Echo server
You are encouraged to solve this task according to the task description, using any language you may know.
Create a network service that sits on TCP port 12321, which accepts connections on that port, and which echoes complete lines (using a carriage-return/line-feed sequence as line separator) back to clients. No error handling is required. For the purposes of testing, it is only necessary to support connections from localhost (127.0.0.1 or perhaps ::1). Logging of connection information to standard output is recommended.
The implementation must be able to handle simultaneous connections from multiple clients. A multi-threaded or multi-process solution may be used. Each connection must be able to echo more than a single line.
The implementation must not stop responding to other clients if one client sends a partial line or stops reading responses.
Ada
single-threaded, one client served at a time.
<lang Ada>with Ada.Text_IO; with Ada.IO_Exceptions; with GNAT.Sockets; procedure Echo_Server is
Receiver : GNAT.Sockets.Socket_Type; Connection : GNAT.Sockets.Socket_Type; Client : GNAT.Sockets.Sock_Addr_Type; Channel : GNAT.Sockets.Stream_Access;
begin
GNAT.Sockets.Create_Socket (Socket => Receiver);
GNAT.Sockets.Set_Socket_Option
(Socket => Receiver,
Option => (Name => GNAT.Sockets.Reuse_Address, Enabled => True));
GNAT.Sockets.Bind_Socket
(Socket => Receiver,
Address => (Family => GNAT.Sockets.Family_Inet,
Addr => GNAT.Sockets.Inet_Addr ("127.0.0.1"),
Port => 12321));
GNAT.Sockets.Listen_Socket (Socket => Receiver);
loop
GNAT.Sockets.Accept_Socket
(Server => Receiver,
Socket => Connection,
Address => Client);
Ada.Text_IO.Put_Line
("Client connected from " & GNAT.Sockets.Image (Client));
Channel := GNAT.Sockets.Stream (Connection);
begin
loop
Character'Output (Channel, Character'Input (Channel));
end loop;
exception
when Ada.IO_Exceptions.End_Error =>
null;
end;
GNAT.Sockets.Close_Socket (Connection);
end loop;
end Echo_Server;</lang>
AutoHotkey
echoserver.ahk, modified from script by zed gecko. <lang AutoHotkey>#SingleInstance Force Network_Port = 12321 Network_Address = 127.0.0.1
NewData := false DataReceived = Gosub Connection_Init return
Connection_Init: OnExit, ExitSub socket := PrepareForIncomingConnection(Network_Address, Network_Port) if socket = -1
ExitApp
Process, Exist DetectHiddenWindows On ScriptMainWindowId := WinExist("ahk_class AutoHotkey ahk_pid " . ErrorLevel) DetectHiddenWindows Off
NotificationMsg = 0x5555 OnMessage(NotificationMsg, "ReceiveData")
ExitMsg = 0x6666 OnMessage(ExitMsg, "ExitData")
FD_READ = 1 FD_CLOSE = 32 FD_CONNECT = 20
if DllCall("Ws2_32\WSAAsyncSelect", "UInt", socket,
"UInt", ScriptMainWindowId, "UInt", ExitMsg, "Int", FD_CLOSE)
{
msgbox, closed
}
if DllCall("Ws2_32\WSAAsyncSelect", "UInt", socket,
"UInt", ScriptMainWindowId, "UInt", NotificationMsg, "Int",
FD_READ|FD_CONNECT)
{
MsgBox % "WSAAsyncSelect() indicated Winsock error "
. DllCall("Ws2_32\WSAGetLastError")
DllCall("Ws2_32\WSAAsyncSelect", "UInt", socket,
"UInt", ScriptMainWindowId, "UInt", ExitMsg, "Int", FD_CLOSE)
ExitApp
}
SetTimer, NewConnectionCheck, 500 return
PrepareForIncomingConnection(IPAddress, Port) {
VarSetCapacity(wsaData, 32)
result := DllCall("Ws2_32\WSAStartup", "UShort", 0x0002, "UInt", &wsaData)
if ErrorLevel
{
MsgBox % "WSAStartup() could not be called due to error %ErrorLevel%. "
. "Winsock 2.0 or higher is required."
