Support q-factor weighting in Accept header

[nflaig]

Problem description

At the moment, Lodestar does not support q-factor weighting in Accept header values.

The following value results in JSON response but it should be SSZ due to higher weight

application/octet-stream;q=1,application/json;q=0.9

The reason for this is that a strict equality check is used on the raw header value to determine the response type and if the value does not exactly match application/octet-stream is will always send a JSON response.

lodestar/packages/api/src/beacon/routes/debug.ts

Line 154 in 8794025

parseReq: ({params, headers}) => [params.state_id, headers.accept === mimeTypeSSZ ? "ssz" : "json"],

This can cause issues when using attestantio client as fetching the state as JSON is a lot slower and without increasing the max heap limit will crash Lodestar for a lot of networks, e.g. mainnet or holesky.

Solution description

Support q-factor weighting in Accept header

Additional context

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept
• https://hapi.dev/module/accept/api/?v=6.0.1#mediatypemediatypeheader-preferences
• https://www.npmjs.com/package/@hapi/accept
• https://www.npmjs.com/package/@fastify/accepts