can be

mapped to the same web address or for routes to fill in non-existent files.

>

> The value `false` can be used if this middleware is mounted at a path that

> is designed to be strictly a single file system directory, which allows for

> short-circuiting 404s for less overhead. This middleware will also reply to

> all methods.



### options.silent



```js

middleware (ROOT_PATH, { silent: true })

```



The `silence` option will stop middleware from printing to stderr on error.



If `silence` is set to `true` and `fallthough` is set to `false`, then express

will print the error to stderr, cancelling out the effect. But still useful,

since you would else get the error message printed twice.



## sniffer



If you are unhappy with the `middleware` you can write your own, using `sniffer`.



> NOTE: `sanctuary` is not required but **express-mime-sniff** uses `sanctuary`,

> so it is included in the package, as a dependency.



```js

import S from 'sanctuary'

import { sniffer } from 'express-mime-sniff'



/* @typedef sniffer

 * sniffer :: String Error, String MimeType, String Path => (Error -> void) -> (MimeType -> void) -> Path -> void

 * @param {{ (string: error):any }} errorHandler Function that will handle an error.

 * @param {{ (string: mimeType):any }} successHandler Function that will get mime-type for `path`.

 * @param {string} path Path to the file you want the mime-type for.

 * @returns {void}

 */



const test = sniffer

  (S.pipe ([console.error, () => process.exit(1)])) // error callback

  (console.log)                                     // success callback



// happy path

test ('spec/fixtures/fake.jpg') // -> "image/png charset=binary"



// sad path

test ('no-such-file.jpg')       // -> "ERROR: cannot stat `no-such-file.jpg' (No such file or directory)"

```



### wrap sniffer in Promise



```js

const promise = new Promise ((resolve, reject) => {

  sniffer (reject) (resolve) ('path/to/file')

})

```



## *nix file program



> Description: Recognize the type of data in a file using "magic" numbers

> The file command is "a file type guesser", a command-line tool that

> tells you in words what kind of data a file contains.



You can usually configure _magic mime-types_ in either `/etc/magic`,

`/etc/magic.mime` or add _magic_ files to `/usr/share/misc/magic/`.

More information with `man magic` or at https://www.darwinsys.com/file/.



[express.static]: http://expressjs.com/en/4x/api.html#express.static

[sanctuary]: https://sanctuary.js.org/