[Docs] Example tunnel fails with compressed replay envelope

Is there an existing issue for this?

I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
I have reviewed the documentation https://docs.sentry.io/
I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases

How do you use Sentry?

Sentry Saas (sentry.io)

Which SDK are you using?

@sentry/sveltekit

SDK Version

8.26.0

Framework Version

Sveltekit 2.5.18

Link to Sentry event

No response

Reproduction Example/SDK Setup

Using the example provided from the documentation does not work with replay requests. The docs show using an array buffer. This works well with traces, however for replays the code error on parsing piece. In this case the envelopeBytes is 0 and envelope empty.

https://docs.sentry.io/platforms/javascript/troubleshooting/#dealing-with-ad-blockers

const SENTRY_HOST = "oXXXXXX.ingest.sentry.io";
const SENTRY_PROJECT_IDS = ["123456"];

export const POST: RequestHandler = async ({ request }) => {
  try {
    const envelopeBytes = await request.arrayBuffer();
    const envelope = new TextDecoder().decode(envelopeBytes);
    console.log(envelopeBytes, envelope);
    const piece = envelope.split('\n')[0];
    const header = JSON.parse(piece);
    const dsn = new URL(header['dsn']);
    const project_id = dsn.pathname?.replace('/', '');

    if (dsn.hostname !== SENTRY_HOST) {
      throw new Error(`Invalid sentry hostname: ${dsn.hostname}`);
    }

    if (!project_id || !SENTRY_PROJECT_IDS.has(project_id)) {
      throw new Error(`Invalid sentry project id: ${project_id}`);
    }

    const upstream_sentry_url = `https://${SENTRY_HOST}/api/${project_id}/envelope/`;
    await fetch(upstream_sentry_url, {
      method: 'POST',
      body: envelopeBytes,
    });

    return json({}, { status: 200 });
  } catch (error) {
    console.error('error tunneling to sentry', error);
    return json({ error: 'error tunneling to sentry' }, { status: 500 });
  }
};

Steps to Reproduce

Create an API route, eg /api/errors/+server.ts.
Export a POST api.
Configure sentry client to tunnel through /api/errors.

Expected Result

The replays get sent to sentry successfully.

Actual Result

Traces are tunneled. Replays result in this error:

// console.log(envelopeBytes, envelope);
ArrayBuffer { [Uint8Contents]: <>, byteLength: 0 }

error tunneling to sentry SyntaxError: Unexpected end of JSON input
    at JSON.parse (<anonymous>)
    at POST (/src/routes/api/errors/+server.ts:17:25)
    at async Module.render_endpoint (/node_modules/.pnpm/@sveltejs+kit@2.5.18_@sveltejs+vite-plugin-svelte@3.1.1_svelte@4.2.18_vite@5.3.3_@types+node@_l5lnugt2i4tpym4dqtslohvg24/node_modules/@sveltejs/kit/src/runtime/server/endpoint.js:49:18)
    at async resolve (/node_modules/.pnpm/@sveltejs+kit@2.5.18_@sveltejs+vite-plugin-svelte@3.1.1_svelte@4.2.18_vite@5.3.3_@types+node@_l5lnugt2i4tpym4dqtslohvg24/node_modules/@sveltejs/kit/src/runtime/server/respond.js:454:17)
    at async documentPolicy (/src/lib/hooks/document-policy.ts:6:20)
    at async /node_modules/.pnpm/@sentry+sveltekit@8.26.0_@opentelemetry+api@1.9.0_@opentelemetry+core@1.25.1_@opentelemetry+a_gixmxtpq6bgq6uyfpgkkbh5rvy/node_modules/@sentry/sveltekit/build/cjs/server/handle.js:140:21
    at async instrumentHandle (/node_modules/.pnpm/@sentry+sveltekit@8.26.0_@opentelemetry+api@1.9.0_@opentelemetry+core@1.25.1_@opentelemetry+a_gixmxtpq6bgq6uyfpgkkbh5rvy/node_modules/@sentry/sveltekit/build/cjs/server/handle.js:128:27)
    at async Module.respond (/node_modules/.pnpm/@sveltejs+kit@2.5.18_@sveltejs+vite-plugin-svelte@3.1.1_svelte@4.2.18_vite@5.3.3_@types+node@_l5lnugt2i4tpym4dqtslohvg24/node_modules/@sveltejs/kit/src/runtime/server/respond.js:330:20)
    at async file:///node_modules/.pnpm/@sveltejs+kit@2.5.18_@sveltejs+vite-plugin-svelte@3.1.1_svelte@4.2.18_vite@5.3.3_@types+node@_l5lnugt2i4tpym4dqtslohvg24/node_modules/@sveltejs/kit/src/exports/vite/dev/index.js:524:22

Hello, thanks for writing in.

The envelopes should not be empty for replays. You could add a guard to exit out early if envelopeBytes is empty, but I'm curious why you're getting empty envelopes to begin with.

Please set debug: true in Sentry.init and paste your logs.

Yes the body of the request is there so I'm not sure why I can't get anything out of it on the server side.

