Port currency fix from PBS-Java

[bretg]

There's a currency conversion issue in PBS. We've fixed this in PBS-Java with prebid/prebid-server-java#457

Here are the requirements and some test cases:

1. the client only ever specifies one entry in the cur array: the one expected by their adServer
   If there are more than one cur specified, use the first and warn.

2. This cur value must be sent to each adapter

3. PBS must try to convert bid responses to the first currency in the array

4. if PBS can't convert a bid, then it should error with "unable to covert bid currency XYZ to desired ad server currency ABC."

Test cases:

1. ad-server-currency is USD. (whether defined in the cur field or in the config is the same behavior)
2. bidderA bids are in EUR. they get converted to USD
3. bidderB bids are in GBP. they get converted to USD
4. bidderC bids are in USD. no conversion needed

[benjaminch]

Hey @bretg !

Sorry about that but would it be possible to explain what are the client and the core server here?

Cheers !

[bretg]

• client: browser or app
• core server: the part of PBS that receives the request, does the DB lookup, and prepares the openrtb for the bidder modules. i.e. everything that's not a bidder module

[stale]

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[hhhjort]

@bretg : Do we see a real need to provide the option to be a string rather than an array? In the Go version, it would take significant number of cycles to check for the possible existence of singe string. It also breaks the openrtb 2.5 spec to provide a single string.

[bretg]

@hhhjort objects to flexibility in accepting a string value for cur outside of the OpenRTB standard.

The core server should allow the cur value to be either a single value or an array. It should convert a string into an array of one string.

I don't know the history for this other than I have a few test files incorrectly formatted. Don't see evidence that the Prebid Server Bid adapter does the wrong thing, so I'm ok with PBS-Go being firm here.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.