return -1
}
if result
{
MsgBox % "WSAStartup() indicated Winsock error "
. DllCall("Ws2_32\WSAGetLastError")
return -1
}
AF_INET = 2
SOCK_STREAM = 1
IPPROTO_TCP = 6
socket := DllCall("Ws2_32\socket", "Int", AF_INET,
"Int", SOCK_STREAM, "Int", IPPROTO_TCP)
if socket = -1
{
MsgBox % "socket() indicated Winsock error "
. DllCall("Ws2_32\WSAGetLastError")
return -1
}
SizeOfSocketAddress = 16
VarSetCapacity(SocketAddress, SizeOfSocketAddress)
InsertInteger(2, SocketAddress, 0, AF_INET)
InsertInteger(DllCall("Ws2_32\htons", "UShort", Port), SocketAddress, 2, 2)
InsertInteger(DllCall("Ws2_32\inet_addr", "Str", IPAddress),
SocketAddress, 4, 4)
if DllCall("Ws2_32\bind", "UInt", socket,
"UInt", &SocketAddress, "Int", SizeOfSocketAddress)
{
MsgBox % "bind() indicated Winsock error "
. DllCall("Ws2_32\WSAGetLastError") . "?"
return -1
}
if DllCall("Ws2_32\listen", "UInt", socket, "UInt", "SOMAXCONN")
{
MsgBox % "LISTEN() indicated Winsock error "
. DllCall("Ws2_32\WSAGetLastError") . "?"
return -1
}
return socket
}
ReceiveData(wParam, lParam) {
global DataReceived
global NewData
global mydata
global ConnectionList
socket := wParam
ReceivedDataSize = 4096
Loop
{
VarSetCapacity(ReceivedData, ReceivedDataSize, 0)
ReceivedDataLength := DllCall("Ws2_32\recv", "UInt",
socket, "Str", ReceivedData, "Int", ReceivedDataSize, "Int", 0)
if ReceivedDataLength = 0
{
StringReplace, ConnectionList, ConnectionList, %socket%`n
DllCall("Ws2_32\closesocket", "UInt", socket)
}
if ReceivedDataLength = -1
{
WinsockError := DllCall("Ws2_32\WSAGetLastError")
if WinsockError = 10035
{
DataReceived = %TempDataReceived%
NewData := true
return 1
}
if WinsockError <> 10054
{
MsgBox % "recv() indicated Winsock error " . WinsockError
StringReplace, ConnectionList, ConnectionList, %socket%`n
DllCall("Ws2_32\closesocket", "UInt", socket)
}
}
mydata := ReceivedData
gosub myreceive
if (A_Index = 1)
TempDataReceived =
TempDataReceived = %TempDataReceived%%ReceivedData%
}
return 1
}
ExitData(wParam, lParam) {
global ConnectionList
socket := wParam
ReceivedDataSize = 16
VarSetCapacity(ReceivedData, ReceivedDataSize, 0)
ReceivedDataLength := DllCall("Ws2_32\recv", "UInt", socket,
"Str", ReceivedData, "Int", ReceivedDataSize, "Int", 0)
StringReplace, ConnectionList, ConnectionList, %socket%`n
DllCall("Ws2_32\closesocket", "UInt", socket)
return 1
}
SendData(wParam,SendData) {
SendDataSize := VarSetCapacity(SendData)
SendDataSize += 1
Loop, parse, wParam, `n
{
If A_LoopField =
Continue
socket := A_LoopField
sendret := DllCall("Ws2_32\send", "UInt", socket,
"Str", SendData, "Int", SendDatasize, "Int", 0)
}
}
InsertInteger(pInteger, ByRef pDest, pOffset = 0, pSize = 4)
{
Loop %pSize%
DllCall("RtlFillMemory", "UInt", &pDest + pOffset + A_Index-1,
"UInt", 1, "UChar", pInteger >> 8*(A_Index-1) & 0xFF)
}
NewConnectionCheck: ConnectionCheck := DllCall("Ws2_32\accept", "UInt", socket,
"UInt", &SocketAddress, "Int", SizeOfSocketAddress)
if ConnectionCheck > 1
ConnectionList = %ConnectionList%%ConnectionCheck%`n
Return
SendProcedure: If ConnectionList <> {
SendText = %A_Hour%:%A_Min%:%A_Sec% SendData(ConnectionList,SendText)
} Return
myreceive:
TrayTip, server, %mydata%, ,16 return
GuiClose: ExitSub: DllCall("Ws2_32\WSACleanup") ExitApp</lang> A client is also available for testing this code.
