ESP32-S3 specific WS message lengths cause WS frame is not properly masked error (IDFGH-14461)

[higaski]

Answers checklist.

• I have read the documentation ESP-IDF Programming Guide and the issue is not addressed there.
• I have updated my IDF branch (master or release) to the latest version and checked that the issue is present there.
• I have searched the issue tracker for a similar issue and not found a similar issue.

IDF version.

ESP-IDF v5.4

Espressif SoC revision.

ESP32-S3 (QFN56) (revision v0.1)

Operating System used.

Linux

How did you build your project?

Command line with CMake

If you are using Windows, please specify command line type.

None

Development Kit.

ESP32-S3 WROOM2 custom board

Power Supply used.

External 3.3V

What is the expected behavior?

Transmitting WebSocket messages of any length should not be an issue.

What is the actual behavior?

I think there still is an issue when transmitting WebSocket messages of a particular length. I have an application which used to transmit 268B messages in bursts of 256 messages at a time. This worked flawlessly so far. Due to changed requirements the message size decreased from 268 to 263B and suddenly ESP-IDF is throwing WS frame is not properly masked errors at me.

Doing some research I think that this might be related to #14473, #14704 or #14706?
Apparently a particular message size transmitted at a specific pattern (263B x 256 in this case) is problematic.

Steps to reproduce.

1. Use the following example https://github.com/higaski/esp_idf_issue_15235
2. Provide WiFi credentials in main.cpp

   #define MY_SSID ""
   #define MY_PASSWORD ""

3. Flash the example onto an ESP32-S3-DevKitC-1 (must be a 32MB flash one, e.g. N32R8V)
4. Open the ws_send.py script (requires websocket-client)
5. Replace the IP address with the one assigned to the ESP32
6. Run the script

Debug Logs.

I (9245) wifi:dp: 1, bi: 102400, li: 3, scale listen interval from 307200 us to 307200 us
I (9245) wifi:set rx beacon pti, rx_bcn_pti: 0, bcn_timeout: 25000, mt_pti: 0, mt_time: 10000
I (9255) wifi:AP's beacon interval = 102400 us, DTIM period = 1
I (10465) esp_netif_handlers: sta ip: 192.168.1.122, mask: 255.255.255.0, gw: 192.168.1.250
I (10465) esp_idf_issue_15235: got ip: 192.168.1.122
I (47935) wifi:<ba-add>idx:1 (ifx:0, 18:a6:f7:df:6d:b5), tid:0, ssn:0, winSize:64
I (48065) esp_idf_issue_15235: WS open
W (49805) httpd_ws: httpd_ws_recv_frame: WS frame is not properly masked.

More Information.

No response

[higaski]

OK, of course it didn't leave me alone. I've tried to create a minimal repro here:
https://github.com/higaski/esp_idf_issue_15235

It contains some HTTP / WS code which reads the received data into a std::vector and then transmits a 0-6 byte random response back. The WS requests are sent from a simple Python script.

Sadly I couldn't reproduce the issue yet. Maybe Python is too slow to burst send the messages fast enough? The original code uses a Web-App to send the data. Maybe the timing is critical.

/edit
😄
ok, couple of seconds later, splitting the Python send/recv into two different loops, it now repros immediately.