Pubmatic: Fix Shared Memory Overwriting

[guscarreon]

Copy of reference field Banner needed to be made inside adapters/pubmatic/pubmatic.go in order to avoid a data race on shared memory. Authors of source code should be notified and encourage to make any changes to this PR if they disagree with the proposed approach.

[SyntaxNode]

Please contact PubMatic using their bidder info email address to inform them of this change.

[guscarreon]

@sachin-pubmatic,
Recently coded pull request #1756 is meant to enable Prebid Server to find data race conditions in adapter bidder source code. According to this newly coded feature, your adapter might be writing to shared memory and this PR implements an approach to prevent it. Please let us know whether or not you agree with the changes proposed in this pull request or if you rather want to code the fix yourself.

When it comes to adapters' source code improvements, we usually wait a week for owners to come back to us. If we get no feedback, we will go ahead to review and merge this pull request ourselves.

We'd love to hear your take on this issue.

[hhhjort]

LGTM

[SyntaxNode]

We received approval via email for this change.

[bjorn-lw]

I just downloaded and tested the latest version of Prebid server (0.155) and noticed that with that version Pubmatic is starting to respond with unexpected banner sizes.

For instance, a request that requests only 160x600 as size, Pubmatic may respond with 600x600.

If I use an earlier version of Prebid Server (sorry, I can currently only test 0.139.1 easily) this problem does not occur.

But after looking at what has changed in the pubmatic adapter, this looks like something that maybe is causing this. I have no idea why though, and I may be completely off.

I will compile earlier versions and test until the problem goes away to see exactly in which version it happens.

[bjorn-lw]

The issue is NOT present in 0.152.0.

Sorry for not being too helpful in locating the source of the issue, GO is not my first language, but I will make an honest try.

EDIT: I realize this may have to do with the update of the OpenRTB library. I will try 0.153 as well.

EDIT 2: The problem is pinpointed to 0.153.0 -> This is the version where it starts to fail.

So with this PR there seems to be a problem at least with the Pubmatic Adapter.