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, 66 insertions, 17 deletions

diff --git a/src/wallet/wallet2.h b/src/wallet/wallet2.h
index 52118c426..3635cf227 100644
--- a/src/wallet/wallet2.h
+++ b/src/wallet/wallet2.h
@@ -64,10 +64,21 @@
 #include "node_rpc_proxy.h"
 #include "message_store.h"
 #include "wallet_light_rpc.h"
+#include "wallet_rpc_helpers.h"
 
 #undef MONERO_DEFAULT_LOG_CATEGORY
 #define MONERO_DEFAULT_LOG_CATEGORY "wallet.wallet2"
 
+#define THROW_ON_RPC_RESPONSE_ERROR(r, error, res, method, ...) \
+  do { \
+    handle_payment_changes(res, std::integral_constant<bool, HasCredits<decltype(res)>::Has>()); \
+    throw_on_rpc_response_error(r, error, res.status, method); \
+    THROW_WALLET_EXCEPTION_IF(res.status != CORE_RPC_STATUS_OK, ## __VA_ARGS__); \
+  } while(0)
+
+#define THROW_ON_RPC_RESPONSE_ERROR_GENERIC(r, err, res, method) \
+  THROW_ON_RPC_RESPONSE_ERROR(r, err, res, method, tools::error::wallet_generic_rpc_error, method, res.status)
+
 class Serialization_portability_wallet_Test;
 class wallet_accessor_test;
 
@@ -988,6 +999,9 @@ private:
       if(ver < 28)
         return;
       a & m_cold_key_images;
+      if(ver < 29)
+        return;
+      a & m_rpc_client_secret_key;
     }
 
     /*!
@@ -1061,6 +1075,14 @@ private:
     void device_derivation_path(const std::string &device_derivation_path) { m_device_derivation_path = device_derivation_path; }
     const ExportFormat & export_format() const { return m_export_format; }
     inline void set_export_format(const ExportFormat& export_format) { m_export_format = export_format; }
+    bool persistent_rpc_client_id() const { return m_persistent_rpc_client_id; }
+    void persistent_rpc_client_id(bool persistent) { m_persistent_rpc_client_id = persistent; }
+    void auto_mine_for_rpc_payment_threshold(float threshold) { m_auto_mine_for_rpc_payment_threshold = threshold; }
+    float auto_mine_for_rpc_payment_threshold() const { return m_auto_mine_for_rpc_payment_threshold; }
+    crypto::secret_key get_rpc_client_secret_key() const { return m_rpc_client_secret_key; }
+    void set_rpc_client_secret_key(const crypto::secret_key &key) { m_rpc_client_secret_key = key; m_node_rpc_proxy.set_client_secret_key(key); }
+    uint64_t credits_target() const { return m_credits_target; }
+    void credits_target(uint64_t threshold) { m_credits_target = threshold; }
 
     bool get_tx_key_cached(const crypto::hash &txid, crypto::secret_key &tx_key, std::vector<crypto::secret_key> &additional_tx_keys) const;
     void set_tx_key(const crypto::hash &txid, const crypto::secret_key &tx_key, const std::vector<crypto::secret_key> &additional_tx_keys);
@@ -1108,15 +1130,15 @@ private:
     const transfer_details &get_transfer_details(size_t idx) const;
 
     uint8_t get_current_hard_fork();
-    void get_hard_fork_info(uint8_t version, uint64_t &earliest_height) const;
-    bool use_fork_rules(uint8_t version, int64_t early_blocks = 0) const;
-    int get_fee_algorithm() const;
+    void get_hard_fork_info(uint8_t version, uint64_t &earliest_height);
+    bool use_fork_rules(uint8_t version, int64_t early_blocks = 0);
+    int get_fee_algorithm();
 
     std::string get_wallet_file() const;
     std::string get_keys_file() const;
     std::string get_daemon_address() const;
     const boost::optional<epee::net_utils::http::login>& get_daemon_login() const { return m_daemon_login; }
-    uint64_t get_daemon_blockchain_height(std::string& err) const;
+    uint64_t get_daemon_blockchain_height(std::string& err);
     uint64_t get_daemon_blockchain_target_height(std::string& err);
    /*!
     * \brief Calculates the approximate blockchain height from current date/time.
@@ -1211,21 +1233,37 @@ private:
 
     uint64_t get_blockchain_height_by_date(uint16_t year, uint8_t month, uint8_t day);    // 1<=month<=12, 1<=day<=31
 
