MQTT client hard crash when configuring a last will message on esp32

[ApolloRoboto]

Bug description

MQTT client hard crash when configuring a last will message on esp32 when creating the client.

Full stack trace here:

Guru Meditation Error: Core  0 panic'ed (LoadProhibited). Exception was unhandled.

Core  0 register dump:
PC      : 0x400014dc  PS      : 0x00060830  A0      : 0x80001459  A1      : 0x3ffbba30
A2      : 0x00000001  A3      : 0xfffffffd  A4      : 0x000000ff  A5      : 0x0000ff00
A6      : 0x00ff0000  A7      : 0xff000000  A8      : 0x8008b6f2  A9      : 0x3ffbba00
A10     : 0x3ffafc50  A11     : 0x3ffc870c  A12     : 0x00000019  A13     : 0x3ffc89ac
A14     : 0x00000000  A15     : 0x656e696c  SAR     : 0x00000016  EXCCAUSE: 0x0000001c
EXCVADDR: 0x00000001  LBEG    : 0x4000c2e0  LEND    : 0x4000c2f6  LCOUNT  : 0x00000000


Backtrace: 0x400014d9:0x3ffbba30 0x40001456:0x3ffbba40 0x40001445:0x3ffbba60 0x40142882:0x3ffbba80 0x40142ebc:0x3ffbbac0 0x400db13c:0x3ffbbb10 0x400d5a68:0x3ffbbce0 0x400d6fdb:0x3ffbbd00 0x40199a93:0x3ffbbec0 0x400d6dec:0x3ffbbee0 0x400df894:0x3ffbbf00 0x400df837:0x3ffbbf30 0x400ea87b:0x3ffbbf70 0x400d6ddc:0x3ffbbfb0 0x400d713b:0x3ffbbfe0 0x400ded27:0x3ffbc000 0x401a0ef3:0x3ffbc020
0x40142882 - esp_mqtt_set_config
    at /mnt/c/Users/Apollo/Repositories/rust-esp32-led-panel/.embuild/espressif/esp-idf/v5.3.2/components/mqtt/esp-mqtt/mqtt_client.c:464
0x40142ebc - esp_mqtt_client_init
    at /mnt/c/Users/Apollo/Repositories/rust-esp32-led-panel/.embuild/espressif/esp-idf/v5.3.2/components/mqtt/esp-mqtt/mqtt_client.c:867
0x400db13c - esp_idf_svc::mqtt::client::EspMqttClient::new_raw
    at /home/apollo/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/esp-idf-svc-0.51.0/src/mqtt/client.rs:480
0x400d5a68 - esp_idf_svc::mqtt::client::EspMqttClient::new_nonstatic_cb
    at /home/apollo/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/esp-idf-svc-0.51.0/src/mqtt/client.rs:435
0x400d6fdb - rust_esp32_led_panel::main
    at /mnt/c/Users/Apollo/Repositories/rust-esp32-led-panel/src/main.rs:60
0x40199a93 - core::ops::function::FnOnce::call_once
    at /home/apollo/.rustup/toolchains/esp/lib/rustlib/src/rust/library/core/src/ops/function.rs:250
0x400d6dec - std::rt::lang_start::{{closure}}
    at /home/apollo/.rustup/toolchains/esp/lib/rustlib/src/rust/library/std/src/rt.rs:199
0x400df894 - core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &F>::call_once
    at /home/apollo/.rustup/toolchains/esp/lib/rustlib/src/rust/library/core/src/ops/function.rs:284
0x400df837 - std::panic::catch_unwind
    at /home/apollo/.rustup/toolchains/esp/lib/rustlib/src/rust/library/std/src/panic.rs:359
0x400ea87b - std::panic::catch_unwind
    at /home/apollo/.rustup/toolchains/esp/lib/rustlib/src/rust/library/std/src/panic.rs:359
0x400d6ddc - std::rt::lang_start
    at /home/apollo/.rustup/toolchains/esp/lib/rustlib/src/rust/library/std/src/rt.rs:198
0x400d713b - main
    at ??:??
0x400ded27 - app_main
    at /home/apollo/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/esp-idf-sys-0.36.1/src/start.rs:46
0x401a0ef3 - main_task
    at /mnt/c/Users/Apollo/Repositories/rust-esp32-led-panel/.embuild/espressif/esp-idf/v5.3.2/components/freertos/app_startup.c:208

Would you like to work on a fix?
no, I'm not familiar with the source enough

To Reproduce

Here's a minimal main.rs file.

