rpc: fix wrongly formatted JSON for pruned tx

Fix for #4399.
Also unifies code for serializing pruned tx to binary/json into one.

(Cherry-picked from #4586)

src/rpc/core_rpc_server.cpp

@@ -212,23 +212,15 @@ namespace cryptonote
     return true;
   }
   //------------------------------------------------------------------------------------------------------------------------------
-  static cryptonote::blobdata get_pruned_tx_blob(cryptonote::transaction &tx)
-  {
-    std::stringstream ss;
-    binary_archive<true> ba(ss);
-    bool r = tx.serialize_base(ba);
-    CHECK_AND_ASSERT_MES(r, cryptonote::blobdata(), "Failed to serialize rct signatures base");
-    return ss.str();
-  }
-  //------------------------------------------------------------------------------------------------------------------------------
-  static cryptonote::blobdata get_pruned_tx_json(cryptonote::transaction &tx)
-  {
-    std::stringstream ss;
-    json_archive<true> ar(ss);
-    bool r = tx.serialize_base(ar);
-    CHECK_AND_ASSERT_MES(r, cryptonote::blobdata(), "Failed to serialize rct signatures base");
-    return ss.str();
-  }
+  class pruned_transaction {
+    transaction& tx;
+  public:
+    pruned_transaction(transaction& tx) : tx(tx) {}
+    BEGIN_SERIALIZE_OBJECT()
+      bool r = tx.serialize_base(ar);
+      if (!r) return false;
+    END_SERIALIZE()
+  };
   //------------------------------------------------------------------------------------------------------------------------------
   bool core_rpc_server::on_get_blocks(const COMMAND_RPC_GET_BLOCKS_FAST::request& req, COMMAND_RPC_GET_BLOCKS_FAST::response& res)
   {
@@ -564,10 +556,11 @@ namespace cryptonote
 
       crypto::hash tx_hash = *vhi++;
       e.tx_hash = *txhi++;
-      blobdata blob = req.prune ? get_pruned_tx_blob(tx) : t_serializable_object_to_blob(tx);
+      pruned_transaction pruned_tx{tx};
+      blobdata blob = req.prune ? t_serializable_object_to_blob(pruned_tx) : t_serializable_object_to_blob(tx);
       e.as_hex = string_tools::buff_to_hex_nodelimer(blob);
       if (req.decode_as_json)
-        e.as_json = req.prune ? get_pruned_tx_json(tx) : obj_to_json_str(tx);
+        e.as_json = req.prune ? obj_to_json_str(pruned_tx) : obj_to_json_str(tx);
       e.in_pool = pool_tx_hashes.find(tx_hash) != pool_tx_hashes.end();
       if (e.in_pool)
       {