KCP-Go

https://github.com/xtaci/kcp-go
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KCP-Go is a high-performance Reliable-UDP library for Go, providing smooth, resilient, ordered,...
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### Serve KCP over Existing UDP Connection (Go)

Source: https://context7.com/xtaci/kcp-go/llms.txt

This Go snippet demonstrates how to serve KCP connections over an existing UDP connection. It's particularly useful when fine-grained control over the underlying UDP socket is required. Dependencies include the 'net' and 'github.com/xtaci/kcp-go/v5' packages. It takes a UDP connection as input and returns a KCP listener.

```go
package main

import (
    "log"
    "net"
    "github.com/xtaci/kcp-go/v5"
)

func main() {
    // Example 1: Serve KCP over existing UDP connection
    // Useful when you need fine-grained control over the socket
    udpAddr, err := net.ResolveUDPAddr("udp", ":9999")
    if err != nil {
        log.Fatal(err)
    }

    udpConn, err := net.ListenUDP("udp", udpAddr)
    if err != nil {
        log.Fatal(err)
    }

    // Configure UDP socket before passing to KCP
    udpConn.SetReadBuffer(4194304)  // 4MB
    udpConn.SetWriteBuffer(4194304) // 4MB

    // ServeConn wraps existing connection (kcp-go will not close it)
    listener, err := kcp.ServeConn(nil, 10, 3, udpConn)
    if err != nil {
        log.Fatal(err)
    }
    defer listener.Close()

    log.Println("KCP serving on existing UDP connection")
}
```

--------------------------------

### Dial KCP Connection with Encryption and FEC (Go)

Source: https://context7.com/xtaci/kcp-go/llms.txt

This Go code snippet shows how a client can establish a KCP connection to a server. It uses the same key derivation and encryption method as the server and specifies matching FEC parameters. The client also configures low-latency KCP parameters, sets read/write deadlines, sends a message, receives a response, and prints connection statistics.

```Go
package main

import (
    "crypto/sha1"
    "fmt"
    "log"
    "time"
    "github.com/xtaci/kcp-go/v5"
    "golang.org/x/crypto/pbkdf2"
)

func main() {
    // Must use same key derivation as server
    key := pbkdf2.Key([]byte("my-secret-pass"), []byte("my-salt"), 4096, 32, sha1.New)
    block, err := kcp.NewAESBlockCrypt(key)
    if err != nil {
        log.Fatal(err)
    }

    // Connect with matching FEC parameters (10 data, 3 parity)
    conn, err := kcp.DialWithOptions("server.example.com:9999", block, 10, 3)
    if err != nil {
        log.Fatal(err)
    }
    defer conn.Close()

    // Configure for low latency (same as server)
    conn.SetNoDelay(1, 10, 2, 1)
    conn.SetStreamBuffer(4194304)
    conn.SetWindowSize(1024, 1024)

    // Set timeouts
    conn.SetReadDeadline(time.Now().Add(30 * time.Second))
    conn.SetWriteDeadline(time.Now().Add(30 * time.Second))

    // Send data
    message := []byte("Hello KCP!")
    if _, err := conn.Write(message); err != nil {
        log.Fatal(err)
    }

    // Receive response
    buf := make([]byte, 4096)
    n, err := conn.Read(buf)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Printf("Received: %s\n", buf[:n])

    // Get connection statistics
    fmt.Printf("Connection stats: %+v\n", conn.GetSnmp())
}

