fix(core): Fix coercion of serialized tool and function messages (#7653)

langchain-ai · Feb 5, 2025 · 1efb550 · 1efb550
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diff --git a/langchain-core/src/messages/tests/base_message.test.ts b/langchain-core/src/messages/tests/base_message.test.ts
@@ -404,6 +404,43 @@ describe("Message like coercion", () => {
       }),
     ]);
   });
+  it("should convert serialized messages", async () => {
+    const originalMessages = [
+      new SystemMessage({
+        id: "foobar",
+        content: "6",
+        additional_kwargs: {},
+      }),
+      new SystemMessage({
+        content: "6.1",
+        additional_kwargs: {
+          __openai_role__: "developer",
+        },
+      }),
+      new HumanMessage({
+        content: [{ type: "image_url", image_url: { url: "7.1" } }],
+      }),
+      new AIMessage({
+        content: [{ type: "text", text: "8.1" }],
+        tool_calls: [
+          {
+            id: "8.5",
+            name: "8.4",
+            args: { "8.2": "8.3" },
+            type: "tool_call",
+          },
+        ],
+      }),
+      new ToolMessage({
+        name: undefined,
+        content: "10.2",
+        tool_call_id: "10.2",
+      }),
+    ];
+    const serialized = JSON.parse(JSON.stringify(originalMessages));
+    const deserialized = serialized.map(coerceMessageLikeToMessage);
+    expect(deserialized).toEqual(originalMessages);
+  });
 });
 
 describe("usage_metadata serialized", () => {

diff --git a/langchain-core/src/messages/utils.ts b/langchain-core/src/messages/utils.ts
@@ -87,6 +87,16 @@ function _constructMessageFromParams(
       className === "SystemMessageChunk"
     ) {
       type = "system";
+    } else if (
+      className === "FunctionMessage" ||
+      className === "FunctionMessageChunk"
+    ) {
+      type = "function";
+    } else if (
+      className === "ToolMessage" ||
+      className === "ToolMessageChunk"
+    ) {
+      type = "tool";
     } else {
       type = "unknown";
     }