3 files changed, 37 insertions, 11 deletions

diff --git a/src/core/lib/channel/channelz_registry.cc b/src/core/lib/channel/channelz_registry.cc
index 218e3e2094..89d0573280 100644
--- a/src/core/lib/channel/channelz_registry.cc
+++ b/src/core/lib/channel/channelz_registry.cc
@@ -79,12 +79,13 @@ void ChannelzRegistry::MaybePerformCompactionLocked() {
   }
 }
 
-int ChannelzRegistry::FindByUuidLocked(intptr_t target_uuid) {
-  size_t left = 0;
-  size_t right = entities_.size() - 1;
+int ChannelzRegistry::FindByUuidLocked(intptr_t target_uuid,
+                                       bool direct_hit_needed) {
+  int left = 0;
+  int right = int(entities_.size() - 1);
   while (left <= right) {
-    size_t true_middle = left + (right - left) / 2;
-    size_t first_non_null = true_middle;
+    int true_middle = left + (right - left) / 2;
+    int first_non_null = true_middle;
     while (first_non_null < right && entities_[first_non_null] == nullptr) {
       first_non_null++;
     }
@@ -102,14 +103,14 @@ int ChannelzRegistry::FindByUuidLocked(intptr_t target_uuid) {
       right = true_middle - 1;
     }
   }
-  return -1;
+  return direct_hit_needed ? -1 : right;
 }
 
 void ChannelzRegistry::InternalUnregister(intptr_t uuid) {
   GPR_ASSERT(uuid >= 1);
   MutexLock lock(&mu_);
   GPR_ASSERT(uuid <= uuid_generator_);
-  int idx = FindByUuidLocked(uuid);
+  int idx = FindByUuidLocked(uuid, true);
   GPR_ASSERT(idx >= 0);
   entities_[idx] = nullptr;
   num_empty_slots_++;
@@ -121,7 +122,7 @@ BaseNode* ChannelzRegistry::InternalGet(intptr_t uuid) {
   if (uuid < 1 || uuid > uuid_generator_) {
     return nullptr;
   }
-  int idx = FindByUuidLocked(uuid);
+  int idx = FindByUuidLocked(uuid, true);
   return idx < 0 ? nullptr : entities_[idx];
 }
 
@@ -132,7 +133,8 @@ char* ChannelzRegistry::InternalGetTopChannels(intptr_t start_channel_id) {
   grpc_json* json_iterator = nullptr;
   InlinedVector<BaseNode*, 10> top_level_channels;
   bool reached_pagination_limit = false;
-  for (size_t i = 0; i < entities_.size(); ++i) {
+  int start_idx = GPR_MAX(FindByUuidLocked(start_channel_id, false), 0);
+  for (size_t i = start_idx; i < entities_.size(); ++i) {
     if (entities_[i] != nullptr &&
         entities_[i]->type() ==
             grpc_core::channelz::BaseNode::EntityType::kTopLevelChannel &&
@@ -173,7 +175,8 @@ char* ChannelzRegistry::InternalGetServers(intptr_t start_server_id) {
   grpc_json* json_iterator = nullptr;
   InlinedVector<BaseNode*, 10> servers;
   bool reached_pagination_limit = false;
-  for (size_t i = 0; i < entities_.size(); ++i) {
+  int start_idx = GPR_MAX(FindByUuidLocked(start_server_id, false), 0);
+  for (size_t i = start_idx; i < entities_.size(); ++i) {
     if (entities_[i] != nullptr &&
         entities_[i]->type() ==
             grpc_core::channelz::BaseNode::EntityType::kServer &&
diff --git a/src/core/lib/channel/channelz_registry.h b/src/core/lib/channel/channelz_registry.h
index ea6ab6c8e5..326f0201c7 100644
--- a/src/core/lib/channel/channelz_registry.h
+++ b/src/core/lib/channel/channelz_registry.h
@@ -92,7 +92,9 @@ class ChannelzRegistry {
   void MaybePerformCompactionLocked();
 
   // Performs binary search on entities_ to find the index with that uuid.
-  int FindByUuidLocked(intptr_t uuid);
+  // If direct_hit_needed, then will return -1 in case of absence.
+  // Else, will return idx of the first uuid higher than the target.
+  int FindByUuidLocked(intptr_t uuid, bool direct_hit_needed);
 
   // protects members
   gpr_mu mu_;
diff --git a/test/core/channel/channelz_test.cc b/test/core/channel/channelz_test.cc
index 48e558dfc0..4a1f53b924 100644
--- a/test/core/channel/channelz_test.cc
+++ b/test/core/channel/channelz_test.cc
@@ -402,6 +402,27 @@ TEST_F(ChannelzRegistryBasedTest, GetTopChannelsMiddleUuidCheck) {
   gpr_free(json_str);
 }
 
+TEST_F(ChannelzRegistryBasedTest, GetTopChannelsNoHitUuid) {
+  grpc_core::ExecCtx exec_ctx;
+  ChannelFixture pre_channels[40];  // will take uuid[1, 40]
+  (void)pre_channels;               // suppress unused variable error
+  ServerFixture servers[10];        // will take uuid[41, 50]
+  (void)servers;                    // suppress unused variable error
+  ChannelFixture channels[10];      // will take uuid[51, 60]
+  (void)channels;                   // suppress unused variable error
+  // query in the middle of the server channels
+  char* json_str = ChannelzRegistry::GetTopChannels(45);
+  grpc_json* parsed_json = grpc_json_parse_string(json_str);
+  ValidateJsonArraySize(parsed_json, "channel", 10);
+  grpc_json* json_channels = GetJsonChild(parsed_json, "channel");
+  std::vector<intptr_t> uuids = GetUuidListFromArray(json_channels);
+  for (size_t i = 0; i < uuids.size(); ++i) {
+    EXPECT_EQ(static_cast<intptr_t>(51 + i), uuids[i]);
+  }
+  grpc_json_destroy(parsed_json);
+  gpr_free(json_str);
+}
+
 TEST_F(ChannelzRegistryBasedTest, GetTopChannelsUuidAfterCompaction) {
   const intptr_t kLoopIterations = 50;
   grpc_core::ExecCtx exec_ctx;