imp.ext.prebid.adunitcode is removed from imp.ext.prebid when rebuildImp is called

[Abyfall]

Hi guys, after upgrading to prebid server 3.1 we noticed that we couldn't retrieve the adUnitCode from imp.ext.prebid.adunitcode anymore.

It still present in the Prebid Server ORTB2 Extension Summary section of the doc so I assume it's a bug from prebid-server.

I tracked down the issue to the rebuildImpExt() & (e *ImpExt) marshal()

prebid-server/openrtb_ext/request_wrapper.go

Lines 1751 to 1767 in 6e150f3

	func (e *ImpExt) marshal() (json.RawMessage, error) {
	if e.prebidDirty {
	if e.prebid != nil {
	prebidJson, err := jsonutil.Marshal(e.prebid)
	if err != nil {
	return nil, err
	}
	if len(prebidJson) > jsonEmptyObjectLength {
	e.ext[prebidKey] = json.RawMessage(prebidJson)
	} else {
	delete(e.ext, prebidKey)
	}
	} else {
	delete(e.ext, prebidKey)
	}
	e.prebidDirty = false
	}

Those will recreate the imp.ext.prebid with the help of ExtImpPrebid struct. But as this struct doesn't contains the adunitcode, the value which was originally set is dropped.

This issue seems to exist since some time but we didn't face it before because we always had e.prebidDirty == false preventing thhe call to rebuildImpExt. This isn't the case anymore since the introduction of moveRewardedFromPrebidExtTo26 which always sets prebidDirty if prebid object was found in imp.ext.

prebid-server/openrtb_ext/convert_up.go

Lines 167 to 175 in dd07431

	func moveRewardedFromPrebidExtTo26(i *ImpWrapper) {
	// read and clear prebid ext
	impExt, _ := i.GetImpExt()
	rwddPrebidExt := (*int8)(nil)
	if p := impExt.GetPrebid(); p != nil {
	rwddPrebidExt = p.IsRewardedInventory
	p.IsRewardedInventory = nil
	impExt.SetPrebid(p)
	}

As a side note I think we should change moveRewardedFromPrebidExtTo26

prebid-server/openrtb_ext/convert_up.go

Line 171 in dd07431

if p := impExt.GetPrebid(); p != nil {

to also check if p.IsRewardedInventory is not nil before replacing the whole prebid field and flagging it as dirty

[bretg]

Thanks for the bug report @Abyfall. A community PR would be welcomed here.

[Abyfall]

Thanks @bretg I just pushed a PR that solves this issue