daemon, wallet: new pay for RPC use system

Daemons intended for public use can be set up to require payment
in the form of hashes in exchange for RPC service. This enables
public daemons to receive payment for their work over a large
number of calls. This system behaves similarly to a pool, so
payment takes the form of valid blocks every so often, yielding
a large one off payment, rather than constant micropayments.

This system can also be used by third parties as a "paywall"
layer, where users of a service can pay for use by mining Monero
to the service provider's address. An example of this for web
site access is Primo, a Monero mining based website "paywall":
https://github.com/selene-kovri/primo

This has some advantages:
 - incentive to run a node providing RPC services, thereby promoting the availability of third party nodes for those who can't run their own
 - incentive to run your own node instead of using a third party's, thereby promoting decentralization
 - decentralized: payment is done between a client and server, with no third party needed
 - private: since the system is "pay as you go", you don't need to identify yourself to claim a long lived balance
 - no payment occurs on the blockchain, so there is no extra transactional load
 - one may mine with a beefy server, and use those credits from a phone, by reusing the client ID (at the cost of some privacy)
 - no barrier to entry: anyone may run a RPC node, and your expected revenue depends on how much work you do
 - Sybil resistant: if you run 1000 idle RPC nodes, you don't magically get more revenue
 - no large credit balance maintained on servers, so they have no incentive to exit scam
 - you can use any/many node(s), since there's little cost in switching servers
 - market based prices: competition between servers to lower costs
 - incentive for a distributed third party node system: if some public nodes are overused/slow, traffic can move to others
 - increases network security
 - helps counteract mining pools' share of the network hash rate
 - zero incentive for a payer to "double spend" since a reorg does not give any money back to the miner

And some disadvantages:
 - low power clients will have difficulty mining (but one can optionally mine in advance and/or with a faster machine)
 - payment is "random", so a server might go a long time without a block before getting one
 - a public node's overall expected payment may be small

Public nodes are expected to compete to find a suitable level for
cost of service.

The daemon can be set up this way to require payment for RPC services:

  monerod --rpc-payment-address 4xxxxxx \
    --rpc-payment-credits 250 --rpc-payment-difficulty 1000

These values are an example only.

The --rpc-payment-difficulty switch selects how hard each "share" should
be, similar to a mining pool. The higher the difficulty, the fewer
shares a client will find.
The --rpc-payment-credits switch selects how many credits are awarded
for each share a client finds.
Considering both options, clients will be awarded credits/difficulty
credits for every hash they calculate. For example, in the command line
above, 0.25 credits per hash. A client mining at 100 H/s will therefore
get an average of 25 credits per second.
For reference, in the current implementation, a credit is enough to
sync 20 blocks, so a 100 H/s client that's just starting to use Monero
and uses this daemon will be able to sync 500 blocks per second.

The wallet can be set to automatically mine if connected to a daemon
which requires payment for RPC usage. It will try to keep a balance
of 50000 credits, stopping mining when it's at this level, and starting
again as credits are spent. With the example above, a new client will
mine this much credits in about half an hour, and this target is enough
to sync 500000 blocks (currently about a third of the monero blockchain).

There are three new settings in the wallet:

 - credits-target: this is the amount of credits a wallet will try to
reach before stopping mining. The default of 0 means 50000 credits.

 - auto-mine-for-rpc-payment-threshold: this controls the minimum
credit rate which the wallet considers worth mining for. If the
daemon credits less than this ratio, the wallet will consider mining
to be not worth it. In the example above, the rate is 0.25

 - persistent-rpc-client-id: if set, this allows the wallet to reuse
a client id across runs. This means a public node can tell a wallet
that's connecting is the same as one that connected previously, but
allows a wallet to keep their credit balance from one run to the
other. Since the wallet only mines to keep a small credit balance,
this is not normally worth doing. However, someone may want to mine
on a fast server, and use that credit balance on a low power device
such as a phone. If left unset, a new client ID is generated at
each wallet start, for privacy reasons.

To mine and use a credit balance on two different devices, you can
use the --rpc-client-secret-key switch. A wallet's client secret key
can be found using the new rpc_payments command in the wallet.
Note: anyone knowing your RPC client secret key is able to use your
credit balance.

