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Logger

In development, logs are a common debugging tool. This chapter introduces the logging functionality of CKB Script.

note

Even if the output is not captured, the logging still consumes cycles.

debug!​

Output a debug message.

This macro only compiled under debug build and does nothing in release build. To debug the release build, include -C debug-assertions in the environment variable RUSTFLAGS before calling cargo build.

note

In ckb-script-templates, debug-assertions is enabled by default. To disable it, comment out the line CUSTOM_RUSTFLAGS := -C debug-assertions in the contract's Makefile.

Syntax​

macro_rules! debug {
    ($fmt:literal) => { ... }
    ($fmt:literal, $($args:expr),+) => { ... }

Parameters​

  • fmt: Format control.
  • args: Optional arguments.

Return​

None

Remarks​

This macro uses alloc::format to format fmt and args into a string, then calls syscalls::debug to output the log message.
(Since it uses alloc, you need to add the default_alloc! macro and include extern crate alloc;. See Rust API Introduction for details.)

Logger​

Initializes script logging (log level set to LevelFilter::Trace).

Syntax​

pub fn init() -> Result<(), SetLoggerError>

rust-script-templates/log

Parameters​

None

Return​

If Failed: return SetLoggerError.

Example​

Code

ckb_std::logger::init().unwrap();

trace!("Trace Message");
debug!("debug Message");
info!("Info Message");
warn!("Warning Message");
error!("Error Message");
Script log: [TRACE contracts/log/src/main.rs:25] Trace Message
Script log: [DEBUG contracts/log/src/main.rs:26] debug Message
Script log: [INFO  contracts/log/src/main.rs:27] Info Message
Script log: [WARN  contracts/log/src/main.rs:28] Warning Message
Script log: [ERROR contracts/log/src/main.rs:29] Error Message

(Different types will have different colors)

Print​

By default, ckb-debugger prints logs, for example:

Script log: Hello World!

Here, Script log: is a prefix automatically added by ckb-debugger, and Hello World! is the content output by the contract.
Each call to debug! automatically adds a newline (similar to println!).

Logging is implemented internally by setting a callback function. See TransactionScriptsVerifier::set_debug_printer.

note

Developers can also customize or modify the callback function to handle log output in testcase.