```

--------------------------------

### Configure Encryption Algorithms with KCP-Go

Source: https://context7.com/xtaci/kcp-go/llms.txt

This Go code snippet shows how to configure various encryption algorithms (AES, Salsa20, TEA, Triple DES, None) for KCP connections. It uses PBKDF2 for key derivation and demonstrates how to create block ciphers, which can then be used with KCP's listener creation functions.

```go
package main

import (
    "crypto/sha1"
    "log"
    "github.com/xtaci/kcp-go/v5"
    "golang.org/x/crypto/pbkdf2"
)

func main() {
    password := []byte("secure-password")
    salt := []byte("random-salt")

    // AES-128: Best choice with hardware acceleration (AES-NI)
    // Fastest on modern CPUs, ~913 MB/s
    aesKey := pbkdf2.Key(password, salt, 4096, 16, sha1.New)
    aesBlock, err := kcp.NewAESBlockCrypt(aesKey)
    if err != nil {
        log.Fatal(err)
    }

    // Salsa20: Fast software encryption, ~906 MB/s
    // Good alternative when AES-NI not available
    salsa20Key := pbkdf2.Key(password, salt, 4096, 32, sha1.New)
    salsa20Block, err := kcp.NewSalsa20BlockCrypt(salsa20Key)
    if err != nil {
        log.Fatal(err)
    }

    // TEA: Lightweight encryption, ~195 MB/s
    // Lower CPU usage, suitable for embedded devices
    teaKey := pbkdf2.Key(password, salt, 4096, 16, sha1.New)
    teaBlock, err := kcp.NewTEABlockCrypt(teaKey)
    if err != nil {
        log.Fatal(err)
    }

    // Triple DES: Strong but slow, ~25 MB/s
    // Use only for compatibility requirements
    tripleDesKey := pbkdf2.Key(password, salt, 4096, 24, sha1.New)
    tripleDesBlock, err := kcp.NewTripleDESBlockCrypt(tripleDesKey)
    if err != nil {
        log.Fatal(err)
    }

    // No encryption: Maximum throughput, ~65597 MB/s
    // Only use in trusted networks or when upper layer handles encryption
    noneBlock, err := kcp.NewNoneBlockCrypt(nil)
    if err != nil {
        log.Fatal(err)
    }

    // Use any block cipher with ListenWithOptions or DialWithOptions
    listener, err := kcp.ListenWithOptions(":8888", aesBlock, 10, 3)
    if err != nil {
        log.Fatal(err)
    }
    defer listener.Close()

    log.Printf("Server started with AES encryption")

    // Alternative ciphers can be passed to create different listeners
    _ = salsa20Block
    _ = teaBlock
    _ = tripleDesBlock
    _ = noneBlock
}

```

--------------------------------

### Configure KCP-Go Stream Mode and Buffers in Go

Source: https://context7.com/xtaci/kcp-go/llms.txt

Demonstrates setting KCP-Go connections to stream mode for efficient bulk data transfer and message mode for discrete packets. It covers `SetStreamBuffer`, `SetReadBuffer`, `SetWriteBuffer`, and showcases reading with `io.ReadFull` and `io.Copy`. Optimal for bulk data transfers and file operations.

```go
package main

import (
    "io"
    "log"
    "github.com/xtaci/kcp-go/v5"
)

func main() {
    conn, err := kcp.Dial("server.example.com:9999")
    if err != nil {
        log.Fatal(err)
    }
    defer conn.Close()

    // SetStreamBuffer enables stream mode with automatic buffering
    // Accumulates small writes into larger packets to improve efficiency
    // Essential for bulk data transfers and file operations
    //
    // size: Maximum bytes to buffer before flushing (default: 4MB)
    // Set to 0 to disable stream buffering (message mode)

    // Stream mode: Optimal for continuous data flow
    // Use case: File transfer, video streaming, database synchronization
    conn.SetStreamBuffer(4194304) // 4MB buffer

    // Example: Efficient file transfer with stream mode
    file := make([]byte, 100*1024*1024) // 100MB file

    // Writes are buffered and sent in optimal packet sizes
    for i := 0; i < len(file); i += 8192 {
        end := i + 8192
        if end > len(file) {
            end = len(file)
        }

        n, err := conn.Write(file[i:end])
        if err != nil {
            log.Fatal(err)
        }
        _ = n
    }

    // Message mode: Optimal for discrete messages
    // Use case: RPC, command-response protocols, gaming packets
    conn.SetStreamBuffer(0) // Disable buffering

    // Each write becomes a distinct message/packet
    messages := [][]byte{
        []byte("MESSAGE_1"),
        []byte("MESSAGE_2"),
        []byte("MESSAGE_3"),
    }

    for _, msg := range messages {
        // Each write is sent immediately as individual packet
        if _, err := conn.Write(msg); err != nil {
            log.Fatal(err)
        }
    }

    // Configure read buffer behavior
    conn.SetReadBuffer(4194304)   // OS-level socket buffer: 4MB
    conn.SetWriteBuffer(4194304)  // OS-level socket buffer: 4MB

    // Reading in stream mode: Read() may return partial data
    buf := make([]byte, 4096)
    n, err := conn.Read(buf)
    if err != nil && err != io.EOF {
        log.Fatal(err)
    }
    log.Printf("Read %d bytes (may be partial)", n)

    // Read exact amount using io.ReadFull
    exact := make([]byte, 1024)
    if _, err := io.ReadFull(conn, exact); err != nil {
        log.Fatal(err)
    }
    log.Printf("Read exactly %d bytes", len(exact))

    // Using io.Copy for bulk streaming
    // Automatically uses optimal buffer sizes
    writer := &dataWriter{}
    written, err := io.Copy(writer, conn)
    if err != nil {
        log.Fatal(err)
    }
    log.Printf("Streamed %d bytes", written)
}

type dataWriter struct {
    total int64
}

func (w *dataWriter) Write(p []byte) (n int, err error) {
    w.total += int64(len(p))
    return len(p), nil
}

