Implement EXTCODEHASH opcode for Constantinople

Closes #719

eth/vm/forks/constantinople/constants.py

@@ -0,0 +1 @@
+GAS_EXTCODEHASH_EIP1052 = 400

eth/vm/forks/constantinople/opcodes.py

@@ -13,8 +13,12 @@
 from eth.vm.forks.byzantium.opcodes import (
     BYZANTIUM_OPCODES
 )
+from eth.vm.forks.constantinople.constants import (
+    GAS_EXTCODEHASH_EIP1052
+)
 from eth.vm.logic import (
-    arithmetic
+    arithmetic,
+    context,
 )
 from eth.vm.opcode import (
     as_opcode
@@ -37,6 +41,11 @@
         mnemonic=mnemonics.SAR,
         gas_cost=constants.GAS_VERYLOW,
     ),
+    opcode_values.EXTCODEHASH: as_opcode(
+        logic_fn=context.extcodehash,
+        mnemonic=mnemonics.EXTCODEHASH,
+        gas_cost=GAS_EXTCODEHASH_EIP1052,
+    ),
 }
 
 CONSTANTINOPLE_OPCODES = merge(

eth/vm/logic/context.py

@@ -138,6 +138,20 @@ def extcodecopy(computation):
     computation.memory_write(mem_start_position, size, padded_code_bytes)
 
 
+def extcodehash(computation):
+    """
+    Return the code hash for a given address.
+    EIP: https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1052.md
+    """
+    account = force_bytes_to_address(computation.stack_pop(type_hint=constants.BYTES))
+    account_db = computation.state.account_db
+
+    if not account_db.account_exists(account):
+        computation.stack_push(constants.NULL_BYTE)
+    else:
+        computation.stack_push(account_db.get_code_hash(account))
+
+
 def returndatasize(computation):
     size = len(computation.return_data)
     computation.stack_push(size)

eth/vm/mnemonics.py

@@ -50,6 +50,7 @@
 GASPRICE = 'GASPRICE'
 EXTCODESIZE = 'EXTCODESIZE'
 EXTCODECOPY = 'EXTCODECOPY'
+EXTCODEHASH = 'EXTCODEHASH'
 RETURNDATASIZE = 'RETURNDATASIZE'
 RETURNDATACOPY = 'RETURNDATACOPY'
 #

eth/vm/opcode_values.py

@@ -56,6 +56,7 @@
 GASPRICE = 0x3a
 EXTCODESIZE = 0x3b
 EXTCODECOPY = 0x3c
+EXTCODEHASH = 0x3f
 RETURNDATASIZE = 0x3d
 RETURNDATACOPY = 0x3e
 

tests/core/opcodes/test_opcodes.py

@@ -6,10 +6,18 @@
     to_canonical_address,
     int_to_big_endian,
 )
-
 from eth import (
     constants
 )
+from eth.db.backends.memory import (
+    MemoryDB
+)
+from eth.db.chain import (
+    ChainDB
+)
+from eth.rlp.headers import (
+    BlockHeader,
+)
 from eth.utils.padding import (
     pad32
 )
@@ -24,16 +32,23 @@
     HomesteadVM,
     FrontierVM,
 )
-
 from eth.vm.message import (
     Message,
 )
 
 
 NORMALIZED_ADDRESS_A = "0x0f572e5295c57f15886f9b263e2f6d2d6c7b5ec6"
 NORMALIZED_ADDRESS_B = "0xcd1722f3947def4cf144679da39c4c32bdc35681"
+ADDRESS_WITH_CODE = ("0xddd722f3947def4cf144679da39c4c32bdc35681", b'pseudocode')
+EMPTY_ADDRESS_IN_STATE = NORMALIZED_ADDRESS_A
+ADDRESS_NOT_IN_STATE = NORMALIZED_ADDRESS_B
 CANONICAL_ADDRESS_A = to_canonical_address("0x0f572e5295c57f15886f9b263e2f6d2d6c7b5ec6")
 CANONICAL_ADDRESS_B = to_canonical_address("0xcd1722f3947def4cf144679da39c4c32bdc35681")
+GENESIS_HEADER = BlockHeader(
+    difficulty=constants.GENESIS_DIFFICULTY,
+    block_number=constants.GENESIS_BLOCK_NUMBER,
+    gas_limit=constants.GENESIS_GAS_LIMIT,
+)
 
 
 def prepare_computation(vm_class):
@@ -52,11 +67,17 @@ def prepare_computation(vm_class):
         origin=CANONICAL_ADDRESS_B,
     )
 
+    vm = vm_class(GENESIS_HEADER, ChainDB(MemoryDB()))
+
     computation = vm_class._state_class.computation_class(
-        state=None,
+        state=vm.state,
         message=message,
         transaction_context=tx_context,
     )
+
+    computation.state.account_db.touch_account(decode_hex(EMPTY_ADDRESS_IN_STATE))
+    computation.state.account_db.set_code(decode_hex(ADDRESS_WITH_CODE[0]), ADDRESS_WITH_CODE[1])
+
     return computation
 
 
@@ -378,3 +399,34 @@ def test_sar(vm_class, val1, val2, expected):
 
     result = computation.stack_pop(type_hint=constants.UINT256)
     assert encode_hex(pad32(int_to_big_endian(result))) == expected
+
+
+@pytest.mark.parametrize(
+    'vm_class, address, expected',
+    (
+        (
+            ConstantinopleVM,
+            ADDRESS_NOT_IN_STATE,
+            '0x0000000000000000000000000000000000000000000000000000000000000000',
+        ),
+        (
+            ConstantinopleVM,
+            EMPTY_ADDRESS_IN_STATE,
+            '0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470',
+        ),
+        (
+            ConstantinopleVM,
+            ADDRESS_WITH_CODE[0],
+            # equivalent to encode_hex(keccak(ADDRESS_WITH_CODE[1])),
+            '0xb6f5188e2984211a0de167a56a92d85bee084d7a469d97a59e1e2b573dbb4301'
+        ),
+    )
+)
+def test_extcodehash(vm_class, address, expected):
+    computation = prepare_computation(vm_class)
+
+    computation.stack_push(decode_hex(address))
+    computation.opcodes[opcode_values.EXTCODEHASH](computation)
+
+    result = computation.stack_pop(type_hint=constants.BYTES)
+    assert encode_hex(pad32(result)) == expected