Don't write impression tracking URLs to Prebid Cache if SDK is on charge of tracking

[YuriyVelichkoPI]

Background

The Mobile Committee is actively working on reducing discrepancies in impression tracking. There are several POC approaches, and one of them assumes that impression URLs (burl, imp .. any other one from the bid response) will be tracked by Prebid SDK code.

In short - the Prebid SDK will track the viewability of Google's Ad View and track an impression event(s) once the ad view is on the screen.

Objectves

However, If SDK tracks the impression - the PUC should not fire burl and Prebid's win event .

From our current perspective, the most efficient way to disable tracking of burl by PUC without any AdOps work is to extract respective fields from the OpenRTB before caching it. In this case, PUC just won't have pixels to track.

If there is any other approach that won't affect the current publisher's setup - please let us know.

This feature will be opt-in on the SDK side. So, the default behavior will remain as is.

But if SDK sends some flag that indicates that it will track the impression, the PBS shouldn't cache the respective URLs.

The proposed OpenRTB request field: $.ext.prebid.sdk.nativeimptracker. The value should be 1 to activate the feature.
The affected fields: so far we propose to extract the following fields before caching:

• bid.burl
• bid.ext.prebid.events.imp

Later, this list can be expanded.

[bretg]

I'd propose we expand any refactoring here to include a more general tracking-of-multiple-things approach like the one suggested at prebid/Prebid.js#12216 (comment)

There are 3 sets of tracking that PBS could emit:

1. seatbid.bid.ext.prebid.events - the 'win' event is consumed by the PBSbidAdapter and fired as a BIDS_WON event. PBSDK fires the win event in the "Prebid-Rendered" scenarios.
2. When instructed to cache bids, PBS adds PBC entries: wurl and burl - the PUC fires these URLs in the mobile app and AMP scenarios.
3. This new seatbid[].bid[].ext.eventtrackers[] - the idea is that PBSDK would fire all of these events at the appropriate times instead of using either approaches 1 or 2 above.
4. When instructed to cache bids, PBS adds eventtrackers[] to what's cached in PBC.

Here's a proposal:

1. A new request flag indicates that the client is needs the tracking strings on seatbid[].bid[].ext.eventtrackers. The flag proposal is ext.prebid.options.trackloc: 2. (1=the old location, which is the default)
2. If trackloc: 1, PBS returns tracking on legacy scenario locations 1 and 2 above.
3. If trackloc: 2, PBS returns tracking on new scenario location 3 and 4 above:
   1. If seatbid[].bid[].ext.eventtrackers already exists in the ORTB response, PBS should assume the bidder has placed its tracking URLs there already. If it doesn't exist, PBS should create it and add any burl found in the response.
   2. PBS should add its own win and imp tracking URLs.
   3. PBJS can merge the PBS-supplied array with URLs received from other bid adapters.
   4. Upon BIDS_WON and IMP events, the client is expected to loop through the array:
      1. Look at the 'type' field. If type=1, then this pixel should be triggered when in view. If type=500, it's triggered when the ad server reports the win.
      2. Look at the 'method' field. If 1, drop an . Otherwise do nothing.