Distributed programming
You are encouraged to solve this task according to the task description, using any language you may know.
Write two programs (or one program with two modes) which run on networked computers, and send some messages between them.
The protocol used may be language-specific or not, and should be suitable for general distributed programming; that is, the protocol should be generic (not designed just for the particular example application), readily capable of handling the independent communications of many different components of a single application, and the transferring of arbitrary data structures natural for the language.
This task is intended to demonstrate high-level communication facilities beyond just creating sockets.
Ada
Ada defines facilities for distributed systems in its standard (Annex E, also called DSA).
This example works with PolyORB and the GNAT GPL 2010 compiler from AdaCore.
server.ads:
package Server is
pragma Remote_Call_Interface;
procedure Foo;
function Bar return Natural;
end Server;
server.adb:
package body Server is
Count : Natural := 0;
procedure Foo is
begin
Count := Count + 1;
end Foo;
function Bar return Natural is
begin
return Count;
end Bar;
end Server;
client.adb:
with Server;
with Ada.Text_IO;
procedure Client is
begin
Ada.Text_IO.Put_Line ("Calling Foo...");
Server.Foo;
Ada.Text_IO.Put_Line ("Calling Bar: " & Integer'Image (Server.Bar));
end Client;
required config (dsa.cfg):
configuration DSA is
pragma Starter (None);
-- Server
Server_Partition : Partition := (Server);
procedure Run_Server is in Server_Partition;
-- Client
Client_Partition : Partition;
for Client_Partition'Termination use Local_Termination;
procedure Client;
for Client_Partition'Main use Client;
end DSA;
compilation:
$po_gnatdist dsa.cfg
[...]
------------------------------
---- Configuration report ----
------------------------------
Configuration :
Name : dsa
Main : run_server
Starter : none
Partition server_partition
Main : run_server
Units :
- server (rci)
- run_server (normal)
- polyorb.dsa_p.partitions (rci, from PCS)
Environment variables :
- "POLYORB_DSA_NAME_SERVICE"
Partition client_partition
Main : client
Termination : local
Units :
- client (normal)
Environment variables :
- "POLYORB_DSA_NAME_SERVICE"
-------------------------------
[...]
preparation (run PolyORB name service):
$ po_ioc_naming POLYORB_CORBA_NAME_SERVICE=IOR:010000002b00000049444[...] POLYORB_CORBA_NAME_SERVICE=corbaloc:iiop:1.2@10.200.[...]
You have to set the environment variable POLYORB_DSA_NAME_SERVICE to one of the two values given by po_ioc_naming for the server/client partitions.
running server:
$ ./server_partition
running client:
$ ./client_partition Calling Foo... Calling Bar: 1 $ ./client_partition Calling Foo... Calling Bar: 2
AutoHotkey
See Distributed program/AutoHotkey.
C
Using PVM [1] This program is in a sense both a server and a client, depending on if its task is spawned with a command-line argument: if yes, it spawns another task of the same executible on the parallel virtual machine and waits for it to transmit data; if no, it transmits data and is done.
#include <stdio.h>
#include <stdlib.h>
#include <pvm3.h>
int main(int c, char **v)
{
int tids[10];
int parent, spawn;
int i_data, i2;
double f_data;
if (c > 1) {
spawn = pvm_spawn("/tmp/a.out", 0, PvmTaskDefault, 0, 1, tids);
if (spawn <= 0) {
printf("Can't spawn task\n");
return 1;
}
printf("Spawning successful\n");
/* pvm_recv(task_id, msgtag). msgtag identifies what kind of data it is,
* for here: 1 = (int, double), 2 = (int, int)
* The receiving order is intentionally swapped, just to show.
* task_id = -1 means "receive from any task"
*/
pvm_recv(-1, 2);
pvm_unpackf("%d %d", &i_data, &i2);
printf("got msg type 2: %d %d\n", i_data, i2);
pvm_recv(-1, 1);
pvm_unpackf("%d %lf", &i_data, &f_data);
printf("got msg type 1: %d %f\n", i_data, f_data);
} else {
parent = pvm_parent();
pvm_initsend(PvmDataDefault);
i_data = rand();
f_data = (double)rand() / RAND_MAX;
pvm_packf("%d %lf", i_data, f_data);
pvm_send(parent, 1); /* send msg type 1 */
pvm_initsend(PvmDataDefault);
i2 = rand();
pvm_packf("%d %d", i_data, i2);
pvm_send(parent, 2); /* send msg type 2 */
}
pvm_exit();
return 0;
}
- Output:
(running it on PVM console, exe is /tmp/a.out)
pvm> spawn -> /tmp/a.out 1
spawn -> /tmp/a.out 1
[2]
1 successful
t40028
pvm> [2:t40029] EOF
[2:t40028] Spawning successful
[2:t40028] got msg type 2: 1804289383 1681692777
[2:t40028] got msg type 1: 1804289383 0.394383
[2:t40028] EOF
[2] finished
C#
Start the program with "server" parameter to start the server, and "client" to start the client. The client will send data to the server and receive a response. The server will wait for data, display the data received, and send a response.
using System;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Runtime.Serialization.Formatters.Binary;
using System.Threading.Tasks;
using static System.Console;
class DistributedProgramming
{
const int Port = 555;
async static Task RunClient()
{
WriteLine("Connecting");
var client = new TcpClient();
await client.ConnectAsync("localhost", Port);
using (var stream = client.GetStream())
{
WriteLine("Sending loot");
var data = Serialize(new SampleData());
await stream.WriteAsync(data, 0, data.Length);
WriteLine("Receiving thanks");
var buffer = new byte[80000];
var bytesRead = await stream.ReadAsync(buffer, 0, buffer.Length);
var thanks = (string)Deserialize(buffer, bytesRead);
WriteLine(thanks);
}
client.Close();
}
async static Task RunServer()
{
WriteLine("Listening");
var listener = new TcpListener(IPAddress.Any, Port);
listener.Start();
var client = await listener.AcceptTcpClientAsync();
using (var stream = client.GetStream())
{
WriteLine("Receiving loot");
var buffer = new byte[80000];
var bytesRead = await stream.ReadAsync(buffer, 0, buffer.Length);
var data = (SampleData)Deserialize(buffer, bytesRead);
WriteLine($"{data.Loot} at {data.Latitude}, {data.Longitude}");
WriteLine("Sending thanks");
var thanks = Serialize("Thanks!");
await stream.WriteAsync(thanks, 0, thanks.Length);
}
client.Close();
listener.Stop();
Write("Press a key");
ReadKey();
}
static byte[] Serialize(object data)
{
using (var mem = new MemoryStream())
{
new BinaryFormatter().Serialize(mem, data);
return mem.ToArray();
}
}
static object Deserialize(byte[] data, int length)
{
using (var mem = new MemoryStream(data, 0, length))
{
return new BinaryFormatter().Deserialize(mem);
}
}
static void Main(string[] args)
{
if (args.Length == 0) return;
switch (args[0])
{
case "client": RunClient().Wait(); break;
case "server": RunServer().Wait(); break;
}
}
}
[Serializable]
class SampleData
{
public decimal Latitude = 44.33190m;
public decimal Longitude = 114.84129m;
public string Loot = "140 tonnes of jade";
}
D
Uses the rpc library: https://github.com/adamdruppe/misc-stuff-including-D-programming-language-web-stuff/blob/master/rpc.d
This library is not standard, so this code (by Adam D. Ruppe) could and should be rewritten using more standard means.
