Request: Add CORS header config to demo.mtconnect.org agent

[robot-ranger]

Is it possible to add the CORS header config (https://github.com/mtconnect/cppagent?tab=readme-ov-file#rest-service-configuration) to the demo agent at https://demo.mtconnect.org/probe?

Im am working on browser-based client and getting CORS errors trying to get response docs. It is working against my local agent (that does have the above CORS config applied), but I would like to test against an "unknown" device model.

[robot-ranger]

for what its worth, we plan on opening up this client in a public repo. Gotta be functional first, though.

[robot-ranger]

@wsobel I assumed the agent running at demo.mtconnect.org referenced the file I comitted to close this issue, but im still getting CORS denials when connecting to demo.mtconnect.org from a browser webapp.

cli apps connect fine - i believe this is only relevant for browser-based webapp clients.

are you willing to open up the CORS on demo.mtconnect.org to allow for browser webapp demonstration?

[wsobel]

The demo agent is running using the docker compose demo and has nginx with reverse proxy. I'll check if they are passing through the CORS preflight and OPTIONS. I thought it should be working. I may need to add
extra headers as well.

Please tell me what you're trying to do with CORS and what's not working.I may need to just patch the nginx config or the cfg file for additional headers.

[robot-ranger]

for context, I had previously transcribed the client used in the digital twin demo to typescript: https://github.com/processrobotics/mtconnect-ts/blob/main/src/MTConnect.ts

I am trying to use the probe() method from my lib above, but the browser shows:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://demo.mtconnect.org:5000/probe. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). Status code: 200.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/CORS/Errors/CORSMissingAllowOrigin

the same webapp works fine wen directed to my local agents, albeit those are configured to allow all with the following in agent.json:

"HttpHeaders": {
        "Access-Control-Allow-Origin": "*",
        "Access-Control-Allow-Methods": "GET",
        "Access-Control-Allow-Headers": "Accept"
    },

[robot-ranger]

side note: i get 301: Moved Permanently when i omit port 5000 in the url:
request header without port 5000:

GET /probe HTTP/1.1
Host: demo.mtconnect.org
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:150.0) Gecko/20100101 Firefox/150.0
Accept: application/json
Accept-Language: en-US,en;q=0.9
Accept-Encoding: gzip, deflate
Referer: http://localhost:5173/
Origin: http://localhost:5173
Connection: keep-alive
Sec-GPC: 1
Priority: u=4

response header without port 5000:

HTTP/1.1 301 Moved Permanently
Server: nginx/1.18.0 (Ubuntu)
Date: Sun, 10 May 2026 21:47:25 GMT
Content-Type: text/html
Content-Length: 178
Connection: keep-alive
Location: https://demo.mtconnect.org/probe

request header WITH port 5000 in url:

GET /probe HTTP/1.1
Host: demo.mtconnect.org:5000
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:150.0) Gecko/20100101 Firefox/150.0
Accept: application/json
Accept-Language: en-US,en;q=0.9
Accept-Encoding: gzip, deflate
Referer: http://localhost:5173/
Origin: http://localhost:5173
Connection: keep-alive
Sec-GPC: 1
Priority: u=4

response header WITH port 5000 in url:

HTTP/1.1 200 OK
Server: MTConnectAgent
Date: Sun, 10 May 2026 21:49:56 GMT
Expires: -1
Cache-Control: no-store, max-age=0
Content-Type: application/mtconnect+json
Content-Length: 43320

[robot-ranger]

well i just noticed that firefox actually gets a 200 OK response, and it DOES get the response doc content. but then blocks it from being used in scripts locally due to CORS?!

[wsobel]

I'll check it out tomorrow. Port 5000 is supposed to be blocked, but oops. Nothing too bad,just bypassing nginx. I'll check the headers and make sure cross scripting is enabled. I can also now allow GET and OPTIONS methods.

[robot-ranger]

Does the agent at demo.mtconnect.org allow/support websocket?

its been in my mind to start moving toward websocket over http... if the demo.mtconnect.org has ws maybe now is as good a time as any...

[wsobel]

It should work. The agent supports websockets and if something doesn't work, it would be a change to nginx to pass wesocket request through to the agent.

Tell me if you have issues. I'll get to this tomorrow.

[robot-ranger]

no immediate rush. our webapp works on our local agents, i just wanted to pressure test it a bit with an "unknown" agent and devices model.

[wsobel]

I added the header:

$  StandardsCommittee curl -I -X OPTIONS https://demo.mtconnect.org/probe
HTTP/1.1 204 No Content
Server: nginx/1.18.0 (Ubuntu)
Date: Tue, 12 May 2026 18:42:45 GMT
Content-Type: text/plain
Content-Length: 0
Connection: keep-alive
Expires: -1
Cache-Control: no-store, max-age=0
Access-Control-Allow-Origin: *
Allow: GET, OPTIONS
Access-Control-Allow-Methods: GET, OPTIONS
Access-Control-Allow-Headers: Content-Type, Accept, Accept-Encoding
Access-Control-Max-Age: 86400

and

➜  StandardsCommittee curl -i https://demo.mtconnect.org/
HTTP/1.1 200 OK
Server: nginx/1.18.0 (Ubuntu)
Date: Tue, 12 May 2026 18:47:36 GMT
Content-Type: application/xml
Content-Length: 46372
Connection: keep-alive
Expires: -1
Cache-Control: no-store, max-age=0
Access-Control-Allow-Origin: *

Check if that helps. I can add additional headers if necessary.

I may need to add Access-Control-Allow-Headers: Origin, Content-Type, Accept, Accept-Encoding to the allow headers line. I can modify if necessary.

btw. I did not modify nginx, this is all coming directly from the agent.