rpc: allow batch JSON-RPC requests

Close #1509

pkg/rpc/response/types.go

@@ -24,6 +24,12 @@ type Raw struct {
 	Result json.RawMessage `json:"result,omitempty"`
 }
 
+// AbstractResult is an interface which represents either single JSON-RPC 2.0 response
+// or batch JSON-RPC 2.0 response.
+type AbstractResult interface {
+	RunForErrors(f func(jsonErr *Error))
+}
+
 // Abstract represents abstract JSON-RPC 2.0 response, it differs from Raw in
 // that Result field is an interface here.
 type Abstract struct {
@@ -31,6 +37,25 @@ type Abstract struct {
 	Result interface{} `json:"result,omitempty"`
 }
 
+// RunForErrors implements AbstractResult interface.
+func (a Abstract) RunForErrors(f func(jsonErr *Error)) {
+	if a.Error != nil {
+		f(a.Error)
+	}
+}
+
+// AbstractBatch represents abstract JSON-RPC 2.0 batch-response.
+type AbstractBatch []Abstract
+
+// RunForErrors implements AbstractResult interface.
+func (ab AbstractBatch) RunForErrors(f func(jsonErr *Error)) {
+	for _, a := range ab {
+		if a.Error != nil {
+			f(a.Error)
+		}
+	}
+}
+
 // Notification is a type used to represent wire format of events, they're
 // special in that they look like requests but they don't have IDs and their
 // "method" is actually an event name.