implement certificate compression using common certificate sets

fixes #47

crypto/cert_sets.go

@@ -0,0 +1,24 @@
+package crypto
+
+import (
+	"bytes"
+
+	"github.com/lucas-clemente/quic-go-certificates"
+)
+
+type certSet [][]byte
+
+var certSets = map[uint64]certSet{
+	certsets.CertSet1Hash: certsets.CertSet1,
+	certsets.CertSet2Hash: certsets.CertSet2,
+}
+
+// findCertInSet searches for the cert in the set. Negative return value means not found.
+func (s *certSet) findCertInSet(cert []byte) int {
+	for i, c := range *s {
+		if bytes.Equal(c, cert) {
+			return i
+		}
+	}
+	return -1
+}