```

--------------------------------

### Configure kcp-go Listeners with FEC Options

Source: https://context7.com/xtaci/kcp-go/llms.txt

Demonstrates how to create kcp-go listeners with different Forward Error Correction (FEC) configurations. Each configuration specifies the number of data shards and parity shards, influencing recovery capability and bandwidth overhead. It covers settings from no FEC to maximum FEC, and efficient FEC with larger shard groups.

```go
package main

import (
    "log"
    "github.com/xtaci/kcp-go/v5"
)

func main() {
    // FEC parameters: (dataShards, parityShards)
    //
    // dataShards: Number of original data packets in a group
    // parityShards: Number of redundant parity packets generated
    //
    // Recovery capability: Can recover from up to 'parityShards' packet losses
    // Bandwidth overhead: parityShards / dataShards * 100%
    //
    // Example: (10, 3) = 30% overhead, recovers from 3 packet losses per 10 packets

    // Conservative FEC: 20% overhead, handles up to 2 lost packets per 10
    // Good for: Domestic connections, stable networks
    listener1, err := kcp.ListenWithOptions(":8001", nil, 10, 2)
    if err != nil {
        log.Fatal(err)
    }
    defer listener1.Close()

    // Moderate FEC: 30% overhead, handles up to 3 lost packets per 10
    // Good for: International connections, moderate packet loss (1-3%)
    listener2, err := kcp.ListenWithOptions(":8002", nil, 10, 3) {
    if err != nil {
        log.Fatal(err)
    }
    defer listener2.Close()

    // Aggressive FEC: 50% overhead, handles up to 5 lost packets per 10
    // Good for: Intercontinental, high-loss networks (3-10% loss)
    listener3, err := kcp.ListenWithOptions(":8003", nil, 10, 5) {
    if err != nil {
        log.Fatal(err)
    }
    defer listener3.Close()

    // Maximum FEC: 100% overhead, handles up to 10 lost packets per 10
    // Good for: Extreme conditions, satellite, very unstable links
    listener4, err := kcp.ListenWithOptions(":8004", nil, 10, 10) {
    if err != nil {
        log.Fatal(err)
    }
    defer listener4.Close()

    // No FEC: No overhead, relies on KCP retransmission only
    // Good for: Local network, low latency requirements, stable connections
    listener5, err := kcp.ListenWithOptions(":8005", nil, 0, 0) {
    if err != nil {
        log.Fatal(err)
    }
    defer listener5.Close()

    // Efficient FEC: Larger shard groups reduce overhead
    // (20, 3) = 15% overhead instead of 30% with (10, 3)
    // Trade-off: Increased latency due to larger batching window
    listener6, err := kcp.ListenWithOptions(":8006", nil, 20, 3) {
    if err != nil {
        log.Fatal(err)
    }
    defer listener6.Close()

    log.Println("FEC-enabled listeners started on ports 8001-8006")

    // Client must use matching FEC parameters
    conn, err := kcp.DialWithOptions("server:8002", nil, 10, 3)
    if err != nil {
        log.Fatal(err)
    }
    defer conn.Close()

    // Monitor FEC effectiveness
    stats := conn.GetSnmp()
    log.Printf("FEC recovered %d packets out of %d parity shards",
        stats.FECRecovered, stats.FECParityShards)

    if stats.FECErrs > 0 {
        log.Printf("Warning: FEC failed to recover %d packets (increase parity shards)",
            stats.FECErrs)
    }
}

