In quic, include minplaintextpacketsize when deterine whether removing soft limit for crypto frames. protected by enabled gfe2_reloadable_flag_quic_fix_min_crypto_frame_size. PiperOrigin-RevId: 317743102 Change-Id: I43d56a2b3daea603cac4d2746f58426610875b0f

diff --git a/quic/core/quic_connection_test.cc b/quic/core/quic_connection_test.cc
index affd89f..d0f38a5 100644
--- a/quic/core/quic_connection_test.cc
+++ b/quic/core/quic_connection_test.cc

@@ -11345,6 +11345,44 @@
   }
 }
 
+// Regresstion test for b/156232673.
+TEST_P(QuicConnectionTest, CoalescePacketOfLowerEncryptionLevel) {
+  if (!connection_.version().CanSendCoalescedPackets()) {
+    return;
+  }
+  if (GetQuicReloadableFlag(quic_fix_min_crypto_frame_size)) {
+    EXPECT_CALL(visitor_, OnHandshakePacketSent()).Times(1);
+  } else {
+    EXPECT_CALL(visitor_, OnHandshakePacketSent()).Times(0);
+  }
+  {
+    QuicConnection::ScopedPacketFlusher flusher(&connection_);
+    use_tagging_decrypter();
+    connection_.SetEncrypter(ENCRYPTION_HANDSHAKE,
+                             std::make_unique<TaggingEncrypter>(0x01));
+    connection_.SetEncrypter(ENCRYPTION_FORWARD_SECURE,
+                             std::make_unique<TaggingEncrypter>(0x02));
+    connection_.SetDefaultEncryptionLevel(ENCRYPTION_FORWARD_SECURE);
+    SendStreamDataToPeer(2, string(1286, 'a'), 0, NO_FIN, nullptr);
+    connection_.SetDefaultEncryptionLevel(ENCRYPTION_HANDSHAKE);
+    // Try to coalesce a HANDSHAKE packet after 1-RTT packet.
+    if (GetQuicReloadableFlag(quic_fix_min_crypto_frame_size)) {
+      // Verify soft max packet length gets resumed and handshake packet gets
+      // successfully sent.
+      connection_.SendCryptoDataWithString("a", 0, ENCRYPTION_HANDSHAKE);
+    } else {
+      // Problematic: creator thinks there is space to consume 1-byte, however,
+      // extra paddings make the serialization fail because of
+      // MinPlaintextPacketSize.
+      EXPECT_CALL(visitor_,
+                  OnConnectionClosed(_, ConnectionCloseSource::FROM_SELF));
+      EXPECT_QUIC_BUG(
+          connection_.SendCryptoDataWithString("a", 0, ENCRYPTION_HANDSHAKE),
+          "AppendPaddingFrame of 3 failed");
+    }
+  }
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace quic

diff --git a/quic/core/quic_packet_creator.cc b/quic/core/quic_packet_creator.cc
index 82b4a27..7672a37 100644
--- a/quic/core/quic_packet_creator.cc
+++ b/quic/core/quic_packet_creator.cc

@@ -198,6 +198,8 @@
   }
   if (framer_->GetMaxPlaintextSize(length) <
       PacketHeaderSize() + MinPlaintextPacketSize(framer_->version())) {
+    // Please note: this would not guarantee to fit next packet if the size of
+    // packet header increases (e.g., encryption level changes).
     QUIC_DLOG(INFO) << length << " is too small to fit packet header";
     return;
   }
@@ -423,8 +425,17 @@
                                           QuicFrame* frame) {
   size_t min_frame_size =
       QuicFramer::GetMinCryptoFrameSize(write_length, offset);
-  if (BytesFree() <= min_frame_size &&
-      (!RemoveSoftMaxPacketLength() || BytesFree() <= min_frame_size)) {
+  size_t min_plaintext_bytes = min_frame_size;
+  if (fix_min_crypto_frame_size_ && queued_frames_.empty()) {
+    // TODO(fayang): to make this more general, we need to move the checking
+    // when trying to add a frame when GetSerializedFrameLength. Remove soft
+    // limit if current packet needs extra padding and the space is too small.
+    QUIC_RELOADABLE_FLAG_COUNT(quic_fix_min_crypto_frame_size);
+    min_plaintext_bytes =
+        std::max(min_frame_size, MinPlaintextPacketSize(framer_->version()));
+  }
+  if (BytesFree() <= min_plaintext_bytes &&
+      (!RemoveSoftMaxPacketLength() || BytesFree() <= min_plaintext_bytes)) {
     return false;
   }
   size_t max_write_length = BytesFree() - min_frame_size;

diff --git a/quic/core/quic_packet_creator.h b/quic/core/quic_packet_creator.h
index c25d8f6..743e46e 100644
--- a/quic/core/quic_packet_creator.h
+++ b/quic/core/quic_packet_creator.h

@@ -601,6 +601,9 @@
 
   const bool avoid_leak_writer_buffer_ =
       GetQuicReloadableFlag(quic_avoid_leak_writer_buffer);
+
+  const bool fix_min_crypto_frame_size_ =
+      GetQuicReloadableFlag(quic_fix_min_crypto_frame_size);
 };
 
 }  // namespace quic