Generic P2P architecture, tutorial and example-codeproject

Generic P2P architecture, tutorial and example

ByDzzxyz| 15 Mar 2004

Generic P2P architecture, tutorial and example that covers basic P2P strategy. Upon completing this tutorial, you will be proficient in basic P2P design and coding.

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Overview of P2P Culture

P2P (Peer to Peer) is when multiple computers think collectively towards a shared objective. computer programs that use less central servers and rely on a collection of computers such as Gnutella, distributed media streaming, networks of DCC based IRC fservers etc. tend to be referred to as being more P2P. computer programs where begin end-users communicate with few central services tend to be referred to as being less P2P or not P2P. to fully understand and leverage P2P technology, one must separate his or her self from the dogma that our computer programs must be united by servers in our physical possession to synchronize activities. rather, think of our computer programs from a more digital-life oriented perspective and break the computer software up over multiple machines and make no single part of the software critical to the collective objective.

P2P Philosophy

�� Single servants are less powerful then a single server but the collective of specified servants is more powerful then any single server ��-Daniel Stephen rule.

For example, a large software company gives each employee a very small amount of responsibility. even if this means you get your month �s coding done in a few days, it is more beneficial to the company as a whole to not rely on any single employee too much and allows the company more overall stability and to ultimately write larger more complex software packages than any single person is capable. your software is more P2P if you leverage this same principle to achieve more bandwidth and computing speed.

Basic P2P terminologypeer or servant

A computer program that acts as both a client and a server for the entire P2P network.

Connection Manager

A light server application that provides a starting point for applications which enter a P2P network. the less the Connection Manager is involved in the objective of your overall application, the more P2P your application is. the more P2P your application is, the less strain on your own hardware.

Simple P2P chat example

This example demonstrates a very simple but highly P2P application. this example consists of two fundamental P2P parts: A Connection Manager and a servant. the Connection Manager shoshould be compiled and executed once. the servant shoshould be compiled and itsConfig. xmlSconnectionmgrTag shocould be set to the IP address or domain name of the computer that is running the Connection Manager. make multiple copies of the servant's executable andConfig. xmlAnd place them on multiple computers. execute each servant on a different machine and they will contact the Connection Manager to resolve each other's location and network with each other. each servant will frequently ask the connection manager who is on the P2P network and keep their own publish list up to date. when a servant leaves the network, an updated list is published to all the other servants and they discontinue attempting to communicate with the servant who left.

Can I still try this out if I only have one computer to work?

Yes. the Connection Manager assigns a new port number to each servant so each servant listens on a unique port number. you can run the servant executable as frequently times as you want on a single machine. for your first test, I wocould suggest running the Connection Manager once and then run the servant a couple of times on the same machine as the Connection Manager. then chat in the servant windows to verify that the P2P network has been constructed on your computer. if you have other computers to work with, simply execute the servant on the other computers and chat to verify that they successfully joined the P2P network.

The configuration file: Put the IP address of the server that has the connection manager here.

   127.0.0.1 

Leave this 85 unless you change the port that the Connection Manager sits on:

85

List the IP addresses or domain names that you wish this servant to ignore:
1.1.1.1

Foouser234.fooisp23423.com

What are the ban tags?

The ban tags allow each servant to list the IP addresses or domain names that they do not wish to get data from.

The Connection Manager

Add a Peer To The Connection Manager. s knowledge of the P2P network.

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Private Sub p2p_ConnectionRequest(Index As Integer, ByVal requestID As Long)    iPortMax = iPortMax + 1    Dim a As Integer    For a = 1 To p2p.UBound        Dim istate As Integer        istate = p2p(a).State        If istate = 0 Or istate = 8 Then            Call EnterCriticalSection(tCritSection)            RemovePeerByOffset CStr(a)            p2p(a).Close            p2p(a).Accept requestID            AddPeer p2p(a).RemoteHostIP, CStr(iPortMax), CStr(a)            Call LeaveCriticalSection(tCritSection)            Exit Sub        End If        DoEvents    Next a    DoEvents    Dim i As Integer    i = p2p.UBound    Call EnterCriticalSection(tCritSection)    Load p2p(i + 1)    p2p(i + 1).Accept requestID    AddPeer p2p(i + 1).RemoteHostIP, CStr(iPortMax), CStr(i + 1)    Call LeaveCriticalSection(tCritSection)End Sub 

A servant wants a list of all its peers.

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Private Sub p2p_DataArrival(Index As Integer, ByVal bytesTotal As Long)    Dim a As String    If p2p(Index).State <> 7 Then p2p(Index).Close: Exit Sub    p2p(Index).GetData a    If a = "needs peer list" Then        On Error GoTo exit_critical_list        Call EnterCriticalSection(tCritSection)        Dim pPersonalPeerDoc As MSXML2.DOMDocument        Set pPersonalPeerDoc = New MSXML2.DOMDocument        pPersonalPeerDoc.loadXML pDoc.xml        pPersonalPeerDoc.selectSingleNode("./peers/peer[offset = '" &_                                           Index & "']/me").Text = "TRUE"        p2p(Index).SendData pPersonalPeerDoc.xmlexit_critical_list:        On Error Resume Next        Call LeaveCriticalSection(tCritSection)    Else        MsgBox Index & " sent: " & a & " to the connection manager"    End IfEnd Sub 

A servant left the network.

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Private Sub p2p_Close(Index As Integer)        Call EnterCriticalSection(tCritSection)            RemovePeerByOffset CStr(Index)        Call LeaveCriticalSection(tCritSection)End Sub

The servants

The Connection Manager has a new list of this servant �s peers.

