Use code strings consistently.

error.go

@@ -47,7 +47,7 @@ var errClientStopped = errors.New("the client has been stopped")
 var errEmptyMethod = &Error{Code: code.InvalidRequest, Message: "empty method name"}
 
 // errNoSuchMethod is the error reported for an unknown method name.
-var errNoSuchMethod = &Error{Code: code.MethodNotFound, Message: "no such method"}
+var errNoSuchMethod = &Error{Code: code.MethodNotFound, Message: code.MethodNotFound.String()}
 
 // errDuplicateID is the error reported for a duplicated request ID.
 var errDuplicateID = &Error{Code: code.InvalidRequest, Message: "duplicate request ID"}
@@ -59,7 +59,7 @@ var errInvalidRequest = &Error{Code: code.ParseError, Message: "invalid request
 var errEmptyBatch = &Error{Code: code.InvalidRequest, Message: "empty request batch"}
 
 // errInvalidParams is the error reported for invalid request parameters.
-var errInvalidParams = &Error{Code: code.InvalidParams, Message: "invalid parameters"}
+var errInvalidParams = &Error{Code: code.InvalidParams, Message: code.InvalidParams.String()}
 
 // ErrConnClosed is returned by a server's push-to-client methods if they are
 // called after the client connection is closed.

jrpc2_test.go

@@ -619,7 +619,7 @@ func TestServer_nonLibraryClient(t *testing.T) {
 
 		// The method specified doesn't exist.
 		{`{"jsonrpc":"2.0", "id": 3, "method": "NoneSuch"}`,
-			`{"jsonrpc":"2.0","id":3,"error":{"code":-32601,"message":"no such method","data":"NoneSuch"}}`},
+			`{"jsonrpc":"2.0","id":3,"error":{"code":-32601,"message":"method not found","data":"NoneSuch"}}`},
 
 		// The parameters are of the wrong form.
 		{`{"jsonrpc":"2.0", "id": 4, "method": "X", "params": "bogus"}`,
@@ -654,7 +654,7 @@ func TestServer_nonLibraryClient(t *testing.T) {
 
 		// A batch of invalid requests returns a batch of errors.
 		{`[{"jsonrpc": "2.0", "id": 6, "method":"bogus"}]`,
-			`[{"jsonrpc":"2.0","id":6,"error":{"code":-32601,"message":"no such method","data":"bogus"}}]`},
+			`[{"jsonrpc":"2.0","id":6,"error":{"code":-32601,"message":"method not found","data":"bogus"}}]`},
 
 		// Batch requests return batch responses, even for a singleton.
 		{`[{"jsonrpc": "2.0", "id": 7, "method": "X"}]`, `[{"jsonrpc":"2.0","id":7,"result":"OK"}]`},