Telemetry utilities.

Calling init_telemetry registers a global slog logger using slog_scope::set_global_logger. After that, calling slog_scope::with_logger will return a logger that sends information to the telemetry endpoints. The telemetry! macro is a short-cut for calling slog_scope::with_logger followed with slog_log!.

Note that you are supposed to only ever use telemetry! and not slog_scope::with_logger at the moment. Substrate may eventually be reworked to get proper slog support, including sending information to the telemetry.

The [Telemetry] struct implements Stream and must be polled regularly (or sent to a background thread/task) in order for the telemetry to properly function. Dropping the object will also deregister the global logger and replace it with a logger that discards messages. The Stream generates [TelemetryEvent]s.

Note: Cloning the [Telemetry] and polling from multiple clones has an unspecified behaviour.

Example

use futures::prelude::*;

let telemetry = sc_telemetry::init_telemetry(sc_telemetry::TelemetryConfig {
endpoints: sc_telemetry::TelemetryEndpoints::new(vec![
// The `0` is the maximum verbosity level of messages to send to this endpoint.
("wss://example.com".into(), 0)
]).expect("Invalid URL or multiaddr provided"),
// Can be used to pass an external implementation of WebSockets.
wasm_external_transport: None,
});

// The `telemetry` object implements `Stream` and must be processed.
std::thread::spawn(move || {
futures::executor::block_on(telemetry.for_each(|_| future::ready(())));
});

// Sends a message on the telemetry.
sc_telemetry::telemetry!(sc_telemetry::SUBSTRATE_INFO; "test";
"foo" => "bar",
)