xlog

xlog is a Go logging toolkit for context-aware structured logging. It stores loggers in context, falls back to a global logger, supports zap and slog adapters, and includes OpenTelemetry tracing helpers.

Features

• Context-aware logging - logger is extracted from context
• Global logger fallback support with thread-safe replacement
• Structured logging via field package - clear separation between logging and field constructors
• Backend-agnostic field types - works with Zap, slog, or custom loggers
• Printf-style formatting (Debugf, Infof, etc.)
• All logging levels: Debug, Info, Warn, Error, Fatal, Panic
• Zero allocation when logger is not in context (uses noop adapter)
• OpenTelemetry integration - span management with automatic logger enrichment
• Distributed tracing support with span creation, events, and attributes

Installation

go get github.com/ruko1202/xlog

Quick Start

For a complete working example, see example/app.

Basic Usage

package main

import (
	"context"
	"github.com/ruko1202/xlog"
	"github.com/ruko1202/xlog/xfield"
	"go.uber.org/zap"
)

const (
	appName = "xlogApp"
)

func main() {
	// Create logger and wrap it in adapter
	logger, _ := zap.NewProduction()
	defer logger.Sync()

	// Add logger to context
	ctx := context.Background()
	ctx = xlog.ContextWithLogger(ctx, xlog.NewZapAdapter(logger))

	// Use logging
	xlog.Infof(ctx, "application `%s` started", appName)
	xlog.Debug(ctx, "debug information", field.String("version", "1.0.0"))
}

Using Global Logger

It is convenient if you have background jobs that carry their own context.Context

package main

import (
    "context"
    "github.com/ruko1202/xlog"
    "go.uber.org/zap"
)

func main() {
    // Replace global logger using zap's native function
    logger, _ := zap.NewDevelopment()
    zap.ReplaceGlobals(logger)

    // Use without adding logger to context
    ctx := context.Background()
    xlog.Info(ctx, "using global logger")
}

API

Context Functions

ContextWithLogger(ctx context.Context, logger *zap.Logger) context.Context

Adds a logger to the context.

ctx := xlog.ContextWithLogger(context.Background(), logger)

LoggerFromContext(ctx context.Context) *zap.Logger

Extracts logger from context. If logger is not found, returns the global logger.

logger := xlog.LoggerFromContext(ctx)
logger.Info("direct zap usage")

Global Logger Management

Use zap's native ReplaceGlobals() function to replace the global logger. This is useful for testing or temporarily changing the logger.

logger, _ := zap.NewProduction()
undo := zap.ReplaceGlobals(logger)
defer undo() // Restore previous logger when done

WithOperation(ctx context.Context, operation string, fields ...zap.Field) context.Context

Creates a new context with a named logger for a specific operation.

ctx = xlog.WithOperation(ctx, "payment-processing",
    zap.String("user_id", "12345"),
    zap.String("payment_id", "pay_xyz"),
)
xlog.Info(ctx, "processing payment")

⚠️ Performance Warning: This function has performance overhead due to creating new logger instances (~4μs and allocations per call).

Recommended alternative - use WithFields instead:

// Instead of WithOperation - use WithFields for better performance
ctx = xlog.WithFields(ctx,
    zap.String("operation", "payment-processing"),
    zap.String("user_id", "12345"),
    zap.String("payment_id", "pay_xyz"),
)
xlog.Info(ctx, "processing payment")

Or use fields directly in log calls for single statements:

xlog.Info(ctx, "processing payment",
    zap.String("operation", "payment-processing"),
    zap.String("user_id", "12345"),
    zap.String("payment_id", "pay_xyz"),
)

Use WithOperation only when:

• You need the operation name in the logger namespace (affects log structure)
• Performance is not critical
• The operation context will be used for many log statements

WithFields(ctx context.Context, fields ...zap.Field) context.Context

Creates a new context with additional fields added to the logger. This is the recommended way to add persistent fields to a logger context.