import arsd.rpc;
struct S1 {
int number;
string name;
}
struct S2 {
string name;
int number;
}
interface ExampleNetworkFunctions {
string sayHello(string name);
int add(in int a, in int b) const pure nothrow;
S2 structTest(S1);
void die();
}
// The server must implement the interface.
class ExampleServer : ExampleNetworkFunctions {
override string sayHello(string name) {
return "Hello, " ~ name;
}
override int add(in int a, in int b) const pure nothrow {
return a + b;
}
override S2 structTest(S1 a) {
return S2(a.name, a.number);
}
override void die() {
throw new Exception("death requested");
}
mixin NetworkServer!ExampleNetworkFunctions;
}
class Client {
mixin NetworkClient!ExampleNetworkFunctions;
}
void main(in string[] args) {
import std.stdio;
if (args.length > 1) {
auto client = new Client("localhost", 5005);
// These work like the interface above, but instead of
// returning the value, they take callbacks for success (where
// the arg is the retval) and failure (the arg is the
// exception).
client.sayHello("whoa", (a) { writeln(a); }, null);
client.add(1,2, (a){ writeln(a); }, null);
client.add(10,20, (a){ writeln(a); }, null);
client.structTest(S1(20, "cool!"),
(a){ writeln(a.name, " -- ", a.number); },
null);
client.die(delegate(){ writeln("shouldn't happen"); },
delegate(a){ writeln(a); });
client.eventLoop;
} else {
auto server = new ExampleServer(5005);
server.eventLoop;
}
}
E
Protocol: Pluribus
This service cannot be used except by clients which know the URL designating it, messages are encrypted, and the client authenticates the server. However, it is vulnerable to denial-of-service by any client knowing the URL.
Server
(The protocol is symmetric; this program is the server only in that it is the one which is started first and exports an object.)
def storage := [].diverge()
def logService {
to log(line :String) {
storage.push([timer.now(), line])
}
to search(substring :String) {
var matches := []
for [time, line] ? (line.startOf(substring) != -1) in storage {
matches with= [time, line]
}
return matches
}
}
introducer.onTheAir()
def sturdyRef := makeSturdyRef.temp(logService)
println(<captp>.sturdyToURI(sturdyRef))
interp.blockAtTop()This will print the URL of the service and run it until aborted.
Client
The URL provided by the server is given as the argument to this program.
def [uri] := interp.getArgs()
introducer.onTheAir()
def sturdyRef := <captp>.sturdyFromURI(uri)
def logService := sturdyRef.getRcvr()
logService <- log("foot")
logService <- log("shoe")
println("Searching...")
when (def result := logService <- search("foo")) -> {
for [time, line] in result {
println(`At $time: $line`)
}
}Erlang
The protocol is erlang's own
Server
srv.erl
-module(srv).
-export([start/0, wait/0]).
start() ->
net_kernel:start([srv,shortnames]),
erlang:set_cookie(node(), rosetta),
Pid = spawn(srv,wait,[]),
register(srv,Pid),
io:fwrite("~p ready~n",[node(Pid)]),
ok.
wait() ->
receive
{echo, Pid, Any} ->
io:fwrite("-> ~p from ~p~n", [Any, node(Pid)]),
Pid ! {hello, Any},
wait();
Any -> io:fwrite("Error ~p~n", [Any])
end.
Client
client.erl
-module(client).
-export([start/0, wait/0]).
start() ->
net_kernel:start([client,shortnames]),
erlang:set_cookie(node(), rosetta),
{ok,[[Srv]]} = init:get_argument(server),
io:fwrite("connecting to ~p~n", [Srv]),
{srv, list_to_atom(Srv)} ! {echo,self(), hi},
wait(),
ok.
wait() ->
receive
{hello, Any} -> io:fwrite("Received ~p~n", [Any]);
Any -> io:fwrite("Error ~p~n", [Any])
end.
running it (*comes later)
|erlc srv.erl |erl -run srv start -noshell srv@agneyam ready *-> hi from client@agneyam
|erlc client.erl |erl -run client start -run init stop -noshell -server srv@agneyam connecting to "srv@agneyam" Received hi
Factor
The protocol is the one provided by Factor (concurrency.distributed, concurrency.messaging)
Example summary:
- A server node is listening for messages made of natural data types and structures, and simply prettyprint them.
- A client node is sending such data structure: an array of one string and one hashtable (with one key/value pair).
Server
USING: concurrency.distributed concurrency.messaging threads io.sockets io.servers ;
QUALIFIED: concurrency.messaging
: prettyprint-message ( -- ) concurrency.messaging:receive . flush prettyprint-message ;
[ prettyprint-message ] "logger" spawn dup name>> register-remote-thread
"127.0.0.1" 9000 <inet4> <node-server> start-server
Note: we are using QUALIFIED: with the concurrency.messaging vocabulary because the "receive" word is defined in io.sockets vocabulary too. If someone have a cleaner way to handle this.
Client
USING: concurrency.distributed io.sockets ;
QUALIFIED: concurrency.messaging
{ "Hello Remote Factor!" H{ { "key1" "value1" } } }
"127.0.0.1" 9000 <inet4> "logger" <remote-thread> concurrency.messaging:send
How to Run:
- Copy/Paste the server code in an instance of Factor Listener
- Copy/Paste the client code in another instance of Factor Listener.
