kxio/examples/get.rs

/// This is an example to show fetching a file from a webiste and saving to a file
///
/// The example consts of:
///
/// - The main program, in `main()` - demonstrates how to setup `kxio` for use in prod
/// - A test module - demonstrates how to use `kxio` in tests
/// - sample functions - showing how to use `kxio` the body of your program, and be testable
///
/// NOTE: running this program with `cargo run --example get` will create and delete the file
/// `example-readme.md` in the current directory.
use std::path::Path;

#[tokio::main]
async fn main() -> kxio::Result<()> {
    // Create a `Net` object for making real network requests.
    let net: kxio::net::Net = kxio::net::new();

    // Create a `FileSystem` object for accessing files within the current directory.
    // The object created will return a `PathTraveral` error result if there is an attempt to\
    // access a file outside of this directory.
    let fs: kxio::fs::FileSystem = kxio::fs::new("./");

    // The URL we will fetch - the readme for this library.
    let url = "https://git.kemitix.net/kemitix/kxio/raw/branch/main/README.md";

    // Create a PathBuf to a file within the directory that the `fs` object has access to.
    let file_path = fs.base().join("example-readme.md");

    // Create a generic handle for the file. This doesn't open the file, and always succeeds.
    let path: kxio::fs::PathReal<kxio::fs::PathMarker> = fs.path(&file_path);

    // Other options are;
    // `fs.file(&file_path)` - for a file
    // `fs.dir(&dir_path)` - for a directory

    // Checks if the path exists (whether a file, directory, etc)
    if path.exists()? {
        // extracts the path from the handle
        let pathbuf = path.as_pathbuf();
        eprintln!("The file {} already exists. Aborting!", pathbuf.display());
        return Ok(());
    }

    // Passes a reference to the `fs` and `net` objects for use by your program.
    // Your programs should not know whether they are handling a mock or the real thing.
    // Any file or network access should be made using these handlers to be properly testable.
    download_and_save_to_file(url, &file_path, &fs, &net).await?;
    delete_file(&file_path, &fs)?;

    Ok(())
}

/// An function that uses a `FileSystem` and a `Net` object to interact with the outside world.
async fn download_and_save_to_file(
    url: &str,
    file_path: &Path,
    // The file system abstraction
    fs: &kxio::fs::FileSystem,
    // The network abstraction
    net: &kxio::net::Net,
) -> kxio::Result<()> {
    println!("fetching: {url}");

    // Uses the network abstraction to create a perfectly normal `reqwest::ResponseBuilder`.
    let request: reqwest::RequestBuilder = net.client().get(url);

    // Rather than calling `.build().send()?` on the request, pass it to the `net`
    // This allows the `net` to either make the network request as normal, or, if we are
    // under test, to handle the request as the test dictates.
    // NOTE: if the `.build().send()` is called on the `request` then that WILL result in
    // a real network request being made, even under test conditions. Only ever use the
    // `net.send(...)` function to keep your code testable.
    let response: reqwest::Response = net.send(request).await?;

    let body = response.text().await?;
    println!("fetched {} bytes", body.bytes().len());

    println!("writing file: {}", file_path.display());
    // Uses the file system abstraction to create a handle for a file.
    let file: kxio::fs::PathReal<kxio::fs::FileMarker> = fs.file(file_path);
    // Writes the body to the file.
    file.write(body)?;

    Ok(())
}

/// An function that uses a `FileSystem` object to interact with the outside world.
fn delete_file(file_path: &Path, fs: &kxio::fs::FileSystem) -> kxio::Result<()> {
    println!("reading file: {}", file_path.display());

    // Uses the file system abstraction to create a handle for a file.
    let file: kxio::fs::PathReal<kxio::fs::FileMarker> = fs.file(file_path);
    // Creates a `Reader` which loaded the file into memory.
    let reader: kxio::fs::Reader = file.reader()?;
    let contents: &str = reader.as_str();
    println!("{contents}");

    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    // This test demonstrates how to use the `kxio` to test your program.
    #[tokio::test]
    async fn should_save_remote_body() {
        //given
        // Create a fake/mock network abstraction
        // When `net` goes out of scope it will check that all the expected network requests (see
        // `net.on(...)` below) were all made. If there are any that were not made, the test will
        // be failed. If you want to avoid this, then call `net.reset()` before your test ends.
        let mock_net: kxio::net::MockNet = kxio::net::mock();
        let url = "http://localhost:8080";

        // declare what response should be made for a given request
        let response = mock_net.response().body("contents").expect("response body");
        mock_net
            .on(http::Method::GET)
            .url(url::Url::parse(url).expect("parse url"))
            .respond(response);

        // Create a temporary directory that will be deleted with `fs` goes out of scope
        let fs = kxio::fs::temp().expect("temp fs");
        let file_path = fs.base().join("foo");

        // Create a [Net] from the [MockNet] to pass to the system under tets
        let net = kxio::net::Net::from(mock_net);

        //when
        // Pass the file sytsem and network abstractions to the code to be tested
        download_and_save_to_file(url, &file_path, &fs, &net)
            .await
            .expect("system under test");

        //then
        // Read the file
        let file = fs.file(&file_path);
        let reader = file.reader().expect("reader");
        let contents = reader.as_str();

        assert_eq!(contents, "contents");

        // not needed for this test, but should it be needed, we can avoid checking for any
        // unconsumed request matches.
        // let mock_net = kxio::net::MockNet::try_from(net).expect("recover mock");
        // mock_net.reset();
    }
}