// Add user context to logger
ctx = xlog.WithFields(ctx,
    zap.String("user_id", "12345"),
    zap.String("session_id", "sess_xyz"),
)

// All subsequent logs will include these fields
xlog.Info(ctx, "user action performed")
xlog.Debug(ctx, "processing request")

Performance: Better than WithOperation but still creates new logger instances. For single log statements, passing fields directly is most efficient.

Span Management Functions

xlog provides integration with OpenTelemetry for distributed tracing. These functions help manage spans alongside logging.

ReplaceTracerName(name string) func()

Sets the global tracer name for creating spans and returns a function to restore the previous name. Call this once during application initialization. This function is thread-safe.

restore := xlog.ReplaceTracerName("my-service")
defer restore() // Restore previous tracer name when done

ContextWithTracer(ctx context.Context, tracer trace.Tracer) context.Context

Adds a tracer to the context. If tracer is nil, the global tracer is used.

tracer := otel.GetTracerProvider().Tracer("my-service")
ctx = xlog.ContextWithTracer(ctx, tracer)

TracerFromContext(ctx context.Context) trace.Tracer

Extracts tracer from context. If no tracer is found, returns the global tracer.

tracer := xlog.TracerFromContext(ctx)
ctx, span := tracer.Start(ctx, "my-operation")
defer span.End()

SpanFromContext(ctx context.Context) trace.Span

Extracts the current span from context. If no span is found, returns a NoopSpan (safe to use).

span := xlog.SpanFromContext(ctx)
span.SetAttributes(attribute.String("key", "value"))

WithOperationSpan(ctx context.Context, operation string, fields ...zap.Field) (context.Context, trace.Span)

Creates a new span for an operation and adds it to the context along with an enriched logger. The logger automatically includes the operation name and any additional fields.

ctx, span := xlog.WithOperationSpan(ctx, "process-payment",
    zap.String("user_id", "12345"),
    zap.String("payment_id", "pay_xyz"),
)
defer span.End()

xlog.Info(ctx, "processing payment") // Includes operation and fields

Returns:

• New context with span and enriched logger
• Span instance that should be ended with defer span.End()

Usage pattern:

func handleRequest(ctx context.Context) error {
    ctx, span := xlog.WithOperationSpan(ctx, "handleRequest")
    defer span.End()

    // All logs in this context will include the operation name
    xlog.Info(ctx, "request started")

    // ...

    return nil
}

AddSpanEvent(ctx context.Context, message string)

Adds an event to the current span (if present in context). Useful for marking important moments in trace execution.

xlog.AddSpanEvent(ctx, "database query started")
// ... perform database query ...
xlog.AddSpanEvent(ctx, "database query completed")

SetSpanAttributes(ctx context.Context, attrs ...attribute.KeyValue)

Sets attributes on the current span (if present in context). Use OpenTelemetry attribute types.

import "go.opentelemetry.io/otel/attribute"

xlog.SetSpanAttributes(ctx,
    attribute.String("user.id", "12345"),
    attribute.Int("user.age", 25),
    attribute.Bool("user.premium", true),
)

RecordSpanError(ctx context.Context, err error, options ...trace.EventOption)

Records an error on the current span and sets its status to Error. Safe to call even when no span is present in context.

if err := doSomething(); err != nil {
    xlog.RecordSpanError(ctx, err, trace.WithStackTrace(true))
    return err
}

Note: All span functions work safely even when no span is present in context (no-op behavior).

Logging Functions

All logging functions require context.Context as the first argument.

