Disallow invalid connection ID lengths in QUIC prober

Since we now follow the IETF spec and drop incoming packets with initial destination connection IDs shorter than 8 bytes, our prober API should not be able to generate them.

I've verified that all our callers use this API with a connection ID of length 8 so this change will not impact them.

gfe-relnote: client-only, not flag protected
PiperOrigin-RevId: 258691619
Change-Id: Ic2689216eae314efce8cab8275f93d4417d13d53

quic/core/quic_framer.cc

diff --git a/quic/core/quic_framer.cc b/quic/core/quic_framer.cc
index 5c9887d..e9d6fa9 100644
--- a/quic/core/quic_framer.cc
+++ b/quic/core/quic_framer.cc
@@ -6295,8 +6295,8 @@
     return false;
   }
   if (destination_connection_id_length > kQuicMaxConnectionIdLength ||
-      (destination_connection_id_length > 0 &&
-       destination_connection_id_length < 4)) {
+      destination_connection_id_length <
+          kQuicMinimumInitialConnectionIdLength) {
     QUIC_BUG << "Invalid connection_id_length";
     return false;
   }

quic/core/quic_framer.h

diff --git a/quic/core/quic_framer.h b/quic/core/quic_framer.h
index 3a3faa1..2349a77 100644
--- a/quic/core/quic_framer.h
+++ b/quic/core/quic_framer.h
@@ -585,8 +585,8 @@
   // |packet_length| must be in the range [1200, 65535].
   // |destination_connection_id_bytes| will be sent as the destination
   // connection ID, and must point to |destination_connection_id_length| bytes
-  // of memory. |destination_connection_id_length| must be either 0 or in the
-  // range [4,18]. When targeting Google servers, it is recommended to use a
+  // of memory. |destination_connection_id_length| must be in the range [8,18].
+  // When targeting Google servers, it is recommended to use a
   // |destination_connection_id_length| of 8.
   static bool WriteClientVersionNegotiationProbePacket(
       char* packet_bytes,