Adding API call: get_potential_signatures

This call allows wallets to filter the set of keys that may potentially
sign a transaction prior to calling get_required_signatures to get the
minimum subset.

libraries/app/api.cpp

@@ -1129,6 +1129,26 @@ namespace graphene { namespace app {
                                            [&]( account_id_type id ){ return &id(_db).owner; },
                                            _db.get_global_properties().parameters.max_authority_depth );
     }
+    set<public_key_type> database_api::get_potential_signatures( const signed_transaction& trx )const
+    {
+       set<public_key_type> result;
+       trx.get_required_signatures( _db.get_chain_id(),
+                                    flat_set<public_key_type>(),
+                                    [&]( account_id_type id ){ 
+                                        const auto& auth = &id(_db).active
+                                        for( const auto& k : auth.get_keys() )
+                                          result.insert(k)
+                                        return &auth; },
+                                    [&]( account_id_type id ){ 
+                                        const auto& auth = &id(_db).owner
+                                        for( const auto& k : auth.get_keys() )
+                                          result.insert(k)
+                                        return &auth; },
+                                        },
+                                    _db.get_global_properties().parameters.max_authority_depth );
+
+       return result;
+    }
 
     bool database_api::verify_authority( const signed_transaction& trx )const
     {

libraries/app/include/graphene/app/api.hpp

@@ -331,6 +331,13 @@ namespace graphene { namespace app {
           */
          set<public_key_type> get_required_signatures( const signed_transaction& trx, const flat_set<public_key_type>& available_keys )const;
 
+         /**
+          *  This method will return the set of all public keys that could possibly sign for a given transaction.  This call can
+          *  be used by wallets to filter their set of public keys to just the relevant subset prior to calling @ref get_required_signatures
+          *  to get the minimum subset. 
+          */
+         set<public_key_type> get_potential_signatures( const signed_transaction& trx )const;
+
          /**
           * @return true of the @ref trx has all of the required signatures, otherwise throws an exception
           */
@@ -562,6 +569,7 @@ FC_API(graphene::app::database_api,
        (get_balance_objects)
        (get_vested_balances)
        (get_required_signatures)
+       (get_potential_signatures)
        (verify_authority)
        (get_blinded_balances)
        (get_required_fees)

libraries/fc

@@ -1 +1 @@
-Subproject commit 088dadd12481e75829b83c098f3bc36b7e296ca0
+Subproject commit d11b48a015e0c339cc20f739ef1f8a5b3c57b913