C
This is a rather standard code (details apart); the reference guide for such a code is the Beej's Guide to Network programming. The dependency from POSIX is mainly in the use of the read and write functions, (using the socket as a file descriptor sometimes make things simpler).
<lang c>#include <stdio.h>
- include <stdlib.h>
- include <string.h>
- include <errno.h>
- include <sys/types.h>
- include <sys/socket.h>
- include <netdb.h>
- include <unistd.h>
- include <sys/wait.h>
- include <signal.h>
- define MAX_ENQUEUED 20
- define BUF_LEN 256
- define PORT_STR "12321"
/* ------------------------------------------------------------ */ /* How to clean up after dead child processes */ /* ------------------------------------------------------------ */
void wait_for_zombie(int s) {
while(waitpid(-1, NULL, WNOHANG) > 0) ;
}
/* ------------------------------------------------------------ */ /* Core of implementation of a child process */ /* ------------------------------------------------------------ */
void echo_lines(int csock) {
char buf[BUF_LEN]; int r;
while( (r = read(csock, buf, BUF_LEN)) > 0 ) {
(void)write(csock, buf, r);
}
exit(EXIT_SUCCESS);
}
/* ------------------------------------------------------------ */ /* Core of implementation of the parent process */ /* ------------------------------------------------------------ */
void take_connections_forever(int ssock) {
for(;;) {
struct sockaddr addr;
socklen_t addr_size = sizeof(addr);
int csock;
/* Block until we take one connection to the server socket */
csock = accept(ssock, &addr, &addr_size);
/* If it was a successful connection, spawn a worker process to service it */
if ( csock == -1 ) {
perror("accept");
} else if ( fork() == 0 ) {
close(ssock);
echo_lines(csock);
} else {
close(csock);
}
}
}
/* ------------------------------------------------------------ */ /* The server process's one-off setup code */ /* ------------------------------------------------------------ */
int main() {
struct addrinfo hints, *res; struct sigaction sa; int sock;
/* Look up the address to bind to */
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE;
if ( getaddrinfo(NULL, PORT_STR, &hints, &res) != 0 ) {
perror("getaddrinfo");
exit(EXIT_FAILURE);
}
/* Make a socket */
if ( (sock = socket(res->ai_family, res->ai_socktype, res->ai_protocol)) == -1 ) {
perror("socket");
exit(EXIT_FAILURE);
}
/* Arrange to clean up child processes (the workers) */
sa.sa_handler = wait_for_zombie;
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_RESTART;
if ( sigaction(SIGCHLD, &sa, NULL) == -1 ) {
perror("sigaction");
exit(EXIT_FAILURE);
}
/* Associate the socket with its address */
if ( bind(sock, res->ai_addr, res->ai_addrlen) != 0 ) {
perror("bind");
exit(EXIT_FAILURE);
}
freeaddrinfo(res);
/* State that we've opened a server socket and are listening for connections */
if ( listen(sock, MAX_ENQUEUED) != 0 ) {
perror("listen");
exit(EXIT_FAILURE);
}
/* Serve the listening socket until killed */ take_connections_forever(sock); return EXIT_SUCCESS;
}</lang>
C#
<lang csharp> using System.Net.Sockets; using System.Threading;
namespace ConsoleApplication1 {
class Program
{
static TcpListener listen;
static Thread serverthread;
static void Main(string[] args)
{
listen = new TcpListener(System.Net.IPAddress.Parse("127.0.0.1"), 12321);
serverthread = new Thread(new ThreadStart(DoListen));
serverthread.Start();
}
private static void DoListen()
{
// Listen
listen.Start();
Console.WriteLine("Server: Started server");
while (true)
{
Console.WriteLine("Server: Waiting...");
TcpClient client = listen.AcceptTcpClient();
Console.WriteLine("Server: Waited");
// New thread with client
Thread clientThread = new Thread(new ParameterizedThreadStart(DoClient));
clientThread.Start(client);
}
}
private static void DoClient(object client)
{
// Read data
TcpClient tClient = (TcpClient)client;
Console.WriteLine("Client (Thread: {0}): Connected!", Thread.CurrentThread.ManagedThreadId);
do
{
if (!tClient.Connected)
{
tClient.Close();
Thread.CurrentThread.Abort(); // Kill thread.
