1,download protobuf file to local
wget https://developers.google.com/ad-exchange/rtb/downloads/openrtb-proto.txt
wget https://developers.google.com/ad-exchange/rtb/downloads/openrtb-adx-proto.txt
2,move to protofile
mv openrtb-proto.txt openrtb.proto
mv openrtb-adx-proto.txt openrtb_adx.proto
3,edit two protofile to same package
update openrtb_adx.proto use new package name "your self package name " not "com.google.doubleclick"
eg: package openrtb;
4,generate to go file
protoc --go_out=. openrtb.proto openrtb_adx.proto
5,set protobuf exten field example:
if err := proto.SetExtension(&seatBidBid, openrtb.E_Bid, bidExt); err != nil { logger.Warn( exchange, " set impTrackers Error[", err, "]") return false }