buildInfo is implemented here and here. The body of both run() functions write static data into a BSONObj. This makes buildInfo uniquely simple to convert to the async Command API. We merely do the write and fulfill a promise on a background thread or an unbounded global executor. This allows us to continue onto the networking sink on thread. In a fully async context, this would have three execution contexts:

• Source and parse on a networking reactor
• Write and sink on a command executor
• Clean up on the client executor