}
if (tClient.Available > 0)
{
// Resend
byte pByte = (byte)tClient.GetStream().ReadByte();
Console.WriteLine("Client (Thread: {0}): Data {1}", Thread.CurrentThread.ManagedThreadId, pByte);
tClient.GetStream().WriteByte(pByte);
}
// Pause
Thread.Sleep(100);
} while (true);
}
}
} </lang>
Clojure
<lang lisp>(use '[clojure.contrib.server-socket :only (create-server)]) (use '[clojure.contrib.duck-streams :only (read-lines write-lines)])
(defn echo [input output]
(write-lines (java.io.PrintWriter. output true) (read-lines input)))
(create-server 12321 echo)</lang>
Note here that an auto-flushing PrintWriter needs to be created, otherwise 'output' could simply be passed to write-lines.
Common Lisp
Sockets is not a standard part of Common Lisp but many implementations have support for this. The following example
<lang lisp>(defvar *clients* '()
"This is a list of (socket :input status) which is used with
`socket:socket-status' to test for data ready on a socket.")
(defun echo-server (port)
"Listen on `port' for new client connections and for data arriving on
any existing client connections"
(let ((server (socket:socket-server port)))
(format t "Echo service listening on port ~a:~d~%"
(socket:socket-server-host server)
(socket:socket-server-port server))
(unwind-protect
(loop
(when (socket:socket-status server 0 1)
(echo-accept-client (socket:socket-accept server
:external-format :dos
:buffered t)))
(when *clients*
(socket:socket-status *clients* 0 1)
(mapcar #'(lambda (client)
(when (eq :input (cddr client))
(echo-service-client (car client)))
(when (eq :eof (cddr client))
(echo-close-client (car client)))) *clients*)))
(socket-server-close server))))
(defun echo-accept-client (socket)
"Accept a new client connection and add it to the watch list."
(multiple-value-bind
(host port) (socket:socket-stream-peer socket)
(format t "Connect from ~a:~d~%" host port))
(push (list socket :input nil) *clients*))
(defun echo-service-client (socket)
(let ((line (read-line socket nil nil)))
(princ line socket)
(finish-output socket)))
(defun echo-close-client (socket)
"Close a client connection and remove it from the watch list."
(multiple-value-bind
(host port) (socket:socket-stream-peer socket)
(format t "Closing connection from ~a:~d~%" host port))
(close socket)
(setq *clients* (remove socket *clients* :key #'car)))
(echo-server 12321)</lang>
D
This is a very basic server that processes the buffers one character at a time. In a real-world application, the buffers would be larger. More seriously, it processes one listener at a time. If the currSock.receive() blocks, the loop will not process other clients. This opens the door for a trivial denial-of-service attack. A realistic echo service must multiplex clients.
<lang d> // Tested using DMD 2.048 import std.socket; import std.array;
void main() {
Socket listener = new TcpSocket; assert(listener.isAlive); listener.bind(new InternetAddress(12321)); listener.listen(10);
Socket currSock; uint bytesRead; ubyte buff[1];
while(1)
{
currSock = listener.accept();
while ((bytesRead = currSock.receive(buff)) > 0)
{
currSock.send(buff);
}
currSock.close();
buff.clear();
}
}</lang>
Delphi
<lang Delphi>program EchoServer;
{$APPTYPE CONSOLE}
uses SysUtils, IdContext, IdTCPServer;
type
TEchoServer = class private FTCPServer: TIdTCPServer; public constructor Create; destructor Destroy; override; procedure TCPServerExecute(AContext: TIdContext); end;
constructor TEchoServer.Create; begin
FTCPServer := TIdTCPServer.Create(nil); FTCPServer.DefaultPort := 12321; FTCPServer.OnExecute := TCPServerExecute; FTCPServer.Active := True;
end;
destructor TEchoServer.Destroy; begin
FTCPServer.Active := False; FTCPServer.Free; inherited Destroy;
end;
procedure TEchoServer.TCPServerExecute(AContext: TIdContext); var
lCmdLine: string;
begin
lCmdLine := AContext.Connection.IOHandler.ReadLn;
Writeln('>' + lCmdLine);
AContext.Connection.IOHandler.Writeln('>' + lCmdLine);
if SameText(lCmdLine, 'QUIT') then
begin
AContext.Connection.IOHandler.Writeln('Disconnecting');
AContext.Connection.Disconnect;
end;
end;
var
lEchoServer: TEchoServer;
begin
lEchoServer := TEchoServer.Create;
try
Writeln('Delphi Echo Server');
Writeln('Press Enter to quit');
Readln;
finally
lEchoServer.Free;
end;
end.</lang>
Erlang
<lang erlang> -module(echo). -export([start/0]).
