InternetReadFile如何正确读取二进制文件

手上的一个VB项目(过程中发现，.Net果然是好啊)，需要在一个ActiveX中实现HTTP下载功能，我是采用InternetreadFile这个API来实现，一开始的代码我是这么写的


Function Gethttpdownload(sUrl As String) As boolen




Dim s As String


Dim hOpen As Long


Dim hOpenUrl As Long


Dim bDoLoop As Boolean


Dim bRet As Boolean


Dim sReadBuffer As String * 2048


Dim lNumberOfBytesRead As Long


hOpen = InternetOpen(scUserAgent, INTERNET_OPEN_TYPE_PRECONFIG, vbNullString, vbNullString, 0)


hOpenUrl = InternetOpenUrl(hOpen, sUrl, vbNullString, 0, INTERNET_FLAG_RELOAD, 0)


bDoLoop = True


Do While bDoLoop


sReadBuffer = vbNullString


bRet = InternetReadFile(hOpenUrl, sReadBuffer, Len(sReadBuffer), lNumberOfBytesRead)


s = s & Left$(sReadBuffer, lNumberOfBytesRead)


If Not CBool(lNumberOfBytesRead) Then bDoLoop = False


Loop


FileName = "E:/BitSpirit/Torrent/121212.torrent"


F1 = FreeFile


Open FileName For Binary As F1


Put F1, , s


Close F1


If hOpen <> 0 Then InternetCloseHandle (hOpen)


Gethttpdownload = true


End Function



上面方法，用来获取服务器上的文本类型的文件一点问题，都没有，但是用来下载二进制文件的时候 就出现问题了，里面的数据怎么也不对，研究了下载下来的文件后发现，问题外话应该是在接收数据的变量是个STRING的定长字符串上。但是在网上查了好 久，甚至M$ MSDN上的一个用VB来实现下载的程也是用 string类型来接收数据的而且网上的代码写法，基本上也都是这个样，好来才好现，都是从MSDN上的哪个例程上演变过来的.
我想如果能用一个byte数组来代替定长字符串，哪可能就没有问题了，但是查看了一个VB 对Internetreadfile的申明
Public Declare Function InternetReadFile Lib "wininet.dll" (ByVal hFile As Long, ByVal sBuffer As String, ByVal lNumBytesToRead As Long, lNumberOfBytesRead As Long) As Integer
发现其定义ByVal sBuffer As String 看来只能用String了，在网上查找过程中，发现人家用VC写的 程序中这人参数可以是其它的，所以查看了一下Internetreadfile的原型。发现的确可以， 所以我把internetreadfile的定义修改了一下，为了通用，我为新的internetreadfile定义了一个别名。 Internetreadfilebyte申明如下:
Public Declare Function InternetReadFileByte Lib "wininet.dll" Alias "InternetReadFile" (ByVal hFile As Long, ByRef sBuffer As Byte, ByVal lNumBytesToRead As Long, lNumberOfBytesRead As Long) As Integer
试了一下的确可以，重新修改函数，（在这过程中发现，如果要取到正确数据，还必须取得文件大小。所以增加了HttpQueryInfo的定义）最后完整的函数


Function FileDownload(sUrl As Variant) As Boolean


Dim b(99) As Byte


Dim EndByte() As Byte


Dim s As String


Dim hOpen As Long


Dim hOpenUrl As Long


Dim bDoLoop As Boolean


Dim bRet As Boolean


Dim bbuffer As Byte


Dim sReadBuffer As String


Dim FileName As String


Dim lNumberOfBytesRead As Long


Dim F1 As Integer


Dim strsize As String


Dim size As Long


strsize = String$(1024, " ")




F1 = FreeFile


stTotal = vbNullString


FileName = "E:/BitSpirit/Torrent/121212.torrent"


Open FileName For Binary As F1


hOpen = InternetOpen(scUserAgent, INTERNET_OPEN_TYPE_PRECONFIG, vbNullString, vbNullString, 0)


hOpenUrl = InternetOpenUrl(hOpen, sUrl, vbNullString, 0, INTERNET_FLAG_RELOAD, 0)


bDoLoop = True


HttpQueryInfo hOpenUrl, HTTP_QUERY_CONTENT_LENGTH Or HTTP_QUERY_FLAG_NUMBER, ByVal strsize, Len(strsize), 0


size = CLng(Trim(strsize))


For j = 1 To size / 100


bDoLoop = InternetReadFileByte(hOpenUrl, b(0), 100, lNumberOfBytesRead)




Put F1, , b


If Not CBool(lNumberOfBytesRead) Then Exit For


Next


If size Mod 100 <> 0 Then


tmp = (size Mod 100) - 1


ReDim EndByte(tmp)


bDoLoop = InternetReadFileByte(hOpenUrl, EndByte(0), tmp + 1, lNumberOfBytesRead)


Put F1, , EndByte


End If




If hOpenUrl <> 0 Then InternetCloseHandle (hOpenUrl)


If hOpen <> 0 Then InternetCloseHandle (hOpen)




Close #1


FileDownload = True


End Function



测试了一下，完全成功：）