Pasted

package main
 
import (
    "bufio"
    "encoding/binary"
    "fmt"
    "net"
    "os"
    "strconv"
    "strings"
    "sync"
    "time"
)
 
type Client struct {
    socket   net.Conn
    username string
    inbox    chan string
}
 
type ActiveClients struct {
    mu      sync.RWMutex
    clients map[string]*Client
}
 
func (ac *ActiveClients) add(c *Client) bool {
    ac.mu.Lock()
    defer ac.mu.Unlock()
    if ac.clients == nil {
        ac.clients = make(map[string]*Client, 0)
    }
    if c.inbox == nil {
        c.inbox = make(chan string, 100)
    }
 
    for username := range ac.clients {
        if username == c.username {
            return false
        }
    }
    ac.clients[c.username] = c
    return true
}
 
func (ac *ActiveClients) remove(c Client) bool {
    ac.mu.Lock()
    defer ac.mu.Unlock()
    debug("Removing %v\n", c.username)
 
    if ac.clients == nil {
        return false
    }
 
    _, ok := ac.clients[c.username]
 
    if ok {
        delete(ac.clients, c.username)
    }
    return ok
}
 
func (ac *ActiveClients) forwardMessage(message string, from string) {
    ac.mu.RLock()
    defer ac.mu.RUnlock()
    msgWithFrom := from + ": " + message
 
    for username, c := range ac.clients {
        if username != from {
            debug("Attempting to forward to %v...", username)
            select {
            case c.inbox <- msgWithFrom:
                debug("Forwarding message to %v\n", username)
            default:
                // if buffer is full, drop the message
                debug("Message dropped because %v inbox is full.\n", c.username)
            }
        }
    }
}
 
var wg sync.WaitGroup
var shouldDebug bool = false
 
func debug(message string, vals ...any) {
    if shouldDebug {
        fmt.Printf(message, vals...)
    }
}
 
func uint16ToBytes(i uint16) []byte {
    // return []byte{byte(i >> 8), byte(i & 0xFF)}
    b := make([]byte, 2)
    binary.BigEndian.PutUint16(b, i)
    return b
}
 
func bytesToUint16(b []byte) uint16 {
    return binary.BigEndian.Uint16(b[:2])
}
 
func sendMessage(message string, connection net.Conn, milliseconds int) (int, error) {
    var timeout time.Duration
    msg_bytes := []byte(message)
    msg_size := len(msg_bytes)
    msg := append(uint16ToBytes(uint16(msg_size)), msg_bytes...)
    if milliseconds > 0 {
        timeout = time.Millisecond * time.Duration(milliseconds)
        connection.SetWriteDeadline(time.Now().Add(timeout))
        defer connection.SetWriteDeadline(time.Time{})
    }
    size, err := connection.Write(msg)
    if err != nil {
        if !strings.Contains(err.Error(), "i/o timeout") {
            fmt.Println(err)
        }
    }
    debug("Sent %v bytes to %v\n", size, connection.RemoteAddr())
    return size, err
}
 
func receiveMessage(connection net.Conn, milliseconds int) (string, int, error) {
    var msg_size [2]byte
    var msg []byte
    var timeout time.Duration
    if milliseconds > 0 {
        timeout = time.Millisecond * time.Duration(milliseconds)
        connection.SetReadDeadline(time.Now().Add(timeout))
        defer connection.SetReadDeadline(time.Time{})
    }
    size, err := connection.Read(msg_size[:])
    if err != nil {
        if !strings.Contains(err.Error(), "i/o timeout") {
            fmt.Println(err)
        }
    }
    if err != nil || size == 0 {
        return "", size, err
    }
    size = int(bytesToUint16(msg_size[:]))
    msg = make([]byte, size)
    size, err = connection.Read(msg)
    if err != nil {
        if !strings.Contains(err.Error(), "i/o timeout") {
            fmt.Println(err)
        }
    }
    if err != nil || size == 0 {
        return "", size, err
    }
 
    debug("Received message (%v bytes) from %v\n", size+2, connection.RemoteAddr())
    return string(msg), size, err
}
 
