Poor error handling when loading currency rates

[dgirardi]

Type of issue

Bug

Description

If the currency module is set up to load rates from the network (the default) and no default rates are specified, bid responses are put on hold until rates are available. This is a problem when the file does not load quickly enough or the request fails:

1. if rates are not available by the time an auction times out, bids are lost without necessarily causing an AUCTION_TIMEOUT event. Currently they'll generate NO_BID events instead; with Core & currency module: fix bug where bid responses are collected after auction ends #10558 they'll generate no events.
2. the same happens if rates fail to load - all auctions will wait until the timeout and then end without any bids.

I think it makes sense to address #2 by trying to fetch rates again at the start of the next auction, but I am unsure about #1. If an auction times out and we have pending bids but no rates, should we:

• reject the bids?
• emit AUCTION_TIMEOUT without any timed out bidders?
• postpone the timeout to wait for rates?

[dgirardi]

Consensus is:

• bids should be rejected with a currency-specific reason
• bids that do not actually need a conversion (currency is already the adserver currency) should not wait for rates