Minor optimizations to Bitcoin tx processing (#214)

* Construct unpacking functions for byte format up front to save time
wasted on parsing format string every iteration.

* Store length ahead of time as the overhead adds up.

* Reduce object attribute lookups in hash functions.

* Clean up lib pkg API changes. Unit test new "public" API members.
Underscore prefix for internal hash module funcs. Make bytes.fromhex a
public function.

* Document recent performance findings.

docs/PERFORMANCE-NOTES

@@ -1,4 +1,4 @@
-Just some notes on performance with Python 3.5.  I am taking this into
+Just some notes on performance with Python 3.5. We are taking these into
 account in the code.
 
 - 60% faster to create lists with [] list comprehensions than tuples
@@ -16,11 +16,21 @@ account in the code.
 
 - struct.pack, struct.unpack are over 60% faster than int.to_bytes and
   int.from_bytes.  They are faster little endian (presumably because
-  it matches the host) than big endian regardless of length.
+  it matches the host) than big endian regardless of length. Furthermore,
+  using stored packing and unpacking methods from Struct classes is faster
+  than using the flexible-format struct.[un]pack equivalents.
+
+  After storing the Struct('<Q').unpack_from function as unpack_uint64_from,
+   later calls to unpack_uint64_from(b, 0) are about 30% faster than calls to
+   unpack_from('<Q', b, 0).
+
 
 - single-item list and tuple unpacking.  Suppose b = (1, )
 
    a, = b  is a about 0.4% faster than  (a,) = b
            and about 45% faster than a = b[0]
 
-- multiple assignment is faster using tuples only for 3 or more items
+- multiple assignment is faster using tuples only for 3 or more items
+
+- retrieving a previously stored length of a bytes object can be over 200%
+  faster than a new call to len(b)

lib/hash.py

@@ -29,17 +29,22 @@
 import hashlib
 import hmac
 
-from lib.util import bytes_to_int, int_to_bytes
+from lib.util import bytes_to_int, int_to_bytes, hex_to_bytes
+
+_sha256 = hashlib.sha256
+_sha512 = hashlib.sha512
+_new_hash = hashlib.new
+_new_hmac = hmac.new
 
 
 def sha256(x):
     '''Simple wrapper of hashlib sha256.'''
-    return hashlib.sha256(x).digest()
+    return _sha256(x).digest()
 
 
 def ripemd160(x):
     '''Simple wrapper of hashlib ripemd160.'''
-    h = hashlib.new('ripemd160')
+    h = _new_hash('ripemd160')
     h.update(x)
     return h.digest()
 
@@ -51,7 +56,7 @@ def double_sha256(x):
 
 def hmac_sha512(key, msg):
     '''Use SHA-512 to provide an HMAC.'''
-    return hmac.new(key, msg, hashlib.sha512).digest()
+    return _new_hmac(key, msg, _sha512).digest()
 
 
 def hash160(x):
@@ -73,7 +78,7 @@ hash_to_str = hash_to_hex_str
 
 def hex_str_to_hash(x):
     '''Convert a displayed hex string to a binary hash.'''
-    return bytes(reversed(bytes.fromhex(x)))
+    return bytes(reversed(hex_to_bytes(x)))
 
 
 class Base58Error(Exception):

lib/tx.py

@@ -29,10 +29,11 @@
 
 
 from collections import namedtuple
-from struct import unpack_from
 
-from lib.util import cachedproperty
 from lib.hash import double_sha256, hash_to_str
+from lib.util import (cachedproperty, unpack_int32_from, unpack_int64_from,
+                      unpack_uint16_from, unpack_uint32_from,
+                      unpack_uint64_from)
 
 
 class Tx(namedtuple("Tx", "version inputs outputs locktime")):
@@ -78,6 +79,7 @@ class Deserializer(object):
     def __init__(self, binary, start=0):
         assert isinstance(binary, bytes)
         self.binary = binary
+        self.binary_length = len(binary)
         self.cursor = start
 
     def read_tx(self):
@@ -131,7 +133,7 @@ class Deserializer(object):
     def _read_nbytes(self, n):
         cursor = self.cursor
         self.cursor = end = cursor + n
-        assert len(self.binary) >= end
+        assert self.binary_length >= end
         return self.binary[cursor:end]
 
     def _read_varbytes(self):
@@ -149,27 +151,27 @@ class Deserializer(object):
         return self._read_le_uint64()
 
     def _read_le_int32(self):
-        result, = unpack_from('<i', self.binary, self.cursor)
+        result, = unpack_int32_from(self.binary, self.cursor)
         self.cursor += 4
         return result
 
     def _read_le_int64(self):
-        result, = unpack_from('<q', self.binary, self.cursor)
+        result, = unpack_int64_from(self.binary, self.cursor)
         self.cursor += 8
         return result
 
     def _read_le_uint16(self):
-        result, = unpack_from('<H', self.binary, self.cursor)
+        result, = unpack_uint16_from(self.binary, self.cursor)
         self.cursor += 2
         return result
 
     def _read_le_uint32(self):
-        result, = unpack_from('<I', self.binary, self.cursor)
+        result, = unpack_uint32_from(self.binary, self.cursor)
         self.cursor += 4
         return result
 