The server node should prettyprint the data structure send by the client: { "Hello Remote Factor!" H{ { "key1" "value1" } } }
FreeBASIC
Server
#include "win/winsock2.bi"
Const PORT = 12345
Sub initialize_winsock()
Dim wsadata As WSADATA
If WSAStartup(&h0202, @wsadata) <> 0 Then
Print "WSAStartup failed"
End 1
End If
End Sub
Sub cleanup_winsock()
WSACleanup()
End Sub
Sub handle_client(client_socket As SOCKET)
Dim buffer As zstring * 1024
Dim bytes_received As Integer
Do
bytes_received = recv(client_socket, @buffer, Sizeof(buffer), 0)
If bytes_received <= 0 Then Exit Do
Print "Received: "; buffer
send(client_socket, @buffer, bytes_received, 0)
Loop
closesocket(client_socket)
End Sub
initialize_winsock()
Dim server_socket As SOCKET
server_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)
If server_socket = INVALID_SOCKET Then
Print "Socket creation failed"
cleanup_winsock()
End 1
End If
Dim server_addr As sockaddr_in
server_addr.sin_family = AF_INET
server_addr.sin_port = htons(PORT)
server_addr.sin_addr.S_addr = INADDR_ANY
If bind(server_socket, Cast(sockaddr Ptr, @server_addr), Sizeof(server_addr)) = SOCKET_ERROR Then
Print "Bind failed"
closesocket(server_socket)
cleanup_winsock()
End 1
End If
If listen(server_socket, SOMAXCONN) = SOCKET_ERROR Then
Print "Listen failed"
closesocket(server_socket)
cleanup_winsock()
End 1
End If
Print "Server listening on port "; PORT
Do
Dim client_socket As SOCKET
client_socket = accept(server_socket, NULL, NULL)
If client_socket = INVALID_SOCKET Then
Print "Accept failed"
closesocket(server_socket)
cleanup_winsock()
End 1
End If
handle_client(client_socket)
Loop
closesocket(server_socket)
cleanup_winsock()
Client
#include "win/winsock2.bi"
Const SERVER_IP = "127.0.0.1"
Const PORT = 12345
Sub initialize_winsock()
Dim wsadata As WSADATA
If WSAStartup(&h0202, @wsadata) <> 0 Then
Print "WSAStartup failed"
End 1
End If
End Sub
Sub cleanup_winsock()
WSACleanup()
End Sub
initialize_winsock()
Dim client_socket As SOCKET
client_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)
If client_socket = INVALID_SOCKET Then
Print "Socket creation failed"
cleanup_winsock()
End 1
End If
Dim server_addr As sockaddr_in
server_addr.sin_family = AF_INET
server_addr.sin_port = htons(PORT)
server_addr.sin_addr.S_addr = inet_addr(SERVER_IP)
If connect(client_socket, Cast(sockaddr Ptr, @server_addr), Sizeof(server_addr)) = SOCKET_ERROR Then
Print "Connect failed"
closesocket(client_socket)
cleanup_winsock()
End 1
End If
Dim buffer As zstring * 1024
Do
Print "Enter message: ";
Input "", buffer
send(client_socket, @buffer, Len(buffer), 0)
Dim bytes_received As Integer
bytes_received = recv(client_socket, @buffer, Sizeof(buffer), 0)
If bytes_received <= 0 Then Exit Do
Print "Received: "; buffer
Loop
closesocket(client_socket)
cleanup_winsock()
Go
Standard library net/rpc
Package net/rpc in the Go standard library serializes data with the Go-native "gob" type. The example here sends only a single floating point number, but the package will send any user-defined data type, including of course structs with multiple fields.
Server:
package main
import (
"errors"
"log"
"net"
"net/http"
"net/rpc"
)
type TaxComputer float64
func (taxRate TaxComputer) Tax(x float64, r *float64) error {
if x < 0 {
return errors.New("Negative values not allowed")
}
*r = x * float64(taxRate)
return nil
}
func main() {
c := TaxComputer(.05)
rpc.Register(c)
rpc.HandleHTTP()
listener, err := net.Listen("tcp", ":1234")
if err != nil {
log.Fatal(err)
}
http.Serve(listener, nil)
}
Client:
package main
import (
"fmt"
"log"
"net/rpc"
)
func main() {
client, err := rpc.DialHTTP("tcp", "localhost:1234")
if err != nil {
fmt.Println(err)
return
}
amount := 3.
var tax float64
err = client.Call("TaxComputer.Tax", amount, &tax)
if err != nil {
log.Fatal(err)
}
fmt.Printf("Tax on %.2f: %.2f\n", amount, tax)
}
- Client output:
Tax on 3.00: 0.15
gRPC
The default serialization for gRPC is "protocol buffers." gRPC uses a .proto file to define an interface for the client and server. The .proto has its own syntax, independent of client and server implementation languages. Server and client programs here are Go however.
.proto:
syntax = "proto3";
service TaxComputer {
rpc Tax(Amount) returns (Amount) {}
}
message Amount {
int32 cents = 1;
}
Server:
package main
import (
"errors"
"net"
"golang.org/x/net/context"
"google.golang.org/grpc"
"google.golang.org/grpc/grpclog"
"taxcomputer"
)
type taxServer struct {
rate float64
}
func (s *taxServer) Tax(ctx context.Context,
amt *taxcomputer.Amount) (*taxcomputer.Amount, error) {
if amt.Cents < 0 {
return nil, errors.New("Negative amounts not allowed")
}
return &taxcomputer.Amount{int32(float64(amt.Cents)*s.rate + .5)}, nil
}
func main() {
listener, err := net.Listen("tcp", ":1234")
if err != nil {
grpclog.Fatalf(err.Error())
}
grpcServer := grpc.NewServer()
taxcomputer.RegisterTaxComputerServer(grpcServer, &taxServer{.05})
grpcServer.Serve(listener)
}
Client:
package main
import (
"fmt"
"golang.org/x/net/context"
"google.golang.org/grpc"
"google.golang.org/grpc/grpclog"
"taxcomputer"
)
func main() {
conn, err := grpc.Dial("localhost:1234", grpc.WithInsecure())
if err != nil {
grpclog.Fatalf(err.Error())
}
defer conn.Close()
client := taxcomputer.NewTaxComputerClient(conn)
amt := &taxcomputer.Amount{300}
tax, err := client.Tax(context.Background(), amt)
if err != nil {
grpclog.Fatalf(err.Error())
}
fmt.Println("Tax on", amt.Cents, "cents is", tax.Cents, "cents")
}
- Client output:
Tax on 300 cents is 15 cents
Apache Thrift
See https://thrift.apache.org/
.thrift
Like gRPC, Thrift requires a language independent interface definition file:
service TaxService {
i32 tax(1: i32 amt)
}
Server:
package main
import (
"errors"
"log"
"git.apache.org/thrift.git/lib/go/thrift"
"gen-go/tax"
)
type taxHandler float64
func (r taxHandler) Tax(amt int32) (int32, error) {
if amt < 0 {
return 0, errors.New("Negative amounts not allowed")
}
return int32(float64(amt)*float64(r) + .5), nil
}
func main() {
transport, err := thrift.NewTServerSocket("localhost:3141")
if err != nil {
log.Fatal(err)
}
transFac := thrift.NewTTransportFactory()
protoFac := thrift.NewTCompactProtocolFactory()
proc := tax.NewTaxServiceProcessor(taxHandler(.05))
s := thrift.NewTSimpleServer4(proc, transport, transFac, protoFac)
if err := s.Serve(); err != nil {
log.Fatal(err)
}
}
Client:
package main
import (
"fmt"
"log"
"git.apache.org/thrift.git/lib/go/thrift"
"gen-go/tax"
)
func main() {
transport, err := thrift.NewTSocket("localhost:3141")
if err != nil {
log.Fatal(err)
}
if err := transport.Open(); err != nil {
log.Fatal(err)
}
protoFac := thrift.NewTCompactProtocolFactory()
client := tax.NewTaxServiceClientFactory(transport, protoFac)
amt := int32(300)
t, err := client.Tax(amt)
if err != nil {
log.Print(err)
} else {
fmt.Println("tax on", amt, "is", t)
}
transport.Close()
}
- Client output:
tax on 300 is 15
Haskell
See:
Check license: http://www.haskell.org/haskellwiki/HaskellWiki:Copyrights
JavaScript
Server
var net = require('net')
var server = net.createServer(function (c){
c.write('hello\r\n')
c.pipe(c) // echo messages back
})
server.listen(3000, 'localhost')
Client
var net = require('net')
conn = net.createConnection(3000, '192.168.1.x')
conn.on('connect', function(){
console.log('connected')
conn.write('test')
})
conn.on('data', function(msg){
console.log(msg.toString())
})
Julia
Julia was designed with distributed conmputing. in particular cluster computing, as a primary use target. If a group of CPUs, including multiple cores on a single machine or a cluster running with paswordless ssh login, is used, the following can be set up as an example:
# From Julia 1.0's online docs. File countheads.jl available to all machines:
function count_heads(n)
c::Int = 0
for i = 1:n
c += rand(Bool)
end
c
end
We then run the following on the primary client:
using Distributed
@everywhere include_string(Main, $(read("count_heads.jl", String)), "count_heads.jl")
a = @spawn count_heads(100000000) # runs on an available processor
b = @spawn count_heads(100000000) # runs on another available processor
println(fetch(a)+fetch(b)) # total heads of 200 million coin flips, half on each CPU
- Output:
100001564
LFE
The protocol used is the one native to Erlang (and thus native to LFE, Lisp Flavored Erlang).
