VB Socket Visual Basic socket implementation

Transcription

1 10 VB Socket Visual Basic socket implementation Visual Basic support a WinSock control which allows the connection of hosts over a network. It supports both UDP and TCP. Figure 10. shows a sample Visual Basic screen with a WinSock object (in this case, it is named Winsock1). To set the Procotol used then either select the Properties window on the WinSock object, click Protocol and select either scktcpprotocol, or sckudpprotocol. Otherwise, within the code it can be set to TCP with: Winsock1.Protocol = scktcpprotocol Figure 10.1 WinSock object The WinSock object has various properties, such as: 167

2 obj.remotehost obj.localport Defines the IP address or DNS of the remote host. Defines the local port number The methods that are used with the WinSock object are: obj.connect obj.listen obj.getdata obj.senddata Connects to a remote host (client invoked). Listens for a connection (server invoked). Reads data from the input steam. Sends data to an output stream. The main events are: ConnectionRequest DataArrival Occurs when a remote host wants to make a connection with a server. Occurs when data has arrived from a connection (data is then read with GetData) Creating a server A server must listen for connection. To do this, do the following: 1 Create a new Standard EXE project. 2 Change the name of the default form to myserver. 3 Change the caption of the form to Server Application (see Figure 10.2). 4 Put a Winsock control on the main format and change its name to mytcpserver. 5 Add two TextBox controls to the form. Name the first SendTextData, and the second ShowText (see Figure 10.2). 6 Add the code given below to the form. Figure 10.2 Server setups Private Sub Form_Load() ' Set the local port to 1001 and listen for a connection mytcpserver.localport = Mastering Networks

3 mytcpserver.listen myclient.show Private Sub mytcpserver_connectionrequest (ByVal requestid As Long) ' Check state of socket, if it is not closed then close it. If mytcpserver.state <> sckclosed Then mytcpserver.close ' Accept the request with the requestid parameter. mytcpserver.accept requestid Private Sub SendTextData_Change() ' SendTextData contains the data to be sent. ' This data is setn using the SendData method mytcpserver.senddata = SendTextData.Text Private Sub mytcpserver_dataarrival (ByVal bytestotal As Long) ' Read incoming data into the str variable, ' then display it to ShowText Dim str As String mytcpserver.getdata = str ShowText.Text = str Figure 10.3 shows the server setup. Figure 10.3 Server form Creating a client TCP/UDP 169

4 The client must actively seek a connection. To create a client, do the following: 1 Add a new form to the project, and name it myclient. 2 Change the caption of the form to Client Application. 3 Add a Winsock control to the form and name it mytcpclient. 4 Add two TextBox controls to the form. Name the first SendTextData, and the second ShowText. 5 Draw a CommandButton control on the form and name it cmdconnect. 6 Change the caption of the CommandButton control to Connect. 7 Add the code given below to the form. Private Sub Form_Load() ' In this case it will connect to ' change this to the local IP address or DNS of the local computer mytcpclient.remotehost = " " mytcpclient.remoteport = 1001 Private Sub cmdconnect_click() ' Connect to the server mytcpclient.connect Private Sub SendTextData_Change() tcpclient.senddata txtsend.text Private Sub tcpclient_dataarrival (ByVal bytestotal As Long) Dim str As String mytcpclient.getdata str ShowText.Text = str 170 Mastering Networks

5 Figure 10.4 Client form The program, when it is run, will act as a client and a server. Any text typed in the SendTxtData TextBox will be sent to the ShowText TextBox on the other form Multiple connections In Visual Basic, it is also possible to create multiple connections to a server. This is done by creating multiple occurances of the server object. A new one is created every time there is a new connection (with the Connection_Request event). Each new server accepts the incoming connection. The following code, which has a Winsock control on a form called multserver, is given below. Private ConnectNo As Long Private Sub Form_Load() ConnectNo = 0 multserver(0).localport = 1001 multserver(0).listen Private Sub multserver_connectionrequest _ (Index As Integer, ByVal requestid As Long) If Index = 0 Then ConnectNo = ConnectNo + 1 Load multserver(connectno) multserver(connectno).localport = 0 multserver(connectno).accept requestid Load txtdata(connectno) End If TCP/UDP 171

