Custom Targeting is concatenated for all Bids

[evans-sam]

Custom targeting values from multiple bids with the same key are concatenated and set with the ad server, with

{
  enableSendAllBids: false,
  targetingControls: {
    alwaysIncludeDeals: true
  },
  sendBidsControl: {
    bidLimit: 1
  }
}

bid1: {
  'cpm': 1.0,
  'adserverTargeting': {
    'foo': 'bar',
  },
},

bid2: {
  'cpm': 0.5,
  'adserverTargeting': {
    'foo': 'baz',
  },
},

I would say the expected result targeting would be foo: bar, however the resulting targeting is foo: bar,baz. The test assertions in targeting_spec.js seem to indicate this is not the intended behavior

[dgirardi]

The test assertions in targeting_spec.js seem to indicated this is not the intended behavior

Could you point to one of those assertions? I agree this result is surprising, but it also seems intentional to me (but, unfortunately, I can't find a test for it). Custom keys are set to all unique values across targeted bids.

Prebid.js/src/targeting.js

Lines 372 to 376 in d956c08

	if (data[truncKey]) {
	data[truncKey] = data[truncKey].concat(value).filter(uniques);
	} else {
	data[truncKey] = value;
	}

Behavior was the same in 8.0.0 (and likely earlier) so not a recently introduced change, and fixing it is likely to be breaking.

[evans-sam]

There are many assertions that stipulate the custom targeting is that of the winning bid, however the losing bids either don't have custom targeting set, or it happens to be the same unique value as the winning bid. A simple change to the custom targeting value of a losing bid causes multiple tests to fail that are all around which targeting is set based on enableSendAllBids and alwaysIncludeDeals values. It also seems as though custom targeting keys that are not present in the winning bid are always excluded.

There are no explicit tests around this, so I guess it seems to me to be an unintended side effect. Is a potential solution to introduce a flag in targetingControls? If so, I'd be happy to open a PR

[dgirardi]

an unintended side effect

the explicit filtering for unique values makes me think it was done with some intended use case in mind - but it's not clear to me what that would be.

Is a potential solution to introduce a flag in targetingControls

Yes; possibly allBidsCustomTargeting that defaults to true? We can then consider switching the default in a major version release if we can't figure out the original intent. @patmmccann ?

[evans-sam]

I opened a very simple pull request that checks for that flag. Any additional feedback is greatly appreciated