Workaround to allow lbry-sdk to call server.version and server.features.

Incoming/outgoing JSON is patched using yet another codec (jsonPatchingCodec).
Add more logging of raw/patched JSON.

server/jsonrpc_server.go

@@ -73,17 +73,16 @@ type ServerVersionService struct {
 	Args *Args
 }
 
-type ServerVersionReq struct{}
+type ServerVersionReq [2]string // [client_name, client_version]
 
-type ServerVersionRes string
+type ServerVersionRes [2]string // [version, protocol_version]
 
-// Banner is the json rpc endpoint for 'server.version'.
-// FIXME: This should return a struct with the version and the protocol version.
-// <<-- that comment was written by github, scary shit because it's true
+// Version is the json rpc endpoint for 'server.version'.
 func (t *ServerService) Version(req *ServerVersionReq, res **ServerVersionRes) error {
-	log.Println("Version")
-
-	*res = (*ServerVersionRes)(&t.Args.ServerVersion)
-
+	// FIXME: We may need to do the computation of a negotiated version here.
+	// Also return an error if client is not supported?
+	result := [2]string{t.Args.ServerVersion, t.Args.ServerVersion}
+	*res = (*ServerVersionRes)(&result)
+	log.Printf("Version(%v) -> %v", *req, **res)
 	return nil
 }

server/session.go

@@ -1,7 +1,9 @@
 package server
 
 import (
+	"bytes"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"net"
 	"net/rpc"
@@ -241,7 +243,7 @@ func (sm *sessionManager) addSession(conn net.Conn) *session {
 
 	sm.grp.Add(1)
 	go func() {
-		s1.ServeCodec(&SessionServerCodec{jsonrpc.NewServerCodec(conn), sess})
+		s1.ServeCodec(&sessionServerCodec{jsonrpc.NewServerCodec(newJsonPatchingCodec(conn)), sess})
 		log.Infof("session %v goroutine exit", sess.addr.String())
 		sm.grp.Done()
 	}()
@@ -343,7 +345,7 @@ func (sm *sessionManager) doNotify(notification interface{}) {
 	}
 }
 
-type SessionServerCodec struct {
+type sessionServerCodec struct {
 	rpc.ServerCodec
 	sess *session
 }
@@ -354,13 +356,14 @@ type SessionServerCodec struct {
 //     blockchain.address.listunspent -> blockchain.address.Listunspent
 // This makes the "method" string compatible with rpc.Server
 // requirements.
-func (c *SessionServerCodec) ReadRequestHeader(req *rpc.Request) error {
-	log.Infof("receive header from %v", c.sess.addr.String())
+func (c *sessionServerCodec) ReadRequestHeader(req *rpc.Request) error {
+	log.Infof("from %v receive header", c.sess.addr.String())
 	err := c.ServerCodec.ReadRequestHeader(req)
 	if err != nil {
 		log.Warnf("error: %v", err)
 		return err
 	}
+	log.Infof("from %v receive header: %#v", c.sess.addr.String(), *req)
 	rawMethod := req.ServiceMethod
 	parts := strings.Split(rawMethod, ".")
 	if len(parts) < 2 {
@@ -377,20 +380,21 @@ func (c *SessionServerCodec) ReadRequestHeader(req *rpc.Request) error {
 }
 
 // ReadRequestBody wraps the regular implementation, but updates session stats too.
-func (c *SessionServerCodec) ReadRequestBody(params any) error {
+func (c *sessionServerCodec) ReadRequestBody(params any) error {
+	log.Infof("from %v receive body", c.sess.addr.String())
 	err := c.ServerCodec.ReadRequestBody(params)
 	if err != nil {
 		log.Warnf("error: %v", err)
 		return err
 	}
-	log.Infof("receive body from %v", c.sess.addr.String())
+	log.Infof("from %v receive body: %#v", c.sess.addr.String(), params)
 	// Bump last receive time.
 	c.sess.lastRecv = time.Now()
 	return err
 }
 
