Go Log Utilities

A Go library providing advanced logging utilities focused on log sampling and dynamic log level management, designed to integrate seamlessly with Google's glog library.

Features

• Log Sampling: Reduce log volume with intelligent sampling mechanisms
• Dynamic Log Level Management: Change log levels at runtime via HTTP endpoints
• Multiple Sampler Types: Counter-based, time-based, glog-level-based, and custom samplers
• Thread-Safe: All components are designed for concurrent use
• Extensible: Factory pattern and interface-based design for easy customization

---

Installation

go get github.com/bborbe/log

Quick Start

Basic Log Sampling

package main

import (
    "time"
    "github.com/bborbe/log"
    "github.com/golang/glog"
)

func main() {
    // Sample every 10th log entry
    modSampler := log.NewSampleMod(10)
    
    // Sample once every 10 seconds
    timeSampler := log.NewSampleTime(10 * time.Second)
    
    // Use in your logging code
    if modSampler.IsSample() {
        glog.V(2).Infof("This will be logged every 10th time")
    }
    
    if timeSampler.IsSample() {
        glog.V(2).Infof("This will be logged at most once every 10 seconds")
    }
}

Dynamic Log Level Management

package main

import (
    "context"
    "net/http"
    "time"
    
    "github.com/bborbe/log"
    "github.com/golang/glog"
    "github.com/gorilla/mux"
)

func main() {
    ctx := context.Background()
    
    // Create log level setter that auto-resets after 5 minutes
    logLevelSetter := log.NewLogLevelSetter(
        glog.Level(1), // default level
        5*time.Minute, // auto-reset duration
    )
    
    // Set up HTTP handler for dynamic log level changes
    router := mux.NewRouter()
    router.Handle("/debug/loglevel/{level}", 
        log.NewSetLoglevelHandler(ctx, logLevelSetter))
    
    http.ListenAndServe(":8080", router)
}

Now you can change log levels at runtime:

curl http://localhost:8080/debug/loglevel/4

Sampler Types

ModSampler

Samples every Nth log entry based on a counter:

sampler := log.NewSampleMod(100) // Sample every 100th log

TimeSampler

Samples based on time intervals:

sampler := log.NewSampleTime(30 * time.Second) // Sample at most once per 30 seconds

GlogLevelSampler

Samples based on glog verbosity levels:

sampler := log.NewSamplerGlogLevel(3) // Sample when glog level >= 3

ListSampler

Combines multiple samplers with OR logic:

sampler := log.SamplerList{
    log.NewSampleTime(10 * time.Second),
    log.NewSamplerGlogLevel(4),
}

FuncSampler

Create custom sampling logic:

sampler := log.SamplerFunc(func() bool {
    // Your custom sampling logic
    return shouldSample()
})

TrueSampler

Always samples (useful for testing or special cases):

sampler := log.SamplerTrue{}

Factory Pattern

Use the factory pattern for dependency injection:

// Use the default factory
factory := log.DefaultSamplerFactory
sampler := factory.Sampler()

// Or create a custom factory
customFactory := log.SamplerFactoryFunc(func() log.Sampler {
    return log.NewSampleMod(50)
})

---

Full Example

Here's a complete, runnable example demonstrating multiple features working together in a production-like scenario:

package main

import (
    "context"
    "net/http"
    "time"

    "github.com/bborbe/log"
    "github.com/golang/glog"
    "github.com/gorilla/mux"
)

func main() {
    ctx := context.Background()

    // Combine time-based and level-based sampling
    // This will sample if EITHER condition is met (OR logic):
    // - At most once every 10 seconds, OR
    // - When glog verbosity is >= 4
    sampler := log.SamplerList{
        log.NewSampleTime(10 * time.Second),
        log.NewSamplerGlogLevel(4),
    }

    // Set up dynamic log level management
    // Default level: 1, auto-resets after 5 minutes
    logLevelSetter := log.NewLogLevelSetter(glog.Level(1), 5*time.Minute)

    // Create HTTP server with debug endpoint
    router := mux.NewRouter()
    router.Handle("/debug/loglevel/{level}",
        log.NewSetLoglevelHandler(ctx, logLevelSetter))

    // Start HTTP server in background
    go func() {
        if err := http.ListenAndServe(":8080", router); err != nil {
            glog.Fatalf("HTTP server failed: %v", err)
        }
    }()

    // Example application loop with sampled logging
    for i := 0; i < 1000; i++ {
        // High-frequency operation
        processItem(i)

        // Sampled logging to avoid log spam
        if sampler.IsSample() {
            glog.V(2).Infof("Processed item %d", i)
        }

        time.Sleep(100 * time.Millisecond)
    }
}

func processItem(i int) {
    // Your application logic here
    _ = i
}

You can change log levels at runtime:

# Increase verbosity to see more logs
curl http://localhost:8080/debug/loglevel/4

# Response: set loglevel to 4 completed
# Log level will auto-reset to 1 after 5 minutes

---

HTTP Log Level Management

The library provides built-in HTTP handlers for runtime log level changes:

• Endpoint: GET/POST /debug/loglevel/{level}
• Auto-reset: Automatically reverts to default level after specified duration
• Thread-safe: Safe for concurrent access

Example integration with gorilla/mux:

router := mux.NewRouter()
logLevelSetter := log.NewLogLevelSetter(glog.Level(1), 5*time.Minute)
router.Handle("/debug/loglevel/{level}",
    log.NewSetLoglevelHandler(context.Background(), logLevelSetter))

---

Development

Running Tests

make test

Code Generation (Mocks)

make generate

Full Development Workflow

make precommit  # Format, test, lint, and check

Testing Framework

The library uses:

• Ginkgo v2 for BDD-style testing
• Gomega for assertions
• Counterfeiter for mock generation

---

Testing

Testing Code That Uses Log Samplers

When testing code that uses this library, you have several options for controlling sampling behavior:

Option 1: Use TrueSampler for Always Sampling

import (
    "testing"
    "github.com/bborbe/log"
    "github.com/golang/glog"
)

func TestYourCode(t *testing.T) {
    // Use TrueSampler to ensure logs always sample during tests
    sampler := log.NewSamplerTrue()

    // Your test code here
    if sampler.IsSample() {
        glog.V(2).Infof("This will always log in tests")
    }
}

Option 2: Use SamplerFunc for Controlled Testing

func TestWithControlledSampling(t *testing.T) {
    shouldSample := true
    sampler := log.SamplerFunc(func() bool {
        return shouldSample
    })

    // Test when sampling is enabled
    if sampler.IsSample() {
        glog.V(2).Infof("Sampled log")
    }

    // Test when sampling is disabled
    shouldSample = false
    if sampler.IsSample() {
        t.Error("Should not sample")
    }
}

Option 3: Use Mock Samplers (Counterfeiter)

import (
    "testing"
    "github.com/bborbe/log/mocks"
)

func TestWithMockSampler(t *testing.T) {
    mockSampler := &mocks.LogSampler{}

    // Configure mock behavior
    mockSampler.IsSampleReturns(true)

    // Your test code using the mock
    result := mockSampler.IsSample()
    if !result {
        t.Error("Expected sampling to be enabled")
    }

    // Verify mock was called
    if mockSampler.IsSampleCallCount() != 1 {
        t.Error("Expected IsSample to be called once")
    }
}

Testing with Ginkgo/Gomega

import (
    . "github.com/onsi/ginkgo/v2"
    . "github.com/onsi/gomega"
    "github.com/bborbe/log"
)

var _ = Describe("YourComponent", func() {
    var sampler log.Sampler

    BeforeEach(func() {
        sampler = log.NewSamplerTrue()
    })

    It("should sample logs", func() {
        Expect(sampler.IsSample()).To(BeTrue())
    })
})

---

License

This project is licensed under the BSD 3-Clause License - see the LICENSE file for details.

Contributing

1. Fork the repository
2. Create your feature branch
3. Add tests for your changes
4. Run make precommit to ensure code quality
5. Submit a pull request

Dependencies

• glog - Core logging functionality
• gorilla/mux - HTTP routing for log level endpoints
• github.com/bborbe/time - Time utilities