The wallet has a few new commands too:

 - start_mining_for_rpc: start mining to acquire more credits,
regardless of the auto mining settings
 - stop_mining_for_rpc: stop mining to acquire more credits
 - rpc_payments: display information about current credits with
the currently selected daemon

The node has an extra command:

 - rpc_payments: display information about clients and their
balances

The node will forget about any balance for clients which have
been inactive for 6 months. Balances carry over on node restart.

6 files changed, 78 insertions, 12 deletions

diff --git a/src/daemon/command_parser_executor.cpp b/src/daemon/command_parser_executor.cpp
index d47823735..8e78f3bd1 100644
--- a/src/daemon/command_parser_executor.cpp
+++ b/src/daemon/command_parser_executor.cpp
@@ -794,6 +794,13 @@ bool t_command_parser_executor::pop_blocks(const std::vector<std::string>& args)
   return false;
 }
 
+bool t_command_parser_executor::rpc_payments(const std::vector<std::string>& args)
+{
+  if (args.size() != 0) return false;
+
+  return m_executor.rpc_payments();
+}
+
 bool t_command_parser_executor::version(const std::vector<std::string>& args)
 {
   std::cout << "Monero '" << MONERO_RELEASE_NAME << "' (v" << MONERO_VERSION_FULL << ")" << std::endl;
diff --git a/src/daemon/command_parser_executor.h b/src/daemon/command_parser_executor.h
index 25587dea8..5c94c540e 100644
--- a/src/daemon/command_parser_executor.h
+++ b/src/daemon/command_parser_executor.h
@@ -143,6 +143,8 @@ public:
 
   bool pop_blocks(const std::vector<std::string>& args);
 
+  bool rpc_payments(const std::vector<std::string>& args);
+
   bool version(const std::vector<std::string>& args);
 
   bool prune_blockchain(const std::vector<std::string>& args);
diff --git a/src/daemon/command_server.cpp b/src/daemon/command_server.cpp
index e44ce9137..b00e253c7 100644
--- a/src/daemon/command_server.cpp
+++ b/src/daemon/command_server.cpp
@@ -296,6 +296,11 @@ t_command_server::t_command_server(
     , "Remove blocks from end of blockchain"
     );
     m_command_lookup.set_handler(
+      "rpc_payments"
+    , std::bind(&t_command_parser_executor::rpc_payments, &m_parser, p::_1)
+    , "Print information about RPC payments."
+    );
+    m_command_lookup.set_handler(
       "version"
     , std::bind(&t_command_parser_executor::version, &m_parser, p::_1)
     , "Print version information."
diff --git a/src/daemon/core.h b/src/daemon/core.h
index 91dbb7a4b..9a3579e20 100644
--- a/src/daemon/core.h
+++ b/src/daemon/core.h
@@ -59,16 +59,6 @@ public:
     : m_core{nullptr}
     , m_vm_HACK{vm}
   {
-  }
-
-  // TODO - get rid of circular dependencies in internals
-  void set_protocol(t_protocol_raw & protocol)
-  {
-    m_core.set_cryptonote_protocol(&protocol);
-  }
-
-  bool run()
-  {
     //initialize core here
     MGINFO("Initializing core...");
 #if defined(PER_BLOCK_CHECKPOINT)
@@ -78,9 +68,19 @@ public:
 #endif
     if (!m_core.init(m_vm_HACK, nullptr, get_checkpoints))
     {
-      return false;
+      throw std::runtime_error("Failed to initialize core");
     }
     MGINFO("Core initialized OK");
+  }
+
+  // TODO - get rid of circular dependencies in internals
+  void set_protocol(t_protocol_raw & protocol)
+  {
+    m_core.set_cryptonote_protocol(&protocol);
+  }
+
+  bool run()
+  {
     return true;
   }
 
diff --git a/src/daemon/rpc_command_executor.cpp b/src/daemon/rpc_command_executor.cpp
index 75c54d048..f552db2b8 100644
--- a/src/daemon/rpc_command_executor.cpp
+++ b/src/daemon/rpc_command_executor.cpp
@@ -37,6 +37,7 @@
 #include "cryptonote_core/cryptonote_core.h"
 #include "cryptonote_basic/difficulty.h"
 #include "cryptonote_basic/hardfork.h"
+#include "rpc/rpc_payment_signature.h"
 #include <boost/format.hpp>
 #include <ctime>
 #include <string>
@@ -60,6 +61,13 @@ namespace {
     }
   }
 
