http-conduit: Requests may be retained in Responses

[JackKelly-Bellroy]

A colleague (@kokobd) did a lot of digging into space leaks while using amazonka, and we've observed that large requests cause a noticeable space leak. This sounds similar to brendanhay/amazonka#475

When http-conduit constructs a response, it stores the original request in a record field and overwrites its body:

http-client/http-client/Network/HTTP/Client/Response.hs

Line 164 in 6f742e8

, responseOriginalRequest = req {requestBody = ""}

We suspect that this record update is never forced (there are no bang-patterns or other strictness tools that we can see), so the original request body cannot be garbage collected until execution leaves the ResourceT.

It might be necessary to add bang patterns to (at least) the responseOriginalRequest field of Response and the requestBody field of Request. It is probably safe for the fields of the RequestBody constructors to remain lazy.