Allow long header lengths in versions without IETF frames

This is safe without an explicit flag because QuicFramer::WriteIetfLongHeaderLength returns true when the version does not support long header lengths, which is the case for all versions other than v99.

http://google3/third_party/quic/core/quic_framer.cc?l=826&rcl=268972396

The goal of this change is to allow creating v49 which supports long header lengths but not IETF frames.

gfe-relnote: refactor without behavior change, protected by disabled v99 flag
PiperOrigin-RevId: 269738816
Change-Id: I5b69f7a0393e81856a7dc1efcd4a5baa1ebb8dab

quic/core/quic_framer.cc

diff --git a/quic/core/quic_framer.cc b/quic/core/quic_framer.cc
index db6b867..010d478 100644
--- a/quic/core/quic_framer.cc
+++ b/quic/core/quic_framer.cc
@@ -872,9 +872,6 @@
     }
     return writer.length();
   }
-  // TODO(dschinazi) if we enable long header lengths before v99, we need to
-  // add support for fixing up lengths in QuicFramer::BuildDataPacket.
-  DCHECK(!QuicVersionHasLongHeaderLengths(transport_version()));
 
   size_t i = 0;
   for (const QuicFrame& frame : frames) {
@@ -1009,6 +1006,10 @@
     ++i;
   }
 
+  if (!WriteIetfLongHeaderLength(header, &writer, length_field_offset, level)) {
+    return 0;
+  }
+
   return writer.length();
 }
 

quic/core/quic_versions.h

diff --git a/quic/core/quic_versions.h b/quic/core/quic_versions.h
index 98ffc2c..8a992ec 100644
--- a/quic/core/quic_versions.h
+++ b/quic/core/quic_versions.h
@@ -411,8 +411,6 @@
 // length field as defined by IETF QUIC draft-13 and later.
 QUIC_EXPORT_PRIVATE inline bool QuicVersionHasLongHeaderLengths(
     QuicTransportVersion transport_version) {
-  // TODO(dschinazi) if we enable long header lengths before v99, we need to
-  // add support for fixing up lengths in QuicFramer::BuildDataPacket.
   return transport_version == QUIC_VERSION_99;
 }