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.

1 files changed, 402 insertions, 0 deletions

diff --git a/src/rpc/rpc_payment.cpp b/src/rpc/rpc_payment.cpp
new file mode 100644
index 000000000..0637db728
--- /dev/null
+++ b/src/rpc/rpc_payment.cpp
@@ -0,0 +1,402 @@
+// Copyright (c) 2018-2019, The Monero Project
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+// 
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+// 
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+// 
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include <boost/archive/portable_binary_iarchive.hpp>
+#include <boost/archive/portable_binary_oarchive.hpp>
+#include "cryptonote_config.h"
+#include "include_base_utils.h"
+#include "string_tools.h"
+#include "file_io_utils.h"
+#include "int-util.h"
+#include "common/util.h"
+#include "serialization/crypto.h"
+#include "common/unordered_containers_boost_serialization.h"
+#include "cryptonote_basic/cryptonote_boost_serialization.h"
+#include "cryptonote_basic/cryptonote_format_utils.h"
+#include "cryptonote_basic/difficulty.h"
+#include "core_rpc_server_error_codes.h"
+#include "rpc_payment.h"
+
+#undef MONERO_DEFAULT_LOG_CATEGORY
+#define MONERO_DEFAULT_LOG_CATEGORY "daemon.rpc.payment"
+
+#define STALE_THRESHOLD 15 /* seconds */
+
+#define PENALTY_FOR_STALE 0
+#define PENALTY_FOR_BAD_HASH 20
+#define PENALTY_FOR_DUPLICATE 20
+
+#define DEFAULT_FLUSH_AGE (3600 * 24 * 180) // half a year
+#define DEFAULT_ZERO_FLUSH_AGE (60 * 2) // 2 minutes
+
+#define RPC_PAYMENT_NONCE_TAIL 0x58
+
+namespace cryptonote
+{
+  rpc_payment::client_info::client_info():
+    cookie(0),
+    top(crypto::null_hash),
+    previous_top(crypto::null_hash),
+    credits(0),
+    update_time(time(NULL)),
+    last_request_timestamp(0),
+    block_template_update_time(0),
+    credits_total(0),
+    credits_used(0),
+    nonces_good(0),
+    nonces_stale(0),
+    nonces_bad(0),
+    nonces_dupe(0)
+  {
+  }
+
+  rpc_payment::rpc_payment(const cryptonote::account_public_address &address, uint64_t diff, uint64_t credits_per_hash_found):
+    m_address(address),
+    m_diff(diff),
+    m_credits_per_hash_found(credits_per_hash_found),
+    m_credits_total(0),
+    m_credits_used(0),
+    m_nonces_good(0),
+    m_nonces_stale(0),
+    m_nonces_bad(0),
+    m_nonces_dupe(0)
+  {
+  }
+
+  uint64_t rpc_payment::balance(const crypto::public_key &client, int64_t delta)
+  {
+    client_info &info = m_client_info[client]; // creates if not found
+    uint64_t credits = info.credits;
+    if (delta > 0 && credits > std::numeric_limits<uint64_t>::max() - delta)
+      credits = std::numeric_limits<uint64_t>::max();
+    else if (delta < 0 && credits < (uint64_t)-delta)
+      credits = 0;
+    else
+      credits += delta;
+    if (delta)
+      MINFO("Client " << client << ": balance change from " << info.credits << " to " << credits);
+    return info.credits = credits;
+  }
+
+  bool rpc_payment::pay(const crypto::public_key &client, uint64_t ts, uint64_t payment, const std::string &rpc, bool same_ts, uint64_t &credits)
+  {
+    client_info &info = m_client_info[client]; // creates if not found
+    if (ts < info.last_request_timestamp || (ts == info.last_request_timestamp && !same_ts))
+    {
+      MDEBUG("Invalid ts: " << ts << " <= " << info.last_request_timestamp);
+      return false;
+    }
+    info.last_request_timestamp = ts;
+    if (info.credits < payment)
+    {
+      MDEBUG("Not enough credits: " << info.credits << " < " << payment);
+      credits = info.credits;
+      return false;
+    }
+    info.credits -= payment;
+    add64clamp(&info.credits_used, payment);
+    add64clamp(&m_credits_used, payment);
+    MDEBUG("client " << client << " paying " << payment << " for " << rpc << ", " << info.credits << " left");
+    credits = info.credits;
+    return true;
+  }
+
+  bool rpc_payment::get_info(const crypto::public_key &client, const std::function<bool(const cryptonote::blobdata&, cryptonote::block&, uint64_t &seed_height, crypto::hash &seed_hash)> &get_block_template, cryptonote::blobdata &hashing_blob, uint64_t &seed_height, crypto::hash &seed_hash, const crypto::hash &top, uint64_t &diff, uint64_t &credits_per_hash_found, uint64_t &credits, uint32_t &cookie)
