rpc: implement full bi-directional communication (#18471)

New APIs added:

    client.RegisterName(namespace, service) // makes service available to server
    client.Notify(ctx, method, args...)     // sends a notification
    ClientFromContext(ctx)                  // to get a client in handler method

This is essentially a rewrite of the server-side code. JSON-RPC
processing code is now the same on both server and client side. Many
minor issues were fixed in the process and there is a new test suite for
JSON-RPC spec compliance (and non-compliance in some cases).

List of behavior changes:

- Method handlers are now called with a per-request context instead of a
  per-connection context. The context is canceled right after the method
  returns.
- Subscription error channels are always closed when the connection
  ends. There is no need to also wait on the Notifier's Closed channel
  to detect whether the subscription has ended.
- Client now omits "params" instead of sending "params": null when there
  are no arguments to a call. The previous behavior was not compliant
  with the spec. The server still accepts "params": null.
- Floating point numbers are allowed as "id". The spec doesn't allow
  them, but we handle request "id" as json.RawMessage and guarantee that
  the same number will be sent back.
- Logging is improved significantly. There is now a message at DEBUG
  level for each RPC call served.

rpc/types.go

@@ -17,13 +17,11 @@
 package rpc
 
 import (
+	"context"
 	"fmt"
 	"math"
-	"reflect"
 	"strings"
-	"sync"
 
-	mapset "github.com/deckarep/golang-set"
 	"github.com/ethereum/go-ethereum/common/hexutil"
 )
 
@@ -35,57 +33,6 @@ type API struct {
 	Public    bool        // indication if the methods must be considered safe for public use
 }
 
-// callback is a method callback which was registered in the server
-type callback struct {
-	rcvr        reflect.Value  // receiver of method
-	method      reflect.Method // callback
-	argTypes    []reflect.Type // input argument types
-	hasCtx      bool           // method's first argument is a context (not included in argTypes)
-	errPos      int            // err return idx, of -1 when method cannot return error
-	isSubscribe bool           // indication if the callback is a subscription
-}
-
-// service represents a registered object
-type service struct {
-	name          string        // name for service
-	typ           reflect.Type  // receiver type
-	callbacks     callbacks     // registered handlers
-	subscriptions subscriptions // available subscriptions/notifications
-}
-
-// serverRequest is an incoming request
-type serverRequest struct {
-	id            interface{}
-	svcname       string
-	callb         *callback
-	args          []reflect.Value
-	isUnsubscribe bool
-	err           Error
-}
-
-type serviceRegistry map[string]*service // collection of services
-type callbacks map[string]*callback      // collection of RPC callbacks
-type subscriptions map[string]*callback  // collection of subscription callbacks
-
-// Server represents a RPC server
-type Server struct {
-	services serviceRegistry
-
-	run      int32
-	codecsMu sync.Mutex
-	codecs   mapset.Set
-}
-
-// rpcRequest represents a raw incoming RPC request
-type rpcRequest struct {
-	service  string
-	method   string
-	id       interface{}
-	isPubSub bool
-	params   interface{}
-	err      Error // invalid batch element
-}
-
 // Error wraps RPC errors, which contain an error code in addition to the message.
 type Error interface {
 	Error() string  // returns the message
@@ -96,24 +43,19 @@ type Error interface {
 // a RPC session. Implementations must be go-routine safe since the codec can be called in
 // multiple go-routines concurrently.
 type ServerCodec interface {
-	// Read next request
-	ReadRequestHeaders() ([]rpcRequest, bool, Error)
-	// Parse request argument to the given types
-	ParseRequestArguments(argTypes []reflect.Type, params interface{}) ([]reflect.Value, Error)
-	// Assemble success response, expects response id and payload
-	CreateResponse(id interface{}, reply interface{}) interface{}
-	// Assemble error response, expects response id and error
-	CreateErrorResponse(id interface{}, err Error) interface{}
-	// Assemble error response with extra information about the error through info
-	CreateErrorResponseWithInfo(id interface{}, err Error, info interface{}) interface{}
-	// Create notification response
-	CreateNotification(id, namespace string, event interface{}) interface{}
-	// Write msg to client.
-	Write(msg interface{}) error
-	// Close underlying data stream
+	Read() (msgs []*jsonrpcMessage, isBatch bool, err error)
 	Close()
-	// Closed when underlying connection is closed
+	jsonWriter
+}
+
+// jsonWriter can write JSON messages to its underlying connection.
+// Implementations must be safe for concurrent use.
+type jsonWriter interface {
+	Write(context.Context, interface{}) error
+	// Closed returns a channel which is closed when the connection is closed.
 	Closed() <-chan interface{}
+	// RemoteAddr returns the peer address of the connection.
+	RemoteAddr() string
 }
 
 type BlockNumber int64