Remove ioutil.ReadAll, except for in tests, and set a message size limit #2305
Description
ioutil.ReadAll should generally not be used
in HTTP APIs, since it doesn't have a size limit. Our
current HTTP API is for internal use, but it's still a good
precautionary measure, in my opinion. We should probably just set
a limit, constant or configurable, for the maximum size
of an HTTP request body. Perhaps write our own version
of io.LimitedReader that returns a meaningful error
instead of an io.EOF.