Provide a more natural interface in apply_context and have wasm_interface...

Provide a more natural interface in apply_context and have wasm_interface provide the shim code to accommodate the contract API.

libraries/chain/apply_context.cpp

@@ -224,16 +224,13 @@ const contracts::table_id_object& apply_context::find_or_create_table( name scop
    });
 }
 
-size_t apply_context::get_active_producers(account_name* producers, size_t len) {
+vector<account_name> apply_context::get_active_producers() const {
    const auto& gpo = controller.get_global_properties();
-   int index = 0;
+   vector<account_name> accounts;
    for(const auto& producer : gpo.active_producers.producers)
-   {
-      *(producers + index) = producer.producer_name;
-      if (++index >= len)
-         break;
-   }
-   return index;
+      accounts.push_back(producer.producer_name);
+
+   return accounts;
 }
 
 } } /// eosio::chain

libraries/chain/include/eosio/chain/apply_context.hpp

@@ -94,7 +94,7 @@ class apply_context {
       bool                     all_authorizations_used()const;
       vector<permission_level> unused_authorizations()const;
 
-      size_t get_active_producers(account_name* producers, size_t len);
+      vector<account_name> get_active_producers() const;
 
       const chain_controller&       controller;
       const chainbase::database&    db;  ///< database where state is stored

libraries/chain/wasm_interface.cpp

@@ -449,8 +449,10 @@ class producer_api : public context_aware_api {
       using context_aware_api::context_aware_api;
 
       int get_active_producers(array_ptr<chain::account_name> producers, size_t datalen) {
-         auto actual_num_prod = context.get_active_producers(producers, datalen / sizeof(chain::account_name));
-         return actual_num_prod * sizeof(chain::account_name);
+         auto active_producers = context.get_active_producers();
+         size_t len = std::min(datalen / sizeof(chain::account_name), active_producers.size());
+         memcpy(producers, active_producers.data(), len);
+         return active_producers.size() * sizeof(chain::account_name);
       }
 };