public async Task <string> Evaluate()
{
try
{
await Expand();
StringBuilder sb = new StringBuilder();
foreach (string text in await DnsResolver.LookupText(Domain))
{
sb.Append(text); // No white-space delimiter
}
SpfStatement.Reset("=" + sb.ToString());
Explanation explanation = new Explanation(SpfStatement, Qualifier);
await explanation.Expand();
return(explanation.Domain);
}
catch (Exception)
{
return(null);
}
}
public override async Task Expand()
{
if (_expanded)
{
return;
}
_expanded = true;
SpfStatement.Reset(Domain);
StringBuilder sb = new StringBuilder();
char ch;
while ((ch = SpfStatement.PeekNextCharacter()) > ' ')
{
SpfStatement.Position++;
if (ch == '%')
{
switch (ch = SpfStatement.PeekNextCharacter())
{
case (char)0:
sb.Append('%');
break;
case '%':
SpfStatement.Position++;
sb.Append('%');
break;
case '_':
SpfStatement.Position++;
sb.Append(' ');
break;
case '-':
SpfStatement.Position++;
sb.Append("%20");
break;
case '{':
SpfStatement.Position++;
char macroLetter = char.ToLower(SpfStatement.NextCharacter());
int? digit;
bool reverse;
if (char.IsDigit(SpfStatement.PeekNextCharacter()))
{
digit = SpfStatement.NextInteger();
if (digit == 0)
{
throw new Exception("Invalid number of digits.");
}
}
else
{
digit = null;
}
if (char.ToLower(SpfStatement.PeekNextCharacter()) == 'r')
{
SpfStatement.Position++;
reverse = true;
}
else
{
reverse = false;
}
int start = SpfStatement.Position;
while ((ch = SpfStatement.PeekNextCharacter()) == '.' || ch == '-' || ch == '+' ||
ch == ',' || ch == '/' || ch == '_' || ch == '=')
{
SpfStatement.Position++;
}
string delimiter =
SpfStatement.Statement.Substring(start, SpfStatement.Position - start);
ch = SpfStatement.NextCharacter();
if (ch != '}')
{
throw new Exception("Expected }");
}
string s;
switch (macroLetter)
{
case 's': // sender
s = SpfStatement.Sender;
break;
case 'l': // local-part of sender
s = SpfStatement.Sender;
int i = s.IndexOf('@');
if (i < 0)
{
s = string.Empty;
}
else
{
s = s.Substring(0, i);
}
break;
case 'o': // domain of sender
s = SpfStatement.Sender;
i = s.IndexOf('@');
if (i >= 0)
{
s = s.Substring(i + 1);
}
break;
case 'd': // domain
s = SpfStatement.Domain;
break;
case 'i':
switch (SpfStatement.IpAddress.AddressFamily)
{
case AddressFamily.InterNetwork:
s = SpfStatement.IpAddress.ToString();
break;
case AddressFamily.InterNetworkV6:
byte[] bin = SpfStatement.IpAddress.GetAddressBytes();
StringBuilder sb2 = new StringBuilder();
byte b, b2;
for (i = 0; i < 16; i++)
{
b = bin[i];
b2 = (byte)(b >> 4);
if (b2 < 10)
{
sb2.Append((char)('0' + b2));
}
else
{
sb2.Append((char)('a' + b2 - 10));
}
sb2.Append('.');
b2 = (byte)(b & 15);
if (b2 < 10)
{
sb2.Append((char)('0' + b2));
}
else
{
sb2.Append((char)('a' + b2 - 10));
}
if (i < 15)
{
sb2.Append('.');
}
}
s = sb2.ToString();
break;
default:
throw new Exception("Invalid client address.");
}
break;
case 'p':
try
{
if (SpfStatement.RemainingQueries-- <= 0)
{
throw new Exception("DNS Lookup maximum reached.");
}
string[] domainNames =
await DnsResolver.LookupDomainName(SpfStatement.IpAddress);
// First check if domain is found.
s = null;
foreach (string domainName in domainNames)
{
if (String.Compare(domainName, SpfStatement.Domain,
StringComparison.OrdinalIgnoreCase) == 0 &&
await this.MatchReverseIp(domainName))
{
s = domainName;
break;
}
}
if (s is null)
{
// Second, check if sub-domain is found.
foreach (string domainName in domainNames)
{
if (domainName.EndsWith("." + SpfStatement.Domain,
StringComparison.CurrentCultureIgnoreCase) &&
await this.MatchReverseIp(domainName))
{
s = domainName;
break;
}
}
if (s is null)
{
if (domainNames.Length == 0)
{
s = "unknown";
}
else
{
s = domainNames[DnsResolver.Next(domainNames.Length)];
}
}
}
}
catch (ArgumentException)
{
s = "unknown";
}
catch (TimeoutException)
{
s = "unknown";
}
break;
case 'v':
switch (SpfStatement.IpAddress.AddressFamily)
{
case AddressFamily.InterNetwork:
s = "in-addr";
break;
case AddressFamily.InterNetworkV6:
s = "ip6";
break;
default:
throw new Exception("Invalid client address.");
}
break;
case 'h':
s = SpfStatement.HeloDomain;
break;
case 'c':
this.AssertExplanation();
s = SpfStatement.IpAddress.ToString();
break;
case 'r':
this.AssertExplanation();
s = SpfStatement.HostDomain;
break;
case 't':
this.AssertExplanation();
int seconds = (int)Math.Round((DateTime.UtcNow - UnixEpoch).TotalSeconds);
s = seconds.ToString();
break;
default:
throw new Exception("Unknown macro.");
}
if (reverse || digit.HasValue || !string.IsNullOrEmpty(delimiter))
{
if (string.IsNullOrEmpty(delimiter))
{
delimiter = ".";
}
string[] parts = s.Split(new string[] { delimiter }, StringSplitOptions.None);
int i = parts.Length;
if (reverse)
{
Array.Reverse(parts);
}
if (digit.HasValue && digit.Value < i)
{
i = digit.Value;
}
bool first = true;
int j = parts.Length - i;
while (i-- > 0)
{
if (first)
{
first = false;
}
else
{
sb.Append('.');
}
sb.Append(parts[j++]);
}
}
else
{
sb.Append(s);
}
break;
default:
SpfStatement.Position++;
sb.Append('%');
sb.Append(ch);
break;
}
}
else
{
sb.Append(ch);
}
}
Domain = sb.ToString();
}