290 lines
8.6 KiB
Go
290 lines
8.6 KiB
Go
/*
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mprpc is a simple bidirectional RPC library using the MessagePack-RPC spec.
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It fully implements the spec and additionally provides Go `error“ handling by
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converting the error to a standard format for other clients.
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mprpc does not have a typical server/client designation - both use "handlers",
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which expose methods to be called over the network. A "client" would be an
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RPCConn which doesn't expose any services, and a "server" would be an RPCConn
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that doesn't make any `Call`s to the other side.
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This lack of discrete server and client enables mprpc to implement a basic
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"streaming" architecture on top of the MessagePack-RPC spec, which does not
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include streaming primitives. Instead, we can provide simple "service handlers"
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as a callback/destination for streaming data.
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For example, a "client" could subscribe to events from the "server", by
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providing a callback service to point events to. Then, the "server" would
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Notify() the callback service with the new event as an argument every time it
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occured. While this may be less optimal than protocol-level streaming, it is
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far simpler.
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The idiomatic way to use mprpc is to use the generic functions that are provided
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as helpers. They allow the programmer to easily wrap functions in a closure that
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automatically encodes and decodes the parameters and results to their
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MessagePack representations. See the Make* generic functions for more information.
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// Assume myParam and myResult are MessagePack-enabled structs.
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// Use `msgp` to generate the required functions for them.
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// this is our plain function - we can call it locally to test.
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func myPlainFunction(p myParam) (r myResult, err error)
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// wrapped is a ServiceFunc that can be passed to rpcConn.RegisterHandler
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var wrapped := MakeService(myPlainFunction)
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The generic functions allow for flexiblity and elegant code while still keeping
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the underlying implementation reflect-free. For more complex functions (i.e
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multiple parameters or return types), a second layer of indirection can be used.
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*/
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package mprpc
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import (
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"net"
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"github.com/tinylib/msgp/msgp"
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"golang.org/x/exp/slog"
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)
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// ServiceFunc is a RPC service handler.
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// It can be created manually, or by using the generic MakeService function on a
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//
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// func(msgp.Encoder) (msgp.Deocder, error)
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//
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// type.
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type ServiceFunc func(params msgp.Raw) (res msgp.Raw, err error)
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// RPCConn is a single RPC communication pair.
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// It is used by both the
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// "server" aka listener, and client.
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type RPCConn struct {
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// TODO: use io.readwritecloser?
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conn net.Conn
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handlers map[string]ServiceFunc
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ct rpcConnTrack
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slog.Logger
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}
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// Call intiates an RPC call to a remote method and returns the
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// response, or the error, if any. To make calling easier, you can
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// construct a "Caller" with MakeCaller
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func (rpc *RPCConn) Call(method string, params msgp.Raw) (msgp.Raw, error) {
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// TODO: error handling.
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id, cb := rpc.ct.Claim()
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req := NewRequest(id, method, params)
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w := msgp.NewWriter(rpc.conn)
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req.EncodeMsg(w)
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// block and wait for response.
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resp := <-cb
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return resp.Result, &resp.Error
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}
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// Notify initiates a notification to a remote method. It does not
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// return any information. There is no response from the server.
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// This method will not block. An error is returned if there is a local
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// problem.
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func (rpc *RPCConn) Notify(method string, params msgp.Raw) {
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// TODO: return an error if there's a local problem?
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req := NewNotification(method, params)
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w := msgp.NewWriter(rpc.conn)
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req.EncodeMsg(w)
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}
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// Register a new handler to be called by the remote side. An error
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// is returned if the handler name is already in use.
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func (rpc *RPCConn) RegisterHandler(name string, fn ServiceFunc) error {
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// TODO: check if name in use.
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// TODO: mutex lock for sync (or use sync.map?
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rpc.handlers[name] = fn
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rpc.Logger.Info("registered a new handler", "name", name, "fn", fn)
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return nil
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}
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// Serve runs the server. It will dispatch goroutines to handle each
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// method call. This can (and should in most cases) be run in the background to allow for
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// sending and receving on the same connection.
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func (rpc *RPCConn) Serve() {
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// construct a stream reader.
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msgReader := msgp.NewReader(rpc.conn)
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// read a request/notification from the connection.
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var rawmsg msgp.Raw = make(msgp.Raw, 0, 4)
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for {
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rawmsg.DecodeMsg(msgReader)
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rpcIntf, err := parseRPC(rawmsg)
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if err != nil {
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rpc.Logger.Warn("Could not parse RPC message", "err", err)
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continue
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}
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switch rpcObject := rpcIntf.(type) {
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case Request:
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// the object is a request - we must dispatch a goroutine
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// that will call the handler and also send a return value.
