New RPC and daemon command to get output histogram

This is a list of existing output amounts along with the number
of outputs of that amount in the blockchain.

The daemon command takes:
- no parameters: all outputs with at least 3 instances
- one parameter: all outputs with at least that many instances
- two parameters: all outputs within that many instances

The default starts at 3 to avoid massive spamming of all dust
outputs in the blockchain, and is the current minimum mixin
requirement.

An optional vector of amounts may be passed, to request
histogram only for those outputs.

src/rpc/core_rpc_server.cpp

@@ -1041,6 +1041,38 @@ namespace cryptonote
     return true;
   }
   //------------------------------------------------------------------------------------------------------------------------------
+  bool core_rpc_server::on_get_output_histogram(const COMMAND_RPC_GET_OUTPUT_HISTOGRAM::request& req, COMMAND_RPC_GET_OUTPUT_HISTOGRAM::response& res, epee::json_rpc::error& error_resp)
+  {
+    if(!check_core_busy())
+    {
+      error_resp.code = CORE_RPC_ERROR_CODE_CORE_BUSY;
+      error_resp.message = "Core is busy.";
+      return false;
+    }
+
+    std::map<uint64_t, uint64_t> histogram;
+    try
+    {
+      histogram = m_core.get_blockchain_storage().get_output_histogram(req.amounts);
+    }
+    catch (const std::exception &e)
+    {
+      res.status = "Failed to get output histogram";
+      return true;
+    }
+
+    res.histogram.clear();
+    res.histogram.reserve(histogram.size());
+    for (const auto &i: histogram)
+    {
+      if (i.second >= req.min_count && (i.second <= req.max_count || req.max_count == 0))
+        res.histogram.push_back(COMMAND_RPC_GET_OUTPUT_HISTOGRAM::entry(i.first, i.second));
+    }
+
+    res.status = CORE_RPC_STATUS_OK;
+    return true;
+  }
+  //------------------------------------------------------------------------------------------------------------------------------
   bool core_rpc_server::on_fast_exit(const COMMAND_RPC_FAST_EXIT::request& req, COMMAND_RPC_FAST_EXIT::response& res)
   {
 	  cryptonote::core::set_fast_exit();

src/rpc/core_rpc_server.h

@@ -109,6 +109,7 @@ namespace cryptonote
         MAP_JON_RPC_WE("setbans",                on_set_bans,                   COMMAND_RPC_SETBANS)
         MAP_JON_RPC_WE("getbans",                on_get_bans,                   COMMAND_RPC_GETBANS)
         MAP_JON_RPC_WE("flush_txpool",           on_flush_txpool,               COMMAND_RPC_FLUSH_TRANSACTION_POOL)
+        MAP_JON_RPC_WE("get_output_histogram",   on_get_output_histogram,       COMMAND_RPC_GET_OUTPUT_HISTOGRAM)
       END_JSON_RPC_MAP()
     END_URI_MAP2()
 
@@ -149,6 +150,7 @@ namespace cryptonote
     bool on_set_bans(const COMMAND_RPC_SETBANS::request& req, COMMAND_RPC_SETBANS::response& res, epee::json_rpc::error& error_resp);
     bool on_get_bans(const COMMAND_RPC_GETBANS::request& req, COMMAND_RPC_GETBANS::response& res, epee::json_rpc::error& error_resp);
     bool on_flush_txpool(const COMMAND_RPC_FLUSH_TRANSACTION_POOL::request& req, COMMAND_RPC_FLUSH_TRANSACTION_POOL::response& res, epee::json_rpc::error& error_resp);
+    bool on_get_output_histogram(const COMMAND_RPC_GET_OUTPUT_HISTOGRAM::request& req, COMMAND_RPC_GET_OUTPUT_HISTOGRAM::response& res, epee::json_rpc::error& error_resp);
     //-----------------------
 
 private:

src/rpc/core_rpc_server_commands_defs.h

@@ -986,5 +986,46 @@ namespace cryptonote
       END_KV_SERIALIZE_MAP()
     };
   };
+
+  struct COMMAND_RPC_GET_OUTPUT_HISTOGRAM
+  {
+    struct request
+    {
+      std::vector<uint64_t> amounts;
+      uint64_t min_count;
+      uint64_t max_count;
+
+      BEGIN_KV_SERIALIZE_MAP()
+        KV_SERIALIZE(amounts);
+        KV_SERIALIZE(min_count);
+        KV_SERIALIZE(max_count);
+      END_KV_SERIALIZE_MAP()
+    };
+
+    struct entry
+    {
+      uint64_t amount;
+      uint64_t instances;
+
+      BEGIN_KV_SERIALIZE_MAP()
+        KV_SERIALIZE(amount);
+        KV_SERIALIZE(instances);
+      END_KV_SERIALIZE_MAP()
+
+      entry(uint64_t amount, uint64_t instances): amount(amount), instances(instances) {}
+      entry() {}
+    };
+
+    struct response
+    {
+      std::string status;
+      std::vector<entry> histogram;
+
+      BEGIN_KV_SERIALIZE_MAP()
+        KV_SERIALIZE(status)
+        KV_SERIALIZE(histogram)
+      END_KV_SERIALIZE_MAP()
+    };
+  };
 }