type-is

What is type-is?

The type-is npm package is used to determine the MIME type of the content represented by a request or response object. It can check if the content type matches any of the given MIME types, which can be useful for handling requests in web applications, especially when dealing with REST APIs or any other HTTP-based interfaces.

What are type-is's main functionalities?

Check content type

This feature allows you to check if a given content type matches one of the specified MIME types. In the code sample, it checks if 'image/png' is an image MIME type.

const typeis = require('type-is');
const contentType = 'image/png';
const result = typeis.is(contentType, ['image/*']); // returns 'image/png'

Determine if request has body

This feature checks if the request object has a body by inspecting the 'Content-Type' header.

const typeis = require('type-is');
const req = { headers: { 'content-type': 'text/html' } };
const hasBody = typeis.hasBody(req); // returns true

Determine the type of request

This feature determines the type of the request by checking if the 'Content-Type' header matches any of the provided MIME types.

const typeis = require('type-is');
const req = { headers: { 'content-type': 'application/json' } };
const result = typeis(req, ['json', 'urlencoded', 'multipart']); // returns 'json'

Other packages similar to type-is

mime-types

The mime-types package is similar to type-is in that it provides functionality for looking up MIME types based on file extensions and vice versa. However, it does not directly deal with request objects and is more focused on the mapping between MIME types and file extensions.

content-type

The content-type package is used to parse and format 'Content-Type' headers. Unlike type-is, it does not provide methods to check if a request or response matches a specific content type, but it can be used to construct and deconstruct 'Content-Type' headers.

accepts

The accepts package is designed to deal with the HTTP Accept header, allowing servers to negotiate content type with clients. It is similar to type-is in that it helps determine the type of content, but it focuses on what the client can accept, rather than what the server is receiving or sending.

README

type-is

Infer the content-type of a request.

Install

This is a Node.js module available through the npm registry. Installation is done using the npm install command:

$ npm install type-is

API

var http = require('http')
var typeis = require('type-is')

http.createServer(function (req, res) {
  var istext = typeis(req, ['text/*'])
  res.end('you ' + (istext ? 'sent' : 'did not send') + ' me text')
})

typeis(request, types)

Checks if the request is one of the types. If the request has no body, even if there is a Content-Type header, then null is returned. If the Content-Type header is invalid or does not matches any of the types, then false is returned. Otherwise, a string of the type that matched is returned.

The request argument is expected to be a Node.js HTTP request. The types argument is an array of type strings.

Each type in the types array can be one of the following:

• A file extension name such as json. This name will be returned if matched.
• A mime type such as application/json.
• A mime type with a wildcard such as */* or */json or application/*. The full mime type will be returned if matched.
• A suffix such as +json. This can be combined with a wildcard such as */vnd+json or application/*+json. The full mime type will be returned if matched.

Some examples to illustrate the inputs and returned value:

// req.headers.content-type = 'application/json'

typeis(req, ['json']) // => 'json'
typeis(req, ['html', 'json']) // => 'json'
typeis(req, ['application/*']) // => 'application/json'
typeis(req, ['application/json']) // => 'application/json'

typeis(req, ['html']) // => false

typeis.hasBody(request)

Returns a Boolean if the given request has a body, regardless of the Content-Type header.

Having a body has no relation to how large the body is (it may be 0 bytes). This is similar to how file existence works. If a body does exist, then this indicates that there is data to read from the Node.js request stream.

if (typeis.hasBody(req)) {
  // read the body, since there is one

  req.on('data', function (chunk) {
    // ...
  })
}

typeis.is(mediaType, types)

Checks if the mediaType is one of the types. If the mediaType is invalid or does not matches any of the types, then false is returned. Otherwise, a string of the type that matched is returned.

The mediaType argument is expected to be a media type string. The types argument is an array of type strings.

Each type in the types array can be one of the following:

• A file extension name such as json. This name will be returned if matched.
• A mime type such as application/json.
• A mime type with a wildcard such as */* or */json or application/*. The full mime type will be returned if matched.
• A suffix such as +json. This can be combined with a wildcard such as */vnd+json or application/*+json. The full mime type will be returned if matched.

Some examples to illustrate the inputs and returned value:

var mediaType = 'application/json'

typeis.is(mediaType, ['json']) // => 'json'
typeis.is(mediaType, ['html', 'json']) // => 'json'
typeis.is(mediaType, ['application/*']) // => 'application/json'
typeis.is(mediaType, ['application/json']) // => 'application/json'

typeis.is(mediaType, ['html']) // => false

typeis.match(expected, actual)

Match the type string expected with actual, taking in to account wildcards. A wildcard can only be in the type of the subtype part of a media type and only in the expected value (as actual should be the real media type to match). A suffix can still be included even with a wildcard subtype. If an input is malformed, false will be returned.

typeis.match('text/html', 'text/html') // => true
typeis.match('*/html', 'text/html') // => true
typeis.match('text/*', 'text/html') // => true
typeis.match('*/*', 'text/html') // => true
typeis.match('*/*+json', 'application/x-custom+json') // => true

typeis.normalize(type)

Normalize a type string. This works by performing the following:

• If the type is not a string, false is returned.
• If the string starts with + (so it is a +suffix shorthand like +json), then it is expanded to contain the complete wildcard notation of */*+suffix.
• If the string contains a /, then it is returned as the type.
• Else the string is assumed to be a file extension and the mapped media type is returned, or false is there is no mapping.

This includes two special mappings:

• 'multipart' -> 'multipart/*'
• 'urlencoded' -> 'application/x-www-form-urlencoded'

Examples

Example body parser

var express = require('express')
var typeis = require('type-is')

var app = express()

app.use(function bodyParser (req, res, next) {
  if (!typeis.hasBody(req)) {
    return next()
  }

  switch (typeis(req, ['urlencoded', 'json', 'multipart'])) {
    case 'urlencoded':
      // parse urlencoded body
      throw new Error('implement urlencoded body parsing')
    case 'json':
      // parse json body
      throw new Error('implement json body parsing')
    case 'multipart':
      // parse multipart body
      throw new Error('implement multipart body parsing')
    default:
      // 415 error code
      res.statusCode = 415
      res.end()
      break
  }
})

License

MIT