 // WriteResponse wraps the regular implementation, but updates session stats too.
-func (c *SessionServerCodec) WriteResponse(resp *rpc.Response, reply any) error {
+func (c *sessionServerCodec) WriteResponse(resp *rpc.Response, reply any) error {
 	log.Infof("respond to %v", c.sess.addr.String())
 	err := c.ServerCodec.WriteResponse(resp, reply)
 	if err != nil {
@@ -400,3 +404,143 @@ func (c *SessionServerCodec) WriteResponse(resp *rpc.Response, reply any) error
 	c.sess.lastSend = time.Now()
 	return err
 }
+
+// serverRequest is a duplicate of serverRequest from
+// net/rpc/jsonrpc/server.go  with an added Version which
+// we can check.
+type serverRequest struct {
+	Version string           `json:"jsonrpc"`
+	Method  string           `json:"method"`
+	Params  *json.RawMessage `json:"params"`
+	Id      *json.RawMessage `json:"id"`
+}
+
+// serverResponse is a duplicate of serverResponse from
+// net/rpc/jsonrpc/server.go with an added Version which
+// we can set at will.
+type serverResponse struct {
+	Version string           `json:"jsonrpc"`
+	Id      *json.RawMessage `json:"id"`
+	Result  any              `json:"result,omitempty"`
+	Error   any              `json:"error,omitempty"`
+}
+
+// jsonPatchingCodec is able to intercept the JSON requests/responses
+// and tweak them. Currently it appears we need to add a
+// "jsonrpc": "1.0" or "jsonrpc": "2.0" to make the client happy.
+type jsonPatchingCodec struct {
+	conn      net.Conn
+	inBuffer  *bytes.Buffer
+	dec       *json.Decoder
+	enc       *json.Encoder
+	outBuffer *bytes.Buffer
+}
+
+func newJsonPatchingCodec(conn net.Conn) *jsonPatchingCodec {
+	buf1, buf2 := bytes.NewBuffer(nil), bytes.NewBuffer(nil)
+	return &jsonPatchingCodec{
+		conn:      conn,
+		inBuffer:  buf1,
+		dec:       json.NewDecoder(buf1),
+		enc:       json.NewEncoder(buf2),
+		outBuffer: buf2,
+	}
+}
+
+func (c *jsonPatchingCodec) Read(p []byte) (n int, err error) {
+	if c.outBuffer.Len() > 0 {
+		// Return remaining decoded bytes.
+		return c.outBuffer.Read(p)
+	}
+	// Buffer contents consumed. Try to decode more JSON.
+
+	// Read until framing newline. This allows us to print the raw request.
+	for !bytes.ContainsAny(c.inBuffer.Bytes(), "\n") {
+		var buf [1024]byte
+		n, err = c.conn.Read(buf[:])
+		if err != nil {
+			return 0, err
+		}
+		c.inBuffer.Write(buf[:n])
+	}
+	log.Infof("raw request: %v", c.inBuffer.String())
+
+	var req serverRequest
+	err = c.dec.Decode(&req)
+	if err != nil {
+		return 0, err
+	}
+
+	if req.Params != nil {
+		n := len(*req.Params)
+		if n < 2 || (*req.Params)[0] != '[' && (*req.Params)[n-1] != ']' {
+			// This is an error, but we're not going to try to correct it.
+			goto encode
+		}
+		// FIXME: The heuristics here don't cover all possibilities.
+		// For example: [{obj1}, {obj2}] or ["foo,bar"] would not
+		// be handled correctly.
+		bracketed := (*req.Params)[1 : n-1]
+		n = len(bracketed)
+		if n > 1 && (bracketed[0] == '{' || bracketed[0] == '[') {
+			// Probable single object or list argument.
+			goto encode
+		}
+		args := strings.Split(string(bracketed), ",")
+		if len(args) <= 1 {
+			// No commas at all. Definitely a single argument.
+			goto encode
+		}
+		// The params look like ["arg1", "arg2", "arg3", ...].
+		// We're in trouble because our jsonrpc library does not
+		// handle this. So pack these args in an inner list.
+		// The handler method will receive ONE list argument.
+		params := json.RawMessage(fmt.Sprintf("[[%s]]", bracketed))
+		req.Params = &params
+	} else {
+		// Add empty argument list if params omitted.
+		params := json.RawMessage("[]")
+		req.Params = &params
+	}
+
+encode:
+	// Encode the request. This allows us to print the patched request.
+	buf, err := json.Marshal(req)
+	if err != nil {
+		return 0, err
+	}
+	log.Infof("patched request: %v", string(buf))
+
+	err = c.enc.Encode(req)
+	if err != nil {
+		return 0, err
+	}
+	return c.outBuffer.Read(p)
+}
+
+func (c *jsonPatchingCodec) Write(p []byte) (n int, err error) {
+	log.Infof("raw response: %v", string(p))
+	var resp serverResponse
+	err = json.Unmarshal(p, &resp)
+	if err != nil {
+		return 0, err
+	}
+
+	// Add "jsonrpc": "2.0" if missing.
+	if len(resp.Version) == 0 {
+		resp.Version = "2.0"
+	}
+
+	buf, err := json.Marshal(resp)
+	if err != nil {
+		return 0, err
+	}
+	log.Infof("patched response: %v", string(buf))
+
+	// Add newline for framing.
+	return c.conn.Write(append(buf, '\n'))
+}
+
+func (c *jsonPatchingCodec) Close() error {
+	return c.conn.Close()
+}