PDPv0: pull piece should accept an array of URLs instead of just 1

[LexLuthr]

We should update pull piece handler to accept an array of URLs per piece_cid instead of a single URL.

A far better design would be to just take the provider identifier and assemble the URL ourselves. This saves us from bad URLS, typos, bad clients and security issues

[ZenGround0]

A far better design would be to just take the provider identifier and assemble the URL ourselves. This saves us from bad URLS, typos, bad clients and security issues

This seems like a good idea to me ^

@rvagg any issues with sending over the provider identifier as a data source from the synapse side?

[rvagg]

Fine by me on the array, and this doesn't necessarily have to be a breaking change, a custom JSON unmarshaller should deal with any awkwardness in maintaining backward compat.

On the provider ID: the current design lets you fetch pieces from a location that a client might have parked it in, like the Storacha data, rather than strictly requiring it be on another SP. It's not a hard requirement that we support that, the primary use here is purely SP<>SP transfers and will continue to be so. If we can work in the optionality to provide a provider ID or a URL then that would be nice? An array of both would be neat, perhaps you know that your piece is on 3 different SPs plus it's also in S3.