support for proxy contracts for from_etherscan

boa/explorer.py

@@ -6,22 +6,42 @@
 
 SESSION = requests.Session()
 
-
-def fetch_abi_from_etherscan(
-    address: str, uri: str = "https://api.etherscan.io/api", api_key: str = None
-):
-    address = Address(address)
-
-    params = dict(module="contract", action="getabi", address=address)
+def _fetch_etherscan(uri: str, api_key: str = None, **params) -> dict:
     if api_key is not None:
         params["apikey"] = api_key
 
     res = SESSION.get(uri, params=params)
     res.raise_for_status()
-
     data = res.json()
 
     if int(data["status"]) != 1:
         raise ValueError(f"Failed to retrieve data from API: {data}")
 
+    return data
+
+
+def fetch_abi_from_etherscan(
+    address: str, uri: str = "https://api.etherscan.io/api", api_key: str = None
+):
+    # resolve implementation address if `address` is a proxy contract
+    address = _resolve_implementation_address(address, uri, api_key)
+
+    # fetch ABI of `address`
+    params = dict(module="contract", action="getabi", address=address)
+    data = _fetch_etherscan(uri, api_key, **params)
+
     return json.loads(data["result"].strip())
+
+
+# fetch the address of a contract; resolves at most one layer of indirection
+# if the address is a proxy contract.
+def _resolve_implementation_address(address: str, uri: str, api_key: str):
+    params = dict(module="contract", action="getsourcecode", address=address)
+    data = _fetch_etherscan(uri, api_key, **params)
+    source_data = data["result"][0]
+
+    # check if the contract is a proxy
+    if int(source_data["Proxy"]) == 1:
+        return source_data["Implementation"]
+    else:
+        return address

boa/interpret.py

@@ -126,4 +126,4 @@ def from_etherscan(
     return ABIContractFactory.from_abi_dict(abi, name=name).at(addr)
 
 
-__all__ = ["BoaError"]
+__all__ = []

tests/integration/fork/test_from_etherscan.py

@@ -0,0 +1,36 @@
+import os
+import pytest
+
+import boa
+
+crvusd = "0xf939E0A03FB07F59A73314E73794Be0E57ac1b4E"
+voting_agent = "0xE478de485ad2fe566d49342Cbd03E49ed7DB3356"
+
+@pytest.fixture(scope="module")
+def api_key():
+    return os.environ.get("ETHERSCAN_API_KEY")
+
+
+@pytest.fixture(scope="module")
+def crvusd_contract(api_key):
+    contract = boa.from_etherscan(crvusd, name="crvUSD", api_key=api_key)
+
+    return contract
+
+
+@pytest.fixture(scope="module")
+def proxy_contract(api_key):
+    contract = boa.from_etherscan(voting_agent, name="VotingAgent", api_key=api_key)
+
+    return contract
+
+
+def test_crvusd_contract(crvusd_contract):
+    assert crvusd_contract.totalSupply() > 0
+    assert crvusd_contract.symbol() == "crvUSD"
+
+
+def test_proxy_contract(proxy_contract):
+    assert proxy_contract.minTime() == 43200
+    assert proxy_contract.voteTime() == 604800
+    assert proxy_contract.minBalance() == 2500000000000000000000