Preserve the full HttpResponse in generateContentStream responses

[dani29]

Description

Hi! I ran into this while adding response-level observability around generateContentStream().

Each streamed GenerateContentResponse has an sdkHttpResponse property typed as HttpResponse. I expected it to include the original Response through responseInternal, which would make the HTTP status and other response metadata available.

In practice, sdkHttpResponse only contains the headers:

{
  headers: {
    "content-type": "text/event-stream"
  }
}

The SDK appears to have the full HttpResponse internally, but replaces it with { headers: chunk.headers } when it creates the public response chunk:

https://github.com/googleapis/js-genai/blob/v2.17.1/src/models.ts#L801-L891

Would it be possible to preserve and return the complete HttpResponse instead? For example, returning the existing chunk would retain both the headers and responseInternal.status.

This would also make the runtime value match the exported HttpResponse type:

https://github.com/googleapis/js-genai/blob/v2.17.1/src/types.ts#L3197-L3216

Reproduction

import { GoogleGenAI } from "@google/genai";

const originalFetch = globalThis.fetch;

globalThis.fetch = async () =>
  new Response(
    `data: ${JSON.stringify({
      candidates: [
        {
          content: {
            role: "model",
            parts: [{ text: "ok" }],
          },
          finishReason: "STOP",
        },
      ],
    })}\n\n`,
    {
      status: 200,
      headers: {
        "content-type": "text/event-stream",
        "x-repro-header": "visible",
      },
    },
  );

try {
  const client = new GoogleGenAI({
    apiKey: "test-key",
    httpOptions: {
      baseUrl: "https://upstream.test",
      apiVersion: "",
    },
  });

  const stream = await client.models.generateContentStream({
    model: "test-model",
    contents: "hello",
  });

  const { value: chunk } = await stream.next();

  console.log({
    headers: chunk.sdkHttpResponse?.headers,
    responseInternal: chunk.sdkHttpResponse?.responseInternal,
    status: chunk.sdkHttpResponse?.responseInternal?.status,
  });
} finally {
  globalThis.fetch = originalFetch;
}

The headers are present, but responseInternal and status are both undefined.

Expected behavior

I would expect sdkHttpResponse to contain the full HttpResponse, so this works:

chunk.sdkHttpResponse.responseInternal.status; // 200

Environment

• @google/genai: 2.17.1
• Node.js: 24.5.0
• OS: macOS

[Varun-S10]

Hi @dani29, Thank you for raising this issue. We have reproduced it on our end. As a workaround, you can intercept the client's internal request stream at initialization to preserve and attach the complete HTTP response object back onto each streamed chunk.

function withFullHttpResponse(client) {
  const apiClient = client.models.apiClient;
  const originalRequestStream = apiClient.requestStream.bind(apiClient);
  const responseQueue = [];
  apiClient.requestStream = async function (...args) {
    const stream = await originalRequestStream(...args);
    return (async function* () {
      for await (const httpChunk of stream) {
        responseQueue.push(httpChunk);
        yield httpChunk;
      }
    })();
  };
  const originalGenerateStream = client.models.generateContentStream.bind(client.models);
  client.models.generateContentStream = async function* (params) {
    const stream = await originalGenerateStream(params);
    for await (const chunk of stream) {
      const fullResponse = responseQueue.shift();
      if (fullResponse) {
        chunk.sdkHttpResponse = fullResponse;
      }
      yield chunk;
    }
  };
  return client;
}
// Usage:
const client = new GoogleGenAI({ apiKey: "YOUR_API_KEY" });
withFullHttpResponse(client);
const stream = await client.models.generateContentStream({
  model: "gemini-2.5-flash",
  contents: "hello",
});
for await (const chunk of stream) {
  console.log(chunk.sdkHttpResponse.responseInternal.status); // 200
}

Could you please give this a try and let us know if it works for you?

[dani29]

I assume this will work, but as an API consumer this is very brittle workaround and not something I'll feel comfortable using in my own code. I raised this issue after filing this issue to Pi.dev (OSS Agentic Harness), and I don't really expect them accepting this patch into their codebase either. Happy to take a stab at contributing, if this is accepted.

[Varun-S10]

Hi @dani29, Thank you for your feedback. We appreciate you taking the time to share your thoughts with us, we will file a bug internally.

[dani29]

Any chance we can contribute a fix, either as external contributors? or is the source of truth for this jdk is internal?