Structured Logging

Functions with structured fields (zap.Field):

• Debug(ctx context.Context, msg string, fields ...zap.Field)
• Info(ctx context.Context, msg string, fields ...zap.Field)
• Warn(ctx context.Context, msg string, fields ...zap.Field)
• Error(ctx context.Context, msg string, fields ...zap.Field)
• Fatal(ctx context.Context, msg string, fields ...zap.Field)
• Panic(ctx context.Context, msg string, fields ...zap.Field)

xlog.Info(ctx, "user logged in",
    zap.String("user_id", "12345"),
    zap.String("ip", "192.168.1.1"),
    zap.Duration("login_time", time.Second*2),
)

Printf-style Logging

Functions with string formatting:

• Debugf(ctx context.Context, template string, args ...any)
• Infof(ctx context.Context, template string, args ...any)
• Warnf(ctx context.Context, template string, args ...any)
• Errorf(ctx context.Context, template string, args ...any)
• Fatalf(ctx context.Context, template string, args ...any)
• Panicf(ctx context.Context, template string, args ...any)

userID := "12345"
xlog.Infof(ctx, "user %s logged in", userID)
xlog.Errorf(ctx, "request processing error: code %d", 500)

Complete Example

The example/app directory contains a complete working application demonstrating xlog integration with OpenTelemetry, distributed tracing, and metrics:

Structure:

• main.go - Application setup, Echo server, OpenTelemetry initialization
• http_handler.go - HTTP handlers with span creation and logging
• otel.go - OpenTelemetry configuration (traces via gRPC, metrics via Prometheus)
• worker.go - Background worker simulating HTTP requests
• compose.yml - Docker Compose setup with Jaeger, Prometheus, and Grafana
• otel-collector-config.yaml - OpenTelemetry Collector configuration

Features demonstrated:

• Context-aware logging with automatic trace ID injection
• Integration with Echo web framework
• OpenTelemetry spans with xlog.WithOperationSpan()
• Distributed tracing with Jaeger
• Prometheus metrics collection
• Trace ID propagation in HTTP headers (X-Request-ID)
• Background workers with proper context handling

Running the example:

cd example

# Start infrastructure (Jaeger, Prometheus, Grafana, OTel Collector)
docker compose up -d

# Run the application
go run app/*.go

# Test the API
curl http://localhost:8080/api/work?user_id=123
curl http://localhost:8080/api/work?user_id=456&fail=true

# View traces: http://localhost:16686 (Jaeger UI)
# View metrics: http://localhost:9090 (Prometheus)
# View dashboards: http://localhost:3000 (Grafana, admin/admin)

Usage Examples

HTTP Handler

Recommended approach using WithFields:

func handleRequest(w http.ResponseWriter, r *http.Request) {
    ctx := r.Context()

    // Add request context using WithFields (performance-friendly)
    ctx = xlog.WithFields(ctx,
        zap.String("request_id", uuid.NewString()),
        zap.String("method", r.Method),
        zap.String("path", r.URL.Path),
        zap.String("query", r.URL.RawQuery),
    )

    xlog.Info(ctx, "request processing started")

    if err := processRequest(ctx, r); err != nil {
        xlog.Error(ctx, "request processing error", zap.Error(err))
        http.Error(w, "Internal Server Error", 500)
        return
    }

    xlog.Info(ctx, "request successfully processed")
}

func processRequest(ctx context.Context, r *http.Request) error {
    // For single log - pass fields directly (most efficient)
    userID := r.URL.Query().Get("userId")
    xlog.Debug(ctx, "processing user request",
        zap.String("operation", "process-request"),
        zap.String("user_id", userID),
    )

    // ... business logic ...

    return nil
}

Alternative (with operation namespace):

If you need the operation name in logger namespace (which affects log structure):

func handleRequest(w http.ResponseWriter, r *http.Request) {
    ctx := r.Context()
    ctx = xlog.WithOperation(ctx, "handleRequest",
        zap.String("request_id", uuid.NewString()),
        zap.String("method", r.Method),
        zap.String("path", r.URL.Path),
    )

    xlog.Info(ctx, "request processing started")
    // ...
}

With distributed tracing:

For complete observability with OpenTelemetry spans:

func handleRequest(w http.ResponseWriter, r *http.Request) {
    ctx := r.Context()
    ctx, span := xlog.WithOperationSpan(ctx, "handleRequest",
        zap.String("method", r.Method),
        zap.String("path", r.URL.Path),
    )
    defer span.End()

    xlog.Info(ctx, "request processing started")
    // Logs will include trace_id and span_id automatically
    // ...
}

See example/app for a complete working example with Echo framework and OpenTelemetry.

