`content-length` header is added in response along with `transfer-encoded: chunk` header in node.js environment

What Happened?

Yo guys!

When do request to anthropic provider (with streaming disabled), response got enriched with content-length header along with transfer-encoded: chunk header, which causes error on the client side due to wrong HTTP/1.1 response structure.

I investigated a issue a bit, adding middleware at the end of the chain and found that content-length header is actually removed.

So I can say that it happens when we give response object to node.js http service, which does this enrichment.

Environment

Node.js: v20.19.5, v22.14.0 and v22.16.0. Command: npm run dev:node

Positive

When run with wrangler - issue is not present.

What Should Have Happened?

content-length header must not be present in response along with transfer-encoded: chunk header. According to HTTP/1.1 spec.

Relevant Code Snippet

import { ChatOpenAI } from '@langchain/openai';

const AI_GATEWAY_URL = 'http://localhost:8787/v1';
const AI_GATEWAY_API_KEY = 'super-duper-secret-unhackable-api-key';

const model = new ChatOpenAI({
  apiKey: AI_GATEWAY_API_KEY,
  configuration: {
    baseURL: AI_GATEWAY_URL,
    defaultHeaders: createHeaders({
      strictOpenAiCompliance: false,
      config: {
        strategy: {
          mode: 'loadbalance',
        },
        targets: [
          {
            provider: 'anthropic',
            api_key: process.env.ANTHROPIC_API_KEY,
            override_params: {
              model: 'claude-haiku-4-5-20251001',
            },
          },
        ],
      },
    }),
  },
});
    
await model.invoke('Hello, world!');

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