Tear down occurs on each protocol level, stack-wise.
Open RWC
Open ML (with NewMessageLayer)
Open RPC (with NewServer/ NewClient)
Close RPC (with Close() from Client())
Close ML
* in Server: after error / receive of Close request
* in Client: after getting ACK for Close request from Server
Close RWC
To achieve this, a DataType for RPC control messages was added, which
has a separate set of endpoints. Not exactly pretty, but works for now.
The necessity of the RST frame remains to be determined. However, it is
nice to have a way to signal the other side something went terribly
wrong in the middle of an operation. Example: A frameBridingWriter fails
to read the next chunk of a file it is supposed to send, it can just
send an RST frame to signal this operation failed... Wouldn't trailers
make sense then?
The existing ByteStreamRPC requires writing RPC stub + server code
for each RPC endpoint. Does not scale well.
Goal: adding a new RPC call should
- not require writing an RPC stub / handler
- not require modifications to the RPC lib
The wire format is inspired by HTTP2, the API by net/rpc.
Frames are used for framing messages, i.e. a message is made of multiple
frames which are glued together using a frame-bridging reader / writer.
This roughly corresponds to HTTP2 streams, although we're happy with
just one stream at any time and the resulting non-need for flow control,
etc.
Frames are typed using a header. The two most important types are
'Header' and 'Data'.
The RPC protocol is built on top of this:
- Client sends a header => multiple frames of type 'header'
- Client sends request body => mulitiple frames of type 'data'
- Server reads a header => multiple frames of type 'header'
- Server reads request body => mulitiple frames of type 'data'
- Server sends response header => ...
- Server sends response body => ...
An RPC header is serialized JSON and always the same structure.
The body is of the type specified in the header.
The RPC server and client use some semi-fancy reflection tequniques to
automatically infer the data type of the request/response body based on
the method signature of the server handler; or the client parameters,
respectively.
This boils down to a special-case for io.Reader, which are just dumped
into a series of data frames as efficiently as possible.
All other types are (de)serialized using encoding/json.
The RPC layer and Frame Layer log some arbitrary messages that proved
useful during debugging. By default, they log to a non-logger, which
should not have a big impact on performance.
pprof analysis shows the implementation spends its CPU time
60% waiting for syscalls
30% in memmove
10% ...
On a Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz CPU, Linux 4.12, the
implementation achieved ~3.6GiB/s.
Future optimization may include spice(2) / vmspice(2) on Linux, although
this doesn't fit so well with the heavy use of io.Reader / io.Writer
throughout the codebase.
The existing hackaround for local calls was re-implemented to fit the
new interface of PRCServer and RPCClient.
The 'R'PC method invocation is a bit slower because reflection is
involved inbetween, but otherwise performance should be no different.
The RPC code currently does not support multipart requests and thus does
not support the equivalent of a POST.
Thus, the switch to the new rpc code had the following fallout:
- Move request objects + constants from rpc package to main app code
- Sacrifice the hacky 'push = pull me' way of doing push
-> need to further extend RPC to support multipart requests or
something to implement this properly with additional interfaces
-> should be done after replication is abstracted better than separate
algorithms for doPull() and doPush()
Pushing is achieved by inverting the roles on the established
connection, i.e. the client tells the server what data it should pull
from the client (PullMeRequest).
Role inversion is achieved by moving the server loop to the serverLoop
function of ByteStreamRPC, which can be called from both the Listen()
function (server-side) and the PullMeRequest() client-side function.
A donwside of this PullMe approach is that the replication policies
become part of the rpc, because the puller must follow the policy.
JSONDecoder was buffering more of connection data than just the JSON.
=> Unchunker didn't bother and just started unchunking.
While chaining JSONDecoder.Buffered() and the connection using
ChainedReader works, it's still not a clean architecture.
=> Every JSON message is now wrapped in a chunked stream
(chunked and unchunked)
=> no special-cases
=> Keep ChainedReader, might be useful later on...