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Private Sub Winsock1_DataArrival(ByVal bytesTotal As Long)    Dim document As String    If Winsock1.State <> 7 Then Winsock1.Close: Exit Sub    Winsock1.GetData document    pDoc1.loadXML document    Dim pPeerList As MSXML2.IXMLDOMNodeList    Set pPeerList = pDoc1.selectNodes("./peers/peer/port")    userList1.Clear    Dim i As Integer    For i = 0 To pPeerList.length - 1        If pPeerList(i).Text = _          pDoc1.selectSingleNode("./peers/peer[me = 'TRUE']/port").Text Then            userList1.AddItem "*" & pPeerList(i).Text        Else            userList1.AddItem pPeerList(i).Text        End If    Next    servants1(0).Close    servants1(0).LocalPort = _      CInt(pDoc1.selectSingleNode("./peers/peer[me = 'TRUE']/port").Text)    servants1(0).ListenEnd Sub

This servant is ing to all of its peers and publishing some data to all of them.

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Private Sub txtSend1_KeyPress(KeyAscii As Integer)On Error Resume Next If KeyAscii = 13 Then  iSendsLeft1 = pDoc1.selectNodes("./peers/peer").length  Dim i As Integer  For i = 0 To pDoc1.selectNodes("./peers/peer").length - 1   Dim iIp As String   Dim iPort As Integer   iIp = _    pDoc1.selectNodes("./peers/peer").Item(i).selectSingleNode("./ip").Text   iPort = _    CInt(pDoc1.selectNodes("./peers/peer").Item(i).selectSingleNode("./port").Text)   Dim strState As String   While send1.State = 6       DoEvents   Wend   send1.Close   send1.Connect iIp, iPort  Next End If DoEventsEnd Sub

A peer of this servant wants to connect.

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Private Sub servants1_ConnectionRequest(Index As Integer,_                                          ByVal requestID As Long)    Dim remoteip As String    Dim remoteaddy As String    remoteip = servants1(Index).RemoteHostIP    remoteaddy = servants1(Index).RemoteHost    If (pConfig.selectNodes("./config/bans/ban[target = '"_      & remoteip & "']").length = 0) _      And (pConfig.selectNodes("./config/bans/ban[target = '" _      & remoteaddy & "']").length = 0) Then        Dim a As Integer        For a = 1 To servants1.UBound            If servants1(a).State = 0 Or servants1(a).State = 8 Then                Call EnterCriticalSection(tCritSection)                servants1(a).Close                servants1(a).Accept requestID                Call LeaveCriticalSection(tCritSection)                Exit Sub            End If            DoEvents        Next a        DoEvents        Call EnterCriticalSection(tCritSection)        Dim i As Integer        i = servants1.UBound        Load servants1(i + 1)        servants1(i + 1).Accept requestID        Call LeaveCriticalSection(tCritSection)    End IfEnd Sub

A peer of this servant has some data for it.

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Private Sub servants1_DataArrival(Index As Integer,_                                   ByVal bytesTotal As Long)On Error Resume Next    Dim a As String    If servants1(Index).State <> 7 Then servants1(Index).Close: Exit Sub    servants1(Index).GetData a    txtChat1.Text = txtChat1.Text & vbCrLf & aEnd Sub

Why don't my P2P servants communicate with other servants on the Internet when they are behind a router?

Some routers have default communication restrictions called A. Firewall. these restrictions are intended to prevent a virus from misusing your computer and to force you to explain icitly disable them if and when you need more access to the Internet. one of the most common restrictions that harm P2P networks is when the router blocks most outgoing ports by default. you can test to see if your router is blocking a port:

1. Run a copy of the Connection Manager on a computer behind your router.
2. On a computer outside the router on the internet, open a DOS box and type in Telnet 85.
3. Your connection manager on the computer behind the firewall shocould display:

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               ip of peer        2224        1        FALSE    

If not then you need to enable port 85 in your router for the Connection Manager. This also has to be done for each peer behind a router with a built in firewall.

You can still leverage P2P Technology on your personal network (behind your router) as long as all of your peers and your Connection Manager are behind your firewall. each peer must be configured with the IP address of the Connection Manager that the router has assigned to it. I wowould highly suggest having the router assign the Connection Manager machine a static IP. this way, peers do not have to be reconfigured each time you reboot the box with the Connection Manager on it. the servants, however, can just get a dynamic IP address from your router every time they boot up because they will use the Connection Manager to resolve each other's location.

But I really need both servants behind routers and servants on the Internet to all be part of my P2P network.

This topic is outside the scope of this article, but in short here is one common solution used by other P2P technologies:

1. Set your connection manager on a box that is intended to be a web server. if your Connection Manager is behind a router then configure your router to block all incoming ports but make the router forward port 85 connections to the machine that is running the Connection Manager.
2. Have each servant report to the Connection Manager any peers that they are unable to contact. have the Connection Manager determine if they are behind a port blocking router by seeing if the suspicious servant sends another heart beat. if most peers are complaining that they can't connect to a suspicous servant but the suspicous servant continuously asks the Connection Manager for a user list then the Connection Manager can conclude that the servant is probably behind A port blocking router.
3. If the Connection Manager makes this determination, have it records y the suspicous servant that it needs to pull from another peer. for the life of the suspicous servant instance, it pulls from another peer who publishes any data that it gets. the chosen peer must not itself be a suspicious peer behind a router.

This will slow the P2P network down but will allow peers behind port blocking routers to join the P2P network. I wocould not suggest having the Connection Manager just assume that a peer is suspicous instantly when the other peers complain about it, rather it shoshould have a threshold of 2 or 3 complaints from each of the other peers before telling it that it is suspicious and assigning it a chosen peer to pull from.

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