rpc, p2p/simulations: use github.com/gorilla/websocket (#20289)

* rpc: improve codec abstraction

rpc.ServerCodec is an opaque interface. There was only one way to get a
codec using existing APIs: rpc.NewJSONCodec. This change exports
newCodec (as NewFuncCodec) and NewJSONCodec (as NewCodec). It also makes
all codec methods non-public to avoid showing internals in godoc.

While here, remove codec options in tests because they are not
supported anymore.

* p2p/simulations: use github.com/gorilla/websocket

This package was the last remaining user of golang.org/x/net/websocket.
Migrating to the new library wasn't straightforward because it is no
longer possible to treat WebSocket connections as a net.Conn.

* vendor: delete golang.org/x/net/websocket

* rpc: fix godoc comments and run gofmt

rpc/types.go

@@ -45,19 +45,19 @@ 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() (msgs []*jsonrpcMessage, isBatch bool, err error)
-	Close()
+	readBatch() (msgs []*jsonrpcMessage, isBatch bool, err error)
+	close()
 	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
+	writeJSON(context.Context, interface{}) error
 	// Closed returns a channel which is closed when the connection is closed.
-	Closed() <-chan interface{}
+	closed() <-chan interface{}
 	// RemoteAddr returns the peer address of the connection.
-	RemoteAddr() string
+	remoteAddr() string
 }
 
 type BlockNumber int64