Note that using MqttClientConfiguration::default(); doesn't crash.

use esp_idf_hal::peripherals::Peripherals;
use esp_idf_svc::eventloop::EspSystemEventLoop;
use esp_idf_svc::mqtt::client::{EspMqttClient, LwtConfiguration, MqttClientConfiguration, QoS};
use log::info;

// wifi example from https://github.com/esp-rs/std-training/blob/main/common/lib/wifi/src/lib.rs
mod wifi;

#[derive(Debug)]
#[toml_cfg::toml_config]
pub struct Config {
    #[default("localhost")]
    mqtt_host: &'static str,
    #[default("1883")]
    mqtt_user: &'static str,
    #[default("")]
    mqtt_pass: &'static str,
    #[default("")]
    wifi_ssid: &'static str,
    #[default("")]
    wifi_pass: &'static str,
}

fn main() -> ! {
    esp_idf_svc::sys::link_patches();
    esp_idf_svc::log::EspLogger::initialize_default();

    let sysloop = EspSystemEventLoop::take().unwrap();
    let peripherals = Peripherals::take().unwrap();

    let _wifi = wifi::wifi(
        CONFIG.wifi_ssid,
        CONFIG.wifi_pass,
        peripherals.modem,
        sysloop,
    )
    .unwrap();

    // let mqtt_config = MqttClientConfiguration::default();
    let mqtt_config = MqttClientConfiguration {
        lwt: Some(LwtConfiguration {
            topic: "dt/device/status/offline",
            qos: QoS::AtLeastOnce,
            retain: false,
            payload: &[],
        }),
        ..Default::default()
    };

    let mqtt_broker_url = match CONFIG.mqtt_user.is_empty() {
        false => format!("mqtt://@{}", CONFIG.mqtt_host),
        true => format!(
            "mqtt://{}:{}@{}",
            CONFIG.mqtt_user, CONFIG.mqtt_pass, CONFIG.mqtt_host
        ),
    };

    // crashes here
    let mut mqtt_client =
        EspMqttClient::new_cb(&mqtt_broker_url, &mqtt_config, move |_message_event| {
            info!("Recived a message event");
        })
        .expect("Couldn't create a new mqtt client");

    mqtt_client
        .publish("dt/device/status/online", QoS::AtLeastOnce, false, &[])
        .unwrap();

    loop {
        // do nothing
    }
}

cargo build
espflash flash --monitor .\target\xtensa-esp32-espidf\debug\rust-esp32-led-panel

Expected behavior

Not to crash and is connected to the MQTT broker with a last will.

Environment

• Crate (esp-idf-svc) version: 0.51.0
• ESP-IDF branch or tag: v5.3.2
• Target device (MCU): esp32
• OS: WSL2 Ubuntu (Windows 10)

[ivmarkov]

@Apollo-Roboto Sorry for the late reply here.

Can you replace the last will message payload from &[] to something with non-zero length? As in e.g. b"Last will" and see if it would still crash?

There is a very weird code in the MQTT client that seems to treat last will payload len = 0 as an indication that what we pass is a C string (which we obviously don't!).

Let me know if it works for you. If it does, the fix is a one liner where we should pass NULL as a last will payload if its Rust slice length is 0.

[ApolloRoboto]

I tried it with this non zero length payload and I can confirm that it doesn't crash anymore! I also receive the last will properly when I shutdown the micro controller.

LwtConfiguration {
    topic: "dt/device/status",
    qos: QoS::AtLeastOnce,
    retain: false,
    payload: b"offline", // also works with &[0]
}