Tracker Checker: Improve errors. More concrete errors

[josecelano]

Parent issue: https://github.com/torrust/torrust-tracker/issues/669 Relates to:

• https://github.com/torrust/torrust-tracker/issues/682
• https://github.com/torrust/torrust-tracker/issues/679
• https://github.com/torrust/torrust-tracker/issues/678
• https://github.com/torrust/torrust-tracker/issues/683

Currently, you can run the Tracker Checker with this input:

TORRUST_CHECKER_CONFIG='{
    "udp_trackers": ["144.126.245.19:6969"],
    "http_trackers": ["https://tracker.torrust-demo.com"],
    "health_checks": ["https://tracker.torrust-demo.com/health_check"]
}' cargo run --bin tracker_checker

When something is wrong you only get three types of errors or the application panics.

For example:

TORRUST_CHECKER_CONFIG='{
    "udp_trackers": [],
    "http_trackers": [],
    "health_checks": ["https://localhost:1515"]
}' cargo run --bin tracker_checker

Output:

Running checks for trackers ...
UDP trackers ...
HTTP trackers ...
Health checks ...
✗ - Health API at https://localhost:1515/ is failing: reqwest::Error { kind: Request, url: Url { scheme: "https", cannot_be_a_base: false, username: "", password: None, host: Some(Domain("localhost")), port: Some(1515), path: "/", query: None, fragment: None }, source: hyper::Error(Connect, ConnectError("tcp connect error", Os { code: 111, kind: ConnectionRefused, message: "Connection refused" })) }

Errors are defined with this enum:

#[derive(Debug)]
pub enum CheckError {
    UdpError { socket_addr: SocketAddr },
    HttpError { url: Url },
    HealthCheckError { url: Url },
}

But depending on the service there could be different reasons. For example:

For the Health Check:

• The connection can be refused.
• The response status code could not be 200.
• Etcetera.

For the UDP tracker:

• You could not bind the client to a local port.
• You could not send a packet to the remote server.
• Etcetera.

We should introduce a second level of types for errors. For example:

#[derive(Debug)]
pub enum CheckError {
    Udp { error: UdpError },
    Http { error: HttpError },
    HealthCheck { error: HealthCheckError },
}

#[derive(Debug)]
pub enum HealthCheckError {
    ConnectionRefused { url: Url },
    NotOkResponse { url: Url, status: StatusCode },
    HealthCheck { error: HealthCheckError },
}

// ...

This issue should be implemented after implementing other issues related to timeout errors. Because those issues might introduce new errors.