The log package initializes the default slog logger with tint for colorized, structured output and injects request-scoped values from context. Simply import this package to configure the global logger.
Functions
WithIdempotencyKey
func WithIdempotencyKey(ctx context.Context, key string) context.Context
The parent context to derive from.
The idempotency key to attach to the context. This will appear as idempotency_key in log output.
context.Context - A new context with the idempotency key attached.
Example:
package main
import (
"context"
"log/slog"
_ "github.com/aarock1234/go-template/pkg/log"
)
func handleRequest(ctx context.Context, requestID string) {
// Attach idempotency key to context
ctx = log.WithIdempotencyKey(ctx, requestID)
// All logs will now include the idempotency_key field
slog.InfoContext(ctx, "processing request")
// Output: INFO processing request idempotency_key=req-123
processOrder(ctx)
}
func processOrder(ctx context.Context) {
// The idempotency key propagates through the call chain
slog.InfoContext(ctx, "order processed successfully")
// Output: INFO order processed successfully idempotency_key=req-123
}
Types
ContextHandler
type ContextHandler struct {
slog.Handler
}
slog.Handler to inject request-scoped values from the context into every log record. This handler is automatically configured during package initialization.
Methods:
Handle
func (h *ContextHandler) Handle(ctx context.Context, r slog.Record) error
slog.Record with request-scoped values from the context. This method is called automatically by the slog package.
The context containing request-scoped values.
The log record to handle.
error - Any error from the underlying handler.
Configuration
Automatic Initialization
The package automatically configures the default logger during initialization. Simply import the package:
import _ "github.com/aarock1234/go-template/pkg/log"
LOG_LEVEL Environment Variable
Control the minimum log level with the LOG_LEVEL environment variable:
debug - Most verbose, includes all logsinfo - Standard informational messages (default)warn or warning - Warning messageserror - Error messages only
Example:
# In your .env file or shell
LOG_LEVEL=debug
package main
import (
"log/slog"
_ "github.com/aarock1234/go-template/pkg/log"
)
func main() {
slog.Debug("debug message") // Only shown if LOG_LEVEL=debug
slog.Info("info message") // Shown at info and above
slog.Warn("warning message") // Shown at warn and above
slog.Error("error message") // Always shown unless level is higher
}
Color Output
Colorized output is automatically enabled when:
- Writing to a terminal (TTY)
- Platform supports ANSI colors (handled by go-colorable)
Output is automatically non-colorized when:
- Redirecting to a file
- Running in environments without TTY support
- CI/CD pipelines
Log timestamps use a human-readable format:
Mon, Jan 2 2006, 3:04:05 pm MST
Tue, Mar 4 2026, 2:30:45 pm UTC INFO server started port=8080
Usage Patterns
Basic Logging
package main
import (
"log/slog"
_ "github.com/aarock1234/go-template/pkg/log"
)
func main() {
slog.Info("server starting", slog.Int("port", 8080))
slog.Error("database connection failed", slog.String("error", "timeout"))
}
HTTP Request Logging
package main
import (
"context"
"log/slog"
"net/http"
"github.com/aarock1234/go-template/pkg/log"
)
func requestLogger(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// Extract or generate request ID
requestID := r.Header.Get("X-Request-ID")
if requestID == "" {
requestID = generateID()
}
// Attach to context
ctx := log.WithIdempotencyKey(r.Context(), requestID)
r = r.WithContext(ctx)
slog.InfoContext(ctx, "request received",
slog.String("method", r.Method),
slog.String("path", r.URL.Path),
)
next.ServeHTTP(w, r)
})
}
Structured Error Logging
func processPayment(ctx context.Context, amount int) error {
if amount <= 0 {
slog.ErrorContext(ctx, "invalid payment amount",
slog.Int("amount", amount),
slog.String("error", "amount must be positive"),
)
return errors.New("invalid amount")
}
slog.InfoContext(ctx, "payment processed",
slog.Int("amount", amount),
)
return nil
}
Dependencies
The package uses:
