Moving Data through slow media

Windows Sockets

Windows Sockets made easy

• At this point I would like to mention I/O Completion Ports, scalability and resources.
• This code does not use I/O Completion Ports.
• If you are developing an application which will ultimately have thousands of connections then you need to use I/O Completion Ports and/or many servers.
• I/O Completion Ports use a pool of 50 or more Worker Threads...
• If you have a peak of fewer than 50 simultaneous Connections then this code (using one Thread per Connection) will use fewer System Resources and be far faster to code!

class CSocketArchive : public CArchive {
public:
  CSocketArchive(CFile* pFile, UINT nMode, int nBufSize=4096) : CArchive(pFile, nMode, nBufSize) {};
  void ClearIndex() {
    if(IsStoring()) {
      if(m_nMapCount>1) {
        m_pStoreMap->RemoveAll();
        m_pStoreMap->SetAt(NULL,(void*)(DWORD)0);
        m_nMapCount=1;
      }
    }else while(m_nMapCount-->1) m_pLoadArray->RemoveAt(m_nMapCount);
  }
};

CSocketClient

  CSocketClient Chat("127.0.0.1", 23);
  Chat.Send("Hi");
  if(Chat.GetReply()=="bye") Chat.Disconnect();
  else Chat.Send("bye");

#include "SocketInterface.h"
class CClientDlg : public CDialog {
...
public:
  class CChatClient : public CSocketClient {
    CClientDlg* Dlg;
    void OnReceive() {Dlg->Say(GetReply());}
    void OnClose  () {Dlg->Disconnect();}
    CString GetReply() {
      CString S;
      ArI->ReadString(S); // It'll wait here for as long as the connection is OK. If the connection is broken it returns an empty string.
      return S;
    }
  public:
    void Send(CString Msg) {ArO->WriteString(Msg+"\r\n"); ArO->Flush();}
    CString Connect(CString RemoteIP, BYTE Port, CClientDlg* _Dlg) {Dlg=_Dlg; return CSocketClient::Connect(RemoteIP,Port);}
  } Chat;

  void Say(CString Msg) {if(::IsWindow(m_hWnd)) ((CListBox*)GetDlgItem(IDC_LIST1))->AddString(Msg);}
  void Disconnect() {
    Say("Disconnected");
    GetDlgItem(IDC_Send)->EnableWindow(FALSE);
  }
...
};

BOOL CClientDlg::OnInitDialog() {
  CDialog::OnInitDialog();

  CString S(Chat.Connect("127.0.0.1",23, this)); //Note that you can't connect to yourself: You'll need to be running a Server on this PC to get a connection on 127.0.0.1
  if(!S.IsEmpty()) Say(S); // Report any Error Messages
  
  return TRUE;  // return TRUE  unless you set the focus to a control
}

//When a Send Button is clicked, the text from an Edit Box (IDC_EDIT1) is sent.
void CClientDlg::OnSend() {
  CString S;
  GetDlgItemText(IDC_EDIT1, S);
  Chat.Send(S);
}

CSocketServer

#include "SocketInterface.h"

class CChat;       // <- forward references
class CServerDlg;

class CChatServer : public CSocketServer {
  CServerDlg* Dlg;
public:
  CChatServer(BYTE Port, CServerDlg* Dlg) : CSocketServer(Port), Dlg(Dlg) {}
  void Say(CString Msg);
protected:
  virtual CConnection* New();
};

void CChatServer::Say(CString Msg) {Dlg->Say(Msg);}

CConnection* CChatServer::New() {return new CChat(this);}

class CServerDlg : public CDialog {
  CChatServer* Chat;
public:
  CServerDlg(CWnd* pParent=NULL) : CDialog(CServerDlg::IDD, pParent), Chat(0) {}  // standard constructor
  virtual ~CServerDlg();
  void Say(CString Msg) {if(::IsWindow(m_hWnd)) ((CListBox*)GetDlgItem(IDC_LIST1))->AddString(Msg);}
...
};

class CChat : public CConnection {
  void Say      (CString Msg) {((CChatServer*)GetServer())->Say(ID+Msg);}
  void Broadcast(CString Msg) {Say(Msg); ((CChatServer*)GetServer())->Broadcast(ID+Msg);}
  CString ID;
  CString GetReply() {
    CString S;
    try {
      ArI->ReadString(S); // It'll wait here for as long as the connection is OK. If the connection is broken it returns an empty string.
    }catch(...) {return '¿'+sConnectionBroken;}
    return S;
  }
public:
  CChat(CSocketServer* Me) : CConnection(Me) {}
protected:
  void Sender(CString Msg) {ArO->WriteString(Msg+"\r\n"); ArO->Flush();}
  void OnDisconnect() {Broadcast("Disconnected");}
  void OnConnect() {
    ID.Format("%s(%i): ", RemoteIP, m_hSocket);
    Broadcast("Connected");
    Send("You will appear as "+ID);
  }
  void OnReceive() {
    CString S(GetReply());
    if(*S=='¿') {Say(S.Mid(1)); return;}
    if(!S.CompareNoCase("Bye")) Disconnect();
    Broadcast(S);
  }
};

BOOL CServerDlg::OnInitDialog() {
  CDialog::OnInitDialog();

  Chat=new CChatServer(23,this); // C:\Windows\System32\drivers\etc\SERVICES file lists Telnet as TCP port 23

  return TRUE;  // return TRUE  unless you set the focus to a control
}

CServerDlg::~CServerDlg() {delete Chat;}

void CServerDlg::OnBroadcast() {
  CString S;
  GetDlgItemText(IDC_EDIT1, S);
  Say("Broadcasted: "+S);
  Chat->Broadcast("Server: "+S);
}

#include "Telnet.h"
BOOL CMyApp::InitInstance() {
  CSocketServer(23); // C:\Windows\System32\drivers\etc\SERVICES file lists Telnet as TCP port 23
  ...
}

void OnReceive() {
  Send("Hello");
 ArO << MyObject;
}
Hello will be sent _after_ MyObject!
Use Sender("Hello") or ArO << CString("Hello") << MyObject; to send Messages with objects.

