dynamic_modules: added host information callbacks for dynamic module clusters LB (#43875)

## Description

This PR adds host information callbacks for dynamic module cluster load
balancers, providing parity with the standalone load balancer's host
information API.

This includes host address, weight, health, locality, metadata, active
requests/connections, per-host counter stats, host data get/set, and
locality-aware routing callbacks.

---

**Commit Message:** dynamic_modules: added host information callbacks
for dynamic module clusters LB
**Additional Description:** Added host information callbacks for dynamic
module cluster load balancers
**Risk Level:** Low
**Testing:** Added Tests
**Docs Changes:** Added
**Release Notes:** N/A

Signed-off-by: Rohit Agrawal <rohit.agrawal@databricks.com>

Author: agrawroh

source/extensions/clusters/dynamic_modules/abi_impl.cc

@@ -409,6 +409,42 @@ const Upstream::PrioritySet& DynamicModuleLoadBalancer::prioritySet() const {
   return handle_->cluster_->prioritySet();
 }
 
+bool DynamicModuleLoadBalancer::setHostData(uint32_t priority, size_t index, uintptr_t data) {
+  const auto& host_sets = prioritySet().hostSetsPerPriority();
+  if (priority >= host_sets.size()) {
+    return false;
+  }
+  const auto& hosts = host_sets[priority]->hosts();
+  if (index >= hosts.size()) {
+    return false;
+  }
+  if (data == 0) {
+    per_host_data_.erase({priority, index});
+  } else {
+    per_host_data_[{priority, index}] = data;
+  }
+  return true;
+}
+
+bool DynamicModuleLoadBalancer::getHostData(uint32_t priority, size_t index,
+                                            uintptr_t* data) const {
+  const auto& host_sets = prioritySet().hostSetsPerPriority();
+  if (priority >= host_sets.size()) {
+    return false;
+  }
+  const auto& hosts = host_sets[priority]->hosts();
+  if (index >= hosts.size()) {
+    return false;
+  }
+  auto it = per_host_data_.find({priority, index});
+  if (it != per_host_data_.end()) {
+    *data = it->second;
+  } else {
+    *data = 0;
+  }
+  return true;
+}
+
 // =================================================================================================
 // DynamicModuleClusterFactory
 // =================================================================================================

source/extensions/clusters/dynamic_modules/cluster.cc

@@ -446,9 +446,16 @@ class DynamicModuleLoadBalancer : public Upstream::LoadBalancer {
   // Access the handle for async host selection completion.
   const DynamicModuleClusterHandleSharedPtr& handle() const { return handle_; }
 
+  // Per-host custom data storage.
+  bool setHostData(uint32_t priority, size_t index, uintptr_t data);
+  bool getHostData(uint32_t priority, size_t index, uintptr_t* data) const;
+
 private:
   const DynamicModuleClusterHandleSharedPtr handle_;
   envoy_dynamic_module_type_cluster_lb_module_ptr in_module_lb_;
+
+  // Per-host data storage keyed by (priority, index). This is per-LB-instance (per-worker).
+  absl::flat_hash_map<std::pair<uint32_t, size_t>, uintptr_t> per_host_data_;
 };
 
 /**

source/extensions/clusters/dynamic_modules/cluster.h

@@ -396,6 +396,164 @@ envoy_dynamic_module_callback_cluster_lb_get_healthy_host(
   return nullptr;
 }
 