+  {
+    client_info &info = m_client_info[client]; // creates if not found
+    const uint64_t now = time(NULL);
+    bool need_template = top != info.top || now >= info.block_template_update_time + STALE_THRESHOLD;
+    if (need_template)
+    {
+      cryptonote::block new_block;
+      uint64_t new_seed_height;
+      crypto::hash new_seed_hash;
+      cryptonote::blobdata extra_nonce("\x42\x42\x42\x42", 4);
+      if (!get_block_template(extra_nonce, new_block, new_seed_height, new_seed_hash))
+        return false;
+      if(!remove_field_from_tx_extra(new_block.miner_tx.extra, typeid(cryptonote::tx_extra_nonce)))
+        return false;
+      char data[33];
+      memcpy(data, &client, 32);
+      data[32] = RPC_PAYMENT_NONCE_TAIL;
+      crypto::hash hash;
+      cn_fast_hash(data, sizeof(data), hash);
+      extra_nonce = cryptonote::blobdata((const char*)&hash, 4);
+      if(!add_extra_nonce_to_tx_extra(new_block.miner_tx.extra, extra_nonce))
+        return false;
+      info.previous_block = std::move(info.block);
+      info.block = std::move(new_block);
+      hashing_blob = get_block_hashing_blob(info.block);
+      info.previous_hashing_blob = info.hashing_blob;
+      info.hashing_blob = hashing_blob;
+      info.previous_top = info.top;
+      info.previous_seed_height = info.seed_height;
+      info.seed_height = new_seed_height;
+      info.previous_seed_hash = info.seed_hash;
+      info.seed_hash = new_seed_hash;
+      std::swap(info.previous_payments, info.payments);
+      info.payments.clear();
+      ++info.cookie;
+      info.block_template_update_time = now;
+    }
+    info.top = top;
+    info.update_time = now;
+    hashing_blob = info.hashing_blob;
+    diff = m_diff;
+    credits_per_hash_found = m_credits_per_hash_found;
+    credits = info.credits;
+    seed_height = info.seed_height;
+    seed_hash = info.seed_hash;
+    cookie = info.cookie;
+    return true;
+  }
+
+  bool rpc_payment::submit_nonce(const crypto::public_key &client, uint32_t nonce, const crypto::hash &top, int64_t &error_code, std::string &error_message, uint64_t &credits, crypto::hash &hash, cryptonote::block &block, uint32_t cookie, bool &stale)
+  {
+    client_info &info = m_client_info[client]; // creates if not found
+    if (cookie != info.cookie && cookie != info.cookie - 1)
+    {
+      MWARNING("Very stale nonce");
+      ++m_nonces_stale;
+      ++info.nonces_stale;
+      sub64clamp(&info.credits, PENALTY_FOR_STALE * m_credits_per_hash_found);
+      error_code = CORE_RPC_ERROR_CODE_STALE_PAYMENT;
+      error_message = "Very stale payment";
+      return false;
+    }
+    const bool is_current = cookie == info.cookie;
+    MINFO("client " << client << " sends nonce: " << nonce << ", " << (is_current ? "current" : "stale"));
+    std::unordered_set<uint64_t> &payments = is_current ? info.payments : info.previous_payments;
+    if (!payments.insert(nonce).second)
+    {
+      MWARNING("Duplicate nonce " << nonce << " from " << (is_current ? "current" : "previous"));
+      ++m_nonces_dupe;
+      ++info.nonces_dupe;
+      sub64clamp(&info.credits, PENALTY_FOR_DUPLICATE * m_credits_per_hash_found);
+      error_code = CORE_RPC_ERROR_CODE_DUPLICATE_PAYMENT;
+      error_message = "Duplicate payment";
+      return false;
+    }
+
+    const uint64_t now = time(NULL);
+    if (!is_current)
+    {
+      if (now > info.update_time + STALE_THRESHOLD)
+      {
+        MWARNING("Nonce is stale (top " << top << ", should be " << info.top << " or within " << STALE_THRESHOLD << " seconds");
+        ++m_nonces_stale;
+        ++info.nonces_stale;
+        sub64clamp(&info.credits, PENALTY_FOR_STALE * m_credits_per_hash_found);
+        error_code = CORE_RPC_ERROR_CODE_STALE_PAYMENT;
+        error_message = "stale payment";
+        return false;
+      }
+    }
+
+    cryptonote::blobdata hashing_blob = is_current ? info.hashing_blob : info.previous_hashing_blob;
+    if (hashing_blob.size() < 43)
+    {
+      // not initialized ?
