VB6 Lookup Hostname From IP, Specifying DNS Server
I know how to look up a hostname from an IPv4 in VB using the GetHostByAddr Windows API call (this works great). However, that function does not allow one to specify the DNS server to use. Sometimes the default company DNS servers are fine, but other times I need to specify an external DNS server for lookups, and I don't think doing a shell nslookup and parsing the output is the best method, here.
Note: this is actually going to be used as VBA code in an Excel workbook to help someone else do his job, and it's not worth writing a big application when some simple functionality is all he needs.
I thought I had possibly found an answer in the API call getnameinfo开发者_如何学运维 but careful reading seems to indicate it does not offer a servername parameter.
After some intense searching, I found reference to the pExtra parameter to the DNSQuery function. But I don't even know how to begin to use that in VB6.
Could anyone help me out in any way with doing a DNS lookup from VB6, specifying the servername to use?
A full working solution would of course be nice, but I'm willing to work: just point me in the right direction.
UPDATE: For some odd reason it didn't click that DNSQuery was a Windows API call. It just didn't sound like one. I certainly would have been able to make more headway on the problem if I'd gathered that one tiny detail.
Try this:
Option Explicit
Private Declare Function DnsQuery Lib "dnsapi" Alias "DnsQuery_A" (ByVal strname As String, ByVal wType As Integer, ByVal fOptions As Long, ByVal pServers As Long, ppQueryResultsSet As Long, ByVal pReserved As Long) As Long
Private Declare Function DnsRecordListFree Lib "dnsapi" (ByVal pDnsRecord As Long, ByVal FreeType As Long) As Long
Private Declare Function lstrlen Lib "kernel32" (ByVal straddress As Long) As Long
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, ByVal Source As Long, ByVal Length As Long)
Private Declare Function inet_ntoa Lib "ws2_32.dll" (ByVal pIP As Long) As Long
Private Declare Function inet_addr Lib "ws2_32.dll" (ByVal sAddr As String) As Long
Private Const DnsFreeRecordList As Long = 1
Private Const DNS_TYPE_A As Long = &H1
Private Const DNS_QUERY_BYPASS_CACHE As Long = &H8
Private Type VBDnsRecord
pNext As Long
pName As Long
wType As Integer
wDataLength As Integer
flags As Long
dwTel As Long
dwReserved As Long
prt As Long
others(35) As Byte
End Type
Private Sub Command1_Click()
MsgBox Resolve("google.com", "208.67.222.222")
End Sub
Private Function Resolve(sAddr As String, Optional sDnsServers As String) As String
Dim pRecord As Long
Dim pNext As Long
Dim uRecord As VBDnsRecord
Dim lPtr As Long
Dim vSplit As Variant
Dim laServers() As Long
Dim pServers As Long
Dim sName As String
If LenB(sDnsServers) <> 0 Then
vSplit = Split(sDnsServers)
ReDim laServers(0 To UBound(vSplit) + 1)
laServers(0) = UBound(laServers)
For lPtr = 0 To UBound(vSplit)
laServers(lPtr + 1) = inet_addr(vSplit(lPtr))
Next
pServers = VarPtr(laServers(0))
End If
If DnsQuery(sAddr, DNS_TYPE_A, DNS_QUERY_BYPASS_CACHE, pServers, pRecord, 0) = 0 Then
pNext = pRecord
Do While pNext <> 0
Call CopyMemory(uRecord, pNext, Len(uRecord))
If uRecord.wType = DNS_TYPE_A Then
lPtr = inet_ntoa(uRecord.prt)
sName = String(lstrlen(lPtr), 0)
Call CopyMemory(ByVal sName, lPtr, Len(sName))
If LenB(Resolve) <> 0 Then
Resolve = Resolve & " "
End If
Resolve = Resolve & sName
End If
pNext = uRecord.pNext
Loop
Call DnsRecordListFree(pRecord, DnsFreeRecordList)
End If
End Function
It is not an answer, but very important note to wqw post:
Security Warning on lstrlen
function (lines 5 & 55):
Using this function incorrectly can compromise the security of your application.
lstrlen
assumes that lpString is a null-terminated string, or NULL. If it is not, this could lead to a buffer overrun or a denial of service attack against your application.Consider using one of the following alternatives:
StringCbLength
orStringCchLength
.
You can use the DNS WMI provider to set the DNS of the system then use GetHostByAddr
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