Multipart Related

Fast parsing multipart/related responses in the browser or node. Operates on raw bytes, in a streaming manner. Zero dependencies.

This is a research project and not meant to be production ready (yet).

Multipart construction is planned for the future, too, therefore the generic name.

API

The package exports a MultipartRelated constructor:

MultipartRelated(contentType)

contentType must be a multipart/related Content-Type string including the boundary, as usually sent by the servers. Eg 'multipart/related; boundary="865f3b787e6623728e6aa49fec037303" or 'multipart/related; boundary=865f3b787e6623728e6aa49fec037303.

This class provides a read(chunk) function, which inteded to be used in conjunction with ReadableStream, as you can see in the example above. It returns an array containing the parsed parts, which are already present.

A part is an object containing

• boundary: if the content is grouped together, aka related, this includes the individual boundary. If the part is a sole one, boundary is null. Can be used to group together parts.
• headers: the headers of each individual parts, usually eg Content-Type, Content-Disposition, Content-Length or Content-Encoding but not limited to those.
• data: an Uint8Array containing the raw part data.

Example

import MultipartRelated from 'multipart-related'

// fetch the multipart response
const response = await fetch(url)

// get Content-Type header
const contentType = response.headers.get('Content-Type')

// initialize the multipart parser
const multipart = new MultipartRelated(contentType)

// get the response body stream
const reader = response.body.getReader()

// tie together the process stream
const process = ({ value, done }) => {
  const parts = multipart.read(value)
  // do something with the parts as they arrive
  console.log(parts)

  if (!done) {
    return reader.read().then(process)
  }
}
// ... and kick-off processing
reader.read().then(process)

Tests

Run the tests with npm test or pick individual files via eg node test/multipart-related-parser-test.js.

(c) 2022 Johannes J. Schmidt