Type of change

• Bugfix

Description of change

This PR:

• adds a fix to the logic we were using to update the bidRequests.adUnitsS2SCopy object. This update ensured only valid bids were being included in the s2s request.
• moved this logic so that the updated adUnitsS2SCopy object is properly reflected in the console log messages for easier debugging/troubleshooting.

Additional Context
Currently for s2s requests, we resync the adUnitsS2SCopy object based on the various bids that exist in the bidRequest objects. This resync is to remove any bids that were rejected by the sizeMapping/label filtering checks.

Keeping the adUnitsS2SCopy in sync is important, as this object (not the bidRequest) is used to build the POST request meant for PBS; thus this ensures only validated bids get sent to PBS.

Notes on Fix
The logic used for the sync operated on a combination of the bidder and adUnitCodes to match adUnit.bid with bidRequest.bids to know if they passed the sizeMapping checks. This logic was insufficient when the same adUnitCode was used across different adUnits that used different labels. It allowed bids for the wrong label to pass the screening and get added to the PBS request.

The new logic operates on the bid_id values, which are generated uniquely for each adUnit.bid object and then stored in the corresponding bidRequest.bid object.

By moving this logic to the makeBidRequest function, we can display the updated adUnitsS2SCopy object in the 'Bids Requested' log message (here https://github.com/prebid/Prebid.js/blob/master/src/auction.js#L188 ) instead of digging through debugger.