These examples are done completely in the LFE REPL.
Server
In one terminal window, start up the REPL
$ ./bin/lfe
Erlang/OTP 17 [erts-6.2] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]
LFE Shell V6.2 (abort with ^G)
>
And then enter the following code
> (defun get-server-name ()
(list_to_atom (++ "exampleserver@" (element 2 (inet:gethostname)))))
> (defun start ()
(net_kernel:start `(,(get-server-name) shortnames))
(erlang:set_cookie (node) 'rosettaexample)
(let ((pid (spawn #'listen/0)))
(register 'serverref pid)
(io:format "~p ready~n" (list (node pid)))
'ok))
> (defun listen ()
(receive
(`#(echo ,pid ,data)
(io:format "Got ~p from ~p~n" (list data (node pid)))
(! pid `#(hello ,data))
(listen))
(x
(io:format "Unexpected pattern: ~p~n" `(,x)))))
Client
In another terminal window, start up another LFE REPL and ender the following code:
> (defun get-server-name ()
(list_to_atom (++ "exampleserver@" (element 2 (inet:gethostname)))))
> (defun send (data)
(net_kernel:start '(exampleclient shortnames))
(erlang:set_cookie (node) 'rosettaexample)
(io:format "connecting to ~p~n" `(,(get-server-name)))
(! `#(serverref ,(get-server-name)) `#(echo ,(self) ,data))
(receive
(`#(hello ,data)
(io:format "Received ~p~n" `(,data)))
(x
(io:format "Unexpected pattern: ~p~n" (list x))))
'ok)
To use this code, simply start the server in the server terminal:
> (start)
exampleserver@yourhostname ready
ok
(exampleserver@yourhostname)>
Send some messages from the client terminal:
> (send "hi there")
connecting to exampleserver@yourhostname
Received "hi there"
ok
(exampleclient@yourhostname)> (send 42)
connecting to exampleserver@yourhostname
Received 42
ok
(exampleclient@yourhostname)> (send #(key value))
connecting to exampleserver@yourhostname
Received {key,value}
ok
(exampleclient@yourhostname)>
And check out the results back in the server terminal window:
Got "hi there" from exampleclient@yourhostname
Got 42 from exampleclient@yourhostname
Got {key,value} from exampleclient@yourhostname
Mathematica / Wolfram Language
The following sends a request for a random number to be generated on each of two nodes, these are then transmitted back to be assembled into an array with two elements. Omitting the first line, will cause the program to be run on all configured remote computers.
LaunchKernels[2];
ParallelEvaluate[RandomReal[]]
Nim
import os, nanomsg
proc sendMsg(s: cint, msg: string) =
echo "SENDING \"",msg,"\""
let bytes = s.send(msg.cstring, msg.len + 1, 0)
assert bytes == msg.len + 1
proc recvMsg(s: cint) =
var buf: cstring
let bytes = s.recv(addr buf, MSG, 0)
if bytes > 0:
echo "RECEIVED \"",buf,"\""
discard freemsg buf
proc sendRecv(s: cint, msg: string) =
var to: cint = 100
discard s.setSockOpt(SOL_SOCKET, RCVTIMEO, addr to, sizeof to)
while true:
s.recvMsg
sleep 1000
s.sendMsg msg
proc node0(url: string) =
var s = socket(AF_SP, nanomsg.PAIR)
assert s >= 0
let res = s.bindd url
assert res >= 0
s.sendRecv "node0"
discard s.shutdown 0
proc node1(url: string) =
var s = socket(AF_SP, nanomsg.PAIR)
assert s >= 0
let res = s.connect url
assert res >= 0
s.sendRecv "node1"
discard s.shutdown 0
if paramStr(1) == "node0":
node0 paramStr(2)
elif paramStr(1) == "node1":
node1 paramStr(2)
Usage:
./pair node0 tcp://127.0.0.1:25000 ./pair node1 tcp://127.0.0.1:25000
Objective-C
Distributed Objects are natural to Objective-C, and OpenStep and derivated framework offers an easy way of using remote objects as if it were local. The client must only know the protocol the remote object support. For the rest, calling a remote object's method or local object's method is transparent.
Server
The server vending the object with the name DistributedAction
ActionObjectProtocol.h
#import <Foundation/Foundation.h>
// our protocol allows "sending" "strings", but we can implement
// everything we could for a "local" object
@protocol ActionObjectProtocol
- (NSString *)sendMessage: (NSString *)msg;
@end
ActionObject.h
#import <Foundation/Foundation.h>
#import "ActionObjectProtocol.h"
@interface ActionObject : NSObject <ActionObjectProtocol>
// we do not have much for this example!
@end
ActionObject.m
#import <Foundation/Foundation.h>
#import "ActionObject.h"
@implementation ActionObject
-(NSString *)sendMessage: (NSString *)msg
{
NSLog(@"client sending message %@", msg);
return @"server answers ...";
}
@end
server.m
#import <Foundation/Foundation.h>
#import "ActionObject.h"
int main (void)
{
@autoreleasepool {
ActionObject *action = [[ActionObject alloc] init];
NSSocketPort *port = (NSSocketPort *)[NSSocketPort port];
// initWithTCPPort: 1234 and other methods are not supported yet
// by GNUstep
NSConnection *connect = [NSConnection
connectionWithReceivePort: port
sendPort: port]; // or sendPort: nil
[connect setRootObject: action];
/* "vend" the object ActionObject as DistributedAction; on GNUstep
the Name Server that allows the resolution of the registered name
is bound to port 538 */
if (![connect registerName:@"DistributedAction"
withNameServer: [NSSocketPortNameServer sharedInstance] ])
{
NSLog(@"can't register the server DistributedAction");
exit(EXIT_FAILURE);
}
NSLog(@"waiting for messages...");
[[NSRunLoop currentRunLoop] run];
}
return 0;
}
Client
client.m
#import <Foundation/Foundation.h>
#import "ActionObjectProtocol.h"
int main(void)
{
@autoreleasepool {
id <ActionObjectProtocol> action = (id <ActionObjectProtocol>)
[NSConnection
rootProxyForConnectionWithRegisteredName: @"DistributedAction"
host: @"localhost"
usingNameServer: [NSSocketPortNameServer sharedInstance] ];
if (action == nil)
{
NSLog(@"can't connect to the server");
exit(EXIT_FAILURE);
}
NSArray *args = [[NSProcessInfo processInfo] arguments];
if ([args count] == 1)
{
NSLog(@"specify a message");
exit(EXIT_FAILURE);
}
NSString *msg = args[1];
// "send" (call the selector "sendMessage:" of the (remote) object
// action) the first argument's text as msg, store the message "sent
// back" and then show it in the log
NSString *backmsg = [action sendMessage: msg];
NSLog("%@", backmsg);
}
return 0;
}
OCaml
Minimalistic distributed logger with synchronous channels using the join calculus on top of OCaml.