start() ->
spawn(fun () -> {ok, Sock} = gen_tcp:listen(12321, [{packet, line}]),
echo_loop(Sock)
end).
echo_loop(Sock) ->
{ok, Conn} = gen_tcp:accept(Sock),
io:format("Got connection: ~p~n", [Conn]),
Handler = spawn(fun () -> handle(Conn) end),
gen_tcp:controlling_process(Conn, Handler),
echo_loop(Sock).
handle(Conn) ->
receive
{tcp, Conn, Data} ->
gen_tcp:send(Conn, Data),
handle(Conn);
{tcp_closed, Conn} ->
io:format("Connection closed: ~p~n", [Conn])
end.
</lang>
F#
<lang fsharp>open System.IO open System.Net open System.Net.Sockets
let service (client:TcpClient) =
use stream = client.GetStream()
use out = new StreamWriter(stream, AutoFlush = true)
use inp = new StreamReader(stream)
while not inp.EndOfStream do
match inp.ReadLine() with
| line -> printfn "< %s" line
out.WriteLine(line)
printfn "closed %A" client.Client.RemoteEndPoint
client.Close |> ignore
let EchoService =
let socket = new TcpListener(IPAddress.Loopback, 12321)
do socket.Start()
printfn "echo service listening on %A" socket.Server.LocalEndPoint
while true do
let client = socket.AcceptTcpClient()
printfn "connect from %A" client.Client.RemoteEndPoint
let job = async {
use c = client in try service client with _ -> () }
Async.Start job
[<EntryPoint>] let main _ =
EchoService 0
</lang>
Factor
Connections get logged to /place-where-factor-is/logs/echo-server.
<lang factor>USING: accessors io io.encodings.utf8 io.servers.connection
threads ;
IN: rosetta.echo
CONSTANT: echo-port 12321
- handle-client ( -- )
[ write "\r\n" write flush ] each-line ;
- <echo-server> ( -- threaded-server )
utf8 <threaded-server>
"echo-server" >>name
echo-port >>insecure
[ handle-client ] >>handler ;
- start-echo-server ( -- threaded-server )
<echo-server> [ start-server ] in-thread ;</lang>
Forth
<lang forth>include unix/socket.fs
128 constant size
- (echo) ( sock buf -- sock buf )
begin cr ." waiting..." 2dup 2dup size read-socket nip dup 0> while ." got: " 2dup type rot write-socket repeat drop drop drop ;
create buf size allot
- echo-server ( port -- )
cr ." Listening on " dup .
create-server
dup 4 listen
begin
dup accept-socket
cr ." Connection!"
buf ['] (echo) catch
cr ." Disconnected (" . ." )"
drop close-socket
again ;
12321 echo-server</lang> TODO: use tasker.fs and non-blocking semantics to handle mutliple connections
Go
<lang go>package main
import ( "fmt" "net" "bufio" )
func echo(s net.Conn, i int) { fmt.Printf("%d: %v <-> %v\n", i, s.LocalAddr(), s.RemoteAddr()) b := bufio.NewReader(s) for { line, e := b.ReadBytes('\n') if e != nil { break } s.Write(line) } fmt.Printf("%d: closed\n", i) }
func main() { l, e := net.Listen("tcp", ":12321") for i := 0; e == nil; i++ { var s net.Conn s, e = l.Accept() go echo(s, i) } } </lang>
Haskell
<lang haskell>module Main where import Network (withSocketsDo, accept, listenOn, sClose, PortID(PortNumber)) import Control.Monad (forever) import System.IO (hGetLine, hPutStrLn, hFlush, hClose) import System.IO.Error (isEOFError) import Control.Concurrent (forkIO) import Control.Exception (bracket)
-- For convenience in testing, ensure that the listen socket is closed if the main loop is aborted withListenOn port body = bracket (listenOn port) sClose body
echo (handle, host, port) = catch (forever doOneLine) stop where
doOneLine = do line <- hGetLine handle
print (host, port, init line)
hPutStrLn handle line
hFlush handle
stop error = do putStrLn $ "Closed connection from " ++ show (host, port) ++ " due to " ++ show error
hClose handle
main = withSocketsDo $
withListenOn (PortNumber 12321) $ \listener ->
forever $ do
acc@(_, host, port) <- accept listener
putStrLn $ "Accepted connection from " ++ show (host, port)
forkIO (echo acc)</lang>
Java
<lang java>import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.io.PrintWriter; import java.net.ServerSocket; import java.net.Socket;
public class EchoServer { ServerSocket serverSocket; public EchoServer(){ }