+      error_code = CORE_RPC_ERROR_CODE_WRONG_BLOCKBLOB;
+      error_message = "not initialized";
+      return false;
+    }
+
+    block = is_current ? info.block : info.previous_block;
+    *(uint32_t*)(hashing_blob.data() + 39) = SWAP32LE(nonce);
+    if (block.major_version >= RX_BLOCK_VERSION)
+    {
+      const uint64_t seed_height = is_current ? info.seed_height : info.previous_seed_height;
+      const crypto::hash &seed_hash = is_current ? info.seed_hash : info.previous_seed_hash;
+      const uint64_t height = cryptonote::get_block_height(block);
+      crypto::rx_slow_hash(height, seed_height, seed_hash.data, hashing_blob.data(), hashing_blob.size(), hash.data, 0, 0);
+    }
+    else
+    {
+      const int cn_variant = hashing_blob[0] >= 7 ? hashing_blob[0] - 6 : 0;
+      crypto::cn_slow_hash(hashing_blob.data(), hashing_blob.size(), hash, cn_variant, cryptonote::get_block_height(block));
+    }
+    if (!check_hash(hash, m_diff))
+    {
+      MWARNING("Payment too low");
+      ++m_nonces_bad;
+      ++info.nonces_bad;
+      error_code = CORE_RPC_ERROR_CODE_PAYMENT_TOO_LOW;
+      error_message = "Hash does not meet difficulty (could be wrong PoW hash, or mining at lower difficulty than required, or attempt to defraud)";
+      sub64clamp(&info.credits, PENALTY_FOR_BAD_HASH * m_credits_per_hash_found);
+      return false;
+    }
+
+    add64clamp(&info.credits, m_credits_per_hash_found);
+    MINFO("client " << client << " credited for " << m_credits_per_hash_found << ", now " << info.credits << (is_current ? "" : " (close)"));
+
+    m_hashrate[now] += m_diff;
+    add64clamp(&m_credits_total, m_credits_per_hash_found);
+    add64clamp(&info.credits_total, m_credits_per_hash_found);
+    ++m_nonces_good;
+    ++info.nonces_good;
+
+    credits = info.credits;
+    block = info.block;
+    block.nonce = nonce;
+    stale = !is_current;
+    return true;
+  }
+
+  bool rpc_payment::foreach(const std::function<bool(const crypto::public_key &client, const client_info &info)> &f) const
+  {
+    for (std::unordered_map<crypto::public_key, client_info>::const_iterator i = m_client_info.begin(); i != m_client_info.end(); ++i)
+    {
+      if (!f(i->first, i->second))
+        return false;
+    }
+    return true;
+  }
+
+  bool rpc_payment::load(std::string directory)
+  {
+    TRY_ENTRY();
+    m_directory = std::move(directory);
+    std::string state_file_path = directory + "/" + RPC_PAYMENTS_DATA_FILENAME;
+    MINFO("loading rpc payments data from " << state_file_path);
+    std::ifstream data;
+    data.open(state_file_path, std::ios_base::binary | std::ios_base::in);
+    if (!data.fail())
+    {
+      try
+      {
+        boost::archive::portable_binary_iarchive a(data);
+        a >> *this;
+      }
+      catch (const std::exception &e)
+      {
+        MERROR("Failed to load RPC payments file: " << e.what());
+        m_client_info.clear();
+      }
+    }
+    else
+    {
+      m_client_info.clear();
+    }
+
+    CATCH_ENTRY_L0("rpc_payment::load", false);
+    return true;
+  }
+
+  bool rpc_payment::store(const std::string &directory_) const
+  {
+    TRY_ENTRY();