Database Operations

func getUserByID(ctx context.Context, userID string) (*User, error) {
    xlog.Debug(ctx, "fetching user from database", zap.String("user_id", userID))

    user, err := db.Query(ctx, "SELECT * FROM users WHERE id = ?", userID)
    if err != nil {
        xlog.Error(ctx, "database query error",
            zap.String("user_id", userID),
            zap.Error(err),
        )
        return nil, err
    }

    xlog.Info(ctx, "user found", zap.String("user_id", userID))
    return user, nil
}

Background Tasks

func backgroundWorker(ctx context.Context) {
    // Add worker context using WithFields
    ctx = xlog.WithFields(ctx,
        zap.String("worker", "background-processor"),
    )

    xlog.Info(ctx, "starting background processor")

    for {
        select {
        case <-ctx.Done():
            xlog.Info(ctx, "stopping processor")
            return
        case task := <-taskQueue:
            // Performance-friendly: pass fields directly for one-off logs
            xlog.Debug(ctx, "processing task",
                zap.String("task_id", task.ID),
            )
            if err := processTask(ctx, task); err != nil {
                xlog.Error(ctx, "task processing error",
                    zap.String("task_id", task.ID),
                    zap.Error(err),
                )
            }
        }
    }
}

Logging Levels

• Debug - Detailed debug information
• Info - Informational messages about normal operation
• Warn - Warnings about potential issues
• Error - Errors that need to be handled
• Fatal - Critical errors that terminate the application (calls os.Exit(1))
• Panic - Critical errors that cause panic

Development

Testing

The package includes a comprehensive test suite. To run tests:

# Run all tests
make tloc

# Run tests with coverage
make test-cov

Or using go commands directly:

# Run tests
go test -v ./...

# Run tests with coverage
go test -cover ./...

Code Quality

# Install linter
make bin-deps

# Run linter
make lint

# Format code
make fmt

CI/CD

The project uses GitHub Actions for continuous integration:

• CI Pipeline - Runs on every push and pull request:

  • Linting with golangci-lint v2.3.0
  • Tests on Go 1.23 and 1.24 with race detector
  • Coverage reporting in pull requests
  • Automatic coverage badge updates on main branch

• Release Pipeline - Triggered on version tags (v*):

  • Automated releases using GoReleaser
  • Changelog generation

See .github/workflows/ for workflow configurations.

Performance

xlog provides flexible logger abstraction through adapters (ZapAdapter, SlogAdapter), allowing you to switch between different logging backends while maintaining a consistent API.

📊 Benchmarking: See BENCHMARKING.md for detailed performance guidelines and baseline metrics.

Performance Characteristics

Adapter Overhead: The adapter layer introduces minimal overhead:

• Basic logging: ~2ns/op, 0 allocations
• Context reuse: ~2ns/op, 0 allocations (13% faster than baseline!)
• Context creation in loop: +2-3 allocations per call (avoid this pattern)

Key Performance Metrics:

• Logging with fields directly: ~2ns, 0 allocs
• WithFields (reused context): ~2ns, 0 allocs
• WithOperation (reused context): ~2ns, 0 allocs
• WithOperationSpan: ~670ns, 7 allocs

Performance Best Practices

Follow these patterns to achieve optimal performance with zero allocations in hot paths:

1. ✅ CRITICAL: Always Reuse Context

The most important performance rule. Creating context in a loop causes significant overhead:

// ❌ ANTI-PATTERN: Creates 4-7 allocations per iteration!
for i := 0; i < 1000; i++ {
    ctx := xlog.WithOperation(baseCtx, "process-item")  // 4 allocs, 64ns
    processItem(ctx, items[i])
}

// ✅ BEST PRACTICE: 0 allocations, 32x faster
ctx := xlog.WithOperation(baseCtx, "process-batch")  // One-time cost
for i := 0; i < 1000; i++ {
    processItem(ctx, items[i])  // 0 allocs, 2ns
}

Impact: Reusing context is 32x faster and produces zero allocations vs creating in loop.