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go rpc.dispatch(rpcObject)
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case Notification:
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go rpc.dispatchNotif(rpcObject)
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case Response:
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cbCh, err := rpc.ct.Clear(rpcObject.MsgId)
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if err != nil {
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// TODO: scream
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rpc.Logger.Warn("could not get rpc callback", "msgid", rpcObject.MsgId, "err", err)
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continue
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}
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cbCh <- rpcObject
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}
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}
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}
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func (rpc *RPCConn) dispatch(req Request) {
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result, err := rpc.handlers[req.Method](req.Params)
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if err != nil {
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rpc.Logger.Warn("error dispatching rpc function", "method", req.Method, "err", err)
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}
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// construct the response frame.
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var rpcE *RPCError = MakeRPCError(err)
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w := msgp.NewWriter(rpc.conn)
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response := NewResponse(req.MsgId, *rpcE, result)
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response.EncodeMsg(w)
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}
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func (rpc *RPCConn) dispatchNotif(req Notification) {
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_, err := rpc.handlers[req.Method](req.Params)
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if err != nil {
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// log the error, but don't do anything about it.
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rpc.Logger.Warn("error dispatching rpc function", "method", req.Method, "err", err)
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}
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}
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// Next, we define some helper generic functions that can be used to make
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// implementing a msg wrapper easier.
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type msgpackObject interface {
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msgp.Decodable
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msgp.Encodable
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msgp.MarshalSizer
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msgp.Unmarshaler
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}
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// MakeService is a generic wrapper function. It takes a function with the signature
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// of func(T msgpObject)(R msgpObject, error) where T and R can be *concrete* types.
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// and returns a new function that handles conversion to/from msgp.Raw.
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// the function returned can be used by the RPCConn as a handler function.
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// This function can typically have it's paramters inferred.
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func MakeService[T, R msgpackObject](fn func(T) (R, error)) ServiceFunc {
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return func(p msgp.Raw) (msgp.Raw, error) {
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// decode the raw data into a new underlying type.
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var params T
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// TODO: handler errors
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_, err := params.UnmarshalMsg(p)
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if err != nil {
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return nil, err
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}
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// now, call the function fn with the given params, and record the value.
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resp, err := fn(params)
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if err != nil {
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return nil, err
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}
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return resp.MarshalMsg([]byte{})
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}
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}
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// should the RPCConn/method name be baked into the function or should they be
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// part of the returned function paramters?
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// MakeCaller creates a simple wrapper around a parameter of call. The method name
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// and RPC connection can be given to the returned function to make a RPC call on that
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// function with the given type parameters.
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//
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// This function is slightly obtuse compared to MakeBoundCaller but is more flexible
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// since you can reuse the same function across multiple connections and method names.
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//
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// This generic function must always have it's type paratmers declared explicitly.
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// They cannot be inferred from the given parameters.
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func MakeCaller[T, R msgpackObject]() func(string, T, *RPCConn) (R, error) {
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return func(method string, param T, rpc *RPCConn) (R, error) {
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rawParam, _ := param.MarshalMsg([]byte{})
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rawResponse, err := rpc.Call(method, rawParam)
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if err != nil {
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var emtpyR R
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return emtpyR, err
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}
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var resp R
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_, err = resp.UnmarshalMsg(rawResponse)
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return resp, err
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}
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}
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// MakeBoundCaller is like MakeCaller, except the RPC connection and method name are
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// fixed and cannot be adjusted later. This function is more elegant but less flexible
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// than MakeCaller and should be used when performance is not critical.
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//
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// This generic function must always have it's type paratmers declared explicitly.
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// They cannot be inferred from the given parameters.
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func MakeBoundCaller[T, R msgpackObject](rpc *RPCConn, method string) func(T) (R, error) {
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return func(param T) (R, error) {
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// encode parameters
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// invoke rpc.Call
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// await response
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// unpack values.
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rawParam, _ := param.MarshalMsg([]byte{})
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rawResponse, err := rpc.Call(method, rawParam)
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if err != nil {
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var emtpyR R
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return emtpyR, err
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}
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var resp R
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_, err = resp.UnmarshalMsg(rawResponse)
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return resp, err
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}
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}
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func MakeNotifier[T msgpackObject]() func(string, T, *RPCConn) {
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return func(method string, param T, rpc *RPCConn) {
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rawParam, _ := param.MarshalMsg([]byte{})
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rpc.Notify(method, rawParam)
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}
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}
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