```

--------------------------------

### Control KCP Buffer Sizes and QoS Settings (Go)

Source: https://context7.com/xtaci/kcp-go/llms.txt

This Go snippet illustrates how to control the read and write buffer sizes, as well as set the Differentiated Services Code Point (DSCP) for Quality of Service (QoS) on a KCP listener. It utilizes the 'log' and 'github.com/xtaci/kcp-go/v5' packages. Input is a KCP listener, and it configures its network parameters.

```go
package main

import (
    "log"
    "github.com/xtaci/kcp-go/v5"
)

func main() {
    // Assume 'listener' is an existing kcp.Listener
    // Example 3: Control buffer sizes and QoS settings
    listener, _ := kcp.ServeConn(nil, 10, 3, nil) // Placeholder for illustration

    listener.SetReadBuffer(8388608)   // 8MB read buffer
    listener.SetWriteBuffer(8388608)  // 8MB write buffer
    listener.SetDSCP(46)              // Set DSCP for QoS (EF - Expedited Forwarding)

    log.Println("KCP listener buffer sizes and DSCP configured.")
    listener.Close()
}
```

--------------------------------

### Accept KCP Connections with Timeout (Go)

Source: https://context7.com/xtaci/kcp-go/llms.txt

This Go snippet demonstrates how to accept KCP connections with a specified timeout. It handles potential timeout errors gracefully and logs the remote address of accepted connections. Dependencies include 'log', 'net', and 'github.com/xtaci/kcp-go/v5'. It takes a KCP listener and returns an accepted KCP connection or an error.

```go
package main

import (
    "log"
    "net"
    "time"
    "github.com/xtaci/kcp-go/v5"
)

func main() {
    // Assume 'listener' is an existing kcp.Listener
    // Example 4: Accept connections with timeout
    listener, _ := kcp.ServeConn(nil, 10, 3, nil) // Placeholder for illustration

    listener.SetDeadline(time.Now().Add(30 * time.Second))
    conn, err := listener.AcceptKCP()
    if err != nil {
        if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
            log.Println("Accept timeout")
        } else {
            log.Fatal(err)
        }
    } else {
        defer conn.Close()

        // Get remote address
        log.Printf("Accepted connection from: %s", conn.RemoteAddr())

        // Check if connection owns its underlying socket
        log.Printf("Connection owns socket: %v", conn.GetConv() != 0)
    }
    listener.Close()
}
```