Server
open Printf
let create_logger () =
def log(text) & logs(l) =
printf "Logged: %s\n%!" text;
logs((text, Unix.gettimeofday ())::l) & reply to log
or search(text) & logs(l) =
logs(l) & reply List.filter (fun (line, _) -> line = text) l to search
in
spawn logs([]);
(log, search)
def wait() & finished() = reply to wait
let register name service = Join.Ns.register Join.Ns.here name service
let () =
let log, search = create_logger () in
register "log" log;
register "search" search;
Join.Site.listen (Unix.ADDR_INET (Join.Site.get_local_addr(), 12345));
wait ()
Client
open Printf
let ns_there = Join.Ns.there (Unix.ADDR_INET (Join.Site.get_local_addr(), 12345))
let lookup name = Join.Ns.lookup ns_there name
let log : string -> unit = lookup "log"
let search : string -> (string * float) list = lookup "search"
let find txt =
printf "Looking for %s...\n" txt;
List.iter (fun (line, time) ->
printf "Found: '%s' at t = %f\n%!" (String.escaped line) time)
(search txt)
let () =
log "bar";
find "foo";
log "foo";
log "shoe";
find "foo"
Oz
We show a program that starts a server on a remote machine, exchanges two messages with that server and finally shuts it down.
declare
functor ServerCode
export
port:Prt
define
Stream
Prt = {NewPort ?Stream}
thread
for Request#Reply in Stream do
case Request
of echo(Data) then Reply = Data
[] compute(Function) then Reply = {Function}
end
end
end
end
%% create the server on some machine
%% (just change "localhost" to some machine
%% that you can use with a passwordless rsh login
%% and that has the same Mozart version installed)
RM = {New Remote.manager init(host:localhost)}
%% execute the code encapsulated in the ServerCode functor
Server = {RM apply(ServerCode $)}
%% Shortcut: send a message to Server and receive a reply
fun {Send X}
{Port.sendRecv Server.port X}
end
in
%% echo
{System.showInfo "Echo reply: "#{Send echo(hello)}}
%% compute
{System.showInfo "Result of computation: "#
{Send compute(fun {$} 8 div 4 end)}}
%% shut down server
{RM close}Perl
Using Data::Dumper and Safe to transmit arbitrary data structures as serialized text between hosts. Same code works as both sender and receiver.
use strict;
use warnings;
use Data::Dumper;
use IO::Socket::INET;
use Safe;
sub get_data {
my $sock = IO::Socket::INET->new(
LocalHost => "localhost",
LocalPort => "10000",
Proto => "tcp",
Listen => 1,
Reuse => 1);
unless ($sock) { die "Socket creation failure" }
my $cli = $sock->accept();
# of course someone may be tempted to send you 'system("rm -rf /")',
# to be safe(r), use Safe::
my $safe = Safe->new;
my $x = $safe->reval(join("", <$cli>));
close $cli;
close $sock;
return $x;
}
sub send_data {
my $host = shift;
my $data = shift;
my $sock = IO::Socket::INET->new(
PeerAddr => "$host:10000",
Proto => "tcp",
Reuse => 1);
unless ($sock) { die "Socket creation failure" }
print $sock Data::Dumper->Dump([$data]);
close $sock;
}
if (@ARGV) {
my $x = get_data();
print "Got data\n", Data::Dumper->Dump([$x]);
} else {
send_data('some_host', { a=>100, b=>[1 .. 10] });
}
Phix
From/using the ZeroMQ wrapper from PCAN, a suitable simple publish/subscriber pair. There is also a server/client/broker example. Obviously you can trivially serialize() and deserialize() any Phix data to and from a string.
without js -- (zmq dll/so) puts(1, "durapub:\n") include zmq/zmq.e atom context = zmq_init(1) zmq_assert(context, "zmq_init") --// subscriber tells us when it's ready here atom sync = zmq_socket(context, ZMQ_PULL) zmq_bind(sync, "tcp://*:5564") --// send update via this socket atom publisher = zmq_socket(context, ZMQ_PUB) zmq_bind(publisher, "tcp://*:5565") --// broadcast 10 updates, with pause for update_nbr = 1 to 10 do string s = sprintf("Update %d", { update_nbr }) zmq_s_send(publisher, s) sleep(1) end for zmq_s_send(publisher, "END") sleep(1) zmq_close(sync) zmq_close(publisher) zmq_term(context)
without js -- (zmq dll/so) puts(1, "durasub:\n") include zmq/zmq.e atom context = zmq_init(1) zmq_assert(context, "zmq_init") --// connect our subscriber socket atom subscriber = zmq_socket(context, ZMQ_SUB) atom id = allocate_string("Hello") zmq_setsockopt(subscriber, ZMQ_IDENTITY, id, 5) zmq_setsockopt(subscriber, ZMQ_SUBSCRIBE, 0, 0) zmq_connect(subscriber, "tcp://localhost:5565") free(id) --// synchronise with publisher atom sync = zmq_socket(context, ZMQ_PUSH) zmq_connect(sync, "tcp://localhost:5564") zmq_s_send(sync, "") --// get updates, Ctrl-C break while true do string s = zmq_s_recv(subscriber) printf(1, "%s\n", {s}) if s=="END" then exit end if end while zmq_close(sync) zmq_close(subscriber) zmq_term(context)
PicoLisp
Server
(task (port 12321) # Background server task
(let? Sock (accept @)
(unless (fork) # Handle request in child process
(in Sock
(while (rd) # Handle requests
(out Sock
(pr (eval @)) ) ) ) # Evaluate and send reply
(bye) ) # Exit child process
(close Sock) ) ) # Close socket in parent processClient
(let? Sock (connect "localhost" 12321)
(out Sock (pr '*Pid)) # Query PID from server
(println 'PID (in Sock (rd))) # Receive and print reply
(out Sock (pr '(* 3 4))) # Request some calculation
(println 'Result (in Sock (rd))) # Print result
(close Sock) ) # Close connection to serverOutput:
PID 18372 Result 12
Python
XML-RPC
Protocol: XML-RPC
Server
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import SimpleXMLRPCServer
class MyHandlerInstance:
def echo(self, data):
'''Method for returning data got from client'''
return 'Server responded: %s' % data
def div(self, num1, num2):
'''Method for divide 2 numbers'''
return num1/num2
def foo_function():
'''A function (not an instance method)'''
return True
HOST = "localhost"
PORT = 8000
server = SimpleXMLRPCServer.SimpleXMLRPCServer((HOST, PORT))
# register built-in system.* functions.
server.register_introspection_functions()
# register our instance
server.register_instance(MyHandlerInstance())
# register our function as well
server.register_function(foo_function)
try:
# serve forever
server.serve_forever()
except KeyboardInterrupt:
print 'Exiting...'
