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diff --git a/update-payload-extractor/update_payload/common.py b/update-payload-extractor/update_payload/common.py
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+++ b/update-payload-extractor/update_payload/common.py
@@ -0,0 +1,218 @@
+#
+# Copyright (C) 2013 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+"""Utilities for update payload processing."""
+
+from __future__ import print_function
+
+from update_payload import update_metadata_pb2
+from update_payload.error import PayloadError
+
+
+#
+# Constants.
+#
+PSEUDO_EXTENT_MARKER = (1L << 64) - 1  # UINT64_MAX
+
+SIG_ASN1_HEADER = (
+    '\x30\x31\x30\x0d\x06\x09\x60\x86'
+    '\x48\x01\x65\x03\x04\x02\x01\x05'
+    '\x00\x04\x20'
+)
+
+CHROMEOS_MAJOR_PAYLOAD_VERSION = 1
+BRILLO_MAJOR_PAYLOAD_VERSION = 2
+
+INPLACE_MINOR_PAYLOAD_VERSION = 1
+SOURCE_MINOR_PAYLOAD_VERSION = 2
+OPSRCHASH_MINOR_PAYLOAD_VERSION = 3
+BROTLI_BSDIFF_MINOR_PAYLOAD_VERSION = 4
+PUFFDIFF_MINOR_PAYLOAD_VERSION = 5
+
+#
+# Payload operation types.
+#
+class OpType(object):
+  """Container for operation type constants."""
+  _CLASS = update_metadata_pb2.InstallOperation
+  REPLACE = _CLASS.REPLACE
+  REPLACE_BZ = _CLASS.REPLACE_BZ
+  MOVE = _CLASS.MOVE
+  BSDIFF = _CLASS.BSDIFF
+  SOURCE_COPY = _CLASS.SOURCE_COPY
+  SOURCE_BSDIFF = _CLASS.SOURCE_BSDIFF
+  ZERO = _CLASS.ZERO
+  DISCARD = _CLASS.DISCARD
+  REPLACE_XZ = _CLASS.REPLACE_XZ
+  PUFFDIFF = _CLASS.PUFFDIFF
+  BROTLI_BSDIFF = _CLASS.BROTLI_BSDIFF
+  ALL = (REPLACE, REPLACE_BZ, MOVE, BSDIFF, SOURCE_COPY, SOURCE_BSDIFF, ZERO,
+         DISCARD, REPLACE_XZ, PUFFDIFF, BROTLI_BSDIFF)
+  NAMES = {
+      REPLACE: 'REPLACE',
+      REPLACE_BZ: 'REPLACE_BZ',
+      MOVE: 'MOVE',
+      BSDIFF: 'BSDIFF',
+      SOURCE_COPY: 'SOURCE_COPY',
+      SOURCE_BSDIFF: 'SOURCE_BSDIFF',
+      ZERO: 'ZERO',
+      DISCARD: 'DISCARD',
+      REPLACE_XZ: 'REPLACE_XZ',
+      PUFFDIFF: 'PUFFDIFF',
+      BROTLI_BSDIFF: 'BROTLI_BSDIFF',
+  }
+
+  def __init__(self):
+    pass
+
+
+#
+# Checked and hashed reading of data.
+#
+def IntPackingFmtStr(size, is_unsigned):
+  """Returns an integer format string for use by the struct module.
+
+  Args:
+    size: the integer size in bytes (2, 4 or 8)
+    is_unsigned: whether it is signed or not
+
+  Returns:
+    A format string for packing/unpacking integer values; assumes network byte
+    order (big-endian).
+
+  Raises:
+    PayloadError if something is wrong with the arguments.
+  """
+  # Determine the base conversion format.
+  if size == 2:
+    fmt = 'h'
+  elif size == 4:
+    fmt = 'i'
+  elif size == 8:
+    fmt = 'q'
+  else:
+    raise PayloadError('unsupport numeric field size (%s)' % size)
+
+  # Signed or unsigned?
+  if is_unsigned:
+    fmt = fmt.upper()
+
+  # Make it network byte order (big-endian).
+  fmt = '!' + fmt
+
+  return fmt
+
+
+def Read(file_obj, length, offset=None, hasher=None):
+  """Reads binary data from a file.
+
+  Args:
+    file_obj: an open file object
+    length: the length of the data to read
+    offset: an offset to seek to prior to reading; this is an absolute offset
+            from either the beginning (non-negative) or end (negative) of the
+            file.  (optional)
+    hasher: a hashing object to pass the read data through (optional)
+
+  Returns:
+    A string containing the read data.
+
+  Raises:
+    PayloadError if a read error occurred or not enough data was read.
+  """
+  if offset is not None:
+    if offset >= 0:
+      file_obj.seek(offset)
+    else:
+      file_obj.seek(offset, 2)
+
+  try:
+    data = file_obj.read(length)
+  except IOError, e:
+    raise PayloadError('error reading from file (%s): %s' % (file_obj.name, e))
+
+  if len(data) != length:
+    raise PayloadError(
+        'reading from file (%s) too short (%d instead of %d bytes)' %
+        (file_obj.name, len(data), length))
+
+  if hasher:
+    hasher.update(data)
+
+  return data
+
+
+#
+# Formatting functions.
+#
+def FormatExtent(ex, block_size=0):
+  end_block = ex.start_block + ex.num_blocks
+  if block_size:
+    return '%d->%d * %d' % (ex.start_block, end_block, block_size)
+  else:
+    return '%d->%d' % (ex.start_block, end_block)
+
+
+def FormatSha256(digest):
+  """Returns a canonical string representation of a SHA256 digest."""
+  return digest.encode('base64').strip()
+
+
+#
+# Useful iterators.
+#
+def _ObjNameIter(items, base_name, reverse=False, name_format_func=None):
+  """A generic (item, name) tuple iterators.
+
+  Args:
+    items: the sequence of objects to iterate on
+    base_name: the base name for all objects
+    reverse: whether iteration should be in reverse order
+    name_format_func: a function to apply to the name string
+
+  Yields:
+    An iterator whose i-th invocation returns (items[i], name), where name ==
+    base_name + '[i]' (with a formatting function optionally applied to it).
+  """
+  idx, inc = (len(items), -1) if reverse else (1, 1)
+  if reverse:
+    items = reversed(items)
+  for item in items:
+    item_name = '%s[%d]' % (base_name, idx)
+    if name_format_func:
+      item_name = name_format_func(item, item_name)
+    yield (item, item_name)
+    idx += inc
+
+
+def _OperationNameFormatter(op, op_name):
+  return '%s(%s)' % (op_name, OpType.NAMES.get(op.type, '?'))
+
+
+def OperationIter(operations, base_name, reverse=False):
+  """An (item, name) iterator for update operations."""
+  return _ObjNameIter(operations, base_name, reverse=reverse,
+                      name_format_func=_OperationNameFormatter)
+
+
+def ExtentIter(extents, base_name, reverse=False):
+  """An (item, name) iterator for operation extents."""
+  return _ObjNameIter(extents, base_name, reverse=reverse)
+
+
+def SignatureIter(sigs, base_name, reverse=False):
+  """An (item, name) iterator for signatures."""
+  return _ObjNameIter(sigs, base_name, reverse=reverse)