+__attribute__((weak)) void envoy_dynamic_module_callback_cluster_lb_get_cluster_name(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, envoy_dynamic_module_type_envoy_buffer*) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_cluster_name: "
+               "not implemented in this context");
+}
+
+__attribute__((weak)) size_t envoy_dynamic_module_callback_cluster_lb_get_hosts_count(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_hosts_count: "
+               "not implemented in this context");
+  return 0;
+}
+
+__attribute__((weak)) size_t envoy_dynamic_module_callback_cluster_lb_get_degraded_hosts_count(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_degraded_hosts_count: "
+               "not implemented in this context");
+  return 0;
+}
+
+__attribute__((weak)) size_t envoy_dynamic_module_callback_cluster_lb_get_priority_set_size(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_priority_set_size: "
+               "not implemented in this context");
+  return 0;
+}
+
+__attribute__((weak)) bool envoy_dynamic_module_callback_cluster_lb_get_healthy_host_address(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t,
+    envoy_dynamic_module_type_envoy_buffer*) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_healthy_host_address: "
+               "not implemented in this context");
+  return false;
+}
+
+__attribute__((weak)) uint32_t envoy_dynamic_module_callback_cluster_lb_get_healthy_host_weight(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_healthy_host_weight: "
+               "not implemented in this context");
+  return 0;
+}
+
+__attribute__((weak)) envoy_dynamic_module_type_host_health
+envoy_dynamic_module_callback_cluster_lb_get_host_health(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_host_health: "
+               "not implemented in this context");
+  return envoy_dynamic_module_type_host_health_Unhealthy;
+}
+
+__attribute__((weak)) bool envoy_dynamic_module_callback_cluster_lb_get_host_health_by_address(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, envoy_dynamic_module_type_module_buffer,
+    envoy_dynamic_module_type_host_health*) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_host_health_by_address: "
+               "not implemented in this context");
+  return false;
+}
+
+__attribute__((weak)) bool envoy_dynamic_module_callback_cluster_lb_get_host_address(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t,
+    envoy_dynamic_module_type_envoy_buffer*) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_host_address: "
+               "not implemented in this context");
+  return false;
+}
+
+__attribute__((weak)) uint32_t envoy_dynamic_module_callback_cluster_lb_get_host_weight(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_host_weight: "
+               "not implemented in this context");
+  return 0;
+}
+
+__attribute__((weak)) uint64_t envoy_dynamic_module_callback_cluster_lb_get_host_stat(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t,
+    envoy_dynamic_module_type_host_stat) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_host_stat: "
+               "not implemented in this context");
+  return 0;
+}
+
+__attribute__((weak)) bool envoy_dynamic_module_callback_cluster_lb_get_host_locality(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t,
+    envoy_dynamic_module_type_envoy_buffer*, envoy_dynamic_module_type_envoy_buffer*,
+    envoy_dynamic_module_type_envoy_buffer*) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_host_locality: "
+               "not implemented in this context");
+  return false;
+}
+
+__attribute__((weak)) bool envoy_dynamic_module_callback_cluster_lb_set_host_data(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t, uintptr_t) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_set_host_data: "
+               "not implemented in this context");
+  return false;
+}
+
+__attribute__((weak)) bool envoy_dynamic_module_callback_cluster_lb_get_host_data(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t, uintptr_t*) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_host_data: "
+               "not implemented in this context");
+  return false;
+}
+
+__attribute__((weak)) bool envoy_dynamic_module_callback_cluster_lb_get_host_metadata_string(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t,
+    envoy_dynamic_module_type_module_buffer, envoy_dynamic_module_type_module_buffer,
+    envoy_dynamic_module_type_envoy_buffer*) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_host_metadata_string: "
+               "not implemented in this context");
+  return false;
+}
+
+__attribute__((weak)) bool envoy_dynamic_module_callback_cluster_lb_get_host_metadata_number(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t,
+    envoy_dynamic_module_type_module_buffer, envoy_dynamic_module_type_module_buffer, double*) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_host_metadata_number: "
+               "not implemented in this context");
+  return false;
+}
+
+__attribute__((weak)) bool envoy_dynamic_module_callback_cluster_lb_get_host_metadata_bool(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t,
+    envoy_dynamic_module_type_module_buffer, envoy_dynamic_module_type_module_buffer, bool*) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_host_metadata_bool: "
+               "not implemented in this context");
+  return false;
+}
+
+__attribute__((weak)) size_t envoy_dynamic_module_callback_cluster_lb_get_locality_count(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_locality_count: "
+               "not implemented in this context");
+  return 0;
+}
+
+__attribute__((weak)) size_t envoy_dynamic_module_callback_cluster_lb_get_locality_host_count(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_locality_host_count: "
+               "not implemented in this context");
+  return 0;
+}
+
+__attribute__((weak)) bool envoy_dynamic_module_callback_cluster_lb_get_locality_host_address(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t, size_t,
+    envoy_dynamic_module_type_envoy_buffer*) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_locality_host_address: "
+               "not implemented in this context");
+  return false;
+}
+
+__attribute__((weak)) uint32_t envoy_dynamic_module_callback_cluster_lb_get_locality_weight(
+    envoy_dynamic_module_type_cluster_lb_envoy_ptr, uint32_t, size_t) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_get_locality_weight: "
+               "not implemented in this context");
+  return 0;
+}
+
 __attribute__((weak)) bool envoy_dynamic_module_callback_cluster_lb_context_compute_hash_key(
     envoy_dynamic_module_type_cluster_lb_context_envoy_ptr, uint64_t*) {
   IS_ENVOY_BUG("envoy_dynamic_module_callback_cluster_lb_context_compute_hash_key: "
@@ -646,20 +804,6 @@ __attribute__((weak)) uint32_t envoy_dynamic_module_callback_lb_get_host_weight(
   return 0;
 }
 
-__attribute__((weak)) uint64_t envoy_dynamic_module_callback_lb_get_host_active_requests(
-    envoy_dynamic_module_type_lb_envoy_ptr, uint32_t, size_t) {
-  IS_ENVOY_BUG("envoy_dynamic_module_callback_lb_get_host_active_requests: "
-               "not implemented in this context");
-  return 0;
-}
-
-__attribute__((weak)) uint64_t envoy_dynamic_module_callback_lb_get_host_active_connections(
-    envoy_dynamic_module_type_lb_envoy_ptr, uint32_t, size_t) {
-  IS_ENVOY_BUG("envoy_dynamic_module_callback_lb_get_host_active_connections: "
-               "not implemented in this context");
-  return 0;
-}
-
 __attribute__((weak)) bool
 envoy_dynamic_module_callback_lb_get_host_locality(envoy_dynamic_module_type_lb_envoy_ptr, uint32_t,
                                                    size_t, envoy_dynamic_module_type_envoy_buffer*,
@@ -800,11 +944,9 @@ __attribute__((weak)) bool envoy_dynamic_module_callback_lb_get_member_update_ho
   return false;
 }
 
-__attribute__((weak)) uint64_t envoy_dynamic_module_callback_lb_get_host_counter_stat(
-    envoy_dynamic_module_type_lb_envoy_ptr, uint32_t, size_t,
-    envoy_dynamic_module_type_host_counter_stat) {
-  IS_ENVOY_BUG("envoy_dynamic_module_callback_lb_get_host_counter_stat: "
-               "not implemented in this context");
+__attribute__((weak)) uint64_t envoy_dynamic_module_callback_lb_get_host_stat(
+    envoy_dynamic_module_type_lb_envoy_ptr, uint32_t, size_t, envoy_dynamic_module_type_host_stat) {
+  IS_ENVOY_BUG("envoy_dynamic_module_callback_lb_get_host_stat: not implemented in this context");
   return 0;
 }