基于HTTP协议用WinSock实现任意文件下载
HTTP协议是文本格式通讯，下载文件是二进制数据，怎样处理好两种格式，而不受VB独断专行的Unicode转换影响，本代码提供了一个示例。
Option Explicit
Private strURL As String
Private mstrFileName As String, mlngFileNum As Long
Private mlngFileLen As Long, mlngCurByte As Long
Private mblnOnlyLen As Boolean, mblnPutStart As Boolean
Private Sub Form_Load()
strURL = Text1.Text '准备下载的文件URL
mstrFileName = Text2.Text '下载文件在本存放的位置与文件名
Label1.Caption = "文件总字节:0"
Label2.Caption = "已下载字节:0"
Command1.Caption = "开始下载"
Command2.Caption = "取得长度"
End Sub
Private Sub Command1_Click()
mblnOnlyLen = False
DownFile
End Sub
Private Sub Command2_Click()
mblnOnlyLen = True
Label1.Caption = "文件总字节:0"
DownFile
End Sub
Private Sub DownFile()
mblnPutStart = False
Label2.Caption = "已下载字节:0"
Command1.Enabled = False
Command2.Enabled = False
With Winsock1
If .State <> sckClosed Then .Close
.Protocol = sckTCPProtocol
.RemoteHost = "article.tianyaclub.com"
.RemotePort = 80
.Connect
End With
End Sub
Private Sub Winsock1_Connect()
Dim s As String
s = "GET " + strURL + " HTTP/1.0" + vbCrLf
s = s + "Accept: */*" + vbCrLf
s = s & "Pragma: no-cache" & vbCrLf
s = s & "Cache-Control: no-cache" & vbCrLf
s = s & "Connection: close" & vbCrLf & vbCrLf
s = s + vbCrLf
Winsock1.SendData s
End Sub
Private Sub CloseAll()
If Winsock1.State <> sckClosed Then Winsock1.Close
Close #mlngFileNum
Command1.Enabled = True
Command2.Enabled = True
End Sub
Private Sub Winsock1_DataArrival(ByVal bytesTotal As Long)
Dim RevData() As Byte
Dim a() As Byte, b() As String, c() As String
Dim s As String, i As Long, k As Long
On Error GoTo fail
If mblnPutStart = False Then
Winsock1.PeekData RevData, vbArray Or vbByte
k = InStrB(1, RevData, ChrB(13) & ChrB(10) & ChrB(13) & ChrB(10))
If k > 0 Then
Winsock1.GetData RevData, vbArray Or vbByte
a = LeftB(RevData, k - 1)
RevData = MidB(RevData, k + 4)
s = StrConv(a, vbUnicode)
b = Split(s, vbCrLf)
If InStr(1, b(0), "200 OK", vbTextCompare) = 0 Then GoTo fail
For i = 1 To UBound(b)
c = Split(b(i), ": ")
Select Case c(0)
Case "Content-Length"
mlngFileLen = CLng(c(1))
Label1.Caption = "文件总字节:" & mlngFileLen
If mblnOnlyLen Then
CloseAll
Exit Sub
End If
End Select
Next
mblnPutStart = True
mlngCurByte = UBound(RevData) + 1
mlngFileNum = FreeFile
Open mstrFileName For Binary As #mlngFileNum
Else
Exit Sub
End If
Else
Winsock1.GetData RevData, vbArray Or vbByte
mlngCurByte = mlngCurByte + bytesTotal
End If
Put #mlngFileNum, , RevData
Label2.Caption = "已下载字节:" & mlngCurByte
If mlngCurByte = mlngFileLen Then
CloseAll
MsgBox "下载成功！"
End If
Exit Sub
fail:
CloseAll
MsgBox "网络传输错误，文件下载失败！"
End Sub