meros

What is meros?

The meros npm package is designed to handle multipart responses in a more convenient and efficient way. It is particularly useful for dealing with GraphQL multipart responses, allowing clients to process parts of the response as they arrive, rather than waiting for the entire response. This can improve performance and user experience in applications that consume streaming APIs or need to handle large, multipart responses.

What are meros's main functionalities?

Parsing GraphQL multipart responses

This code sample demonstrates how to use meros to parse a GraphQL multipart response from a fetch request. It checks if the response is of type 'multipart/mixed' and then uses meros to asynchronously iterate over each part of the response, logging the body of each part if it is JSON.

import { meros } from 'meros';

const response = await fetch('/graphql', {
  body: JSON.stringify({ query }),
  method: 'POST',
});

if (response.headers.get('content-type').includes('multipart/mixed')) {
  const parts = await meros(response);
  for await (const part of parts) {
    if (part.json) {
      console.log(part.body);
    }
  }
}

Other packages similar to meros

graphql-helix

GraphQL Helix is a collection of utility functions for building your own GraphQL HTTP server. It supports multipart responses similar to meros but is more focused on the server-side handling of GraphQL requests, including features for query execution and subscription support.

subscriptions-transport-ws

This package is a transport layer for handling GraphQL subscriptions over WebSocket. While it doesn't directly deal with multipart responses, it offers a real-time data fetching capability that can be seen as an alternative approach to handling streaming data, compared to the multipart response handling in meros.

README

npm add meros makes reading multipart responses simple

⚡ Features

• No dependencies
• Seemless api
• Super performant
• Supports any¹ content-type
• preamble and epilogue don't yield
• Browser/Node Compatible
• Plugs into existing libraries like Relay and rxjs

🚀 Usage

Visit /examples for more info!

// Relies on bundler/environment detection
import { meros } from 'meros';

const parts = await fetch('/api').then(meros);

// As a simple Async Generator
for await (const part of parts) {
  // Do something with this part
}

// Used with rxjs streams
from(parts).subscribe((part) => {
  // Do something with it
});

Specific Environment

Browser

import { meros } from 'meros/browser';
// import { meros } from 'https://cdn.skypack.dev/meros';

const parts = await fetch('/api').then(meros);

Node

import http from 'http';
import { meros } from 'meros/node';

const response = await new Promise((resolve) => {
  const request = http.get(`http://example.com/api`, (response) => {
    resolve(response);
  });
  request.end();
});

const parts = await meros(response);

🔎 API

Meros offers two flavours, both for the browser and for node; but their api's are fundamentally the same.

Note: The type Response is used loosely here and simply alludes to Node's IncomingMessage or the browser's Response type.

meros(response: Response, options?: Options)

Returns: Promise<Response | AsyncGenerator<Part | Part[]>

Meros returns a promise that will resolve to an AsyncGenerator if the response is of multipart/mixed mime, or simply returns the Response if something else; helpful for middlewares. The idea here being that you run meros as a chain off fetch.

fetch('/api').then(meros);

If the content-type is NOT a multipart, then meros will resolve with the response argument.

Example on how to handle this case

import { meros } from 'meros';

const response = await fetch('/api'); // Assume this isnt multipart
const parts = await meros(response);

if (parts[Symbol.asyncIterator] < 'u') {
  for await (const part of parts) {
    // Do something with this part
  }
} else {
  const data = await parts.json();
}

each Part gives you access to:

• json: boolean ~ Tells you the body would be a JavaScript object of your defined generic T.
• headers: object ~ A key-value pair of all headers discovered from this part.
• body: T | Fallback ~ Is the body of the part, either as a JavaScript object (noted by json) or the base type of the environment (Buffer | string, for Node and Browser respectively).

options.multiple: boolean

Default: false

Setting this to true will yield once for all available parts of a chunk, rather than yielding once per part. This is an optimization technique for technologies like GraphQL where rather than commit the payload to the store, to be added-to in the next process-tick we can simply do that synchronously.

Warning: This will alter the behaviour and yield arrays—than yield payloads.

const chunks = await fetch('/api').then((response) => meros(response, { multiple: true }));

// As a simple Async Generator
for await (const parts of chunks) {
  for (const part of parts) {
    // Do something with this part, maybe aggregate?
  }
}

💨 Benchmark

via the /bench directory with Node v18.0.0

Node
✔ meros        ~ 1,271,218 ops/sec ± 0.84%
✘ it-multipart ~   700,039 ops/sec ± 0.72%
--
it-multipart (FAILED @ "should match reference patch set")

Browser
✔ meros                   ~ 800,941 ops/sec ± 1.06%
✘ fetch-multipart-graphql ~ 502,175 ops/sec ± 0.75%
--
fetch-multipart-graphql (FAILED @ "should match reference patch set")

🎒 Notes

Why the name? meros comes from Ancient Greek μέρος méros, meaning "part".

This library aims to implement RFC1341 in its entirety, however we aren't there yet. That being said, you may very well use this library in other scenarios like streaming in file form uploads.

Another goal here is to aide in being the defacto standard transport library to support @defer and @stream GraphQL directives

Caveats

• No support the /alternative , /digest or /parallel subtype at this time.
• No support for nested multiparts

❤ Thanks

Special thanks to Luke Edwards for performance guidance and high level api design.

😇 Compassion

This library is simple, a meer few hundred bytes. It's easy to copy, and easy to alter. If you do, that is fine ❤️ im all for the freedom of software. But please give credit where credit is due.

License

MIT © Marais Rossouw

Footnotes

• By default, we'll look for JSON, and parse that for you. If not, we'll give you the body as what was streamed. ↩