func server(numberOfClients int, hostInterface string) {
    shouldDebug = true
    users := ActiveClients{}
    listener, err := net.Listen("tcp", hostInterface)
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
 
    for i := 0; i < numberOfClients; i++ {
        wg.Add(1)
        go listen(listener, &users)
    }
 
    wg.Wait()
}
 
func listen(listener net.Listener, users *ActiveClients) {
    defer wg.Done()
    var username string
    var thisClient Client
    var lg sync.WaitGroup
    signalShouldEnd := make(chan bool, 1)
 
loop:
    connection, err := listener.Accept()
    if err != nil {
        debug(err.Error() + "\n")
        return
    }
 
    debug("Received connection from %v\n", connection.RemoteAddr())
 
    hasSetUsername := false
    lg.Add(2)
    go func() {
        defer lg.Done()
        for {
            // wait up to 100ms for the client to send a message
            message, size, err := receiveMessage(connection, 100)
            if err != nil {
                if strings.Contains(err.Error(), "i/o timeout") {
                    // timed out, so go back to start of loop
                    // fmt.Println("i/o timeout")
                    continue
                }
                debug(err.Error())
                select {
                case signalShouldEnd <- true:
                    if users.remove(thisClient) {
                        users.forwardMessage("Goodbye "+thisClient.username, "server")
                    }
                default:
                }
                return
            }
 
            if size > 0 {
                if !hasSetUsername {
                    username = message
                    if username == "server" {
                        sendMessage("server: error: username is invalid; please send new username", connection, 0)
                        break
                    }
                    thisClient = Client{
                        socket:   connection,
                        username: username,
                    }
                    ok := users.add(&thisClient)
                    if !ok {
                        sendMessage("server: error: username is invalid; please send new username", connection, 0)
                        break
                    } else {
                        users.forwardMessage("Welcome "+username, "server")
                    }
                    hasSetUsername = true
                } else {
                    users.forwardMessage(message, username)
                }
            }
 
            select {
            case <-signalShouldEnd:
                return
            default:
            }
        }
    }()
 
    go func() {
        defer lg.Done()
        for {
            select {
            case incoming := <-thisClient.inbox:
                debug("Message found in inbox; sending to %v\n", thisClient.username)
                _, err := sendMessage(incoming, thisClient.socket, 0)
                if err != nil {
                    if !strings.Contains(err.Error(), "i/o timeout") {
                        debug(err.Error() + "\n")
                        select {
                        case signalShouldEnd <- true:
                            if users.remove(thisClient) {
                                users.forwardMessage("Goodbye "+thisClient.username, "server")
                            }
                        default:
                        }
                        return
                    }
                    continue
                }
            case <-signalShouldEnd:
                return
            default:
                time.Sleep(time.Millisecond * 10)
            }
        }
    }()
 
    lg.Wait()
    debug("Recycling server socket for new client\n")
    goto loop
}
 
func client(host string, username string) {
    connection, err := net.Dial("tcp", host+":1337")
    endSignals := []string{"bye", "quit", "exit"}
 
    if err != nil {
        debug("%v\n", err)
        return
    }
 
    go func() {
        for {
            message, size, err := receiveMessage(connection, 100)
 
            if err != nil {
                if strings.Contains(err.Error(), "i/o timeout") {
                    continue
                }
                debug("%v\n", err)
                os.Exit(0)
            }
 
            if size == 0 {
                continue
            }
 
            // fmt.Printf("Received %v bytes: ", size)
            fmt.Println(message)
        }
    }()
 
    fmt.Println("Connected to server.")
 
