First pass at integrating gas price oracles

nucypher/utilities/oracles.py

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+"""
+ This file is part of nucypher.
+
+ nucypher is free software: you can redistribute it and/or modify
+ it under the terms of the GNU Affero General Public License as published by
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ nucypher is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU Affero General Public License for more details.
+
+ You should have received a copy of the GNU Affero General Public License
+ along with nucypher.  If not, see <https://www.gnu.org/licenses/>.
+"""
+from abc import ABC, abstractmethod
+from typing import Optional
+
+import requests
+from web3 import Web3
+from web3.types import Wei
+
+
+class Oracle(ABC):
+
+    class OracleError(RuntimeError):
+        """Base class for Oracle-related exceptions"""
+
+    api_url = NotImplemented  # TODO: Deal with API keys
+
+    def _probe_oracle(self):
+        try:
+            response = requests.get(self.api_url)
+        except requests.exceptions.ConnectionError as e:
+            error = f"Failed to probe oracle at {self.api_url}: {str(e)}"
+            raise self.OracleError(error)
+
+        if response.status_code != 200:
+            error = f"Failed to probe oracle at {self.api_url} with status code {response.status_code}"
+            raise self.OracleError(error)
+
+        self._raw_data = response.json()
+
+
+class EthereumGasPriceOracle(Oracle):
+    """Base class for Ethereum gas price oracles"""
+
+    _speed_names = NotImplemented
+    _default_speed = NotImplemented
+
+    @abstractmethod
+    def _parse_gas_prices(self):
+        return NotImplementedError
+
+    def get_gas_price(self, speed: Optional[str] = None) -> Wei:
+        speed = speed or self._default_speed
+        self._parse_gas_prices()
+        gas_price_wei = Wei(self.gas_prices[speed])
+        return gas_price_wei
+
+    @classmethod
+    def construct_gas_strategy(cls):
+        def oracle_based_gas_price_strategy(web3, transaction_params=None) -> Wei:
+            oracle = cls()
+            gas_price = oracle.get_gas_price()
+            return gas_price
+        return oracle_based_gas_price_strategy
+
+
+class EtherchainGasPriceOracle(EthereumGasPriceOracle):
+    """Gas price oracle from Etherchain"""
+
+    api_url = "https://www.etherchain.org/api/gasPriceOracle"
+    _speed_names = ('safeLow', 'standard', 'fast', 'fastest')
+    _default_speed = 'fast'
+
+    def _parse_gas_prices(self):
+        self._probe_oracle()
+        self.gas_prices = {k: int(Web3.toWei(v, 'gwei')) for k, v in self._raw_data.items()}
+
+
+class UpvestGasPriceOracle(EthereumGasPriceOracle):
+    """Gas price oracle from Upvest"""
+
+    api_url = "https://fees.upvest.co/estimate_eth_fees"
+    _speed_names = ('slow', 'medium', 'fast', 'fastest')
+    _default_speed = 'fastest'
+
+    def _parse_gas_prices(self):
+        self._probe_oracle()
+        self.gas_prices = {k: int(Web3.toWei(v, 'gwei')) for k, v in self._raw_data['estimates'].items()}
+
+
+
+# TODO: We can implement here other oracles, like the ETH/USD (e.g., https://api.coinmarketcap.com/v1/ticker/ethereum/)
+# suggested in a comment in nucypher.blockchain.eth.interfaces.BlockchainInterface#sign_and_broadcast_transaction

tests/unit/test_oracles.py

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+"""
+This file is part of nucypher.
+
+nucypher is free software: you can redistribute it and/or modify
+it under the terms of the GNU Affero General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+nucypher is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Affero General Public License for more details.
+
+You should have received a copy of the GNU Affero General Public License
+along with nucypher.  If not, see <https://www.gnu.org/licenses/>.
+"""
+
+from unittest.mock import patch
+
+import pytest
+from requests.exceptions import ConnectionError
+from web3 import Web3
+
+from nucypher.utilities.oracles import Oracle, EtherchainGasPriceOracle, UpvestGasPriceOracle
+
+
+def test_probe_oracle(mocker):
+
+    oracle = Oracle()
+    oracle.api_url = "http://foo.bar"
+
+    with patch('requests.get', side_effect=ConnectionError("Bad connection")) as mocked_get:
+        with pytest.raises(Oracle.OracleError, match="Bad connection"):
+            oracle._probe_oracle()
+        mocked_get.assert_called_once_with(oracle.api_url)
+
+    bad_response = mocker.Mock()
+    bad_response.status_code = 400
+    with patch('requests.get') as mocked_get:
+        mocked_get.return_value = bad_response
+        with pytest.raises(Oracle.OracleError, match="status code 400"):
+            oracle._probe_oracle()
+        mocked_get.assert_called_once_with(oracle.api_url)
+
+    json = {'foo': 'bar'}
+    good_response = mocker.Mock()
+    good_response.status_code = 200
+    good_response.json = mocker.Mock(return_value=json)
+    with patch('requests.get') as mocked_get:
+        mocked_get.return_value = good_response
+        oracle._probe_oracle()
+        mocked_get.assert_called_once_with(oracle.api_url)
+        assert oracle._raw_data == json
+
+
+def test_etherchain():
+    etherchain_json = {
+        "safeLow": "99.0",
+        "standard": "105.0",
+        "fast": "108.0",
+        "fastest": "119.9"
+    }
+    oracle = EtherchainGasPriceOracle()
+    with patch.object(oracle, '_probe_oracle'):
+        oracle._raw_data = etherchain_json
+        assert oracle.get_gas_price('safeLow') == Web3.toWei(99.0, 'gwei')
+        assert oracle.get_gas_price('standard') == Web3.toWei(105.0, 'gwei')
+        assert oracle.get_gas_price('fast') == Web3.toWei(108.0, 'gwei')
+        assert oracle.get_gas_price('fastest') == Web3.toWei(119.9, 'gwei')
+        assert oracle.get_gas_price() == oracle.get_gas_price('fast')  # Default
+
+
+def test_upvest():
+    upvest_json = {
+        "success": True,
+        "updated": "2020-08-19T02:38:00.172Z",
+        "estimates": {
+            "fastest": 105.2745,
+            "fast": 97.158,
+            "medium": 91.424,
+            "slow": 87.19
+        }
+    }
+    oracle = UpvestGasPriceOracle()
+    with patch.object(oracle, '_probe_oracle'):
+        oracle._raw_data = upvest_json
+        assert oracle.get_gas_price('slow') == Web3.toWei(87.19, 'gwei')
+        assert oracle.get_gas_price('medium') == Web3.toWei(91.424, 'gwei')
+        assert oracle.get_gas_price('fast') == Web3.toWei(97.158, 'gwei')
+        assert oracle.get_gas_price('fastest') == Web3.toWei(105.2745, 'gwei')
+        assert oracle.get_gas_price() == oracle.get_gas_price('fastest')  # Default