+    const std::string &directory = directory_.empty() ? m_directory : directory_;
+    MDEBUG("storing rpc payments data to " << directory);
+    if (!tools::create_directories_if_necessary(directory))
+    {
+      MWARNING("Failed to create data directory: " << directory);
+      return false;
+    }
+    const boost::filesystem::path state_file_path = (boost::filesystem::path(directory) / RPC_PAYMENTS_DATA_FILENAME);
+    if (boost::filesystem::exists(state_file_path))
+    {
+      std::string state_file_path_old = state_file_path.string() + ".old";
+      boost::system::error_code ec;
+      boost::filesystem::remove(state_file_path_old, ec);
+      std::error_code e = tools::replace_file(state_file_path.string(), state_file_path_old);
+      if (e)
+        MWARNING("Failed to rename " << state_file_path << " to " << state_file_path_old << ": " << e);
+    }
+    std::ofstream data;
+    data.open(state_file_path.string(), std::ios_base::binary | std::ios_base::out | std::ios::trunc);
+    if (data.fail())
+    {
+      MWARNING("Failed to save RPC payments to file " << state_file_path);
+      return false;
+    };
+    boost::archive::portable_binary_oarchive a(data);
+    a << *this;
+    return true;
+    CATCH_ENTRY_L0("rpc_payment::store", false);
+  }
+
+  unsigned int rpc_payment::flush_by_age(time_t seconds)
+  {
+    unsigned int count = 0;
+    const time_t now = time(NULL);
+    time_t seconds0 = seconds;
+    if (seconds == 0)
+    {
+      seconds = DEFAULT_FLUSH_AGE;
+      seconds0 = DEFAULT_ZERO_FLUSH_AGE;
+    }
+    const time_t threshold = seconds > now ? 0 : now - seconds;
+    const time_t threshold0 = seconds0 > now ? 0 : now - seconds0;
+    for (std::unordered_map<crypto::public_key, client_info>::iterator i = m_client_info.begin(); i != m_client_info.end(); )
+    {
+      std::unordered_map<crypto::public_key, client_info>::iterator j = i++;
+      const time_t t = std::max(j->second.last_request_timestamp, j->second.update_time);
+      const bool erase = t < ((j->second.credits == 0) ? threshold0 : threshold);
+      if (erase)
+      {
+        MINFO("Erasing " << j->first << " with " << j->second.credits << " credits, inactive for " << (now-t)/86400 << " days");
+        m_client_info.erase(j);
+        ++count;
+      }
+    }
+    return count;
+  }
+
+  uint64_t rpc_payment::get_hashes(unsigned int seconds) const
+  {
+    const uint64_t now = time(NULL);
+    uint64_t hashes = 0;
+    for (std::map<uint64_t, uint64_t>::const_reverse_iterator i = m_hashrate.crbegin(); i != m_hashrate.crend(); ++i)
+    {
+      if (now > i->first + seconds)
+        break;
+      hashes += i->second;
+    }
+    return hashes;
+  }
+
+  void rpc_payment::prune_hashrate(unsigned int seconds)
+  {
+    const uint64_t now = time(NULL);
+    std::map<uint64_t, uint64_t>::iterator i;
+    for (i = m_hashrate.begin(); i != m_hashrate.end(); ++i)
+    {
+      if (now <= i->first + seconds)
+        break;
+    }
+    m_hashrate.erase(m_hashrate.begin(), i);
+  }
+
+  bool rpc_payment::on_idle()
+  {
+    flush_by_age();
+    prune_hashrate(3600);
+    return true;
+  }
+}