send Function

Declare Function send Lib "wsock32.dll" (ByVal s As Long, buf As Any, ByVal length As Long, ByVal flags As Long) As Long

Platforms

Windows 95: Supported.
Windows 98: Supported.
Windows NT: Requires Windows NT 3.1 or later.
Windows 2000: Supported.
Windows CE: Requires Windows CE 1.0 or later.

Description & Usage

send sends data to a network host via a connected socket. The socket must have already been connected to another computer via connect. The Winsock implementation automatically assembles the data into whatever packets, datagrams, or other units that are transported via the protocol being used.

Return Value

If successful, the function returns the number of bytes successfully sent through the socket (although the network host may not necessarily have received them). If an error occured, the function returns SOCKET_ERROR (use WSAGetLastError to get the error code).

Visual Basic-Specific Issues

If specifying a string for buf, the ByVal keyword must be placed in front of it. See the example for a demonstration.

Parameters

s

A descriptor of the connected socket to send the data through.

buf

The data to send to the network host.

length

The size in bytes of the data passed as buf.

flags

A combination of the following flags specifying additional options:

MSG_DONTROUTE: Do not subject the data to routing. The Winsock implementation may choose to ignore this option if specified.
MSG_OOB: Send out-of-band data only.

Constant Definitions

Const SOCKET_ERROR = -1
Const MSG_DONTROUTE = &H4
Const MSG_OOB = &H1

Example

Download the main page of this web site (http://www.vbapi.com). This example supports a very crude implementation of HyperText Transport Protocol (HTTP), sending a request to the server and receiving the document. The document downloaded, with HTTP headers removed, is output to the Debug window. To use this example, place a command button named cmdDownload on a form window.

Note the careful use of GoTo in this example. Since there are lots of things that can go wrong, and WSACleanup must be called at the end no matter what happens, the GoTo skip down to the end if an unrecoverable error occurs. If VB had better exception handling, I would use that instead of GoTo.

' This code is licensed according to the terms and conditions listed here.

' Declarations and such needed for the example:
' (Copy them to the (declarations) section of a module.)
Public Type WSADATA
	wVersion As Integer
	wHighVersion As Integer
	szDescription As String * 257
	szSystemStatus As String * 129
	iMaxSockets As Long
	iMaxUdpDg As Long
	lpVendorInfo As Long
End Type
Public Declare Function WSAStartup Lib "wsock32.dll" (ByVal wVersionRequested As Integer, lpWSAData _
	As WSADATA) As Long
Public Declare Function WSACleanup Lib "wsock32.dll" () As Long
Public Type HOSTENT
	h_name As Long
	h_aliases As Long
	h_addrtype As Integer
	h_length As Integer
	h_addr_list As Long
End Type
Public Const AF_INET = 2
Public Declare Function gethostbyname Lib "wsock32.dll" (ByVal name As String) As Long
Public Declare Function htons Lib "wsock32.dll" (ByVal hostshort As Integer) As Integer
Public Declare Function socket Lib "wsock32.dll" (ByVal af As Long, ByVal prototype As Long, ByVal _
	protocol As Long) As Long
Public Const SOCK_STREAM = 1
Public Type SOCKADDR
	sin_family As Integer
	sin_port As Integer
	sin_addr As Long
	sin_zero As String * 8
End Type
Public Declare Function connect Lib "wsock32.dll" (ByVal s As Long, name As SOCKADDR, ByVal namelen _
	As Long) As Long
Public Declare Function send Lib "wsock32.dll" (ByVal s As Long, buf As Any, ByVal length As Long, _
	ByVal flags As Long) As Long
Public Declare Function recv Lib "wsock32.dll" (ByVal s As Long, buf As Any, ByVal length As Long, _
	ByVal flags As Long) As Long
Public Declare Function closesocket Lib "wsock32.dll" (ByVal s As Long) As Long
Public Declare Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" (Destination As Any, Source _
	As Any, ByVal Length As Long)

' A useful API macro.
Public Function MAKEWORD(ByVal bLow As Byte, ByVal bHigh As Byte) As Integer
	MAKEWORD = Val("&H" & Right("00" & Hex(bHigh), 2) & Right("00" & Hex(bLow), 2))
End Function

