Bug in LangGraph API server for graphs in relative paths.

[tjrivera]

Hi folks,

Not sure where the best place to put this is as I can't find the actual code for the LangGraph API server/LangGraph Studio and figure its not on GitHub

Issue:

I have a graph defined within a monorepo and have my langgraph.json file in the root of my repository. My langgraph configuration looks like:

{
  "node_version": "20",
  "dockerfile_lines": [],
  "dependencies": ["./packages/agents", "./packages/core"],
  "graphs": {
    "agent": "./packages/agents/src/test/graph.ts:graph"
  },
  "env": "packages/agents/.env"
}

I found that I can get the graph to build and load into studio, but that my Input form was not rendering properly -- I could only enter raw input i.e. { messages: [{...}]} instead of the nice form with the ability to select Human, AI, System, etc.

Bad build:

Expected build:

Checking my logs I found warnings of:

langgraph-api-1       | Failed to obtain symbol "__langgraph__graph__input": Unsupported type: 0 extends 1 & ValueType ? ValueType | undefined : Wrap<MatchBaseMessageArray<ValueType>> extends Wrap<...> ? import("/Users/tyler/code/test/node_modules/@langchain/core/dist/messages/base").BaseMessage[] : Wrap<...> extends Wrap<...> ? import("/Users/tyler/code/plum-fit-web/node_modules/@langchain/core/dist/messages/base").BaseMess...
langgraph-api-1       | Failed to obtain symbol "__langgraph__graph__input": Unsupported type: 0 extends 1 & ValueType ? ValueType | undefined : Wrap<MatchBaseMessageArray<ValueType>> extends Wrap<...> ? import("/Users/tyler/code/plum-fit-web/node_modules/@langchain/core/dist/messages/base").BaseMessage[] : Wrap<...> extends Wrap<...> ? import("/Users/tyler/code/test/node_modules/@langchain/core/dist/messages/base").BaseMess...

I tracked this down to the /api/langgraph_api/js/src/parser/parser.mts in the API server container:

    host.compilerHost.resolveModuleNames = (moduleNames, containingFile) => {
      const resolvedModules: (ts.ResolvedModule | undefined)[] = [];
      for (const moduleName of moduleNames) {
        let target = containingFile;
        const relative = path.relative(dirname, containingFile);
        if (
          moduleName.startsWith("@langchain/langgraph") &&
          relative &&
          !relative.startsWith("..") &&
          !path.isAbsolute(relative)
        ) {
          target = path.resolve(__dirname, relative);
        }

        resolvedModules.push(
          ts.resolveModuleName(
            moduleName,
            target,
            compilerOptions,
            host.compilerHost
          ).resolvedModule
        );
      }

      return resolvedModules;
    };

and noticed that it is only taking into account the @langchain/langgraph package, whereas the BaseMessage types are in @langchain/core. Updating the conditional to:

        if (
          (
            moduleName.startsWith("@langchain/langgraph") || 
            moduleName.startsWith("@langchain/core")
          ) &&
          relative &&
          !relative.startsWith("..") &&
          !path.isAbsolute(relative)
        ) {
          target = path.resolve(__dirname, relative);
        }

seems to resolve the issue. My current workaround is creating a patch file:

--- parser.mts	2025-01-04 23:23:38.820551112 +0000
+++ parser.mts	2025-01-04 23:24:19.279845893 +0000
@@ -373,7 +373,7 @@
         let target = containingFile;
         const relative = path.relative(dirname, containingFile);
         if (
-          moduleName.startsWith("@langchain/langgraph") &&
+          (moduleName.startsWith("@langchain/langgraph") || moduleName.startsWith("@langchain/core")) &&
           relative &&
           !relative.startsWith("..") &&
           !path.isAbsolute(relative)

and including the patch in my dockerfile lines:

{
  "node_version": "20",
  "dockerfile_lines": [
    "COPY packages/agents/langgraph_api.patch /tmp/langgraph_api.patch",
    "RUN patch --forward -p0 /api/langgraph_api/js/src/parser/parser.mts < /tmp/langgraph_api.patch"
  ],
  "dependencies": ["./packages/agents", "./packages/core"],
  "graphs": {
    "agent": "./packages/agents/src/fitness/graph.ts:graph"
  },
  "env": "packages/agents/.env"
}

I'm happy to submit a patch for this, but if that's not possible, hope this report helps resolve on yourside. Thanks.