paycheck: unit tests + fixes to checker module

This adds missing unit tests for the checker module, bundled with fixes
to some bugs that surfaced due to unit tests. This includes:

* A fake extent (signified by start_block == UINT64_MAX) that
  accompanies a signature data blob bears different requirements than
  previously implemented.  Specifically, the extent sequence must have
  exactly one extent; and the number of blocks is not necessarily one,
  rather it is the correct number that corresponds to the actual length
  of the signature blob.

* REPLACE/REPLACE_BZ operations must contain data.

* MOVE operation validation must ensure that all of the actual message
  extents are being used.

* BSDIFF operation must contain data (the diff).

* Signature pseudo-operation should be a REPLACE.

BUG=chromium-os:34911,chromium-os:33607,chromium-os:7597
TEST=Passes unittests (upcoming); works with actual payloads.

Change-Id: I4d839d1d4da1fbb4a493b208958a139368e2c8ca
Reviewed-on: https://gerrit.chromium.org/gerrit/45429
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>

1 files changed, 3 insertions, 19 deletions

diff --git a/scripts/update_payload/payload.py b/scripts/update_payload/payload.py
index 6dda644a..dbb385a1 100644
--- a/scripts/update_payload/payload.py
+++ b/scripts/update_payload/payload.py
@@ -19,7 +19,7 @@ import update_metadata_pb2
 # Helper functions.
 #
 def _ReadInt(file_obj, size, is_unsigned, hasher=None):
-  """Read a binary-encoded integer from a file.
+  """Reads a binary-encoded integer from a file.
 
   It will do the correct conversion based on the reported size and whether or
   not a signed number is expected. Assumes a network (big-endian) byte
@@ -36,24 +36,8 @@ def _ReadInt(file_obj, size, is_unsigned, hasher=None):
     PayloadError if an read error occurred.
 
   """
-  # 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()
-
-  # Our numeric values are in network byte order (big-endian).
-  fmt = '!' + fmt
-
-  return struct.unpack(fmt, common.Read(file_obj, size, hasher=hasher))[0]
+  return struct.unpack(common.IntPackingFmtStr(size, is_unsigned),
+                       common.Read(file_obj, size, hasher=hasher))[0]
 
 
 #