69. Logger Standardization and Logging Best Practices

Date: 2025-08-18

Status

Accepted

Context

The tmail-flutter application uses a custom app_logger abstraction to unify logging across platforms (Web and Mobile) and environments (debug vs production).

Over time, logging usage became inconsistent:

logError was used in non-critical or recoverable scenarios.
Error-level logs generated excessive noise in monitoring tools (e.g. Sentry).
There was no clear, documented guideline describing when to use each log level.
Reviewers requested a descriptive piece of developer documentation explaining good logging practices.

As part of PR #4205, the logging system was refactored to normalize log severity usage and prepare the codebase for reliable integration with Sentry and similar monitoring tools.

Decision

Defined log levels and intent

Level	Function	Intended usage
critical	logCritical	System-level, unrecoverable failures (extremely rare)
error	logError	Critical, actionable failures that must be monitored
warning	logWarning	Recoverable issues or degraded behavior
info	logInfo / log	Normal application lifecycle events
debug	logDebug	Developer debugging information
trace	logVerbose	High-volume diagnostic logs

Restriction of logError usage

logError is restricted to infrastructure-level classes where failures are non-recoverable and must be monitored.

Allowed classes:

AuthorizationInterceptors
CacheExceptionThrower
RemoteExceptionThrower

All other cases must use logWarning.

Logger behavior

Platform-aware formatting (Web vs Mobile)
Consistent message normalization
Debug-only printing unless explicitly enabled

Error boundary

Global error handling is implemented via initLogger, ensuring framework and async errors are logged as warnings rather than errors.

Consequences

Benefits

Reduced noise in error monitoring
Clear logging conventions
Improved reviewability
Better Sentry signal quality

Trade-offs

Stricter logging rules
Reduced visibility for non-critical failures

Developer Logging Guidelines

Use logError only for critical, non-recoverable issues
Use logWarning for handled or recoverable failures
Avoid logging sensitive data
Prefer descriptive messages with context

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