2. ✅ Pass Fields Directly for Single Logs

For one-off log statements, pass fields directly (most efficient):

// ✅ BEST: 0 allocations
xlog.Info(ctx, "processing order",
    field.String("order_id", orderID),
    field.String("status", "pending"),
)

3. ✅ Use WithFields for Multiple Logs

When logging multiple times with the same fields, create enriched context once:

// ✅ GOOD: Create context once, reuse many times
ctx = xlog.WithFields(ctx,
    field.String("user_id", userID),
    field.String("session_id", sessionID),
)

// All subsequent logs include these fields with 0 allocations
xlog.Info(ctx, "user authenticated")  // 0 allocs
xlog.Debug(ctx, "loading preferences")  // 0 allocs
xlog.Info(ctx, "session started")  // 0 allocs

4. ⚠️ Use WithOperation Sparingly

WithOperation creates a named logger (affects log namespace). Use only when needed:

// ✅ WHEN TO USE: You need operation in logger namespace
ctx = xlog.WithOperation(ctx, "payment-processor",
    field.String("user_id", userID),
)

// ⚠️ ALTERNATIVE: Use WithFields + operation field (same performance)
ctx = xlog.WithFields(ctx,
    field.String("operation", "payment-processor"),
    field.String("user_id", userID),
)

5. ✅ Appropriate Span Granularity

Spans have moderate cost (~670ns, 7 allocs). Create them at appropriate granularity:

// ❌ BAD: Span per row (thousands of allocations)
for row := range rows {
    ctx, span := xlog.WithOperationSpan(ctx, "validate-row")
    validate(row)
    span.End()
}

// ✅ GOOD: One span for entire batch
ctx, span := xlog.WithOperationSpan(ctx, "validate-batch")
defer span.End()
for row := range rows {
    validate(row)  // 0 allocations
}

6. ✅ Prefer Structured Logging

Structured fields are more efficient and enable better log analysis:

// ⚠️ Less efficient and harder to query
xlog.Infof(ctx, "user %s logged in from IP %s", userID, ip)

// ✅ Efficient and queryable
xlog.Info(ctx, "user logged in",
    field.String("user_id", userID),
    field.String("ip", ip),
)

Performance Anti-Patterns to Avoid

Anti-Pattern	Impact	Fix
WithOperation/WithFields in loop	+4-7 allocs/iter, 32x slower	Create context once before loop
WithOperationSpan per item	+7 allocs/iter, 670ns	Create span for batch
Printf-style logging	String allocations	Use structured fields
Unused enriched context	Wasted allocations	Pass fields directly if logging once

Measured Performance (Apple M4 Pro)

Based on comprehensive benchmarking with statistical significance (n=10):

Operation	Time	Allocations	Use Case
Basic logging	~2ns	0	Hot path logging
Context reuse	~2ns	0	Multiple logs with same context
Context creation (WithOperation)	~61ns	4	Setup phase only
Context creation (WithFields)	~99ns	5	Setup phase only
WithOperationSpan	~670ns	7	Request/operation boundaries

Key Insight: The adapter overhead is negligible (~2ns) when using proper patterns (context reuse). Anti-patterns (create in loop) show 100% allocation increase.

License

MIT

Dependencies

• go.uber.org/zap - underlying logger
• go.opentelemetry.io/otel - OpenTelemetry tracing
• github.com/stretchr/testify - for testing