Unable to connect to the device via websocket

[joneuhauser]

I've tried this on two different machines now, so I don't think it's with my setup as per #1024.

When opening a trace file with trace_processor and opening the UI, the terminal shows

./trace_processor pipe_next2.pftrace --httpd --http-port 9001
[670.680] processor_shell.cc:1742 Trace loaded: 1163.21 MB in 37.95s (30.7 MB/s)
670.680]            httpd.cc:102 [HTTP] Starting RPC server on localhost:9001
[670.680]            httpd.cc:107 [HTTP] This server can be used by reloading https://ui.perfetto.dev and clicking on YES on the "Trace Processor native acceleration" dialog or through the Python API (see https://perfetto.dev/docs/analysis/trace-processor#python-api).
[712.517]       http_server.cc:83 [HTTP] New connection
[712.517]      http_server.cc:231 [HTTP] POST /status [body=0B, origin="https://ui.perfetto.dev"]
[718.422]      http_server.cc:231 [HTTP] POST /status [body=0B, origin="https://ui.perfetto.dev"]
[718.427]       http_server.cc:83 [HTTP] New connection
[718.427]      http_server.cc:231 [HTTP] GET /websocket [body=0B, origin="https://ui.perfetto.dev"]
[718.427]       http_server.cc:90 [HTTP] Client disconnected

and in the Web UI, I see

trace_processor_shell --httpd is unreachable or crashed.

Websocket closed (1006: ) (ERR:ws)

Any workarounds for this issue?

[joneuhauser]

When I open localhost:9001, I can see the Perfetto message. localhost:9001/websocket returns a 404.

[LalitMaganti]

Are you on the latest version of trace_processor? Try updating like:

curl -LO https://get.perfetto.dev/trace_processor

This is one of our most used features both internally and externally so if this was an issue on our side, we'd have a lot of users very loudly complaining about it and we have it fixed within a day :)

[joneuhauser]

On the second device where I've tested it, I've downloaded the trace_processor only today - but just to be sure, I tried it again and ran into the same error. What else can I try?

[LalitMaganti]

For one the 404 on /websocket is a total red herring. /websocket is not a normal HTTP endpoint, it's really a special endpoint which means "I want to be upgrade to a websocket" and as such it's only meaningful if the upgrade handshake marker is present.

I would try first using something like https://github.com/vi/websocat to check you are able to establish a connection from a command line. Something like:

websocat ws://localhost:9001/websocket --origin http://localhost:10000

Just tested this on my machine and this was able to successfully create a connection. Note the protocol is a binary one so you cannot actually send messages but it will at least establish if there's a connection possible from your machine to trace processor.

If that works then you should go to ui.perfetto.dev and open Chrome Devtools and start checking if the websocket data is flowing correctly (and for how long) between the browser and the command line. Annotated screenshot:

One or both of these should point to some next steps hopefully.

[joneuhauser]

Just downloaded Chrome to check the devtools, and alas, it works there! So the issue appears to be limited to Firefox. Thanks for your help!

[rsavitski]

FYI there's a parallel attempt to make --httpd work with Firefox: #1302