A Simple HTTP Server

We're now turning our board into a tiny web server that upon receiving a GET request serves data from the internal temperature sensor.

Setup

You can find a prepared project skeleton in intro/http-server/. It includes establishing a Wi-Fi connection, but you must configure it to use your network's credentials in cfg.toml.

intro/http-server/examples/https-server.rs contains a solution. You can run it with the following command:

cargo run --example http_server

Serving Requests

To connect to your board with your browser, you need to know the board's IP address.

✅ Run the skeleton code in intro/http-server. The output should yield the board's IP address like this:

I (3862) esp_netif_handlers: sta ip: 192.168.178.54, mask: ...
...
Server awaiting connection

The sta ip is the "station", the Wi-Fi term for an interface connected to an access point. This is the address you'll put in your browser (or other HTTP client like curl).

🔎 ESP-IDF tries to register the hostname espressif in your local network, so often http://espressif/ instead of http://<sta ip>/ will also work.

You can change the hostname by setting CONFIG_LWIP_LOCAL_HOSTNAME in sdkconfig.defaults, e.g.: CONFIG_LWIP_LOCAL_HOSTNAME="esp32c3"

Sending HTTP data to a client involves:

• Creating an instance of EspHttpServer
• Looping in the main function, so it doesn't terminate - termination would result in the server going out of scope and subsequently shutting down
• Setting a separate request handler function for each requested path you want to serve content. Any unconfigured path will result in a 404 error. These handler functions are realized inline as Rust closures via:

#![allow(unused)]
fn main() {
server.fn_handler(path, Method::Get, |request| {
    // ...
    // construct a response
    let mut response = request.into_ok_response()?;
    // now you can write your desired data
    response.write_all(&some_buf)?;
    // once you're done the handler expects a `Completion` as result,
    // this is achieved via:
    Ok(())
});

}

✅ Create a EspHttpServer instance using a default esp_idf_svc::http::server::Configuration. The default configuration will cause it to listen on port 80 automatically.

✅ Verify that a connection to http://<sta ip>/ yields a 404 (not found) error stating This URI does not exist.

✅ Write a request handler for requests to the root path ("/"). The request handler sends a greeting message at http://<sta ip>/, using the provided index_html() function to generate the HTML String.

Dynamic Data

We can also report dynamic information to a client. The skeleton includes a configured temp_sensor that measures the board's internal temperature.

✅ Write a second handler that reports the chip temperature at http://<sta ip>/temperature, using the provided temperature(val: f32) function to generate the HTML String. 💡 If you want to send a response string, it needs to be converted into a &[u8] slice via a_string.as_bytes() 💡 The temperature sensor needs exclusive (mutable) access. Passing it as owned value into the handler will not work (since it would get dropped after the first invocation) - you can fix this by making the handler a move || closure, wrapping the sensor in an Arc<Mutex<_>>, keeping one clone() of this Arc in your main function and moving the other into the closure.

Troubleshooting

• httpd_txrx: httpd_resp_send_err can be solved by restarting, or cargo clean if nothing happens.
• Make sure your computer and the Rust ESP Board are using the same Wi-Fi network.