--------------------------------

### Monitor KCP Connection Statistics in Go

Source: https://context7.com/xtaci/kcp-go/llms.txt

This Go code snippet demonstrates how to establish a KCP connection, send data, and then retrieve detailed per-connection SNMP statistics. It covers metrics for data transfer, reliability, Forward Error Correction (FEC), and errors, as well as system-wide statistics. It also includes a goroutine to periodically print updated connection statistics.

```go
package main

import (
    "fmt"
    "log"
    "time"
    "github.com/xtaci/kcp-go/v5"
)

func main() {
    conn, err := kcp.Dial("server.example.com:9999")
    if err != nil {
        log.Fatal(err)
    }
    defer conn.Close()

    // Perform some data transfer
    data := make([]byte, 1024*1024) // 1MB
    conn.Write(data)

    // Get per-connection statistics
    stats := conn.GetSnmp()

    fmt.Println("=== Connection Statistics ===")
    fmt.Printf("Bytes Sent: %d\n", stats.BytesSent)
    fmt.Printf("Bytes Received: %d\n", stats.BytesReceived)
    fmt.Printf("Packets In: %d\n", stats.InPkts)
    fmt.Printf("Packets Out: %d\n", stats.OutPkts)
    fmt.Printf("UDP Bytes In: %d\n", stats.InBytes)
    fmt.Printf("UDP Bytes Out: %d\n", stats.OutBytes)

    fmt.Println("\n=== Reliability Metrics ===")
    fmt.Printf("Retransmitted Segments: %d\n", stats.RetransSegs)
    fmt.Printf("Fast Retransmissions: %d\n", stats.FastRetransSegs)
    fmt.Printf("Early Retransmissions: %d\n", stats.EarlyRetransSegs)
    fmt.Printf("Lost Segments (inferred): %d\n", stats.LostSegs)
    fmt.Printf("Duplicate Segments: %d\n", stats.RepeatSegs)

    fmt.Println("\n=== FEC Statistics ===")
    fmt.Printf("FEC Packets Recovered: %d\n", stats.FECRecovered)
    fmt.Printf("FEC Recovery Errors: %d\n", stats.FECErrs)
    fmt.Printf("FEC Parity Shards Sent: %d\n", stats.FECParityShards)
    fmt.Printf("Complete Shard Sets: %d\n", stats.FECFullShardSet)

    fmt.Println("\n=== Error Statistics ===")
    fmt.Printf("Input Errors: %d\n", stats.InErrs)
    fmt.Printf("Checksum Errors: %d\n", stats.InCsumErrors)
    fmt.Printf("KCP Protocol Errors: %d\n", stats.KCPInErrors)

    // Calculate derived metrics
    if stats.OutPkts > 0 {
        retransRate := float64(stats.RetransSegs) / float64(stats.OutSegs) * 100
        fmt.Printf("\nRetransmission Rate: %.2f%%\n", retransRate)
    }

    if stats.FECParityShards > 0 {
        fecRecoveryRate := float64(stats.FECRecovered) / float64(stats.FECParityShards) * 100
        fmt.Printf("FEC Recovery Rate: %.2f%%\n", fecRecoveryRate)
    }

    // Get default system-wide statistics
    defaultSnmp := kcp.DefaultSnmp.Copy()
    fmt.Printf("\n=== System-Wide Statistics ===\n")
    fmt.Printf("Current Connections: %d\n", defaultSnmp.CurrEstab)
    fmt.Printf("Max Connections: %d\n", defaultSnmp.MaxConn)
    fmt.Printf("Active Opens: %d\n", defaultSnmp.ActiveOpens)
    fmt.Printf("Passive Opens: %d\n", defaultSnmp.PassiveOpens)

    // Monitor statistics over time
    go func() {
        ticker := time.NewTicker(5 * time.Second)
        defer ticker.Stop()

        for range ticker.C {
            s := conn.GetSnmp()
            fmt.Printf("[%s] TX: %d bytes, RX: %d bytes, Retrans: %d\n",
                time.Now().Format("15:04:05"),
                s.BytesSent,
                s.BytesReceived,
                s.RetransSegs,
            )
        }
    }()

    time.Sleep(30 * time.Second)
}

