be more specific for error message (#1409)

### What problem does this PR solve?

#918 

### Type of change

- [x] Refactoring

graph/canvas.py

@@ -121,7 +121,6 @@ class Canvas(ABC):
                     if desc["to"] not in cpn["downstream"]:
                         cpn["downstream"].append(desc["to"])
 
-
         self.path = self.dsl["path"]
         self.history = self.dsl["history"]
         self.messages = self.dsl["messages"]
@@ -136,9 +135,21 @@ class Canvas(ABC):
         self.dsl["answer"] = self.answer
         self.dsl["reference"] = self.reference
         self.dsl["embed_id"] = self._embed_id
-        dsl = deepcopy(self.dsl)
+        dsl = {
+            "components": {}
+        }
+        for k in self.dsl.keys():
+            if k in ["components"]:continue
+            dsl[k] = deepcopy(self.dsl[k])
+
         for k, cpn in self.components.items():
-            dsl["components"][k]["obj"] = json.loads(str(cpn["obj"]))
+            if k not in dsl["components"]:
+                dsl["components"][k] = {}
+            for c in cpn.keys():
+                if c == "obj":
+                    dsl["components"][k][c] = json.loads(str(cpn["obj"]))
+                    continue
+                dsl["components"][k][c] = deepcopy(cpn[c])
         return json.dumps(dsl, ensure_ascii=False)
 
     def reset(self):
@@ -161,6 +172,9 @@ class Canvas(ABC):
             except Exception as e:
                 ans = ComponentBase.be_output(str(e))
             self.path[-1].append(cpn_id)
+            if kwargs.get("stream"):
+                assert isinstance(ans, partial)
+                return ans
             self.history.append(("assistant", ans.to_dict("records")))
             return ans
 
@@ -190,6 +204,8 @@ class Canvas(ABC):
             cpn = self.get_component(cpn_id)
             if not cpn["downstream"]: break
 
+            if self._find_loop(): raise OverflowError("Too much loops!")
+
             if cpn["obj"].component_name.lower() in ["switch", "categorize", "relevant"]:
                 switch_out = cpn["obj"].output()[1].iloc[0, 0]
                 assert switch_out in self.components, \
@@ -249,3 +265,27 @@ class Canvas(ABC):
 
     def get_embedding_model(self):
         return self._embed_id
+
+    def _find_loop(self, max_loops=2):
+        path = self.path[-1][::-1]
+        if len(path) < 2: return False
+
+        for i in range(len(path)):
+            if path[i].lower().find("answer") >= 0:
+                path = path[:i]
+                break
+
+        if len(path) < 2: return False
+
+        for l in range(1, len(path) // 2):
+            pat = ",".join(path[0:l])
+            path_str = ",".join(path)
+            if len(pat) >= len(path_str): return False
+            path_str = path_str[len(pat):]
+            loop = max_loops
+            while path_str.find(pat) >= 0 and loop >= 0:
+                loop -= 1
+                path_str = path_str[len(pat):]
+            if loop < 0: return True
+
+        return False