Log Forwarding

The Anvil SDK can forward your driver's log messages to Anvil in real time, so they appear on the Logs page alongside your events and errors. No changes to your existing logging code required.

Automatic Forwarding (Recommended)

Pass your logger to Anvil:Init() and all log calls are automatically intercepted and forwarded:

Anvil:Init("YOUR_API_KEY", C4:GetDriverFileName(), {
    logger = myLogger
})

That's it. Calls to myLogger:info(), myLogger:error(), etc. now appear in Anvil automatically. Your logger continues to work exactly as before — same methods, same output. Every call is forwarded regardless of the log level set in Composer, so the Logs page always has the full picture even when the controller's own output is filtered.

Custom Method Names

For each canonical level (fatal, error, warn, info, debug, trace), Anvil probes your logger for a method matching common case variants in this order: lowercase → PascalCase → UPPERCASE. The first match is wrapped automatically.

In practice this means most loggers work with no logMap at all:

• A Pino-style logger with info/error/etc. — picked by the lowercase variant
• Snap One's standard c4_log, with Info/Error/etc. — picked by the PascalCase variant
• A logger using INFO/ERROR — picked by the UPPERCASE variant

logMap is only needed when a method has a genuinely renamed counterpart — typically when the canonical level word doesn't appear in the method name at all. For example, a logger that uses Alert for the fatal level:

Anvil:Init("YOUR_API_KEY", C4:GetDriverFileName(), {
    logger = Log,
    logMap = {
        fatal = "Alert",   -- only the semantic mismatch needs an entry
    }
})

The keys are Anvil's canonical levels (always lowercase), the values are the method names on your logger. Only include levels where the method name doesn't match any case variant of the canonical word.

See the API Reference for full details.

Manual Forwarding

If you don't have a logging library, or prefer to control exactly which messages are forwarded, use Anvil:ForwardLog() directly:

Anvil:ForwardLog("INFO", "Device connected successfully")
Anvil:ForwardLog("DEBUG", "Received response: " .. response)
Anvil:ForwardLog("WARN", "Retrying connection...")

Anvil and the Composer Log Level

Every log line carries the level your code gave it; the level is an attribute of the line itself. What differs between the controller and Anvil is what gets filtered out, and when.

The log level you set in Composer controls local output: lines below it are never written to the controller's log files. That filter exists to protect the controller's limited storage from verbose output, which is also why drivers conventionally revert it to a quiet level on a timer. Anvil doesn't apply it. The SDK forwards every line your logger emits, whatever the Composer level happens to be, and you narrow things down afterwards with the level filters on the Logs page.

This is why Anvil can show DEBUG lines while Composer is set to INFO. The Composer level decides what lands in the controller's log files; it has no effect on what streams to Anvil. On controllers without the Anvil Agent, the SDK captures and retains no logs at all (see Agent Discovery).

Log Levels

Level	Purpose
FATAL	Critical failures
ERROR	Error conditions
WARN	Warning conditions
INFO	General informational messages
DEBUG	Debug messages for development
TRACE	Detailed diagnostic information