Added Regex destination matching

ruleset.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"regexp"
+
+	"github.com/armon/go-socks5"
+	"golang.org/x/net/context"
+)
+
+// PermitDestAddrPattern returns a RuleSet which selectively allows addresses
+func PermitDestAddrPattern(pattern string) socks5.RuleSet {
+	return &PermitDestAddrPatternRuleSet{pattern}
+}
+
+// PermitDestAddrPatternRuleSet is an implementation of the RuleSet which
+// enables filtering supported destination address
+type PermitDestAddrPatternRuleSet struct {
+	AllowedFqdnPattern string
+}
+
+func (p *PermitDestAddrPatternRuleSet) Allow(ctx context.Context, req *socks5.Request) (context.Context, bool) {
+	match, _ := regexp.MatchString(p.AllowedFqdnPattern, req.DestAddr.FQDN)
+	return ctx, match
+}