server.server_close()
Client
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import xmlrpclib
HOST = "localhost"
PORT = 8000
rpc = xmlrpclib.ServerProxy("http://%s:%d" % (HOST, PORT))
# print what functions does server support
print 'Server supports these functions:',
print ' '.join(rpc.system.listMethods())
# echo something
rpc.echo("We sent this data to server")
# div numbers
print 'Server says: 8 / 4 is: %d' % rpc.div(8, 4)
# control if foo_function returns True
if rpc.foo_function():
print 'Server says: foo_function returned True'
HTTP
Protocol: HTTP
Server
#!/usr/bin/python
# -*- coding: utf-8 -*-
import BaseHTTPServer
HOST = "localhost"
PORT = 8000
# we just want to write own class, we replace do_GET method. This could be extended, I just added basics
# see; http://docs.python.org/lib/module-BaseHTTPServer.html
class MyHTTPHandler(BaseHTTPServer.BaseHTTPRequestHandler):
def do_GET(self):
# send 200 (OK) message
self.send_response(200)
# send header
self.send_header("Content-type", "text/html")
self.end_headers()
# send context
self.wfile.write("<html><head><title>Our Web Title</title></head>")
self.wfile.write("<body><p>This is our body. You wanted to visit <b>%s</b> page</p></body>" % self.path)
self.wfile.write("</html>")
if __name__ == '__main__':
server = BaseHTTPServer.HTTPServer((HOST, PORT), MyHTTPHandler)
try:
server.serve_forever()
except KeyboardInterrupt:
print 'Exiting...'
server.server_close()
Client
#!/usr/bin/python
# -*- coding: utf-8 -*-
import httplib
HOST = "localhost"
PORT = 8000
conn = httplib.HTTPConnection(HOST, PORT)
conn.request("GET", "/somefile")
response = conn.getresponse()
print 'Server Status: %d' % response.status
print 'Server Message: %s' % response.read()
Socket, Pickle format
Protocol: raw socket / pickle format
This example builds a very basic RPC mechanism on top of sockets and the pickle module. Please note that the pickle module is not secure - a malicious client can build malformed data to execute arbitrary code on the server. If untrusted clients can access the server, the json module could be used as a substitute, but we lose the ability to transfer arbitrary Python objects that way.
Server
#!/usr/bin/python
# -*- coding: utf-8 -*-
import SocketServer
import pickle
HOST = "localhost"
PORT = 8000
class RPCServer(SocketServer.ThreadingMixIn, SocketServer.TCPServer):
# The object_to_proxy member should be set to the object we want
# methods called on. Unfortunately, we can't do this in the constructor
# because the constructor should not be overridden in TCPServer...
daemon_threads = True
class RPCHandler(SocketServer.StreamRequestHandler):
def handle(self):
in_channel = pickle.Unpickler(self.rfile)
out_channel = pickle.Pickler(self.wfile, protocol=2)
while True:
try:
name, args, kwargs = in_channel.load()
print 'got %s %s %s' % (name, args, kwargs)
except EOFError:
# EOF means we're done with this request.
# Catching this exception to detect EOF is a bit hackish,
# but will work for a quick demo like this
break
try:
method = getattr(self.server.object_to_proxy, name)
result = method(*args, **kwargs)
except Exception, e:
out_channel.dump(('Error',e))
else:
out_channel.dump(('OK',result))
class MyHandlerInstance(object):
def echo(self, data):
'''Method for returning data got from client'''
return 'Server responded: %s' % data
def div(self, dividend, divisor):
'''Method to divide 2 numbers'''
return dividend/divisor
def is_computer_on(self):
return True
if __name__ == '__main__':
rpcserver = RPCServer((HOST, PORT), RPCHandler)
rpcserver.object_to_proxy = MyHandlerInstance()
try:
rpcserver.serve_forever()
except KeyboardInterrupt:
print 'Exiting...'
rpcserver.server_close()
Client
#!/usr/bin/python
# -*- coding: utf-8 -*-
import socket
import pickle
HOST = "localhost"
PORT = 8000
class RPCClient(object):
def __init__(self, host, port):
self.socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
self.socket.connect((host, port))
self.rfile = self.socket.makefile('rb')
self.wfile = self.socket.makefile('wb')
self.in_channel = pickle.Unpickler(self.rfile)
self.out_channel = pickle.Pickler(self.wfile, protocol=2)
def _close(self):
self.socket.close()
self.rfile.close()
self.wfile.close()
# Make calling remote methods easy by overriding attribute access.
# Accessing any attribute on our instances will give a proxy method that
# calls the method with the same name on the remote machine.
def __getattr__(self, name):
def proxy(*args, **kwargs):
self.out_channel.dump((name, args, kwargs))
self.wfile.flush() # to make sure the server won't wait forever
status, result = self.in_channel.load()
if status == 'OK':
return result
else:
raise result
return proxy
if __name__ == '__main__':
# connect to server and send data
rpcclient = RPCClient(HOST, PORT)
print 'Testing the echo() method:'
print rpcclient.echo('Hello world!')
print
print 'Calculating 42/2 on the remote machine:'
print rpcclient.div(42, 2)
print
print 'is_computer_on on the remote machine returns:'
print rpcclient.is_computer_on()
print
print 'Testing keyword args:'
print '42/2 is:', rpcclient.div(divisor=2, dividend=42)
rpcclient._close()
del rpcclient
Pyro
Note: You should install Pyro (http://pyro.sourceforge.net) first and run pyro-ns binary to run code below.
Server
#!/usr/bin/python
# -*- coding: utf-8 -*-
import Pyro.core
import Pyro.naming
# create instance that will return upper case
class StringInstance(Pyro.core.ObjBase):
def makeUpper(self, data):
return data.upper()
class MathInstance(Pyro.core.ObjBase):
def div(self, num1, num2):
return num1/num2
if __name__ == '__main__':
server = Pyro.core.Daemon()
name_server = Pyro.naming.NameServerLocator().getNS()
server.useNameServer(name_server)
server.connect(StringInstance(), 'string')
server.connect(MathInstance(), 'math')
try:
server.requestLoop()
except KeyboardInterrupt:
print 'Exiting...'
server.shutdown()
Client
#!/usr/bin/python
# -*- coding: utf-8 -*-
import Pyro.core
DATA = "my name is eren"
NUM1 = 10
NUM2 = 5
string = Pyro.core.getProxyForURI("PYRONAME://string")
math = Pyro.core.getProxyForURI("PYRONAME://math")
print 'We sent: %s' % DATA
print 'Server responded: %s\n' % string.makeUpper(DATA)
print 'We sent two numbers to divide: %d and %d' % (NUM1, NUM2)
print 'Server responded the result: %s' % math.div(NUM1, NUM2)
Spread
Note: You should install Spread (http://www.spread.org) and its python bindings (http://www.python.org/other/spread/)
Server
You don't need any code for server. You should start "spread" daemon by typing "spread -c /etc/spread.conf -n localhost". If you want more configuration, look at /etc/spread.conf.