```

--------------------------------

### Tune KCP Performance Parameters with KCP-Go

Source: https://context7.com/xtaci/kcp-go/llms.txt

This Go code snippet illustrates how to tune KCP's performance parameters using the SetNoDelay function and other methods like SetWindowSize, SetStreamBuffer, SetMtu, and SetACKNoDelay. These settings allow for balancing latency, throughput, and reliability based on application needs.

```go
package main

import (
    "log"
    "github.com/xtaci/kcp-go/v5"
)

func main() {
    conn, err := kcp.Dial("server.example.com:9999")
    if err != nil {
        log.Fatal(err)
    }
    defer conn.Close()

    // SetNoDelay(nodelay, interval, resend, nc)
    //
    // nodelay: 0=disable, 1=enable no-delay mode
    //   Affects RTO calculation: disabled uses normal min RTO (100ms),
    //   enabled uses no-delay min RTO (30ms)
    //
    // interval: Internal update interval in milliseconds (10-100)
    //   Lower = more CPU, lower latency; Higher = less CPU, higher latency
    //
    // resend: Fast resend mode
    //   0=disabled, 1=enabled (resend after 1 dup ACK), 2=enabled (resend after 2 dup ACKs)
    //
    // nc: Congestion control
    //   0=enabled (normal mode), 1=disabled (ignore slow start/congestion window)

    // Preset 1: Normal mode - balanced latency and bandwidth
    // Good for general purpose applications
    conn.SetNoDelay(0, 40, 0, 1)

    // Preset 2: Fast mode - optimized for low latency
    // Recommended for gaming, VoIP, real-time applications
    // Increases bandwidth usage by ~20-40%
    conn.SetNoDelay(1, 10, 2, 1)

    // Preset 3: Ultra-fast mode - minimal latency at any cost
    // For extremely latency-sensitive applications
    // Can increase bandwidth usage by 50-100%
    conn.SetNoDelay(1, 5, 2, 1)

    // Preset 4: Slow mode - minimize CPU/bandwidth usage
    // For high connection counts (>5000) or low-power devices
    // Trades latency for system resources
    conn.SetNoDelay(0, 100, 0, 1)

    // Set send/receive window sizes (packets)
    // Larger windows = higher throughput but more memory
    // Default: 32 packets each
    conn.SetWindowSize(128, 128)      // Normal
    conn.SetWindowSize(512, 512)      // High throughput
    conn.SetWindowSize(1024, 1024)    // Maximum throughput

    // Set stream mode buffer size (bytes)
    // Accumulates small writes into larger packets
    // Default: 4MB recommended for bulk transfers
    conn.SetStreamBuffer(4194304)

    // Set MTU and maximum segment size
    // Smaller MTU = less packet loss impact, more overhead
    // Larger MTU = better throughput, worse loss impact
    // Default: 1400 bytes (safe for most networks)
    conn.SetMtu(1400)           // Default, works everywhere
    conn.SetMtu(1200)           // Conservative, for poor networks
    conn.SetMtu(9000)           // Jumbo frames, LAN only

    // Enable ACK acknowledgment without delay (testing/debugging)
    conn.SetACKNoDelay(false)   // Normal: batch ACKs
    conn.SetACKNoDelay(true)    // Immediate: send ACK per packet

    log.Println("KCP parameters configured")
}

```

--------------------------------

### Set Connection Timeouts and Deadlines in Go

Source: https://context7.com/xtaci/kcp-go/llms.txt

This Go code snippet demonstrates setting overall, read, and write deadlines for a kcp connection. It shows how to handle timeout errors for both read and write operations, and how to clear deadlines. Useful for managing connection health and preventing indefinite blocking.

```go
package main

import (
    "io"
    "log"
    "net"
    "time"
    "github.com/xtaci/kcp-go/v5"
)

func main() {
    conn, err := kcp.Dial("server.example.com:9999")
    if err != nil {
        log.Fatal(err)
    }
    defer conn.Close()

    // Set overall deadline for both read and write operations
    // Deadline is an absolute time point
    conn.SetDeadline(time.Now().Add(30 * time.Second))

    // Set separate read deadline
    // Useful for implementing read timeouts in servers
    conn.SetReadDeadline(time.Now().Add(10 * time.Second))

    buf := make([]byte, 1024)
    n, err := conn.Read(buf)
    if err != nil {
        if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
            log.Println("Read timeout - no data received within 10 seconds")
        } else if err == io.EOF {
            log.Println("Connection closed by peer")
        } else {
            log.Fatal(err)
        }
    } else {
        log.Printf("Read %d bytes: %s", n, buf[:n])
    }

    // Set write deadline
    // Prevents blocking indefinitely if peer's receive window is full
    conn.SetWriteDeadline(time.Now().Add(5 * time.Second))

    data := make([]byte, 1024*1024) // 1MB
    _, err = conn.Write(data)
    if err != nil {
        if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
            log.Println("Write timeout - peer not consuming data fast enough")
        } else {
            log.Fatal(err)
        }
    }

    // Clear deadline by setting to zero value
    // Future operations will not timeout
    conn.SetDeadline(time.Time{})

    // Pattern 1: Heartbeat with timeout
    go func() {
        ticker := time.NewTicker(10 * time.Second)
        defer ticker.Stop()

        for range ticker.C {
            conn.SetWriteDeadline(time.Now().Add(5 * time.Second))
            if _, err := conn.Write([]byte("PING")); err != nil {
                log.Println("Heartbeat failed, closing connection")
                conn.Close()
                return
            }
        }
    }()

    // Pattern 2: Request-response with timeout
    request := []byte("GET /data")
    conn.SetWriteDeadline(time.Now().Add(3 * time.Second))
    if _, err := conn.Write(request); err != nil {
        log.Fatal("Request failed:", err)
    }

    response := make([]byte, 4096)
    conn.SetReadDeadline(time.Now().Add(10 * time.Second))
    n, err = conn.Read(response)
    if err != nil {
        log.Fatal("Response timeout:", err)
    }
    log.Printf("Response: %s", response[:n])

    // Pattern 3: Server accept with timeout
    listener, err := kcp.Listen(":9999")
    if err != nil {
        log.Fatal(err)
    }
    defer listener.Close()

    // Accept will timeout after 30 seconds
    listener.SetDeadline(time.Now().Add(30 * time.Second))
    acceptedConn, err := listener.Accept()
    if err != nil {
        if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
            log.Println("No connections within 30 seconds")
        } else {
            log.Fatal(err)
        }
    } else {
        acceptedConn.Close()
    }
}
```

