Package log is a high-performance and extensible logging library designed specifically for the Go programming language. It provides flexible and structured logging capabilities, including context field extraction, multi-level logging configuration, and multiple output options, making it ideal for server-side applications. ## Core Concepts: Tags: Tags are a core concept in the log package used to categorize logs. By registering a tag via the `RegisterTag` function, you can use regular expressions to match the user-defined tags. This approach allows for a unified API for logging without explicitly creating logger instances. Even third-party libraries can write logs without setting up a logger object. Loggers: A Logger is the object that actually handles the logging process. You can obtain a logger instance using the `GetLogger` function, which is mainly provided for compatibility with legacy projects. This allows you to directly retrieve a logger by its name and log pre-formatted messages using the `Write` function. Context Field Extraction: Contextual data can be extracted and included in log entries via configurable functions: - `log.StringFromContext`: Extracts a string value (e.g., a request ID) from the context. - `log.FieldsFromContext`: Returns a list of structured fields from the context, such as trace IDs or user IDs. Configuration from File: The `log.RefreshFile` function allows loading the logger's configuration from an external file (e.g., XML or JSON). Logger Initialization and Logging: - Using `GetLogger`, you can fetch a logger instance (often for compatibility with older systems). - You can also register custom tags using `RegisterTag` to classify logs according to your needs. Logging Messages: The package provides various logging functions, such as `Tracef`, `Debugf`, `Infof`, `Warnf`, etc., which log messages at different levels (e.g., Trace, Debug, Info, Warn). These functions can either accept structured fields or formatted messages. Structured Logging: The logger also supports structured logging, where fields are captured as key-value pairs and logged with the message. The fields can be provided directly in the log functions or through a map. ## Examples: Using a pre-registered tag: Using structured fields: