In-Memory Logger

Provides a thread-safe in-memory circular buffer logger with WebSocket-based real-time streaming for log data.

Overview

The memlogger package implements a thread-safe in-memory log buffer with WebSocket streaming capabilities. It stores log data in memory and pushes new entries to connected WebSocket clients and event subscribers.

Primary Consumers

• internal/api/v1/cert/renew - Provides WebSocket endpoint for certificate renewal logs
• Diagnostic and debugging interfaces

Non-goals

• Does not persist logs to disk
• Does not provide log rotation or retention policies
• Does not support structured/log levels
• Does not provide authentication for WebSocket connections

Stability

Internal package. Public interfaces are stable.

Public API

Exported Types

MemLogger Interface

type MemLogger io.Writer

The MemLogger is an io.Writer interface. Any data written to it is stored in the circular buffer and broadcast to subscribers.

Exported Functions

GetMemLogger

func GetMemLogger() MemLogger

Returns the global singleton MemLogger instance.

Example:

logger := memlogger.GetMemLogger()
logger.Write([]byte("log message"))

HandlerFunc

func HandlerFunc() gin.HandlerFunc

Returns a Gin middleware handler that upgrades HTTP connections to WebSocket and streams log data.

Example:

router.GET("/logs/ws", memlogger.HandlerFunc())

Events

func Events() (<-chan []byte, func())

Returns a channel for receiving log events and a cancel function to unsubscribe.

Returns:

• <-chan []byte - Channel receiving log entry slices
• func() - Cleanup function that unsubscribes and closes the channel

Example:

ch, cancel := memlogger.Events()
defer cancel()

for event := range ch {
    fmt.Println(string(event))
}

Architecture

Core Components

Component	Responsibility
memLogger	Main struct holding buffer and subscription maps
bytes.Buffer	Circular buffer for log storage (16KB max)
connChans	xsync.Map of WebSocket channels
listeners	xsync.Map of event channels

Write Flow

Buffer Behavior

The circular buffer has fixed maximum size:

Property	Value
Maximum Size	16 KB
Truncate Threshold	8 KB (50%)
Write Chunk Size	4 KB
Write Timeout	10 seconds

Truncation Logic: When the buffer exceeds the maximum size:

1. The buffer is truncated to 8 KB (half the maximum)
2. Oldest entries are removed first
3. Recent logs are always preserved

Thread Safety

Multiple synchronization mechanisms ensure thread safety:

Field	Mutex Type	Purpose
Buffer	sync.RWMutex	Protecting buffer operations
notifyLock	sync.RWMutex	Protecting notification maps
connChans	xsync.Map	Thread-safe WebSocket channel storage
listeners	xsync.Map	Thread-safe event listener storage

Configuration Surface

No explicit configuration. The singleton instance uses fixed constants:

const (
    maxMemLogSize         = 16 * 1024  // 16KB buffer
    truncateSize          = maxMemLogSize / 2  // 8KB
    initialWriteChunkSize = 4 * 1024
    writeTimeout          = 10 * time.Second
)

Dependency and Integration Map

Internal Dependencies

Dependency	Purpose
github.com/yusing/goutils/http/websocket	WebSocket management

External Dependencies

Dependency	Purpose
github.com/gin-gonic/gin	HTTP/WebSocket handling
github.com/puzpuzpuz/xsync/v4	Concurrent map operations

Observability

Logs

No logging in this package. Errors are returned via WebSocket write failures.

Metrics

None exposed.

Failure Modes and Recovery

Failure	Detection	Recovery
WebSocket write timeout	3-second timer	Skip subscriber, continue
Buffer write error	writeBuf returns error	Logged but not returned
Subscriber channel full	Channel send timeout	Skip subscriber, continue
Buffer exceeds max size	truncateIfNeeded	Truncate to 8KB

Concurrency Guarantees

• Multiple goroutines can write concurrently
• Multiple WebSocket connections supported
• Subscriptions can be added/removed during operation
• Buffer truncation is atomic

Usage Examples

Basic Log Writing

import "github.com/yusing/godoxy/internal/logging/memlogger"

logger := memlogger.GetMemLogger()

// Write a simple message
logger.Write([]byte("Application started\n"))

// Write formatted logs
logger.Write([]byte(fmt.Sprintf("[INFO] Request received: %s\n", path)))

WebSocket Endpoint

import (
    "github.com/gin-gonic/gin"
    "github.com/yusing/godoxy/internal/logging/memlogger"
)

func setupRouter(r *gin.Engine) {
    // Real-time log streaming via WebSocket
    r.GET("/api/logs/stream", memlogger.HandlerFunc())
}

Subscribing to Log Events

func monitorLogs(ctx context.Context) {
    ch, cancel := memlogger.Events()
    defer cancel()

    for {
        select {
        case <-ctx.Done():
            return
        case event := <-ch:
            processLogEvent(event)
        }
    }
}

func processLogEvent(event []byte) {
    // Handle the log event
    fmt.Printf("Log: %s", string(event))
}

WebSocket Client

// Client-side JavaScript
const ws = new WebSocket("ws://localhost:8080/api/logs/stream");

ws.onmessage = (event) => {
  console.log("New log entry:", event.data);
};

ws.onclose = () => {
  console.log("Log stream disconnected");
};

ws.onerror = (error) => {
  console.error("Log stream error:", error);
};

Complete Integration

func setupLogging(r *gin.Engine) *memlogger.MemLogger {
    logger := memlogger.GetMemLogger()

    // WebSocket endpoint for real-time logs
    r.GET("/ws/logs", memlogger.HandlerFunc())

    return logger
}

// Elsewhere in the application
func recordRequest(logger memlogger.MemLogger, path string, status int) {
    logger.Write([]byte(fmt.Sprintf("[%s] %s - %d\n",
        time.Now().Format(time.RFC3339), path, status)))
}

Performance Characteristics

• O(1) write operations (amortized)
• O(n) for truncation where n is buffer size
• WebSocket notifications are non-blocking (3-second timeout)
• Memory usage is bounded at 16KB

Testing Notes

• Mock by providing a custom io.Writer implementation
• Test concurrent writes with goroutines
• Verify truncation behavior
• Test WebSocket upgrade failures

Related Packages

• internal/api - HTTP API endpoints
• github.com/gin-gonic/gin - HTTP framework
• github.com/yusing/goutils/http/websocket - WebSocket utilities