cache compressed certificate chains

fixes #227

crypto/cert_cache.go

@@ -0,0 +1,42 @@
+package crypto
+
+import (
+	"hash/fnv"
+	"sync"
+)
+
+var (
+	compressedCertsCache      = map[uint64][]byte{}
+	compressedCertsCacheMutex sync.RWMutex
+)
+
+func getCompressedCert(chain [][]byte, pCommonSetHashes, pCachedHashes []byte) ([]byte, error) {
+	// Hash all inputs
+	hash := fnv.New64a()
+	for _, v := range chain {
+		hash.Write(v)
+	}
+	hash.Write(pCommonSetHashes)
+	hash.Write(pCachedHashes)
+	hashRes := hash.Sum64()
+
+	compressedCertsCacheMutex.RLock()
+	result, isCached := compressedCertsCache[hashRes]
+	compressedCertsCacheMutex.RUnlock()
+	if isCached {
+		return result, nil
+	}
+
+	compressedCertsCacheMutex.Lock()
+	defer compressedCertsCacheMutex.Unlock()
+	result, isCached = compressedCertsCache[hashRes]
+	if isCached {
+		return result, nil
+	}
+	cached, err := compressChain(chain, pCommonSetHashes, pCachedHashes)
+	if err != nil {
+		return nil, err
+	}
+	compressedCertsCache[hashRes] = cached
+	return cached, nil
+}