+  std::string print_float(float f, int prec)
+  {
+    char buf[16];
+    snprintf(buf, sizeof(buf), "%*.*f", prec, prec, f);
+    return buf;
+  }
+
   void print_peer(std::string const & prefix, cryptonote::peer const & peer, bool pruned_only, bool publicrpc_only)
   {
     if (pruned_only && peer.pruning_seed == 0)
@@ -77,8 +85,9 @@ namespace {
     epee::string_tools::xtype_to_string(peer.port, port_str);
     std::string addr_str = peer.host + ":" + port_str;
     std::string rpc_port = peer.rpc_port ? std::to_string(peer.rpc_port) : "-";
+    std::string rpc_credits_per_hash = peer.rpc_credits_per_hash ? print_float(peer.rpc_credits_per_hash / RPC_CREDITS_PER_HASH_SCALE, 2) : "-";
     std::string pruning_seed = epee::string_tools::to_string_hex(peer.pruning_seed);
-    tools::msg_writer() << boost::format("%-10s %-25s %-25s %-5s %-4s %s") % prefix % id_str % addr_str % rpc_port % pruning_seed % elapsed;
+    tools::msg_writer() << boost::format("%-10s %-25s %-25s %-5s %-5s %-4s %s") % prefix % id_str % addr_str % rpc_port % rpc_credits_per_hash % pruning_seed % elapsed;
   }
 
   void print_block_header(cryptonote::block_header_response const & header)
@@ -2362,4 +2371,45 @@ bool t_rpc_command_executor::set_bootstrap_daemon(
     return true;
 }
 
+bool t_rpc_command_executor::rpc_payments()
+{
+    cryptonote::COMMAND_RPC_ACCESS_DATA::request req;
+    cryptonote::COMMAND_RPC_ACCESS_DATA::response res;
+    std::string fail_message = "Unsuccessful";
+    epee::json_rpc::error error_resp;
+
+    if (m_is_rpc)
+    {
+        if (!m_rpc_client->json_rpc_request(req, res, "rpc_access_data", fail_message.c_str()))
+        {
+            return true;
+        }
+    }
+    else
+    {
+        if (!m_rpc_server->on_rpc_access_data(req, res, error_resp) || res.status != CORE_RPC_STATUS_OK)
+        {
+            tools::fail_msg_writer() << make_error(fail_message, res.status);
+            return true;
+        }
+    }
+
+    const uint64_t now = std::chrono::duration_cast<std::chrono::seconds>(std::chrono::system_clock::now().time_since_epoch()).count();
+    uint64_t balance = 0;
+    tools::msg_writer() << boost::format("%64s %16u %16u %8u %8u %8u %8u %s")
+        % "Client ID" % "Balance" % "Total mined" % "Good" % "Stale" % "Bad" % "Dupes" % "Last update";
+    for (const auto &entry: res.entries)
+    {
+      tools::msg_writer() << boost::format("%64s %16u %16u %8u %8u %8u %8u %s")
+          % entry.client % entry.balance % entry.credits_total
+          % entry.nonces_good % entry.nonces_stale % entry.nonces_bad % entry.nonces_dupe
+          % (entry.last_update_time == 0 ? "never" : get_human_time_ago(entry.last_update_time, now).c_str());
+      balance += entry.balance;
+    }
+    tools::msg_writer() << res.entries.size() << " clients with a total of " << balance << " credits";
+    tools::msg_writer() << "Aggregated client hash rate: " << get_mining_speed(res.hashrate);
+
+    return true;
+}
+
 }// namespace daemonize
diff --git a/src/daemon/rpc_command_executor.h b/src/daemon/rpc_command_executor.h
index af7081ef3..783b47373 100644
--- a/src/daemon/rpc_command_executor.h
+++ b/src/daemon/rpc_command_executor.h
@@ -167,6 +167,8 @@ public:
     const std::string &address,
     const std::string &username,
     const std::string &password);
+
+  bool rpc_payments();
 };
 
 } // namespace daemonize