feat: http upload/download progress handlers

[Gozala]

As per #52 this adds onUploadProgress / onDownloadProgress optional handlers. Intention is to allow ipfs-webui to render file upload progress when new content is added.

Fixes #52

[achingbrain]

Is there a way this can work in node too? Shim in xmlhttprequest (disclaimer - I've never used that module, just Googled it) or fall back to http from node core?

[Gozala]

Is there a way this can work in node too? Shim in xmlhttprequest (disclaimer - I've never used that module, just Googled it) or fall back to http from node core?

@achingbrain can we do this as a followup, so we could unblock webui ipfs/ipfs-webui#1534 ?

[Gozala]

Is there a way this can work in node too? Shim in xmlhttprequest (disclaimer - I've never used that module, just Googled it) or fall back to http from node core?

I also looked at the linked library along with numerous others in on npm and it seems that none support upload / download progress events and in fact non that I have looked support node streams. node-fetch is particular in that regard that it switches ReadableStreams for node streams and has it's own Blob implementation that we don't leverage in node code.

We could fall back to plain http module in node, but I am afraid that will wind up in the same ball park as core of node-fetch
https://github.com/node-fetch/node-fetch/blob/8f406b789ab8464c195be87528c42dfcbd912893/src/index.js (probably bit more). So I want to double check that this is indeed the path you want us to take.

[Gozala]

@achingbrain I have added progress events for node as well, by wrapping around request body if onUploadProgress is provided and a stream event listener for response body if onDownloadProgress is provided. Unfortunately both rely on node-fetch implementation details, however I think this is best we can do without re-implementing most of the node-fetch functionality ourselves.

[achingbrain]

Published in v2.4.0

[achingbrain]

I think we might have to revert this - the upload/download progress handlers are useful but XHR has no way of doing streaming downloads so it's broken pubsub in the browser as it works via long-lived requests and the call to make the request doesn't return until the load event occurs, eg. the request has finished.

You can access partially loaded content via the .responseText property when .readyState === 3, but only when the response type is text which breaks when the response is non-printable binary data and .responseText grows over time causing a memory leak so it's not much of a solution.

@Gozala any ideas on this?