public QueryResult Resolve(Query query)
{
// Find potential matches
var matches =
_dnsRuleGroups
.Select(group => new
{
Group = group,
RuleMatchResult = GetRuleMatch(query,
group)
})
.Where(match => match.RuleMatchResult.Match)
.OrderByDescending(match => match.RuleMatchResult.HostnameSimilarity)
.ToArray();
if (!matches.Any())
{
return new QueryResult() { Result = false };
}
var bestMatch = matches.First();
var rule = bestMatch.RuleMatchResult.Rule;
string ruleValue;
if (!string.IsNullOrWhiteSpace(rule.ValueAlias))
{
var result = _dnsValueAliases
.Where(alias =>
alias != null
&&
rule.ValueAlias != null
&&
string.Compare(alias.Name,
rule.ValueAlias,
StringComparison.InvariantCultureIgnoreCase)
== 0)
.FirstOrDefault();
if (result == null)
{
throw new WranglerConfigurationException(
string.Format("Alias {0} is specified in Rule {1} but wasn't found", rule.ValueAlias,
rule.ToString()));
}
ruleValue = result.Value;
}
else
{
ruleValue = rule.Value;
}
return new QueryResult()
{
Result = true,
RecordType = rule.RecordType,
RecordValue = ruleValue,
RuleResult = rule.RuleType
};
}
private double FindHostnameSimilarity(Query query, DnsRule rule)
{
var hostnames = rule.Hostnames;
if (query.QueryType != DnsRecordType.CNAME && query.QueryType != DnsRecordType.A)
{
if (hostnames.Any(hostname => hostname.HostnameType == HostnameType.Exact && hostname.HostnameEntry == query.Question))
{
return 1;
}
return 0;
}
if (hostnames.Any(hostname => hostname.HostnameType == HostnameType.Exact && hostname.HostnameEntry == query.Question))
{
return 1;
}
if (hostnames.Any(hostname => hostname.HostnameType == HostnameType.Wildcard && query.Question.EndsWith(hostname.HostnameEntry)))
{
return 0.9;
}
return 0;
}
private double SimilarRuleTypes(Query query, DnsRule rule)
{
if (rule.RuleType.HasValue && (rule.RuleType.Value == DnsRuleType.NXDomain || rule.RuleType.Value == DnsRuleType.ResolveUpstream))
{
return 0.1;
}
if (rule.RecordType == query.QueryType)
{
return 1;
}
if (query.QueryType == DnsRecordType.A && rule.RecordType == DnsRecordType.CNAME)
{
return 0.9;
}
return 0;
}
private RuleMatchResult GetRuleMatch(Query query, DnsRuleGroup group)
{
// Examine the group's rules and give a result.
var similarRules = group.Rules
.Select(rule => new
{
HostnameSimilarity = FindHostnameSimilarity(query, rule),
TypeSimilarity = SimilarRuleTypes(query, rule),
Rule = rule
})
.Where(result => result.HostnameSimilarity > 0 && result.TypeSimilarity > 0)
.OrderByDescending(rule => rule.HostnameSimilarity)
.ThenByDescending(rule => rule.TypeSimilarity)
.ToArray();
if (!similarRules.Any())
{
return new RuleMatchResult { Match = false };
}
return
similarRules
.Select(
rule =>
new RuleMatchResult
{
HostnameSimilarity = rule.HostnameSimilarity,
Match = true,
Rule = rule.Rule
})
.FirstOrDefault();
}