public void start() { try { serverSocket = new ServerSocket(12321); while(true){ Thread clientThread = new Thread(new ClientHandler(serverSocket.accept())); clientThread.start(); } } catch (IOException e) { e.printStackTrace(); } finally { try { System.out.println("closing server socket"); serverSocket.close(); } catch (IOException e) { e.printStackTrace(); } }
}
public static void main(String[] args) { EchoServer es = new EchoServer(); es.start(); } }
class ClientHandler implements Runnable { private static int numConnections; private int connectionId = 0; Socket clientSocket;
public ClientHandler(Socket s) { connectionId = numConnections++; System.out.println("handling connection, #" + connectionId); clientSocket = s; }
public void run() { PrintWriter out = null; BufferedReader in = null; try { out = new PrintWriter(clientSocket.getOutputStream(), true); in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); String inputLine, outputLine; while((inputLine = in.readLine()) != null){ outputLine = inputLine; System.out.println("recieved: " + outputLine); out.write(outputLine+"\n"); out.flush(); if (outputLine.equals("exit")) break; } } catch(Exception e) { e.printStackTrace(); } finally { out.close(); try { in.close(); clientSocket.close(); System.out.println("closing connection, #" + connectionId); } catch (IOException e) { e.printStackTrace(); } } } }</lang>
JavaScript
<lang javascript>var net = require('net');
var server = net.createServer(function(conn) {
console.log("Connection from " + conn.remoteAddress + " on port " + conn.remotePort);
conn.setEncoding("utf8");
var buffer = "";
conn.on("data", function(data) {
for(var i = 0; i <= data.length; i++) {
var char = data.charAt(i);
buffer += char;
if(char == "\n") {
conn.write(buffer);
buffer = "";
}
}
});
});
server.listen(12321, "localhost");</lang>
Oz
<lang oz>declare
ServerSocket = {New Open.socket init}
proc {Echo Socket}
case {Socket getS($)} of false then skip
[] Line then
{System.showInfo "Received line: "#Line}
{Socket write(vs:Line#"\n")}
{Echo Socket}
end
end
class TextSocket from Open.socket Open.text end
in
{ServerSocket bind(takePort:12321)}
{System.showInfo "Socket bound."}
{ServerSocket listen}
{System.showInfo "Started listening."}
for do
ClientHost ClientPort
ClientSocket = {ServerSocket accept(accepted:$
acceptClass:TextSocket host:?ClientHost port:?ClientPort )}
in
{System.showInfo "Connection accepted from "#ClientHost#":"#ClientPort#"."}
thread
{Echo ClientSocket}
{System.showInfo "Connection lost: "#ClientHost#":"#ClientPort#"."}
{ClientSocket close}
end
end</lang>
Client test code: <lang oz>declare
Socket = {New class $ from Open.socket Open.text end init}
in
{Socket connect(port:12321)}
{Socket write(vs:"Hello\n")}
{System.showInfo "Client received: "#{Socket getS($)}}
{Socket close}</lang>
Example session:
Socket bound. Started listening. Connection accepted from localhost:2048. Received line: Hello Client received: Hello Connection lost: localhost:2048.
Perl
This server will run indefinitely listening in the port 12321 and forking every time a client connects, the childs listen to the client and write back.
This is an example using the IO::Socket module: <lang perl>use IO::Socket; my $use_fork = 1;
my $sock = new IO::Socket::INET (
LocalHost => '127.0.0.1',
LocalPort => '12321',
Proto => 'tcp',
Listen => 1, # maximum queued connections
Reuse => 1,
)
or die "socket: $!"; # no newline, so perl appends stuff
$SIG{CHLD} = 'IGNORE' if $use_fork; # let perl deal with zombies
print "listening...\n"; while (1) { # declare $con 'my' so it's closed by parent every loop
my $con = $sock->accept()
or die "accept: $!"; fork and next if $use_fork; # following are for child only
print "incoming..\n"; print $con $_ while(<$con>); # read each line and write back print "done\n";
last if $use_fork; # if not forking, loop }
- child will reach here and close its copy of $sock before exit</lang>
This is an equivalent program using the Net::Server module: <lang perl>package Echo; use base 'Net::Server::Fork'; sub process_request {
print while <STDIN>;
} Echo->run(port => 12321, log_level => 3);</lang> It also prints the IP address and port number of every connection.