     def _read_le_uint64(self):
-        result, = unpack_from('<Q', self.binary, self.cursor)
+        result, = unpack_uint64_from(self.binary, self.cursor)
         self.cursor += 8
         return result
 

lib/util.py

@@ -34,7 +34,7 @@ import logging
 import re
 import sys
 from collections import Container, Mapping
-from struct import pack
+from struct import pack, Struct
 
 
 class LoggedClass(object):
@@ -309,3 +309,11 @@ def protocol_version(client_req, server_min, server_max):
         result = None
 
     return result
+
+unpack_int32_from = Struct('<i').unpack_from
+unpack_int64_from = Struct('<q').unpack_from
+unpack_uint16_from = Struct('<H').unpack_from
+unpack_uint32_from = Struct('<I').unpack_from
+unpack_uint64_from = Struct('<Q').unpack_from
+
+hex_to_bytes = bytes.fromhex

server/controller.py

@@ -675,7 +675,7 @@ class Controller(util.LoggedClass):
         '''Raise an RPCError if the value is not a valid transaction
         hash.'''
         try:
-            if len(bytes.fromhex(value)) == 32:
+            if len(util.hex_to_bytes(value)) == 32:
                 return
         except Exception:
             pass
@@ -898,7 +898,7 @@ class Controller(util.LoggedClass):
         raw_tx = await self.daemon_request('getrawtransaction', tx_hash)
         if not raw_tx:
             return None
-        raw_tx = bytes.fromhex(raw_tx)
+        raw_tx = util.hex_to_bytes(raw_tx)
         tx, tx_hash = self.coin.DESERIALIZER(raw_tx).read_tx()
         if index >= len(tx.outputs):
             return None

server/daemon.py

@@ -18,7 +18,7 @@ from time import strptime
 
 import aiohttp
 
-import lib.util as util
+from lib.util import LoggedClass, int_to_varint, hex_to_bytes
 from lib.hash import hex_str_to_hash
 
 
@@ -26,7 +26,7 @@ class DaemonError(Exception):
     '''Raised when the daemon returns an error in its results.'''
 
 
-class Daemon(util.LoggedClass):
+class Daemon(LoggedClass):
     '''Handles connections to a daemon at the given URL.'''
 
     WARMING_UP = -28
@@ -208,7 +208,7 @@ class Daemon(util.LoggedClass):
         params_iterable = ((h, False) for h in hex_hashes)
         blocks = await self._send_vector('getblock', params_iterable)
         # Convert hex string to bytes
-        return [bytes.fromhex(block) for block in blocks]
+        return [hex_to_bytes(block) for block in blocks]
 
     async def mempool_hashes(self):
         '''Update our record of the daemon's mempool hashes.'''
@@ -240,7 +240,7 @@ class Daemon(util.LoggedClass):
         txs = await self._send_vector('getrawtransaction', params_iterable,
                                       replace_errs=replace_errs)
         # Convert hex strings to bytes
-        return [bytes.fromhex(tx) if tx else None for tx in txs]
+        return [hex_to_bytes(tx) if tx else None for tx in txs]
 
     async def sendrawtransaction(self, params):
         '''Broadcast a transaction to the network.'''
@@ -336,7 +336,7 @@ class LegacyRPCDaemon(Daemon):
         raw_block = header
         num_txs = len(transactions)
         if num_txs > 0:
-            raw_block += util.int_to_varint(num_txs)
+            raw_block += int_to_varint(num_txs)
             raw_block += b''.join(transactions)
         else:
             raw_block += b'\x00'

tests/lib/test_util.py

@@ -57,6 +57,7 @@ def test_increment_byte_string():
     assert util.increment_byte_string(b'\x01\x01') == b'\x01\x02'
     assert util.increment_byte_string(b'\xff\xff') is None
 
+
 def test_is_valid_hostname():
     is_valid_hostname = util.is_valid_hostname
     assert not is_valid_hostname('')
@@ -116,3 +117,22 @@ def test_protocol_version():
     assert util.protocol_version(["0.8", "0.9"], "1.0", "1.1") is None
     assert util.protocol_version(["1.1", "1.2"], "1.0", "1.1") == (1, 1)
     assert util.protocol_version(["1.2", "1.3"], "1.0", "1.1") is None
+
+
+def test_unpackers():
+    b = bytes(range(256))
+    assert util.unpack_int32_from(b, 0) == (50462976,)
+    assert util.unpack_int32_from(b, 42) == (757869354,)
+    assert util.unpack_int64_from(b, 0) == (506097522914230528,)
+    assert util.unpack_int64_from(b, 42) == (3544384782113450794,)
+
+    assert util.unpack_uint16_from(b, 0) == (256,)
+    assert util.unpack_uint16_from(b, 42) == (11050,)
+    assert util.unpack_uint32_from(b, 0) == (50462976,)
+    assert util.unpack_uint32_from(b, 42) == (757869354,)
+    assert util.unpack_uint64_from(b, 0) == (506097522914230528,)
+    assert util.unpack_uint64_from(b, 42) == (3544384782113450794,)
+
+def test_hex_transforms():
+    h = "AABBCCDDEEFF"
+    assert util.hex_to_bytes(h) == b'\xaa\xbb\xcc\xdd\xee\xff'