Factoring a QuicCryptoServerStreamBase API out of QuicCryptoServerStream

net/quic/crypto/quic_crypto_server_config.cc

Index: net/quic/crypto/quic_crypto_server_config.cc
diff --git a/net/quic/crypto/quic_crypto_server_config.cc b/net/quic/crypto/quic_crypto_server_config.cc
index c523dd487d9f785ea6a1ff713ad338e77004ccd9..d1e2751720acb6bce05d50c1e281c0db11177ec6 100644
--- a/net/quic/crypto/quic_crypto_server_config.cc
+++ b/net/quic/crypto/quic_crypto_server_config.cc
@@ -547,27 +547,10 @@ QuicErrorCode QuicCryptoServerConfig::ProcessClientHello(
       validate_chlo_result.client_hello;
   const ClientHelloInfo& info = validate_chlo_result.info;
 
-  // If the client's preferred version is not the version we are currently
-  // speaking, then the client went through a version negotiation.  In this
-  // case, we need to make sure that we actually do not support this version
-  // and that it wasn't a downgrade attack.
-  QuicTag client_version_tag;
-  if (client_hello.GetUint32(kVER, &client_version_tag) != QUIC_NO_ERROR) {
-    *error_details = "client hello missing version list";
-    return QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER;
-  }
-  QuicVersion client_version = QuicTagToQuicVersion(client_version_tag);
-  if (client_version != version) {
-    // Just because client_version is a valid version enum doesn't mean that
-    // this server actually supports that version, so we check to see if
-    // it's actually in the supported versions list.
-    for (size_t i = 0; i < supported_versions.size(); ++i) {
-      if (client_version == supported_versions[i]) {
-        *error_details = "Downgrade attack detected";
-        return QUIC_VERSION_NEGOTIATION_MISMATCH;
-      }
-    }
-  }
+  QuicErrorCode valid = CryptoUtils::ValidateClientHello(
+      client_hello, version, supported_versions, error_details);
+  if (valid != QUIC_NO_ERROR)
+    return valid;
 
   StringPiece requested_scid;
   client_hello.GetStringPiece(kSCID, &requested_scid);