This is a more complicated example using preforking: <lang perl>package Echo; use base 'Net::Server::PreFork'; sub process_request {
print while <STDIN>;
} Echo->run(port => 12321, log_level => 3);</lang> By default it spawns 5 child processes at startup, makes sure there are always at least 2 and at most 10 spare children available for new requests, each of which will be killed after processing 1000 requests and new ones will take their place.
PHP
<lang PHP>$socket = socket_create(AF_INET,SOCK_STREAM,SOL_TCP); socket_bind($socket, '127.0.0.1', 12321); socket_listen($socket);
$client_count = 0; while (true){
if (($client = socket_accept($socket)) === false) continue; $client_count++;
$client_name = 'Unknown';
socket_getpeername($client, $client_name);
echo "Client {$client_count} ({$client_name}) connected\n";
$pid = pcntl_fork();
if($pid == -1) die('Could not fork');
if($pid){
pcntl_waitpid(-1, $status, WNOHANG);
continue;
}
//In a child process
while(true){
if($input = socket_read($client, 1024)){
socket_write($client, $input);
} else {
socket_shutdown($client);
socket_close($client);
echo "Client {$client_count} ({$client_name}) disconnected\n";
exit();
}
}
}</lang>
PicoLisp
<lang PicoLisp>(setq Port (port 12321))
(loop
(setq Sock (listen Port)) # Listen (NIL (fork) (close Port)) # Accepted (close Sock) ) # Parent: Close socket and continue
- Child:
(prinl (stamp) " -- (Pid " *Pid ") Client connected from " *Adr)
(in Sock
(until (eof) # Echo lines
(out Sock (prinl (line))) ) )
(prinl (stamp) " -- (Pid " *Pid ") Client disconnected") (bye) # Terminate child</lang>
PureBasic
<lang Purebasic>NewMap RecData.s() OpenWindow(0, 100, 200, 200, 100, "Echo Server", #PB_Window_SystemMenu | #PB_Window_MinimizeGadget ) InitNetwork() CreateNetworkServer(1, 12321)
Repeat
Event = NetworkServerEvent()
ClientID = EventClient()
If Event = #PB_NetworkEvent_Connect ; When a new client has been connected...
AddMapElement(RecData(), Str(ClientID))
ElseIf Event = #PB_NetworkEvent_Data
*Buffer = AllocateMemory(20000)
count = ReceiveNetworkData(ClientID, *Buffer, 20000)
For i = 1 To count
RecData(Str(ClientID)) + Mid( PeekS(*Buffer, count), i , 1)
If Right( RecData(Str(ClientID)), 2) = #CRLF$
SendNetworkString (ClientID, RecData(Str(ClientID)))
Debug IPString(GetClientIP(ClientID)) + ":" + Str(GetClientPort(ClientID)) + " " + RecData(Str(ClientID))
RecData(Str(ClientID)) = ""
EndIf
Next
FreeMemory(*Buffer)
ElseIf Event = #PB_NetworkEvent_Disconnect ; When a client has closed the connection...
DeleteMapElement(RecData(), Str(ClientID))
EndIf
Event = WaitWindowEvent(10)
Until Event = #PB_Event_CloseWindow</lang>
Python
<lang python>import SocketServer
HOST = "localhost" PORT = 12321
- this server uses ThreadingMixIn - one thread per connection
- replace with ForkMixIn to spawn a new process per connection
class EchoServer(SocketServer.ThreadingMixIn, SocketServer.TCPServer):
# no need to override anything - default behavior is just fine pass
class EchoRequestHandler(SocketServer.StreamRequestHandler):
"""
Handles one connection to the client.
