From 6e81377686c0db83dc28dca437f3350e758e5c03 Mon Sep 17 00:00:00 2001
From: Brian Johnson <johnsonb@objectcomputing.com>
Date: Tue, 23 Jan 2018 16:07:58 -0600
Subject: [PATCH] Fixed get_active_producers for c API passing buffer byte
 length and added returning the number of bytes written, so user knows how
 many bytes were populated.

---
 contracts/eoslib/chain.h                             | 12 ++++++------
 libraries/chain/apply_context.cpp                    |  5 +++--
 .../chain/include/eosio/chain/apply_context.hpp      |  2 +-
 libraries/chain/wasm_interface.cpp                   |  7 ++++---
 4 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/contracts/eoslib/chain.h b/contracts/eoslib/chain.h
index a15e6f4d4..af3757235 100644
--- a/contracts/eoslib/chain.h
+++ b/contracts/eoslib/chain.h
@@ -21,19 +21,19 @@
 
 extern "C" {
    /**
-    * @brief Return the set of active producers
-    * @details Return the set of active producers
-    *
-    * @param producers - location to store the active producers
+    * Return the set of active producers
+    * @param producers - a pointer to an buffer of account_names
+    * @param datalen - byte length of buffer
+    * @return the number of bytes actually populated
     *
     *  Example:
     *  @code
     *  account_name producers[21];
-    *  get_active_producers(producers, sizeof(account_name)*21);
+    *  uint32_t bytes_populated = get_active_producers(producers, sizeof(account_name)*21);
     *  @endcode
     */
 
-   void get_active_producers( account_name* producers, uint32_t datalen );
+   uint32_t get_active_producers( account_name* producers, uint32_t datalen );
 
    ///@ } chaincapi
 }
diff --git a/libraries/chain/apply_context.cpp b/libraries/chain/apply_context.cpp
index 54c68ccc3..e0fbeb3a1 100644
--- a/libraries/chain/apply_context.cpp
+++ b/libraries/chain/apply_context.cpp
@@ -224,15 +224,16 @@ const contracts::table_id_object& apply_context::find_or_create_table( name scop
    });
 }
 
-void apply_context::get_active_producers(account_name* producers, size_t datalen) {
+size_t apply_context::get_active_producers(account_name* producers, size_t len) {
    const auto& gpo = controller.get_global_properties();
    int index = 0;
    for(const auto& producer : gpo.active_producers.producers)
    {
       *(producers + index) = producer.producer_name;
-      if (++index >= datalen)
+      if (++index >= len)
          break;
    }
+   return index;
 }
 
 } } /// eosio::chain
diff --git a/libraries/chain/include/eosio/chain/apply_context.hpp b/libraries/chain/include/eosio/chain/apply_context.hpp
index eaf67dc9b..06c6d5c4e 100644
--- a/libraries/chain/include/eosio/chain/apply_context.hpp
+++ b/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;
 
-      void get_active_producers(account_name* producers, size_t len);
+      size_t get_active_producers(account_name* producers, size_t len);
 
       const chain_controller&       controller;
       const chainbase::database&    db;  ///< database where state is stored
diff --git a/libraries/chain/wasm_interface.cpp b/libraries/chain/wasm_interface.cpp
index 4e5df22df..468d392f3 100644
--- a/libraries/chain/wasm_interface.cpp
+++ b/libraries/chain/wasm_interface.cpp
@@ -448,8 +448,9 @@ class producer_api : public context_aware_api {
    public:
       using context_aware_api::context_aware_api;
 
-      void get_active_producers(array_ptr<chain::account_name> producers, size_t datalen) {
-         context.get_active_producers(producers, datalen);
+      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);
       }
 };
 
@@ -742,7 +743,7 @@ class transaction_api : public context_aware_api {
 };
 
 REGISTER_INTRINSICS(producer_api,
-   (get_active_producers,      void(int, int))
+   (get_active_producers,      int(int, int))
 );
 
 REGISTER_INTRINSICS(crypto_api,
-- 
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