From b2c773d26f6126517526919a31093d919302e688 Mon Sep 17 00:00:00 2001
From: Yash Tibrewal <yashkt@google.com>
Date: Fri, 29 Mar 2019 17:06:09 -0700
Subject: [PATCH] Global Registry for Service Config Parsers

---
 .../filters/client_channel/service_config.cc  |  2 ++
 .../filters/client_channel/service_config.h   | 36 +++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/src/core/ext/filters/client_channel/service_config.cc b/src/core/ext/filters/client_channel/service_config.cc
index bbf671d979e..e2d23010c8a 100644
--- a/src/core/ext/filters/client_channel/service_config.cc
+++ b/src/core/ext/filters/client_channel/service_config.cc
@@ -33,6 +33,8 @@
 
 namespace grpc_core {
 
+int ServiceConfig::registered_parsers_count = 0;
+
 RefCountedPtr<ServiceConfig> ServiceConfig::Create(const char* json) {
   UniquePtr<char> service_config_json(gpr_strdup(json));
   UniquePtr<char> json_string(gpr_strdup(json));
diff --git a/src/core/ext/filters/client_channel/service_config.h b/src/core/ext/filters/client_channel/service_config.h
index d9063479e32..b211d732d3f 100644
--- a/src/core/ext/filters/client_channel/service_config.h
+++ b/src/core/ext/filters/client_channel/service_config.h
@@ -54,6 +54,15 @@
 
 namespace grpc_core {
 
+/// This is the base class that all service config parsers MUST use to store
+/// parsed service config data.
+class ServiceConfigParsedObject {
+ public:
+  virtual ~ServiceConfigParsedObject() = default;
+
+  GRPC_ABSTRACT_BASE_CLASS;
+};
+
 class ServiceConfig : public RefCounted<ServiceConfig> {
  public:
   /// Creates a new service config from parsing \a json_string.
@@ -96,6 +105,26 @@ class ServiceConfig : public RefCounted<ServiceConfig> {
   static RefCountedPtr<T> MethodConfigTableLookup(
       const SliceHashTable<RefCountedPtr<T>>& table, const grpc_slice& path);
 
+  /// Retrieves the parsed object at index \a index.
+  ServiceConfigParsedObject* GetParsedServiceConfigObject(int index) {
+    GPR_DEBUG_ASSERT(index < registered_parsers_count);
+    return parsed_service_config_objects[index].get();
+  }
+
+  typedef UniquePtr<ServiceConfigParsedObject> (*ServiceConfigParser)(
+      const char* service_config_json);
+
+  /// Globally register a service config parser. On successful registration, it
+  /// returns the index at which the parser was registered. On failure, -1 is
+  /// returned. Each new service config update will go through all the
+  /// registered parser. Each parser is responsible for reading the service
+  /// config json and returning a parsed object. This parsed object can later be
+  /// retrieved using the same index that was returned at registration time.
+  static int RegisterParser(ServiceConfigParser func) {
+    registered_parsers[registered_parsers_count] = func;
+    return registered_parsers_count++;
+  }
+
  private:
   // So New() can call our private ctor.
   template <typename T, typename... Args>
@@ -120,9 +149,16 @@ class ServiceConfig : public RefCounted<ServiceConfig> {
       grpc_json* json, CreateValue<T> create_value,
       typename SliceHashTable<RefCountedPtr<T>>::Entry* entries, size_t* idx);
 
+  static constexpr int kMaxParsers = 32;
+  static int registered_parsers_count;
+  static ServiceConfigParser registered_parsers[kMaxParsers];
+
   UniquePtr<char> service_config_json_;
   UniquePtr<char> json_string_;  // Underlying storage for json_tree.
   grpc_json* json_tree_;
+
+  InlinedVector<UniquePtr<ServiceConfigParsedObject>, kMaxParsers>
+      parsed_service_config_objects;
 };
 
 //