def ReadFromPayload(self, payload_file, hasher=None):
"""Reads the payload header from a file.
Reads the payload header from the |payload_file| and updates the |hasher|
if one is passed. The parsed header is stored in the _PayloadHeader
instance attributes.
Args:
payload_file: a file object
hasher: an optional hasher to pass the value through
Returns:
None.
Raises:
PayloadError if a read error occurred or the header is invalid.
"""
# Verify magic
magic = common.Read(payload_file, len(self._MAGIC), hasher=hasher)
if magic != self._MAGIC:
raise PayloadError('invalid payload magic: %s' % magic)
self.version = _ReadInt(payload_file, self._VERSION_SIZE, True,
hasher=hasher)
self.manifest_len = _ReadInt(payload_file, self._MANIFEST_LEN_SIZE, True,
hasher=hasher)
self.size = (len(self._MAGIC) + self._VERSION_SIZE +
self._MANIFEST_LEN_SIZE)
self.metadata_signature_len = 0
if self.version == common.BRILLO_MAJOR_PAYLOAD_VERSION:
self.size += self._METADATA_SIGNATURE_LEN_SIZE
self.metadata_signature_len = _ReadInt(
payload_file, self._METADATA_SIGNATURE_LEN_SIZE, True,
hasher=hasher)
def _ReadManifest(self):
"""Reads and returns the payload manifest.
Returns:
A string containing the payload manifest in binary form.
Raises:
PayloadError if a read error occurred.
"""
if not self.header:
raise PayloadError('payload header not present')
return common.Read(self.payload_file, self.header.manifest_len,
hasher=self.manifest_hasher)
def ReadDataBlob(self, offset, length):
"""Reads and returns a single data blob from the update payload.
Args:
offset: offset to the beginning of the blob from the end of the manifest
length: the blob's length
Returns:
A string containing the raw blob data.
Raises:
PayloadError if a read error occurred.
"""
return common.Read(self.payload_file, length,
offset=self.payload_file_offset + self.data_offset +
offset)
def _ReadMetadataSignature(self):
"""Reads and returns the metadata signatures.
Returns:
A string containing the metadata signatures protobuf in binary form or
an empty string if no metadata signature found in the payload.
Raises:
PayloadError if a read error occurred.
"""
if not self.header:
raise PayloadError('payload header not present')
return common.Read(self.payload_file,
self.header.metadata_signature_len,
offset=self.payload_file_offset + self.header.size +
self.header.manifest_len)
def _ReadInt(file_obj, size, is_unsigned, hasher=None):
"""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
ordering.
Args:
file_obj: a file object
size: the integer size in bytes (2, 4 or 8)
is_unsigned: whether it is signed or not
hasher: an optional hasher to pass the value through
Returns:
An "unpacked" (Python) integer value.
Raises:
PayloadError if an read error occurred.
"""
return struct.unpack(common.IntPackingFmtStr(size, is_unsigned),
common.Read(file_obj, size, hasher=hasher))[0]
