Log Package

The log package provides structured logging capabilities for Moov applications.

Usage

Basic Logging

import "github.com/moov-io/base/log"

// Create a new logger
logger := log.NewDefaultLogger()

// Log a message with different levels
logger.Info().Log("Application started")
logger.Debug().Log("Debug information")
logger.Warn().Log("Warning message")
logger.Error().Log("Error occurred")

// Log with key-value pairs
logger.Info().Set("request_id", log.String("12345")).Log("Processing request")

// Log formatted messages
logger.Infof("Processing request %s", "12345")

// Log errors
err := someFunction()
if err != nil {
    logger.LogError(err)
}

Using Fields

import "github.com/moov-io/base/log"

// Create a map of fields
fields := log.Fields{
    "request_id": log.String("12345"),
    "user_id":    log.Int(42),
    "timestamp":  log.Time(time.Now()),
}

// Log with fields
logger.With(fields).Info().Log("Request processed")

Using StructContext

The StructContext function allows you to log struct fields automatically by using tags.

import "github.com/moov-io/base/log"

// Define a struct with log tags
type User struct {
    ID       int    `log:"id"`
    Username string `log:"username"`
    Email    string `log:"email,omitempty"` // won't be logged if empty
    Address  Address `log:"address"` // nested struct must have log tag
    Hidden   string // no log tag, won't be logged
}

type Address struct {
    Street  string `log:"street"`
    City    string `log:"city"`
    Country string `log:"country"`
}

// Create a user
user := User{
    ID:       1,
    Username: "johndoe",
    Email:    "[email protected]",
    Address: Address{
        Street:  "123 Main St",
        City:    "New York",
        Country: "USA",
    },
    Hidden: "secret",
}

// Log with struct context
logger.With(log.StructContext(user)).Info().Log("User logged in")

// Log with struct context and prefix
logger.With(log.StructContext(user, log.WithPrefix("user"))).Info().Log("User details")

// Using custom tag other than "log"
type Product struct {
    ID    int     `otel:"product_id"`
    Name  string  `otel:"product_name"`
    Price float64 `otel:"price,omitempty"`
}

product := Product{
    ID:    42,
    Name:  "Widget",
    Price: 19.99,
}

// Use otel tags instead of log tags
logger.With(log.StructContext(product, log.WithTag("otel"))).Info().Log("Product details")

The above will produce log entries with the following fields:

• id=1
• username=johndoe
• [email protected]
• address.street=123 Main St
• address.city=New York
• address.country=USA

With the prefix option, the fields will be:

• user.id=1
• user.username=johndoe
• [email protected]
• user.address.street=123 Main St
• user.address.city=New York
• user.address.country=USA

With the custom tag option, the fields will be extracted from the tag you specify (such as otel):

• product_id=42
• product_name=Widget
• price=19.99

Note that nested structs or pointers to structs must have the specified tag to be included in the context.

Features

• Structured logging with key-value pairs
• Multiple log levels (Debug, Info, Warn, Error, Fatal)
• JSON and LogFmt output formats
• Context-based logging
• Automatic struct field logging with StructContext
• Support for various value types (string, int, float, bool, time, etc.)

Configuration

The default logger format is determined by the MOOV_LOG_FORMAT environment variable:

• json: JSON format
• logfmt: LogFmt format (default)
• nop or noop: No-op logger that discards all logs