Client side debug: https://gist.github.com/johnathanludwig/1bcefb76f2609a2b44eb3820dbdea26e

Server side:

Sentry Logger [log]: [Tracing] Starting sampled root span
  op: http.server
  name: GET /(unprotected)/login
  ID: 4e95db40cdd3ecc2
Sentry Logger [log]: [Tracing] Finishing "http.server" root span "GET /(unprotected)/login" with ID 4e95db40cdd3ecc2
Sentry Logger [log]: SpanExporter exported 1 spans, 0 unsent spans remaining
Sentry Logger [log]: [Tracing] Starting sampled root span
  op: http.server
  name: POST /api/errors
  ID: 4d39a562acc53f42
Sentry Logger [log]: [Tracing] Inheriting parent's sampled decision for HTTP POST: true
Sentry Logger [log]: [Tracing] Starting sampled span
  op: < unknown op >
  name: HTTP POST
  ID: b8cf5def993c2314
  parent ID: 4d39a562acc53f42
  root ID: 4d39a562acc53f42
  root op: http.server
  root description: POST /api/errors
Sentry Logger [log]: [Tracing] Finishing "< unknown op >" span "HTTP POST" with ID b8cf5def993c2314
Sentry Logger [log]: SpanExporter has 1 unsent spans remaining
Sentry Logger [log]: [Tracing] Finishing "http.server" root span "POST /api/errors" with ID 4d39a562acc53f42
Sentry Logger [log]: SpanExporter exported 2 spans, 0 unsent spans remaining
Sentry Logger [log]: Flushing client reports based on interval.
Sentry Logger [log]: Flushing outcomes...
Sentry Logger [log]: No outcomes to send
Sentry Logger [log]: [Tracing] Starting sampled root span
  op: http.server
  name: POST /api/errors
  ID: 3bc95f07de7ced89
error tunneling to sentry SyntaxError: Unexpected end of JSON input
    at JSON.parse (<anonymous>)
    at POST (/Users/johnathanludwig/git/frontend/apps/web/src/routes/api/errors/+server.ts:16:25)
    at async Module.render_endpoint (/Users/johnathanludwig/git/frontend/node_modules/.pnpm/@sveltejs+kit@2.5.18_@sveltejs+vite-plugin-svelte@3.1.1_svelte@4.2.18_vite@5.3.3_@types+node@_l5lnugt2i4tpym4dqtslohvg24/node_modules/@sveltejs/kit/src/runtime/server/endpoint.js:49:18)
    at async resolve (/Users/johnathanludwig/git/frontend/node_modules/.pnpm/@sveltejs+kit@2.5.18_@sveltejs+vite-plugin-svelte@3.1.1_svelte@4.2.18_vite@5.3.3_@types+node@_l5lnugt2i4tpym4dqtslohvg24/node_modules/@sveltejs/kit/src/runtime/server/respond.js:454:17)
    at async /Users/johnathanludwig/git/frontend/node_modules/.pnpm/@sentry+sveltekit@8.26.0_@opentelemetry+api@1.9.0_@opentelemetry+core@1.25.1_@opentelemetry+a_gixmxtpq6bgq6uyfpgkkbh5rvy/node_modules/@sentry/sveltekit/build/cjs/server/handle.js:140:21
    at async instrumentHandle (/Users/johnathanludwig/git/frontend/node_modules/.pnpm/@sentry+sveltekit@8.26.0_@opentelemetry+api@1.9.0_@opentelemetry+core@1.25.1_@opentelemetry+a_gixmxtpq6bgq6uyfpgkkbh5rvy/node_modules/@sentry/sveltekit/build/cjs/server/handle.js:128:27)
    at async Module.respond (/Users/johnathanludwig/git/frontend/node_modules/.pnpm/@sveltejs+kit@2.5.18_@sveltejs+vite-plugin-svelte@3.1.1_svelte@4.2.18_vite@5.3.3_@types+node@_l5lnugt2i4tpym4dqtslohvg24/node_modules/@sveltejs/kit/src/runtime/server/respond.js:330:20)
    at async file:///Users/johnathanludwig/git/frontend/node_modules/.pnpm/@sveltejs+kit@2.5.18_@sveltejs+vite-plugin-svelte@3.1.1_svelte@4.2.18_vite@5.3.3_@types+node@_l5lnugt2i4tpym4dqtslohvg24/node_modules/@sveltejs/kit/src/exports/vite/dev/index.js:524:22
Sentry Logger [log]: [Tracing] Finishing "http.server" root span "POST /api/errors" with ID 3bc95f07de7ced89
Sentry Logger [log]: SpanExporter exported 1 spans, 0 unsent spans remaining

Could you please amend the server side debug log with the logs that occur on app startup?

Also, does this happen if you disable compression?

Sentry.replayIntegration({
  useCompression: false,
});

@jkittner

@jkittner do you mean the kitql proxy solution (#13453 (comment))? If so, I'm not entirely sure how the library handles proxying, so chances are that somewhere in there the compressed body is consumed and an error occurs?

I agree that the tunneling documentation is far from great and we need better examples. (Ideally, we can provide a tunnelRoute option just like in the NextJS SDK in more meta framework SDKs and a base proxy building block for lower level SDKs) Unfortunately, we didn't get to this yet, see #14248

Yes, the kitql solution only works w/o compression. For now disabling it solved the problem for me. I subscribed to the other issue as well.

Going to close this issue as the improvements necessary to fix are tracked in other issues.

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[Docs] Example tunnel fails with compressed replay envelope #13453

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[Docs] Example tunnel fails with compressed replay envelope #13453

Description

Is there an existing issue for this?

How do you use Sentry?

Which SDK are you using?

SDK Version

Framework Version

Link to Sentry event

Reproduction Example/SDK Setup

Steps to Reproduce

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andreiborza commented on Aug 26, 2024

johnathanludwig commented on Aug 26, 2024

andreiborza commented on Aug 26, 2024

33 remaining items

Lms24 commented on Jun 6, 2025

jkittner commented on Jun 6, 2025

Lms24 commented on Aug 7, 2025

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