' *** Place the following code inside the form window. ***

Private Sub cmdDownload_Click()
	Dim wsockinfo As WSADATA  ' info about Winsock
	Dim sock As Long          ' descriptor of the socket to use
	Dim retval As Long        ' generic return value
	Dim pHostinfo As Long     ' pointer to info about the server
	Dim hostinfo As HOSTENT   ' info about the server
	Dim pIPAddress As Long    ' pointer to server's IP address
	Dim ipAddress As Long     ' server's IP address
	Dim sockinfo As SOCKADDR  ' info about the socket
	
	Dim buffer As String      ' communications buffer
	Dim reply As String       ' reply from server
	Dim bytesleft As Long     ' number of bytes left to read of response body
	Dim headerline As String  ' line of HTTP response header
	
	' Initialize a Winsock session.
	retval = WSAStartup(MAKEWORD(2, 2), wsockinfo)
	If retval <> 0 Then
		Debug.Print "Unable to initialize Winsock!"
		Exit Sub
	End If
	
	' Get the IP address of the server to connect to.
	pHostinfo = gethostbyname("www.vbapi.com")
	If pHostinfo = 0 Then
		Debug.Print "Unable to resolve host!"
		GoTo Cleanup
	End If
	CopyMemory hostinfo, ByVal pHostinfo, Len(hostinfo)
	If hostinfo.h_addrtype <> AF_INET Then
		Debug.Print "Couldn't get IP address of www.vbapi.com!"
		GoTo Cleanup
	End If
	CopyMemory pIPAddress, ByVal hostinfo.h_addr_list, 4
	CopyMemory ipAddress, ByVal pIPAddress, 4
	' Create a socket to use for the TCP/IP connection.
	sock = socket(AF_INET, SOCK_STREAM, 0)
	If sock = &HFFFFFFFF Then
		Debug.Print "Unable to create socket!"
		GoTo Cleanup
	End If
	
	' Make a connection to the server.
	With sockinfo
		' Use the IP protocol family.
		.sin_family = AF_INET
		' Connect to port 80 (the typical HTTP port).
		.sin_port = htons(80)
		' IP address of the server to connect to.
		.sin_addr = ipAddress
		' Dummy data that isn't used.
		.sin_zero = String(8, vbNullChar)
	End With
	Debug.Print "Attempting to connect...."
	retval = connect(sock, sockinfo, Len(sockinfo))
	If retval <> 0 Then
		Debug.Print "Unable to connect!"
		GoTo Cleanup
	End If
	
	' Send an HTTP request to GET the document /index.html.
	buffer = "GET / HTTP/1.1" & vbCrLf & _
		"Host: www.vbapi.com" & vbCrLf & _
		"User-Agent: Winsock-Example-Program" & vbCrLf & vbCrLf
	retval = send(sock, ByVal buffer, Len(buffer), 0)
	Debug.Print "Sent request.  Waiting for reply..."
	
	' Read from the socket until the entire HTTP response header is received.
	' (i.e., until the connection times out or a double Cr-Lf pair is received)
	reply = ""
	buffer = Space(1024)  ' read in 1 KB chunks
	Do
		retval = recv(sock, ByVal buffer, Len(buffer), 0)
		reply = reply & Left(buffer, retval)
	Loop Until retval = 0 Or InStr(reply, vbCrLf & vbCrLf) <> 0
	
	' Parse the header to see how many more bytes we need to read.
	Do
		headerline = Left(reply, InStr(reply, vbCrLf) - 1)
		If LCase(Left(headerline, 16)) = "content-length: " Then
			bytesleft = Val(Right(headerline, Len(headerline) - 16))
		End If
		reply = Right(reply, Len(reply) - Len(headerline) - 2)
	Loop While bytesleft = 0 Or Left(reply, 2) = vbCrLf
	
	' Trim the rest of the header out of the reply.
	reply = Right(reply, Len(reply) - InStr(reply, vbCrLf & vbCrLf) - 3)
	bytesleft = bytesleft - Len(reply)
	
	' Read the rest of the content of the response.
	Do Until bytesleft = 0 Or retval = 0
		retval = recv(sock, ByVal buffer, Len(buffer), 0)
	reply = reply & Left(buffer, retval)
	bytesleft = bytesleft - retval
	Loop
	
	' Print the document that was received.
	Debug.Print "Document Retrieved!"
	Debug.Print
	Debug.Print reply
    
Cleanup:
	' Closes the socket, ends the Winsock session.
	retval = closesocket(sock)
	retval = WSACleanup()        
End Sub