After starting daemon, if you want to make sure that it is running, enter spuser -s 4803 command where 4803 is your port set in spread.conf, you will see prompt, type j user, you should see something like this message: Received REGULAR membership for group test with 3 members, where I am member 2
Client (Listener)
#!/usr/bin/python
# -*- coding: utf-8 -*-
import spread
PORT = '4803'
# connect spread daemon
conn = spread.connect(PORT)
# join the room
conn.join('test')
print 'Waiting for messages... If you want to stop this script, please stop spread daemon'
while True:
recv = conn.receive()
if hasattr(recv, 'sender') and hasattr(recv, 'message'):
print 'Sender: %s' % recv.sender
print 'Message: %s' % recv.message
Client (Sender)
#!/usr/bin/python
# -*- coding: utf-8 -*-
import spread
PORT = '4803'
conn = spread.connect(PORT)
conn.join('test')
conn.multicast(spread.RELIABLE_MESS, 'test', 'hello, this is message sent from python')
conn.disconnect()
Racket
Server and client in the same piece of code, running a useless (fib 42) computation, four times, on four hosts (which all happen to be "localhost", but that can change, of course).
#lang racket/base
(require racket/place/distributed racket/place)
(define (fib n)
(if (<= n 1) n (+ (fib (- n 1)) (fib (- n 2)))))
(provide work)
(define (work)
(place ch
(place-channel-put ch (fib (place-channel-get ch)))))
(module+ main
(define places
(for/list ([host '("localhost" "localhost" "localhost" "localhost")]
[port (in-naturals 12345)])
(define-values [node place]
(spawn-node-supervise-place-at host #:listen-port port #:thunk #t
(quote-module-path "..") 'work))
place))
(message-router
(after-seconds 1
(for ([p places]) (*channel-put p 42))
(printf "Results: ~s\n" (map *channel-get places))
(exit))))
Raku
(formerly Perl 6)
Server listens for JSON encoded messages. It processes requests for set|get|dump. 'set' stores a message, 'get' returns message, 'dump' returns all stored messages. Optional parameters for ip address and port.
Server.raku:
./server.raku --usage Usage: server.p6 [--server=<Any>] [--port=<Any>]
#!/usr/bin/env raku
use JSON::Fast ;
sub MAIN( :$server='0.0.0.0' , :$port=3333 ) {
my %db ;
react {
whenever IO::Socket::Async.listen( $server , $port ) -> $conn {
whenever $conn.Supply.lines -> $line {
my %response = 'status' => '' ;
my $msg = from-json $line ;
say $msg.raku;
given $msg{"function"} {
when 'set' {
%db{ $msg<topic> } = $msg<message> ;
%response<status> = 'ok' ;
}
when 'get' {
%response<topic> = $msg<topic> ;
%response<message> = %db{ $msg<topic> } ;
%response<status> = 'ok' ;
}
when 'dump' {
%response = %db ;
}
when 'delete' {
%db{ $msg<topic> }:delete;
%response<status> = 'ok' ;
}
}
$conn.print( to-json(%response, :!pretty) ~ "\n" ) ;
LAST { $conn.close ; }
QUIT { default { $conn.close ; say "oh no, $_";}}
CATCH { default { say .^name, ': ', .Str , " handled in $?LINE";}}
}
}
}
}
client.raku:
Usage: client.raku [--server=<Any>] [--port=<Any>] [--json=<Any>] set <topic> [<message>] client.raku [--server=<Any>] [--port=<Any>] get <topic> client.raku [--server=<Any>] [--port=<Any>] dump
#!/usr/bin/env raku
use JSON::Fast ;
multi MAIN('set', $topic, $message='', :$server='localhost', :$port='3333', :$json='') {
my %msg = function => 'set' , topic=> $topic , message=> $message ;
%msg{"message"} = from-json( $json ) if $json ;
sendmsg( %msg , $server, $port) ;
}
multi MAIN('get', $topic, :$server='localhost', :$port='3333') {
my %msg = function => 'get' , topic=> $topic ;
sendmsg( %msg , $server, $port) ;
}
multi MAIN('delete', $topic, :$server='localhost', :$port='3333') {
my %msg = function => 'delete' , topic=> $topic ;
sendmsg( %msg , $server, $port) ;
}
multi MAIN('dump', :$server='localhost', :$port='3333') {
my %msg = function => 'dump' ;
sendmsg( %msg , $server, $port) ;
}
sub sendmsg( %msg , $server, $port){
my $conn = await IO::Socket::Async.connect( $server , $port );
$conn.print: to-json( %msg,:!pretty)~"\n";
react {
whenever $conn.Supply -> $data {
print $data;
$conn.close;
}
}
}
examples:
echo '{"function":"set","topic":"push","message":["perl5","raku","rakudo"]}' | nc localhost 3333
./client.raku set version raku
{"status": "ok"}
./client.raku get version
{"status": "ok","topic": "version","message": "raku"}
./client.raku --json='["one","two","three"]' set mylist
{"status": "ok"}
./client.raku dump
{"push": ["perl5","raku","rakudo"],"version": "raku","mylist": ["one","two","three"]}
./client.raku delete version
{"status": "ok"}
server output:
${:function("set"), :message($["perl5", "raku", "rakudo"]), :topic("push")}
${:function("set"), :message("raku"), :topic("version")}
${:function("get"), :topic("version")}
${:function("set"), :message($["one", "two", "three"]), :topic("mylist")}
${:function("dump")}
${:function("delete"), :topic("version")}
Ruby
Uses the distributed Ruby (dRuby) from the standard library. The "druby:" protocol uses TCP/IP sockets for communication.
Server
require 'drb/drb'
# The URI for the server to connect to
URI="druby://localhost:8787"
class TimeServer
def get_current_time
return Time.now
end
end
# The object that handles requests on the server
FRONT_OBJECT = TimeServer.new
$SAFE = 1 # disable eval() and friends
DRb.start_service(URI, FRONT_OBJECT)
# Wait for the drb server thread to finish before exiting.
DRb.thread.join
Client
require 'drb/drb'
# The URI to connect to
SERVER_URI = "druby://localhost:8787"
# Start a local DRbServer to handle callbacks.
#
# Not necessary for this small example, but will be required
# as soon as we pass a non-marshallable object as an argument
# to a dRuby call.
DRb.start_service
timeserver = DRbObject.new_with_uri(SERVER_URI)
puts timeserver.get_current_time
Tcl
A rudimentary IRC Server
proc main {} {
global connections
set connections [dict create]
socket -server handleConnection 12345
vwait dummyVar ;# enter the event loop
}
proc handleConnection {channel clientaddr clientport} {
global connections
dict set connections $channel address "$clientaddr:$clientport"
fconfigure $channel -buffering line
fileevent $channel readable [list handleMessage $channel]
}
proc handleMessage {channel} {
global connections
if {[gets $channel line] == -1} {
disconnect $channel
} else {
if {[string index [string trimleft $line] 0] eq "/"} {
set words [lassign [split [string trim $line]] command]
handleCommand $command $words $channel
} else {
echo $line $channel
}
}
}
proc disconnect {channel} {
global connections
dict unset connections $channel
fileevent $channel readable ""
close $channel
}
proc handleCommand {command words channel} {
global connections
switch -exact -- [string tolower $command] {
/nick {
dict set connections $channel nick [lindex $words 0]
}
/quit {
echo bye $channel
disconnect $channel
}
default {
puts $channel "\"$command\" not implemented"
}
}
}
proc echo {message senderchannel} {
global connections
foreach channel [dict keys $connections] {
if {$channel ne $senderchannel} {
set time [clock format [clock seconds] -format "%T"]
set nick [dict get $connections $channel nick]
puts $channel [format "\[%s\] %s: %s" $time $nick $message]
}
}
}
main
Client
proc main {} {
global argv argc
if {$argc != 2} {
error "usage: [info script] serveraddress serverport"
}
connect {*}$argv
vwait dummyVar
}
proc connect {addr port} {
global sock
set sock [socket $addr $port]
fconfigure $sock -buffering line
fileevent $sock readable getFromServer
fileevent stdin readable sendToServer
}
proc getFromServer {} {
global sock
if {[gets $sock line] == -1} {
puts "disconnected..."