--------------------------------

### Slice vs. List Performance Benchmark (Go)

Source: https://github.com/xtaci/kcp-go/blob/master/README.md

Compares the performance of iterating over a Go slice versus a container/list data structure. The benchmark highlights the significant performance difference due to cache misses associated with list structures compared to the better locality of slices.

```Go
package benchmark2

import "testing"

var data = make([]int, 1000)

// Placeholder for a list-like structure
type Node struct { next *Node; val int }
var listHead *Node

func BenchmarkLoopSlice(b *testing.B) {
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		for _, v := range data {
			_ = v
		}
	}
}

func BenchmarkLoopList(b *testing.B) {
	// Initialize list for benchmark
	listHead = &Node{}
	curr := listHead
	for i := 0; i < 1000; i++ {
		curr.next = &Node{val: i}
		curr = curr.next
	}

	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		curr := listHead.next
		for curr != nil {
			_ = curr.val
			curr = curr.next
		}
	}
}
```

--------------------------------

### Create KCP Listener with Encryption and FEC (Go)

Source: https://context7.com/xtaci/kcp-go/llms.txt

This Go code snippet demonstrates how to create a KCP listener that accepts incoming UDP connections. It configures AES encryption using a derived key and enables Forward Error Correction (FEC) with specified data and parity shards. The listener is set up to handle connections in separate goroutines and configures KCP parameters for low latency.

```Go
package main

import (
    "crypto/sha1"
    "io"
    "log"
    "github.com/xtaci/kcp-go/v5"
    "golang.org/x/crypto/pbkdf2"
)

func main() {
    // Derive encryption key from password
    key := pbkdf2.Key([]byte("my-secret-pass"), []byte("my-salt"), 4096, 32, sha1.New)

    // Create AES block cipher for encryption
    block, err := kcp.NewAESBlockCrypt(key)
    if err != nil {
        log.Fatal(err)
    }

    // Listen with FEC: 10 data shards, 3 parity shards
    // This means for every 10 data packets, 3 redundant parity packets are sent
    listener, err := kcp.ListenWithOptions("0.0.0.0:9999", block, 10, 3)
    if err != nil {
        log.Fatal(err)
    }
    defer listener.Close()

    log.Println("KCP server listening on :9999")

    for {
        // Accept incoming KCP connections
        conn, err := listener.AcceptKCP()
        if err != nil {
            log.Printf("Accept error: %v", err)
            continue
        }

        // Handle connection in goroutine
        go handleConnection(conn)
    }
}

func handleConnection(conn *kcp.UDPSession) {
    defer conn.Close()

    // Configure KCP parameters for low latency
    // nodelay=1: enable no-delay mode
    // interval=10: internal update interval in ms
    // resend=2: fast resend mode
    // nc=1: disable congestion control
    conn.SetNoDelay(1, 10, 2, 1)

    // Set stream buffer sizes
    conn.SetStreamBuffer(4194304) // 4MB buffer
    conn.SetWindowSize(1024, 1024) // send/recv window

    buf := make([]byte, 4096)
    for {
        n, err := conn.Read(buf)
        if err != nil {
            if err != io.EOF {
                log.Printf("Read error: %v", err)
            }
            return
        }

        // Echo back
        if _, err := conn.Write(buf[:n]); err != nil {
            log.Printf("Write error: %v", err)
            return
        }
    }
}

