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Saverio Pieri
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 Posted: Wed Nov 17, 2004 6:19 pm Post subject: DNSResolver Acces Violation |
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I wrote a multithread console application to verify email adresses.
Each thread create a datamodule with TIdDNSResolver e TIdTCPClient.
I have problems with TIdDNSResolver.
To find the primary MX server I wrote the method below:
Even if
FdmVer.dns.QueryResult.Count > 0
when I try to access with
mxitem := TMxRecord(FdmVer.dns.queryresult[i]);
I obtain an Access Violation.
Why?
{*************************************************************************}
function TThreadVerifier.ResolveMxRecod(lpHost,lpDomain : string; dwPort :
longWord) : string;
var
mxitem : TMxRecord;
i : integer;
wPref : Word;
sMx : string;
begin
sMx := '';
FdmVer.dns.QueryResult.Clear;
FdmVer.dns.Host := lpHost;
FdmVer.dns.Port := dwPort;
FdmVer.dns.QueryRecords := [qtMx];
FdmVer.dns.AllowRecursiveQueries := true;
FdmVer.dns.ReceiveTimeout := FTimeout;
FdmVer.dns.Resolve(lpDomain);
wPref := $FFFF;
for i := 0 to FdmVer.dns.QueryResult.Count -1 do
begin
mxitem := TMxRecord(FdmVer.dns.queryresult[i]);
if (mxitem.RecType = qtMX) and( mxitem.Preference <= wPref) then
begin
wPref := mxitem.Preference;
sMx := mxItem.ExchangeServer;
if wPref = 1 then break;
end;
end;
result := sMx;
end;
{*************************************************************************}
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Martin James
Guest
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| Posted: Wed Nov 17, 2004 6:44 pm Post subject: Re: DNSResolver Acces Violation |
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"Saverio Pieri" <spad (AT) interconnessioni (DOT) it> wrote
| Quote: | I wrote a multithread console application to verify email adresses.
Each thread create a datamodule with TIdDNSResolver e TIdTCPClient.
I have problems with TIdDNSResolver.
To find the primary MX server I wrote the method below:
Even if
FdmVer.dns.QueryResult.Count > 0
when I try to access with
mxitem := TMxRecord(FdmVer.dns.queryresult[i]);
I obtain an Access Violation.
|
I enclose my own DNSresolver procedure. It looks almost identical to yours,
except that I have:
thisPref:=TmxRecord(QueryResult.items[mxServerIndex]).preference;
but you have:
mxitem := TMxRecord(FdmVer.dns.queryresult[i]);
...
wPref := mxitem.Preference;
Why there should be a difference, I do not know, but mine works :)
Rgds,
Martin
PS don't be misled by the 'postError' calls in my code - it's just a logging
proc that was origninally used for logging only errors but I used it for
debigging & status later & did not rename it :(
| Quote: |
{*************************************************************************}
function TThreadVerifier.ResolveMxRecod(lpHost,lpDomain : string; dwPort :
longWord) : string;
var
mxitem : TMxRecord;
i : integer;
wPref : Word;
sMx : string;
begin
sMx := '';
FdmVer.dns.QueryResult.Clear;
FdmVer.dns.Host := lpHost;
FdmVer.dns.Port := dwPort;
FdmVer.dns.QueryRecords := [qtMx];
FdmVer.dns.AllowRecursiveQueries := true;
FdmVer.dns.ReceiveTimeout := FTimeout;
FdmVer.dns.Resolve(lpDomain);
wPref := $FFFF;
for i := 0 to FdmVer.dns.QueryResult.Count -1 do
begin
mxitem := TMxRecord(FdmVer.dns.queryresult[i]);
if (mxitem.RecType = qtMX) and( mxitem.Preference <= wPref) then
begin
wPref := mxitem.Preference;
sMx := mxItem.ExchangeServer;
if wPref = 1 then break;
end;
end;
result := sMx;
end;
{*************************************************************************} |
procedure makeAttemptToResolve;
var mxServerIndex:integer;
begin
with myDNSresolver do
begin
try
host:=thisDNSserver;
queryRecords:=[qtMX];
postError('DNS server: '+inSendObject.DNSserver);
postError('Calling resolver');
Resolve(messDomain);
postError('Resolver returns with
'+intToStr(QueryResult.count)+
' records');
prefMin:=65535;
indexPrefMin:=0;
postError('Scan for best preference');
for mxServerIndex:=0 to QueryResult.Count-1 do
begin
thisPref:=TmxRecord(QueryResult.items[mxServerIndex]).preference;
if (thisPref
begin
prefMin:=thisPref;
indexPrefMin:=mxServerIndex;
end;
end;
postError('wBest server is
'+TmxRecord(QueryResult.items[indexPrefMin]).exchangeServer);
result:=TmxRecord(QueryResult.items[indexPrefMin]).exchangeServer;
postError('Domain '+messDomain+' resolved to: '+result);
except
on e:exception do
begin
postError('Resolve attempt '+intToStr(resolveRetryCount)+
' failed: '+ inSendObject.localMailServer+
': '+e.message);
result:='';
end;
end; //try
end; // with
end;
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