An install request is signaled by update_engine by omitting the update_check tag only in the app request for the platform app. That is, the update_engine sends a request with an update_check tag for every DLC appid that is to be intalled, and a request with no update_check tag for the platform appid.

We currently have no way of determining which appid is associated with the platform app based purely on the contents of an incoming request, so we assume that a request is an install request if exactly one appid does not have an associated update_check tag.

It may be possible in the future to differentiate the platform appid based on whether it has certain attributes (e.g. hardware_class, see go/omaha-changes-for-dlc).

It is preferable to have Nebraska make these decisions using the same mechanisms as Omaha, so we should adopt this strategy here if we decide to implement it.

An install is signalled by omitting the update check for the platform                                                                                                                                                                                                                                              
157     # app, which can be found based on the presense of a hardware_class tag,                                                                                                                                                                                                                                             
158     # which is absent on DLC update and install requests. UE does not currently                                                                                                                                                                                                                                          
159     # omit hardware_class for DLCs, so we assume that if we have one appid for                                                                                                                                                                                                                                           
160     # which the update_check tag is omitted, it is the platform app and this is                                                                                                                                                                                                                                          
161     # an install request. This assumption should be fine since we never mix                                                                                                                                                                                                                                              
162     # updates with requests that do not include an update_check tag. 
 

An install request is signaled by update_engine by omitting the update_check tag only in the app request for the platform app. That is, the update_engine sends a request with an update_check tag for every DLC appid that is to be intalled, and a request with no update_check tag for the platform appid.

We currently have no way of determining which appid is associated with the platform app based purely on the contents of an incoming request, so we assume that a request is an install request if exactly one appid does not have an associated update_check tag.

It may be possible in the future to differentiate the platform appid based on whether it has certain attributes (e.g. hardware_class, see go/omaha-changes-for-dlc).

It is preferable to have Nebraska make these decisions using the same mechanisms as Omaha, so we should adopt this strategy here if we decide to implement it.