exit
} else {
puts $line
}
}
proc sendToServer {} {
global sock
set msg [string trim [gets stdin]]
if {[string length $msg] > 0} {
puts $sock $msg
}
}
main
UnixPipes
Uses netcat and a buffer to cycle the server shell's stdout back to netcat's stdin.
Server
: >/tmp/buffer
tail -f /tmp/buffer | nc -l 127.0.0.1 1234 | sh >/tmp/buffer 2>&1
Limitations:
- The server can accept only one connection (but continues to run, not exit, after this connection dies).
- With some systems,
tail -fmight be slow to notice changes to /tmp/buffer.
Client
nc 127.0.0.1 1234
Now you can enter commands in the client terminal and get the output back through the same connection.
Wren
As Wren has no networking support at present, we use embedded programs for both the server and client with a Go host using the net/rpc package in its standard library.
Moreover, as Wren's VM is not re-entrant, we need to run two VMs from the server side, one to call Go from Wren and the other to call Wren from Go.
Server:
We need two Wren scripts one for each VM:
/* Distributed_programming_server.wren */
class Rpc {
foreign static register()
foreign static handleHTTP()
}
foreign class Listener {
construct listen(network, address) {}
}
class HTTP {
foreign static serve(listener)
}
Rpc.register()
Rpc.handleHTTP()
var listener = Listener.listen("tcp", ":1234")
HTTP.serve(listener)
/* Distributed_programming_server_2.wren */
class TaxComputer {
static tax(amount, rate) {
if (amount < 0) Fiber.abort("Negative values not allowed.")
return amount * rate
}
}
We now embed these scripts in the following Go program and run it on one terminal.
/* go run Distributed_programming_server.go */
package main
import(
wren "github.com/crazyinfin8/WrenGo"
"log"
"net"
"net/http"
"net/rpc"
)
type any = interface{}
type TaxComputer float64
var vm2 *wren.VM
var fileName = "Distributed_programming_server.wren"
var fileName2 = "Distributed_programming_server_2.wren"
func (taxRate TaxComputer) Tax(x float64, r *float64) error {
wrenVar, _ := vm2.GetVariable(fileName2, "TaxComputer")
wrenClass, _ := wrenVar.(*wren.Handle)
defer wrenClass.Free()
wrenMethod, _ := wrenClass.Func("tax(_,_)")
defer wrenMethod.Free()
ret, _ := wrenMethod.Call(x, float64(taxRate))
*r = ret.(float64)
return nil
}
func register(vm *wren.VM, parameters []any) (any, error) {
c := TaxComputer(0.05) // 5% tax rate
rpc.Register(c)
return nil, nil
}
func handleHTTP(vm *wren.VM, parameters []any) (any, error) {
rpc.HandleHTTP()
return nil, nil
}
func serve(vm *wren.VM, parameters []any) (any, error) {
handle := parameters[1].(*wren.ForeignHandle)
ifc, _ := handle.Get()
listener := ifc.(*net.Listener)
http.Serve(*listener, nil)
return nil, nil
}
func listen(vm *wren.VM, parameters []any) (any, error) {
network := parameters[1].(string)
address := parameters[2].(string)
listener, err := net.Listen(network, address)
if err != nil {
log.Fatal(err)
}
return &listener, nil
}
func main() {
vm := wren.NewVM()
vm2 = wren.NewVM()
vm2.InterpretFile(fileName2)
rpcMethodMap := wren.MethodMap {
"static register()": register,
"static handleHTTP()": handleHTTP,
}
httpMethodMap := wren.MethodMap { "static serve(_)":serve }
classMap := wren.ClassMap {
"Listener": wren.NewClass(listen, nil, nil),
"Rpc" : wren.NewClass(nil, nil, rpcMethodMap),
"HTTP" : wren.NewClass(nil, nil, httpMethodMap),
}
module := wren.NewModule(classMap)
vm.SetModule(fileName, module)
vm.InterpretFile(fileName)
vm.Free()
vm2.Free()
}
Client:
Just one Wren script needed here:
/* Distributed_programming_client.wren */
import "./fmt" for Fmt
foreign class Client {
construct dialHTTP(network, address) {}
foreign call(serviceMethod, arg)
}
var client = Client.dialHTTP("tcp", "localhost:1234")
var amounts = [3, 5.6]
for (amount in amounts) {
var tax = client.call("TaxComputer.Tax", amount)
Fmt.print("Tax on $0.2f = $0.2f", amount, tax)
}
which we embed in the following Go program and run it on a different terminal.
/* go run Distributed_programming_client.go */
package main
import(
wren "github.com/crazyinfin8/WrenGo"
"log"
"net/rpc"
"strings"
)
type any = interface{}
func dialHTTP(vm *wren.VM, parameters []any) (any, error) {
network := parameters[1].(string)
address := parameters[2].(string)
client, err := rpc.DialHTTP(network, address)
if err != nil {
log.Fatal(err)
}
return &client, nil
}
func call(vm *wren.VM, parameters []any) (any, error) {
handle := parameters[0].(*wren.ForeignHandle)
ifc, _ := handle.Get()
client := ifc.(**rpc.Client)
serviceMethod := parameters[1].(string)
amount := parameters[2].(float64)
var tax float64
err := (*client).Call(serviceMethod, amount, &tax)
if err != nil {
log.Fatal(err)
}
return tax, nil
}
func moduleFn(vm *wren.VM, name string) (string, bool) {
if name != "meta" && name != "random" && !strings.HasSuffix(name, ".wren") {
name += ".wren"
}
return wren.DefaultModuleLoader(vm, name)
}
func main() {
cfg := wren.NewConfig()
cfg.LoadModuleFn = moduleFn
vm := cfg.NewVM()
fileName := "Distributed_programming_client.wren"
clientMethodMap := wren.MethodMap { "call(_,_)": call }
classMap := wren.ClassMap { "Client": wren.NewClass(dialHTTP, nil, clientMethodMap) }
module := wren.NewModule(classMap)
vm.SetModule(fileName, module)
vm.InterpretFile(fileName)
vm.Free()
}
- Output:
Output on the client terminal:
Tax on 3.00 = 0.15 Tax on 5.60 = 0.28
Categories:
- Programming Tasks
- Networking and Web Interaction
- Ada
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