Failure constructing a tool message from params, MESSAGE_COERCION_FAILURE

[arturl]

Checked other resources

• I added a very descriptive title to this issue.
• I searched the LangChain.js documentation with the integrated search.
• I used the GitHub search to find a similar question and didn't find it.
• I am sure that this is a bug in LangChain.js rather than my code.
• The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).

Example Code

see below

Error Message and Stack Trace (if applicable)

"Error: Unable to coerce message from array: only human, AI, system, developer, or tool message coercion is currently supported.
Received: {
  \"lc\": 1,
  \"type\": \"constructor\",
  \"id\": [
    \"langchain_core\",
    \"messages\",
    \"ToolMessage\"
  ],
  \"kwargs\": {
    \"content\": \"{\\\"question\\\":\\\"Show my stacks\\\",\\\"category\\\":\\\"projects/stacks\\\"}\",
    \"tool_call_id\": \"call_6f1y4NtvJtxwEDNuJyOIwdVR\",
    \"additional_kwargs\": {},
    \"response_metadata\": {},
    \"id\": \"6606e71a-9701-4141-af8f-8059bf8238f0\"
  }
}
Troubleshooting URL: https://js.langchain.com/docs/troubleshooting/errors/MESSAGE_COERCION_FAILURE/
    at constructMessageFromParams (/Users/arturl/g/pulumi.ai-2/copilot/nodemodules/@langchain/core/dist/messages/utils.cjs:104:63)
    at coerceMessageLikeToMessage (/Users/arturl/g/pulumi.ai-2/copilot/node_modules/@langchain/core/dist/messages/utils.cjs:124:16)
    at Array.map (<anonymous>)
    at BinaryOperatorAggregate.messagesStateReducer [as operator] (/Users/arturl/g/pulumi.ai-2/copilot/node_modules/@langchain/langgraph/dist/graph/message.cjs:16:36)
    at BinaryOperatorAggregate.update (/Users/arturl/g/pulumi.ai-2/copilot/node_modules/@langchain/langgraph/dist/channels/binop.cjs:57:35)
    at applyWrites (/Users/arturl/g/pulumi.ai-2/copilot/nodemodules/@langchain/langgraph/dist/pregel/algo.cjs:196:46)
    at PregelLoop.tick (/Users/arturl/g/pulumi.ai-2/copilot/node_modules/@langchain/langgraph/dist/pregel/loop.cjs:471:67)
    at CompiledStateGraph._runLoop (/Users/arturl/g/pulumi.ai-2/copilot/node_modules/@langchain/langgraph/dist/pregel/index.cjs:831:31)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async createAndRunLoop (/Users/arturl/g/pulumi.ai-2/copilot/node_modules/@langchain/langgraph/dist/pregel/index.cjs:984:17)"

Description

My code builds a langchain graph where one of the nodes invokes a tool.
The messages are then serialized using BaseCheckpointSaver.

One of the resulting messages looks like this:

{
  "lc": 1,
  "type": "constructor",
  "id": [
    "langchain_core",
    "messages",
    "ToolMessage"
  ],
  "kwargs": {
    "content": "{\"question\":\"What is the weather in Seattle\",\"category\":\"weather\"}",
    "tool_call_id": "call_6f1y4NtvJtxwEDNuJyOIwdVR",
    "additional_kwargs": {},
    "response_metadata": {},
    "id": "6606e71a-9701-4141-af8f-8059bf8238f0"
  }
}

This message fails in _constructMessageFromParams because it does not handle ToolMessage types:

langchainjs/langchain-core/src/messages/utils.ts

Line 91 in 4587906

type = "unknown";

A suggested fix would be add the following lines just before the last else clause:

        else if (className === "ToolMessage") {
            type = "tool";
        }

System Info

"@langchain/core": "^0.3.3",
"@langchain/langgraph": "^0.2.39",
"@langchain/langgraph-checkpoint": "^0.0.13",
"@langchain/langgraph-checkpoint-postgres": "^0.0.1",
"@langchain/openai": "^0.3.2",

Node.js version v18.20.3

[dosubot]

Hey there, @arturl! I'm here to help with any bugs, questions, or contributions you have in mind. Let's tackle this together!

To resolve the "MESSAGE_COERCION_FAILURE" error when processing ToolMessage types in the constructMessageFromParams function, ensure that the params object includes the necessary fields for a ToolMessage. Specifically, the params should have a type of "tool" and include a tool_call_id. If these conditions are not met, the function will throw an error with the "MESSAGE_COERCION_FAILURE" code ^[1].

Additionally, you can modify the code by adding a check for ToolMessage just before the last else clause in the constructMessageFromParams function. Add the following lines:

else if (className === "ToolMessage") {
    type = "tool";
}

This change will allow the function to correctly process ToolMessage types, addressing the error you are experiencing.

To continue talking to Dosu, mention @dosu.

---

^{Help Dosu learn! Give it feedback: Great Response | Irrelevant Answer | Incorrect Sources | Too Verbose | Hallucination | Other}

[jacoblee93]

Thanks for reporting - will fix!

[jacoblee93]

Live, please bump to @langchain/[email protected]!

[arturl]

Thanks for the prompt turnaround @jacoblee93, I will update!

[arturl]

Fix confirmed, thanks again.