sensesp deserializeJson error: EmptyInput

[moj0002]

I seem to get a deserializeJson error on the sensesp client after the initial handshake and it continues in a loop, doesn't seem to hurt anything but I can't figure out where it is coming from, I assume it is from SignalK so I disabled all plugins but that didn't help.

Can the error come from my own sensesp code? The error is emitted from signalk_ws_client.cpp so I assume it is from the outside world. The length of the payload is zero so it makes sense an error is generated.

this is the first message I get and looks fine:
I (10100) signalk_ws_client.cpp: Subscribing to Signal K listeners...
D (10109) signalk_ws_client.cpp: length 184
D (10110) signalk_ws_client.cpp: Websocket payload received: {"name":"signalk-server","version":"2.21.2","self":"vessels.urn:mrn:signalk:uuid:4880f74c-9125-123g-8c6f-a4934d392c0e","roles":["master","main"],"timestamp":"2026-02-11T22:12:55.023Z"

next one I get:
D (20158) signalk_ws_client.cpp: length 0
D (20158) signalk_ws_client.cpp: Websocket payload received:
(233365) signalk_ws_client.cpp: deserializeJson error: EmptyInput
E (233371) signalk_ws_client.cpp: Payload: {"name":"signalk-server","version":"2.21.2","self":"vessels.urn:mrn:signalk:uuid:4880f74c-9125-123g-8c6f-a4934d392c0e","roles":["master","main"],"timestamp":"2026-02-11T22:51:32.162Z"}ܦ2J O >
I assume the line above is just a pointer to the last payload that has not been overwritten yet.

and that continues............ every 1-2 seconds

I have tried both version 3.1.1 and 3.2.2, both with same result.
I am using the BUILDER_CLASS builder; sensesp_app = (&builder)

Not sure where to look, is there a log on the SignalK server I can look in to see if sk is sending an empty payload to the sensesp client?

[moj0002]

Here is what I have been able to find out, would be great if anyone can confirm.........

I flashed a new esp32 with a barebone sensesp app that does not do anything:
SensESPAppBuilder builder;
builder.set_hostname("barebone")
->set_sk_server("x.x.x.x", 3000)
->enable_system_info_sensors()
->get_app();
}
void loop() {
event_loop()->tick();
}

I installed a fresh copy of signalk on a windows machine (2.22.1)
Sensesp version 3.2.2

I still get (233365) signalk_ws_client.cpp: deserializeJson error: EmptyInput

All I can think of is that signalk sends a keep_alive/heartbeat every 10 seconds but the json empty.
The sensor information does show up in signalk data browser as expected.
The message is of ERROR so seems a bit dramatic if this can be ignored.

snippet of log
D (33753) signalk_delta_queue.cpp: delta: {"updates":[{"source":{"label":"barebone"},"values":[{"path":"sensorDevice.barebone.systemHz","value":56986},{"path":"sensorDevice.barebone.freeMemory","value":148564},{"path":"sensorDevice.barebone.uptime","value":32.61}]}]}

E (34592) signalk_ws_client.cpp: deserializeJson error: EmptyInput

D (34754) signalk_delta_queue.cpp: delta: {"updates":[{"source":{"label":"barebone"},"values":[{"path":"sensorDevice.barebone.systemHz","value":56602},{"path":"sensorDevice.barebone.freeMemory","value":148564},{"path":"sensorDevice.barebone.uptime","value":33.61},{"path":"sensorDevice.barebone.wifiSignalLevel","value":-45}]}]}
D (35739) signalk_delta_queue.cpp: delta: {"updates":[{"source":{"label":"barebone"},"values":[{"path":"sensorDevice.barebone.systemHz","value":56488},{"path":"sensorDevice.barebone.freeMemory","value":148564},{"path":"sensorDevice.barebone.uptime","value":34.61}]}]}

I tried to see if I could find the outgoing web socket json messages in signalk server logs but did not have much luck.

[moj0002]

I ended up adding this to the signalk_ws_client in my local code just to quiet the error down, not pretty but works for now

void SKWSClient::on_receive_delta(uint8_t* payload, size_t length) {
// Need to work on null-terminated strings

// 1. SILENCE THE ERROR:
if (length == 0 || payload == nullptr) {
return;
}

[mairas]

Sorry for not picking this up earlier! I'm not sure when the empty input errors were introduced, but like you mentioned, they're bogus. They're simply some keepalive messages that the server sends. I did some work on SensESP during the weekend and, among other things, fixed that issue. I didn't release a new version yet because I want to have Claude perform a thorough review on the whole codebase. Even when working on tangentially related stuff, it has already found and fixed a lot of problems!

[moj0002]

thank you, not a problem, looking forward to the patch release. Maybe Claude also found some SKMetadata areas to harden a bit, that one is very finicky at startup as there seem to be some race conditions with connecting to signalk and wifi and collecting medadata that has not been initialized yet. I ended up enabling mDNS in the UI which seems to slow down the process enough to give the local initialization enough breathing room. Of course could just be my code initially using the wrong "string" type, anyways all working now.