HTTP Client

The goal of this exercise is to write a small HTTP client that connects to a website.

Setup

✅ Go to intro/http-client directory.

✅ Open the prepared project skeleton in intro/http-client.

✅ Add your network credentials to the cfg.toml as in the hardware test.

✅ Open the docs for this project with the following command:

cargo doc --open

intro/http-client/examples/http_client.rs contains the solution. You can run it with the following command:

cargo run --example http_client

Making a Connection

By default, only unencrypted HTTP is available, which rather limits our options of hosts to connect to. We're going to use http://neverssl.com/.

In ESP-IDF, HTTP client connections are managed by http::client::EspHttpClient in the esp-idf-svc crate. It implements the http::client::Client trait from embedded-svc, which defines functions for HTTP request methods like GET or POST. This is a good time to have a look at the documentation you opened with cargo doc --open for esp_idf_svc::http::client::EspHttpConnection and embedded_svc::http::client::Client. See instantiation methods at your disposal.

✅ Create a new EspHttpConnection with default configuration. Look for a suitable constructor in the documentation.

✅ Get a client from the connection you just made.

Calling HTTP functions (e.g. get(url)) on this client returns an embedded_svc::http::client::Request, which must be submitted to reflect the client's option to send some data alongside its request.

The get function uses as_ref(). This means that instead of being restricted to one specific type like just String or just &str, the function can accept anything that implements the AsRef<str> trait. That is any type where a call to .as_ref() will produce a &str. This works for String and &str, but also the Cow<str> enum type which contains either of the previous two.

#![allow(unused)]
fn main() {
    let request = client.request(Method::Get, url.as_ref(), &headers)?;
}

A successful response has a status code in the 2xx range. Followed by the raw html of the website.

✅ Verify the connection was successful.

✅ Return an Error if the status isn't in the 2xx range.

#![allow(unused)]
fn main() {
match status {
        200..=299 => {
        }
        _ => bail!("Unexpected response code: {}", status),
    }
}

The status error can be returned with the Anyhow, crate which contains various functionality to simplify application-level error handling. It supplies a universal anyhow::Result<T>, wrapping the success (Ok) case in T and removing the need to specify the Err type, as long as every error you return implements std::error::Error.

✅ Read the received data chunk by chunk into an u8 buffer using Read::read(&mut reader,&mut buf). Read::read returns the number of bytes read - you're done when this value is 0.

✅ Report the total number of bytes read.

✅ Log the received data to the console. 💡 The response in the buffer is in bytes, so you might need a method to convert from bytes to &str.

Extra Tasks

✅ Handle 3xx, 4xx and 5xx status codes each in a separate match arm

✅ Write a custom Error enum to represent these errors. Implement the std::error::Error trait for your error.

Simulation

This project is available for simulation through two methods:

• Wokwi projects:
  • Exercise
  • Solution
• Wokwi files are also present in the project folder to simulate it with Wokwi VS Code extension:
  1. Press F1, select Wokwi: Select Config File and choose intro/http-client/wokwi.toml
     • Edit the wokwi.toml file to select between exercise and solution simulation
  2. Build you project
  3. Press F1 again and select Wokwi: Start Simulator

Troubleshooting

• missing WiFi name/password: ensure that you've configured cfg.toml according to cfg.toml.example - a common problem is that the package name and config section name don't match.

# Cargo.toml
#...
[package]
name = "http-client"
#...

# cfg.toml
[http-client]
wifi_ssid = "..."
wifi_psk = "..."

• Guru Meditation Error: Core 0 panic'ed (Load access fault). Exception was unhandled. This may be caused by an .unwrap() in your code. Try replacing those with question marks.