Project ID: 02a2426b-21f8-40ec-b870-3c9689f2c88e

Subject: Edge proxy does not handle Expect: 100-continue — requests hang until client timeout

Hello,

We are hitting an issue where the Railway edge proxy appears to swallow requests that carry the Expect: 100-continue header. The origin never receives them and the client hangs until it times out.

Project: pacific-vision

Service: tienda

Public domain: tienda-production-b534.up.railway.app

Custom domain: api.almadigitalrd.com (CNAME to the above)

Runtime: Node.js 22 (Alpine), Express, listening on $PORT (3000)

== What we measured ==

Same Node.js client, same POST, same multipart body, same endpoint. The only variable is the header and the host.

1. Direct to the container, bypassing the edge:

   POST http://127.0.0.1:3000/fe/recepcion/api/ecf with Expect: 100-continue

   -> "100 Continue" received in 5 ms, final response in 8 ms

2. Through the Railway domain:

   POST https://tienda-production-b534.up.railway.app/fe/recepcion/api/ecf with Expect: 100-continue

   -> no "100 Continue", no response, nothing after 8 seconds

3. Through our custom domain:

   POST https://api.almadigitalrd.com/fe/recepcion/api/ecf with Expect: 100-continue

   -> no "100 Continue", no response, nothing after 10 seconds

4. Same endpoint, same body, WITHOUT the Expect header (plain fetch):

   POST https://api.almadigitalrd.com/fe/recepcion/api/ecf

   -> HTTP 200 in 190 ms, consistently

Our application access log records case 4 but shows no entry at all for cases 2 and 3, which suggests the request never reaches the container.

Node's built-in HTTP server answers 100-continue automatically, and case 1 confirms it does so correctly here. The behaviour only appears once the request goes through the edge.

== Reproduction ==

Run from any Node.js 22 environment:

const https = require('https');

const b = Buffer.from('--X\r\nContent-Disposition: form-data; name="xml"; filename="p.xml"\r\nContent-Type: text/xml\r\n\r\n\r\n--X--\r\n');

const t = Date.now();

const r = https.request({

host: 'tienda-production-b534.up.railway.app',

path: '/fe/recepcion/api/ecf',

method: 'POST',

headers: {

'Content-Type': 'multipart/form-data; boundary=X',

'Content-Length': b.length,

'Expect': '100-continue'

}

}, res => { console.log('response', res.statusCode, Date.now() - t, 'ms'); res.resume(); });

r.on('continue', () => { console.log('100 Continue in', Date.now() - t, 'ms'); r.end(b); });

r.on('error', e => console.log('error', e.message));

setTimeout(() => { console.log('nothing after 8s'); process.exit(0); }, 8000);

Swapping the host for 127.0.0.1:3000 from inside the container succeeds in single-digit milliseconds.

== Why this matters to us ==

This service is a receiver endpoint for the Dominican Republic tax authority (DGII) electronic invoicing programme. During certification, their platform calls our endpoint and expects a signed acknowledgement. Their client is .NET-based, and .NET's HTTP stack sends Expect: 100-continue on POST requests by default. Their platform reported "Error: Http Timeout" against our service and automatically rolled our certification back a step, while our own measurements show the endpoint responding in 190 ms.

We cannot change their client, and this is a government certification process with a compliance deadline.

== What we are asking ==

1. Is this a known limitation of the edge proxy?
2. Is there a setting, or any supported way, to make the edge answer 100-continue or forward the request regardless?
3. If not, can you confirm it so we can put a proxy in front that handles it?

Happy to run any additional test you need, and to give you a window to reproduce against the service directly.

Thank you,

Boiko

Alma Consulting SRL