btcjson, rpcclient: revamp package and eliminate duplication

go.mod

@@ -62,4 +62,4 @@ retract (
 	v0.13.0-beta
 )
 
-go 1.17
+go 1.18

rpcclientv2/blochchaincmd.go

@@ -0,0 +1,47 @@
+package rpcclientv2
+
+import (
+	"encoding/json"
+)
+
+type GetDifficultyRpcCmd struct{}
+
+func (u GetDifficultyRpcCmd) Name() string {
+	return "getdifficulty"
+}
+
+func (u GetDifficultyRpcCmd) Marshal() (json.RawMessage, error) {
+	return json.Marshal(u)
+}
+
+type FutureGetDifficulty chan *Response
+
+type GetDifficultyResult float64
+
+func (r FutureGetDifficulty) Receive() (GetDifficultyResult, error) {
+	res, err := ReceiveFuture(r)
+	if err != nil {
+		return 0, err
+	}
+
+	// Unmarshal the result as a float64.
+	var difficulty float64
+	err = json.Unmarshal(res, &difficulty)
+	if err != nil {
+		return 0, err
+	}
+	return GetDifficultyResult(difficulty), nil
+}
+
+type GetDifficultyRpcCall struct {
+}
+
+func (u *GetDifficultyRpcCall) MapReq(arg string) GetDifficultyRpcCmd {
+	return GetDifficultyRpcCmd{}
+}
+
+func (u *GetDifficultyRpcCall) MapResp(resp chan *Response) MessageFuture[GetDifficultyResult] {
+	f := FutureGetDifficulty(resp)
+
+	return &f
+}

rpcclientv2/request.go

@@ -0,0 +1,59 @@
+package rpcclientv2
+
+import (
+	"encoding/json"
+)
+
+type Response struct {
+	Resp json.RawMessage
+	Err  error
+}
+
+type Command interface {
+	Name() string
+	Marshal() (json.RawMessage, error)
+}
+
+type Client interface {
+	SendCmd(cmd Command) chan *Response
+}
+
+type MessageFuture[M any] interface {
+	Receive() (M, error)
+}
+
+func ReceiveFuture(f chan *Response) (json.RawMessage, error) {
+	// Wait for a response on the returned channel.
+	r := <-f
+	return r.Resp, r.Err
+}
+
+type RpcCall[Args any, Cmd Command, Resp any] interface {
+	MapReq(arg Args) Cmd
+
+	MapResp(resp chan *Response) MessageFuture[Resp]
+}
+
+func AsyncRequest[Args any, Cmd Command, Resp any](
+	client Client, cmdReq RpcCall[Args, Cmd, Resp], args Args) MessageFuture[Resp] {
+
+	jsonCmd := cmdReq.MapReq(args)
+
+	resp := client.SendCmd(jsonCmd)
+
+	return cmdReq.MapResp(resp)
+}
+
+type FakeClient struct {
+}
+
+func (m FakeClient) SendCmd(cmd Command) chan *Response {
+	responseChan := make(chan *Response, 1)
+
+	result := Response{
+		Resp: []byte("561651.5"),
+		Err:  nil,
+	}
+	responseChan <- &result
+	return responseChan
+}