```

--------------------------------

### System Time Call Benchmark (Go)

Source: https://github.com/xtaci/kcp-go/blob/master/README.md

Measures the performance overhead of calling the system's time function (`time.Now()`) in Go. This benchmark is relevant for understanding the cost of obtaining timestamps, which is critical for network protocols like KCP that rely on accurate timing for RTT estimation.

```Go
package benchmark2

import (
	"testing"
	"time"
)

func BenchmarkNow(b *testing.B) {
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		time.Now()
	}
}
```

--------------------------------

### Manage KCP Session Lifecycle with Auto-Close (Go)

Source: https://context7.com/xtaci/kcp-go/llms.txt

This Go snippet shows how to manage KCP session lifecycles, including accepting new connections and automatically closing them after a period of inactivity. It uses goroutines for concurrent handling and timers for inactivity detection. Dependencies include 'log', 'net', 'time', and 'github.com/xtaci/kcp-go/v5'. It processes incoming KCP connections and manages their active state.

```go
package main

import (
    "log"
    "net"
    "time"
    "github.com/xtaci/kcp-go/v5"
)

func main() {
    // Assume 'listener' is an existing kcp.Listener
    // Example 5: Close specific session from listener
    // Useful for connection management and cleanup
    listener, _ := kcp.ServeConn(nil, 10, 3, nil) // Placeholder for illustration

    go func() {
        for {
            c, err := listener.AcceptKCP()
            if err != nil {
                return
            }

            // Handle with timeout
            go func(conn *kcp.UDPSession) {
                defer conn.Close()

                // Auto-close after 5 minutes of inactivity
                timer := time.AfterFunc(5*time.Minute, func() {
                    conn.Close()
                })
                defer timer.Stop()

                buf := make([]byte, 4096)
                for {
                    conn.SetReadDeadline(time.Now().Add(5 * time.Minute))
                    n, err := conn.Read(buf)
                    if err != nil {
                        return
                    }
                    timer.Reset(5 * time.Minute)
                    conn.Write(buf[:n])
                }
            }(c)
        }
    }()

    log.Println("KCP session management started.")
    select {} // Keep main goroutine alive
    // listener.Close() // This would typically be called on application shutdown
}
```

--------------------------------

### Create KCP Session with Custom Conversation ID (Go)

Source: https://context7.com/xtaci/kcp-go/llms.txt

This Go snippet shows how to create a KCP session with a custom conversation ID. This is beneficial for multiplexing or implementing custom session management logic. It requires the 'crypto/rand', 'encoding/binary', 'log', 'net', and 'github.com/xtaci/kcp-go/v5' packages. It takes a conversation ID, remote address, and an underlying UDP connection as input, returning a KCP session.

```go
package main

import (
    "crypto/rand"
    "encoding/binary"
    "log"
    "net"
    "github.com/xtaci/kcp-go/v5"
)

func main() {
    // Example 2: Create KCP session with custom conversation ID
    // Useful for multiplexing or custom session management
    var convID uint32
    binary.Read(rand.Reader, binary.LittleEndian, &convID)

    remoteAddr, err := net.ResolveUDPAddr("udp", "server.example.com:9999")
    if err != nil {
        log.Fatal(err)
    }

    localConn, err := net.ListenUDP("udp", nil)
    if err != nil {
        log.Fatal(err)
    }

    // Create session with specific conversation ID and own connection management
    session, err := kcp.NewConn4(convID, remoteAddr, nil, 10, 3, false, localConn)
    if err != nil {
        log.Fatal(err)
    }
    defer session.Close()

    log.Printf("Created KCP session with conversation ID: %d", convID)
}
```
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