golemcloud Logging from a MoonBit Agent
The MoonBit SDK provides a high-level @logging module (from golemcloud/golem_sdk/logging) built on top of wasi:logging/logging. It supports named loggers, log levels, and global level filtering.
Quick Start
The @logging package is already imported in the template moon.pkg. Use the module-level convenience functions:
@logging.info("order created: " + order_id)
@logging.debug("processing item: " + item_id)
@logging.warn("retry attempt " + attempt.to_string())
@logging.error("failed to connect: " + err)
Using a Named Logger
Create a logger with a context name for structured, scoped output. The context string is passed as the WASI context parameter:
let logger : @logging.Logger = @logging.with_name("order-service")
fn process_order(self : Self, order_id : String) -> Unit {
logger.info("processing order: " + order_id)
logger.debug("validating items")
}
Loggers are immutable values — with_name appends a /-separated segment to the context:
let db_logger = logger.with_name("database")
// context is "order-service/database"
db_logger.info("connected to database")
Log Levels
| Function | WASI Level | Use for |
|---|---|---|
@logging.trace(...) / logger.trace(...) |
trace | Fine-grained control flow |
@logging.debug(...) / logger.debug(...) |
debug | Debugging information |
@logging.info(...) / logger.info(...) |
info | Monitoring, normal operations |
@logging.warn(...) / logger.warn(...) |
warn | Hazardous situations |
@logging.error(...) / logger.error(...) |
error | Serious errors |
@logging.critical(...) / logger.critical(...) |
critical | Fatal errors |
Level Filtering
Set a global minimum log level to suppress noisy output:
@logging.set_min_level(INFO) // suppresses trace and debug globally
Per-logger overrides are also supported:
let verbose_logger = logger.with_min_level(TRACE)
If a logger has no per-instance level, it uses the global minimum (default: TRACE).
Setting a Global Context
Set a default context string for all module-level logging functions:
@logging.set_context("my-agent")
@logging.info("started") // context = "my-agent"
Using println
MoonBit's println also works and is captured as stdout:
println("stdout message")
This appears in golem agent stream output but lacks log levels and context. Prefer @logging for structured, filterable logging.
Viewing Logs
Stream live agent output:
golem agent stream '<agent-id>'
Or during an invocation:
golem agent invoke '<agent-id>' '<method>' [args]
Key Points
- No initialization needed — the
@loggingpackage is ready to use out of the box @loggingis pre-imported in the templatemoon.pkgas"golemcloud/golem_sdk/logging" @logging- Named loggers via
@logging.with_name(...)provide scoped context strings - Logs are recorded in the oplog and visible via
golem agent streamandgolem agent invoke - Logging is a side effect — during replay (crash recovery), log calls from replayed operations are skipped