-    bool is_synced() const;
+    bool is_synced();
 
     std::vector<std::pair<uint64_t, uint64_t>> estimate_backlog(const std::vector<std::pair<double, double>> &fee_levels);
     std::vector<std::pair<uint64_t, uint64_t>> estimate_backlog(uint64_t min_tx_weight, uint64_t max_tx_weight, const std::vector<uint64_t> &fees);
 
-    uint64_t get_fee_multiplier(uint32_t priority, int fee_algorithm = -1) const;
-    uint64_t get_base_fee() const;
-    uint64_t get_fee_quantization_mask() const;
-    uint64_t get_min_ring_size() const;
-    uint64_t get_max_ring_size() const;
-    uint64_t adjust_mixin(uint64_t mixin) const;
+    uint64_t get_fee_multiplier(uint32_t priority, int fee_algorithm = -1);
+    uint64_t get_base_fee();
+    uint64_t get_fee_quantization_mask();
+    uint64_t get_min_ring_size();
+    uint64_t get_max_ring_size();
+    uint64_t adjust_mixin(uint64_t mixin);
+
     uint32_t adjust_priority(uint32_t priority);
 
     bool is_unattended() const { return m_unattended; }
 
+    bool get_rpc_payment_info(bool mining, bool &payment_required, uint64_t &credits, uint64_t &diff, uint64_t &credits_per_hash_found, cryptonote::blobdata &hashing_blob, uint64_t &height, uint64_t &seed_height, crypto::hash &seed_hash, crypto::hash &next_seed_hash, uint32_t &cookie);
+    bool daemon_requires_payment();
+    bool make_rpc_payment(uint32_t nonce, uint32_t cookie, uint64_t &credits, uint64_t &balance);
+    bool search_for_rpc_payment(uint64_t credits_target, const std::function<bool(uint64_t, uint64_t)> &startfunc, const std::function<bool(unsigned)> &contfunc, const std::function<bool(uint64_t)> &foundfunc = NULL, const std::function<void(const std::string&)> &errorfunc = NULL);
+    template<typename T> void handle_payment_changes(const T &res, std::true_type) {
+      if (res.status == CORE_RPC_STATUS_OK || res.status == CORE_RPC_STATUS_PAYMENT_REQUIRED)
+        m_rpc_payment_state.credits = res.credits;
+      if (res.top_hash != m_rpc_payment_state.top_hash)
+      {
+        m_rpc_payment_state.top_hash = res.top_hash;
+        m_rpc_payment_state.stale = true;
+      }
+    }
+    template<typename T> void handle_payment_changes(const T &res, std::false_type) {}
+
     // Light wallet specific functions
     // fetch unspent outs from lw node and store in m_transfers
     void light_wallet_get_unspent_outs();
@@ -1338,6 +1376,9 @@ private:
     void enable_dns(bool enable) { m_use_dns = enable; }
     void set_offline(bool offline = true);
 
