Add a data structure QuicMultipathTransmissionsMap which is not in use now.

net/quic/quic_multipath_transmissions_map_test.cc

+#include "net/quic/quic_multipath_transmissions_map.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace net_quic {
+namespace test {
+namespace {
+
+TEST(QuicAcrossPathsTransmissionMapTest, OnPacketRetransmittedOnDifferentPath) {
+  QuicMultipathTransmissionsMap transmission_map;
+  // Packet0's original transmission sent on path 1 with packet number 1.
+  QuicPathIdPacketNumber packet0_0(1, 1);
+  // Packet0's retransmission sent on path 2 with packet number 1.
+  QuicPathIdPacketNumber packet0_1(2, 1);
+  // packet0's 2nd retransmission sent on path 3 with packet number 1.
+  QuicPathIdPacketNumber packet0_2(3, 1);
+
+  transmission_map.OnPacketRetransmittedOnDifferentPath(packet0_0, packet0_1);
+  const QuicMultipathTransmissionsMap::MultipathTransmissionsList*
+      transmission_list1 =
+          transmission_map.MaybeGetTransmissionsOnOtherPaths(packet0_0);
+  EXPECT_EQ(packet0_0, (*transmission_list1)[0]);
+  EXPECT_EQ(packet0_1, (*transmission_list1)[1]);
+
+  transmission_map.OnPacketRetransmittedOnDifferentPath(packet0_1, packet0_2);
+  const QuicMultipathTransmissionsMap::MultipathTransmissionsList*
+      transmission_list2 =
+          transmission_map.MaybeGetTransmissionsOnOtherPaths(packet0_0);
+  EXPECT_EQ(packet0_0, (*transmission_list2)[0]);
+  EXPECT_EQ(packet0_1, (*transmission_list2)[1]);
+  EXPECT_EQ(packet0_2, (*transmission_list2)[2]);
+  // Make sure there is no memory leakage.
+}
+
+TEST(QuicAcrossPathsTransmissionMapTest, MaybeGetTransmissionsOnOtherPaths) {
+  QuicMultipathTransmissionsMap transmission_map;
+  // Packet0's original transmission sent on path 1 with packet number 1.
+  QuicPathIdPacketNumber packet0_0(1, 1);
+  // Packet0's retransmission sent on path 2 with packet number 1.
+  QuicPathIdPacketNumber packet0_1(2, 1);
+  // packet0's 2nd retransmission sent on path 3 with packet number 1.
+  QuicPathIdPacketNumber packet0_2(3, 1);
+
+  transmission_map.OnPacketRetransmittedOnDifferentPath(packet0_0, packet0_1);
+  transmission_map.OnPacketRetransmittedOnDifferentPath(packet0_1, packet0_2);
+
+  const QuicMultipathTransmissionsMap::MultipathTransmissionsList*
+      transmission_list1 =
+          transmission_map.MaybeGetTransmissionsOnOtherPaths(packet0_0);
+  const QuicMultipathTransmissionsMap::MultipathTransmissionsList*
+      transmission_list2 =
+          transmission_map.MaybeGetTransmissionsOnOtherPaths(packet0_1);
+  const QuicMultipathTransmissionsMap::MultipathTransmissionsList*
+      transmission_list3 =
+          transmission_map.MaybeGetTransmissionsOnOtherPaths(packet0_2);
+  // Make sure all three pointers point to the same list.
+  EXPECT_EQ(transmission_list1, transmission_list2);
+  EXPECT_EQ(transmission_list2, transmission_list3);
+  EXPECT_EQ(packet0_0, (*transmission_list1)[0]);
+  EXPECT_EQ(packet0_1, (*transmission_list1)[1]);
+  EXPECT_EQ(packet0_2, (*transmission_list1)[2]);
+
+  // Packet1 which is not transmitted across path.
+  QuicPathIdPacketNumber packet1_0(1, 2);
+  EXPECT_EQ(nullptr,
+            transmission_map.MaybeGetTransmissionsOnOtherPaths(packet1_0));
+  // Make sure there is no memory leakage.
+}
+
+TEST(QuicAcrossPathsTransmissionMapTest, OnPacketHandled) {
+  QuicMultipathTransmissionsMap transmission_map;
+
+  // Packet's original transmission sent on path 1 with packet number 1.
+  QuicPathIdPacketNumber packet0_0(1, 1);
+  // Packet's retransmission sent on path 2 with packet number 1.
+  QuicPathIdPacketNumber packet0_1(2, 1);
+  // packet's 2nd retransmission sent on path 3 with packet number 1.
+  QuicPathIdPacketNumber packet0_2(3, 1);
+  transmission_map.OnPacketRetransmittedOnDifferentPath(packet0_0, packet0_1);
+  transmission_map.OnPacketRetransmittedOnDifferentPath(packet0_1, packet0_2);
+
+  // Packet1's original transmission sent on path 1 with packet number 2.
+  QuicPathIdPacketNumber packet1_0(1, 2);
+  // Packet1's retransmission sent on path 2 with packet number 2.
+  QuicPathIdPacketNumber packet1_1(2, 2);
+  transmission_map.OnPacketRetransmittedOnDifferentPath(packet1_0, packet1_1);
+
+  transmission_map.OnPacketHandled(packet0_0);
+  EXPECT_EQ(nullptr,
+            transmission_map.MaybeGetTransmissionsOnOtherPaths(packet0_0));
+  EXPECT_EQ(nullptr,
+            transmission_map.MaybeGetTransmissionsOnOtherPaths(packet0_1));
+  EXPECT_EQ(nullptr,
+            transmission_map.MaybeGetTransmissionsOnOtherPaths(packet0_2));
+  const QuicMultipathTransmissionsMap::MultipathTransmissionsList*
+      transmission_list =
+          transmission_map.MaybeGetTransmissionsOnOtherPaths(packet1_0);
+  EXPECT_EQ(packet1_0, (*transmission_list)[0]);
+  EXPECT_EQ(packet1_1, (*transmission_list)[1]);
+  // Packet 1 is received on path 2.
+  transmission_map.OnPacketHandled(packet1_1);
+  EXPECT_EQ(nullptr,
+            transmission_map.MaybeGetTransmissionsOnOtherPaths(packet1_0));
+  EXPECT_EQ(nullptr,
+            transmission_map.MaybeGetTransmissionsOnOtherPaths(packet1_1));
+  // Make sure there is no memory leakage.
+}
+
+}  // namespace
+}  // namespace test
+}  // namespace net_quic