Delta Compression

Minimal Data Transfer

The Delta-Compression Process

• All numbers in the string are in Hexadecimal.
• The string contains lines of text separated with '\n' characters.
• A single number on a line indicates a Block from the older File.
• A Block is 512 Bytes except for the last Block which may be shorter (FileSums::GetEndBlockLength()).
• A pair of numbers separated with a '-' indicate a range of adjacent Blocks from the older File ([First Block]-[Last Block] inclusive).
• A pair of numbers separated with a ',' indicate a range of adjacent Bytes from the newer File ([File Position],[Bytes to read]).
• If the Files are equal you get a single line string: 0-FileSums::GetBlockCount() indicating that all the Blocks of the older File make the newer file.
• If the Files are totally different you get a single line string: 0,FileSums::FileLength indicating that all the Bytes of the newer File make the newer file.

#include <afxsock.h> // MFC socket extensions
#include "BlockDelta.h"
class CBlockDeltaTesterDlg : public CDialog {
public:
  CBlockDeltaTesterDlg(CWnd* pParent = NULL); // standard constructor

  void Say(CString Msg) {((CListBox*)GetDlgItem(IDC_LIST1))->AddString(Msg);}
  class CRemoteFileFetcher : public CBlockDelta {
    CBlockDeltaTesterDlg* Dlg;
    static DWORD FAR PASCAL ThreadProc(LPVOID lpData) {((CRemoteFileFetcher*)lpData)->Listen(); return 0;}
    HANDLE hThread;
     DWORD ThreadID;
  public:
    CRemoteFileFetcher(CBlockDeltaTesterDlg* Dlg) : Dlg(Dlg) {hThread=CreateThread((LPSECURITY_ATTRIBUTES)NULL, 0, (LPTHREAD_START_ROUTINE)ThreadProc, (LPVOID)this, 0, &ThreadID);}
    void Say(CString Msg) {Dlg->Say(Msg);}
    virtual void Getting     (CString Remote) {Say("<Getting "+Remote);} // Called when starting to Get a file
    virtual void Putting     (CString Local ) {Say(">Putting "+Local);} // Called when starting to Put a file
    virtual void SetBytesToRead (DWORD Bytes) {CString S; S.Format("<%u Bytes to read" ,Bytes); Say(S);} // Called as soon as BytesToRead is known
    virtual void SetBytesToWrite(DWORD Bytes) {CString S; S.Format(">%u Bytes to write",Bytes); Say(S);} // Called as soon as BytesToWrite is known
    virtual void SetInProgress  (DWORD Bytes) {CString S; S.Format("<%u Bytes in"      ,Bytes); Say(S);} // Called whenever Bytes are received
    virtual void SetOutProgress (DWORD Bytes) {CString S; S.Format(">%u Bytes out"     ,Bytes); Say(S);} // Called whenever Bytes are sent
    virtual void Received  (char Compression) {CString S; S.Format("<%u%% compressed"  ,Compression); Say(S);} // Called when finished Putting (Compression is %Compressed)
    virtual void Sent      (char Compression) {CString S; S.Format(">%u%% compressed"  ,Compression); Say(S);} // Called when finished Getting (Compression is %Compressed)

    void Listen() {
      AfxSocketInit();
      CSocket ServerSocket;
      ServerSocket.Create(14);
      ServerSocket.Listen();
      for(;;) {
        CSocket Socket;
        ServerSocket.Accept(Socket);
        CSocketFile File(&Socket);
        CArchive ArI(&File, CArchive::load);
        CArchive ArO(&File, CArchive::store);
        Put(ArI,ArO);
    } }

  // Returns an error message or "" if everything worked.
    CString Fetch(CString Remote, CString Local, CString Output, CString ServerIP) {
      AfxSocketInit();
      CSocket Socket;
      if(!Socket.Create()
      || !Socket.Connect(ServerIP, 14)) return "Socket creation failed";
      CSocketFile SocketFile(&Socket);
      CArchive ArI(&SocketFile, CArchive::load);
      CArchive ArO(&SocketFile, CArchive::store);
      return Get(Remote,Local,Output, ArI,ArO);
    }
  };
  ... The rest of the dialog class
};

BOOL CBlockDeltaTesterDlg::OnInitDialog() {
  CDialog::OnInitDialog();

  CRemoteFileFetcher RemoteFileFetcher(this);
  CString S;
  S=RemoteFileFetcher.Fetch("Remote.txt","Local.txt","Output.txt", "127.0.0.1");
  if(!S.IsEmpty()) AfxMessageBox(S); // could just return S if this is inside a Function returning a CString.
  
  return TRUE;  // return TRUE  unless you set the focus to a control
}

• LZW.h To compress blocks for transmission
• MD5.h For strong checksum
• CRC32.h For CRoller checksum
• DTree.h For CFO (File Object) data structure
• TreeList.h Used by DTree.h

Remote File Access

Remote DOS