The http.Handler-based transport body reader was returning error types
not understood by the recvMsg parser. See #557 for some background and
examples.
Fix the http.Handler transport and add tests. I copied in a subset of
the http2 package's serverTest type, adapted slightly to work with
grpc. In the process of adding tests, I discovered that
ErrUnexpectedEOF was also not handled by the regular server
transport. Document the rules and fix that crash as well.
Unrelated stuff in this CL:
* make tests listen on localhost:0 instead of :0, to avoid Mac firewall
pop-up dialogs.
* rename parser.s field to parser.r, to be more idiomatic that it's an
io.Reader and not anything fancier. (it's not acting like type
stream, even if that's the typical concrete type)
* move 5 byte temp buffer into parser, rather than allocating it for
each new message. (drop in the bucket improvement in garbage; more
to do later)
* rename http2RSTErrConvTab to http2ErrConvTab, per Qi's earlier
CL. Also add the HTTP/1.1-required error mapping for completeness,
not that it should ever arise with gRPC, also per Qi's earlier CL
referenced in #557.
Fix another bug: cancel the Context provided to an RPC server handler
as soon as that handler returns, so that goroutines started by that
handler can detect that the handler is done and exit. Without this
fix, goroutines started by a handler will keep running, unless the
handler itself arranges to cancel the context.
handlers in request traces, and mark the trace as an error if the
status is not OK.
Install the trace into the Context passed to server handlers using
trace.NewContext, so that code in the server handlers can annotate the
trace using trace.FromContext.