    _, err = sendMessage(username, connection, 0)
    if err != nil {
        fmt.Println(err)
        return
    }
 
    for {
        message := askInput("")
        if contains(endSignals, message) {
            return
        }
        _, err := sendMessage(message, connection, 0)
        if err != nil {
            fmt.Println(err)
            return
        }
    }
}
 
func benchmark(host string, numberOfClients int, numberOfMessages int, baseMessage string) {
    wg.Add(numberOfClients)
    for i := 0; i < numberOfClients; i++ {
        go func(i int) {
            defer wg.Done()
            var bg sync.WaitGroup
            username := "benchmark" + strconv.Itoa(i)
            connection, err := net.Dial("tcp", host+":1337")
            if err != nil {
                fmt.Println(err)
                return
            }
            // current limitation: must wait for username to process
            _, _ = sendMessage(username, connection, 100)
            time.Sleep(time.Millisecond * 100)
 
            bg.Add(numberOfMessages)
            for d := 0; d < numberOfMessages; d++ {
                go func(message string) {
                    defer bg.Done()
                    _, err = sendMessage(message, connection, 100)
                    if err != nil {
                        fmt.Println(err)
                        return
                    }
                }(baseMessage + strconv.Itoa(d))
            }
 
            bg.Add(1)
            go func() {
                defer bg.Done()
                for {
                    message, size, err := receiveMessage(connection, 2000)
                    if err != nil {
                        fmt.Println(err)
                        return
                    }
                    if size == 0 {
                        fmt.Println("aborting from empty receive")
                        return
                    }
                    fmt.Println(message)
                }
            }()
 
            bg.Wait()
        }(i)
    }
    wg.Wait()
}
 
func askInput(query string) string {
    if query != "" {
        fmt.Printf("%v ", query)
    }
    in := bufio.NewReader(os.Stdin)
    data, _ := in.ReadString('\n')
    data, _, _ = strings.Cut(data, "\n")
    data, _, _ = strings.Cut(data, "\r")
    return data
}
 
func contains[T comparable](list []T, query T) bool {
    // contains function adapted from https://stackoverflow.com/a/10485970
    for _, item := range list {
        if item == query {
            return true
        }
    }
    return false
}
 
func usage(programName string) {
    fmt.Printf("usage: %v server numerOfThreads [hostInterface]\n", programName)
    fmt.Println("\thostInterface is of form hostname:port or IP:port")
    fmt.Println("\tuse 0.0.0.0:port to listen on every available IP interface")
    fmt.Println("\tdefault is localhost:1337")
    fmt.Printf("usage: %v client hostIP username\n", programName)
    fmt.Printf("usage: %v benchmark hostIP numberOfClients numberOfMessages baseMessage\n", programName)
    fmt.Println("arguments must be in order shown")
}
 
func main() {
    programName := os.Args[0]
    nameParts := strings.Split(programName, "\\")
    programName = nameParts[len(nameParts)-1]
 
    if len(os.Args) < 2 {
        usage(programName)
        return
    }
 
    mode := os.Args[1]
 
    switch mode {
    case "server", "serve":
        var numberOfClients int
        if len(os.Args) < 3 {
            usage(programName)
            return
        }
        n, _ := strconv.ParseInt(os.Args[2], 10, 16)
        numberOfClients = int(n)
        var hostInterface string
        if len(os.Args) > 3 {
            hostInterface = os.Args[3]
        } else {
            hostInterface = "localhost:1337"
        }
        server(numberOfClients, hostInterface)
    case "client", "connect":
        var host string
        var username string
        if len(os.Args) < 4 {
            usage(programName)
            return
        }
        host = os.Args[2]
        username = os.Args[3]
        client(host, username)
    case "benchmark":
        var host string
        var nClients string
        var numberOfClients int
        var nMsgs string
        var numberOfMessages int
        var message string
        if len(os.Args) < 6 {
            usage(programName)
            return
        }
        host = os.Args[2]
        nClients = os.Args[3]
        nMsgs = os.Args[4]
        message = os.Args[5]
        n, _ := strconv.ParseInt(nClients, 10, 16)
        numberOfClients = int(n)
        n, _ = strconv.ParseInt(nMsgs, 10, 16)
        numberOfMessages = int(n)
        benchmark(host, numberOfClients, numberOfMessages, message)
    default:
        usage(programName)
    }
}
 
// ISC License
 
// Copyleft (c) 2023 k98kurz
 
// Permission to use, copy, modify, and/or distribute this software
// for any purpose with or without fee is hereby granted, provided
// that the above copyleft notice and this permission notice appear in
// all copies.
 
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
// WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
// AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR
// CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
// OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
// NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.