6 Connect event The Connect event connects to a server. If an error occurs then a flag (ErrorOccurred) is set to True, else it is False. Its syntax is: Private Sub object.connect(erroroccurred As Boolean) Close event The Close event occurs when the remote computer closes the connection. Applications should use the Close method to correctly close their connection. Its syntax is: object_close() DataArrival event The DataArrival event occurs when new data arrives, and returns the number of bytes read (bytestotal). Its syntax is: object_dataarrival (bytestotal As Long) Bind method The Bind method specifies the Local port (LocalPort) and the Local IP address (LocalIP) to be used for TCP connections. Its syntax is: object.bind LocalPort, LocalIP Listen method The Listen method creates a socket and goes into listen mode (for server applications). Its stays in this mode until a ConnectionRequest event occurs, which indicates an incoming connection. After this, the Accept method should be used to accept the connection. Its syntax is: object.listen Accept method The Accept method accepts incoming connections after a ConnectionRequest event. Its syntax is: object.accept requestid The requestid parameter is passed into the ConnectionRequest event and is used with the Accept method Close method The Close method closes a TCP connection. Its syntax is: object.close SendData method 172 Mastering Networks

7 The SendData methods sends data (Data) to a remote computer. Its syntax is: object.senddata Data GetData method The GetData method gets data (Data) from an object. Its syntax is: object.getdata data, [type,] [maxlen] TCP/IP services reference Port Service Comment Port Service Comment 1 TCPmux 7 echo 9 discard Null 11 systat Users 13 daytime 15 netstat 17 qotd Quote 18 msp Message send protocol 19 chargen ttytst source 21 ftp 23 telnet 25 smtp Mail 37 time Timserver 39 rlp Resource location 42 nameserver IEN whois Nicname 53 domain DNS 57 mtp Deprecated 67 bootps BOOTP server 67 bootps 68 bootpc BOOTP client 69 tftp 70 gopher Internet Gopher 77 rje Netrjs 79 finger 80 www WWW HTTP 87 link Ttylink 88 kerberos Kerberos v5 95 supdup 101 hostnames 102 iso-tsap ISODE 105 csnet-ns CSO name server 107 rtelnet Remote Telnet 109 pop2 POP version pop3 POP version sunrpc 113 auth Rap ID 115 sftp 117 uucp-path 119 nntp USENET 123 ntp Network Timel 137 netbios-ns NETBIOS Name Service 138 netbios-dgm NETBIOS 139 netbios-ssn NETBIOS session 143 imap2 161 snmp SNMP 162 snmp-trap SNMP trap 163 cmip-man ISO management over IP 164 cmip-agent 177 xdmcp X Display Manager 178 nextstep NeXTStep 179 bgp BGP 191 prospero 194 irc Internet Relay Chat 199 smux SNMP Multiplexer 201 at-rtmp AppleTalk routing 202 at-nbp AppleTalk name binding 204 at-echo AppleTalk echo 206 at-zis AppleTalk zone information 210 z3950 NISO Z39.50 database 213 ipx IPX 220 imap3 Interactive Mail Access 372 ulistserv UNIX Listserv 512 exec Comsat 513 login 513 who Whod 514 shell No passwords used 514 syslog 515 printer Line printer spooler TCP/UDP 173

8 517 talk 518 ntalk 520 route RIP 525 timed Timeserver 526 tempo Newdate 530 courier Rpc 531 conference Chat 532 netnews Readnews 533 netwall Emergency broadcasts 540 uucp Uucp daemon 543 klogin Kerberized rlogin (v5) 544 kshell Kerberized rsh (v5) 174 Mastering Networks