Module fluence_sdk_main::logger

This module enables log messages that could be printed from Wasm side.

This is a client for the Logger Wasm Module in Fluence WasmVm. Together they allow to write messages from Wasm code to log. The logging is basically a 'stdout' and depends on Vm implementation. By default this module is disabled in WasmVm.

Note that this module works only for the Wasm environment and Fluence WasmVm. Don't use it for other targets and Vms.

This module provides implementation for logging facade in crate log. See examples below:

Examples

This example initializes WasmLogger only for Wasm target, for another targets initializes simple_logger. Macroses from crate log used as logging facade.

    #[macro_use] extern crate log;
    extern crate fluence;
    extern crate simple_logger;

    fn main() {
        if cfg!(target_arch = "wasm32") {
            fluence::logger::WasmLogger::init_with_level(log::Level::Info).unwrap();
        } else {
            simple_logger::init_with_level(log::Level::Info).unwrap();
        }

        error!("This message will be logged.");
        trace!("This message will not be logged.");
    }

This example provides method for initialization WasmLogger only for Wasm target without specifying logger level. Macroses from crate log used as logging facade.

    #[macro_use] extern crate log;
    extern crate fluence;

    /// This method initialize WasmLogger and should be called at the start of application
    #[no_mangle]
    #[cfg(target_arch = "wasm32")]
    fn init_logger() {
        fluence::logger::WasmLogger::init().unwrap();
        info!("If you can see this message that logger was successfully initialized.");
    }

You can also use static_lazy for WasmLogger initialization but laziness has some caveats. You need to call lazy_static::initialize() for eager initialization before first logger macros usage.

    #[macro_use] extern crate log;
    #[macro_use] extern crate lazy_static;
    extern crate fluence;

    lazy_static! {
        static ref _LOGGER: () = {
            fluence::logger::WasmLogger::init_with_level(log::Level::Info);
        };
    }

    fn main() {
        if cfg!(target_arch = "wasm32") {
            // There is required to call init in a method or in another `lazy_static!` block
            fluence::logger::WasmLogger::init_with_level(log::Level::Info).unwrap();
        }

        // ...
    }

There is an other possibility to initialize logger from VM wrapper by exported function init_logger. To specify logging level please include sdk with one of these features: wasm_logger_info, wasm_logger_warn, wasm_logger_error. If you specified some of them the most common level will be used.

Structs

WasmLogger

The Wasm Logger.