"""
def handle(self):
print "connection from %s" % self.client_address[0]
while True:
line = self.rfile.readline()
if not line: break
print "%s wrote: %s" % (self.client_address[0], line.rstrip())
self.wfile.write(line)
print "%s disconnected" % self.client_address[0]
- Create the server
server = EchoServer((HOST, PORT), EchoRequestHandler)
- Activate the server; this will keep running until you
- interrupt the program with Ctrl-C
print "server listening on %s:%s" % server.server_address server.serve_forever()</lang>
REBOL
<lang rebol>server-port: open/lines tcp://:12321 forever [
connection-port: first server-port
until [
wait connection-port
error? try [insert connection-port first connection-port]
]
close connection-port
] close server-port</lang>
Ruby
<lang ruby>require 'socket' server = TCPServer.new(12321)
while (connection = server.accept)
Thread.new(connection) do |conn|
port, host = conn.peeraddr[1,2]
client = "#{host}:#{port}"
puts "#{client} is connected"
begin
loop do
line = conn.readline
puts "#{client} says: #{line}"
conn.puts(line)
end
rescue EOFError
conn.close
puts "#{client} has disconnected"
end
end
end</lang>
Scheme
Based on the Guile Internet Socket Server Example. <lang scheme>; Needed in Guile for read-line (use-modules (ice-9 rdelim))
- Variable used to hold child PID returned from forking
(define child #f)
- Start listening on port 12321 for connections from any address
(let ((s (socket PF_INET SOCK_STREAM 0)))
(setsockopt s SOL_SOCKET SO_REUSEADDR 1) (bind s AF_INET INADDR_ANY 12321) (listen s 5) ; Queue size of 5
(simple-format #t "Listening for clients in pid: ~S" (getpid)) (newline)
- Wait for connections forever
(while #t
(let* ((client-connection (accept s))
(client-details (cdr client-connection))
(client (car client-connection)))
- Once something connects fork
(set! child (primitive-fork))
(if (zero? child)
(begin
- Then have child fork to avoid zombie children (grandchildren aren't our responsibility)
(set! child (primitive-fork))
(if (zero? child)
(begin
- Display some connection details
(simple-format #t "Got new client connection: ~S" client-details)
(newline)
(simple-format #t "Client address: ~S"
(gethostbyaddr (sockaddr:addr client-details)))
(newline)
- Wait for input from client and then echo the input back forever (or until client quits)
(do ((line (read-line client)(read-line client))) ((zero? 1))
(display line client)(newline client))))
- Child exits after spawning grandchild.
(primitive-exit))
- Parent waits for child to finish spawning grandchild
(waitpid child)))))</lang>
Tcl
This code is single-threaded. It uses non-blocking I/O to perform the transfers, sitting on top of the event multiplexer system call (e.g., select() on Unix) to decide when to take new connections or service a particular socket. This makes this into a very lightweight echo server in terms of overall system resources.
<lang tcl># How to handle an incoming new connection proc acceptEcho {chan host port} {
puts "opened connection from $host:$port" fconfigure $chan -blocking 0 -buffering line -translation crlf fileevent $chan readable [list echo $chan $host $port]
}
- How to handle an incoming message on a connection
proc echo {chan host port} {
if {[gets $chan line] >= 0} {
puts $chan $line
} elseif {[eof $chan]} {
close $chan
puts "closed connection from $host:$port"
}
# Other conditions causing a short read need no action
}
- Make the server socket and wait for connections
socket -server acceptEcho -myaddr localhost 12321 vwait forever</lang>
Alternative version
A more succinct version (though one harder to adapt to other kinds of services, but closer to the standard unix echo daemon since it has no line-buffering) is to use an asynchronous binary copy. <lang tcl># How to handle an incoming new connection proc acceptEcho {chan host port} {
puts "opened connection from $host:$port" fconfigure $chan -translation binary -buffering none fcopy $chan $chan -command [list done $chan $host $port]
}
- Called to finalize the connection
proc done {chan host port args} {
puts "closed connection from $host:$port" close $chan
}
- Make the server socket and wait for connections
socket -server acceptEcho -myaddr localhost 12321 vwait forever</lang>
- Programming Tasks
- Networking and Web Interaction
- Ada
- AutoHotkey
- C
- C sharp
- Clojure
- Common Lisp
- Common Lisp examples needing attention
- Examples needing attention
- D
- Delphi
- Erlang
- F Sharp
- Factor
- Forth
- Go
- Haskell
- Java
- JavaScript
- Oz
- Perl
- PHP
- PicoLisp
- PureBasic
- Python
- REBOL
- Ruby
- Scheme
- Tcl
- Lotus 123 Macro Scripting/Omit
- TI-83 BASIC/Omit
- TI-89 BASIC/Omit
- M4/Omit
- ML/I/Omit
- PARI/GP/Omit
- Retro/Omit
- Unlambda/Omit