+    uint64_t credits() const { return m_rpc_payment_state.credits; }
+    void credit_report(uint64_t &expected_spent, uint64_t &discrepancy) const { expected_spent = m_rpc_payment_state.expected_spent; discrepancy = m_rpc_payment_state.discrepancy; }
+
   private:
     /*!
      * \brief  Stores wallet information to wallet file.
@@ -1363,7 +1404,7 @@ private:
     void pull_blocks(uint64_t start_height, uint64_t& blocks_start_height, const std::list<crypto::hash> &short_chain_history, std::vector<cryptonote::block_complete_entry> &blocks, std::vector<cryptonote::COMMAND_RPC_GET_BLOCKS_FAST::block_output_indices> &o_indices);
     void pull_hashes(uint64_t start_height, uint64_t& blocks_start_height, const std::list<crypto::hash> &short_chain_history, std::vector<crypto::hash> &hashes);
     void fast_refresh(uint64_t stop_height, uint64_t &blocks_start_height, std::list<crypto::hash> &short_chain_history, bool force = false);
-    void pull_and_parse_next_blocks(uint64_t start_height, uint64_t &blocks_start_height, std::list<crypto::hash> &short_chain_history, const std::vector<cryptonote::block_complete_entry> &prev_blocks, const std::vector<parsed_block> &prev_parsed_blocks, std::vector<cryptonote::block_complete_entry> &blocks, std::vector<parsed_block> &parsed_blocks, bool &error);
+    void pull_and_parse_next_blocks(uint64_t start_height, uint64_t &blocks_start_height, std::list<crypto::hash> &short_chain_history, const std::vector<cryptonote::block_complete_entry> &prev_blocks, const std::vector<parsed_block> &prev_parsed_blocks, std::vector<cryptonote::block_complete_entry> &blocks, std::vector<parsed_block> &parsed_blocks, bool &error, std::exception_ptr &exception);
     void process_parsed_blocks(uint64_t start_height, const std::vector<cryptonote::block_complete_entry> &blocks, const std::vector<parsed_block> &parsed_blocks, uint64_t& blocks_added, std::map<std::pair<uint64_t, uint64_t>, size_t> *output_tracker_cache = NULL);
     uint64_t select_transfers(uint64_t needed_money, std::vector<size_t> unused_transfers_indices, std::vector<size_t>& selected_transfers) const;
     bool prepare_file_names(const std::string& file_path);
@@ -1379,9 +1420,9 @@ private:
     void check_acc_out_precomp(const cryptonote::tx_out &o, const crypto::key_derivation &derivation, const std::vector<crypto::key_derivation> &additional_derivations, size_t i, const is_out_data *is_out_data, tx_scan_info_t &tx_scan_info) const;
     void check_acc_out_precomp_once(const cryptonote::tx_out &o, const crypto::key_derivation &derivation, const std::vector<crypto::key_derivation> &additional_derivations, size_t i, const is_out_data *is_out_data, tx_scan_info_t &tx_scan_info, bool &already_seen) const;
     void parse_block_round(const cryptonote::blobdata &blob, cryptonote::block &bl, crypto::hash &bl_id, bool &error) const;
-    uint64_t get_upper_transaction_weight_limit() const;
-    std::vector<uint64_t> get_unspent_amounts_vector(bool strict) const;
-    uint64_t get_dynamic_base_fee_estimate() const;
+    uint64_t get_upper_transaction_weight_limit();
+    std::vector<uint64_t> get_unspent_amounts_vector(bool strict);
+    uint64_t get_dynamic_base_fee_estimate();
     float get_output_relatedness(const transfer_details &td0, const transfer_details &td1) const;
     std::vector<size_t> pick_preferred_rct_inputs(uint64_t needed_money, uint32_t subaddr_account, const std::set<uint32_t> &subaddr_indices) const;
     void set_spent(size_t idx, uint64_t height);
@@ -1435,7 +1476,10 @@ private:
     void on_device_progress(const hw::device_progress& event);
 
     std::string get_rpc_status(const std::string &s) const;
-    void throw_on_rpc_response_error(const boost::optional<std::string> &status, const char *method) const;
+    void throw_on_rpc_response_error(bool r, const epee::json_rpc::error &error, const std::string &status, const char *method) const;
+
+    std::string get_client_signature() const;
+    void check_rpc_cost(const char *call, uint64_t post_call_credits, uint64_t pre_credits, double expected_cost);
 
     cryptonote::account_base m_account;
     boost::optional<epee::net_utils::http::login> m_daemon_login;
@@ -1516,6 +1560,8 @@ private:
     bool m_track_uses;
     uint32_t m_inactivity_lock_timeout;
     BackgroundMiningSetupType m_setup_background_mining;
+    bool m_persistent_rpc_client_id;
+    float m_auto_mine_for_rpc_payment_threshold;
     bool m_is_initialized;
     NodeRPCProxy m_node_rpc_proxy;
     std::unordered_set<crypto::hash> m_scanned_pool_txs[2];
@@ -1526,6 +1572,9 @@ private:
     bool m_use_dns;
     bool m_offline;
     uint32_t m_rpc_version;
+    crypto::secret_key m_rpc_client_secret_key;
+    rpc_payment_state_t m_rpc_payment_state;
+    uint64_t m_credits_target;
 
     // Aux transaction data from device
     std::unordered_map<crypto::hash, std::string> m_tx_device;
@@ -1569,7 +1618,7 @@ private:
     ExportFormat m_export_format;
   };
 }
-BOOST_CLASS_VERSION(tools::wallet2, 28)
+BOOST_CLASS_VERSION(tools::wallet2, 29)
 BOOST_CLASS_VERSION(tools::wallet2::transfer_details, 12)
 BOOST_CLASS_VERSION(tools::wallet2::multisig_info, 1)
 BOOST_CLASS_VERSION(tools::wallet2::multisig_info::LR, 0)