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"""Helper methods for doing binary transfers to/from a Notecard."""

import sys

from .cobs import cobs_encode, cobs_decode

from .notecard import Notecard, CARD_INTRA_TRANSACTION_TIMEOUT_SEC

BINARY_RETRIES = 2

if sys.implementation.name == 'cpython':

import hashlib

def _md5_hash(data):

"""Create an MD5 digest of the given data."""

return hashlib.md5(data).hexdigest()

else:

from .md5 import digest as _md5_hash

def binary_store_decoded_length(card: Notecard):

"""Get the length of the decoded binary data store."""

rsp = card.Transaction({'req': 'card.binary'})

# Ignore {bad-bin} errors, but fail on other types of errors.

if 'err' in rsp and '{bad-bin}' not in rsp['err']:

raise Exception(

f'Error in response to card.binary request: {rsp["err"]}.')

return rsp['length'] if 'length' in rsp else 0

def binary_store_reset(card: Notecard):

"""Reset the binary data store."""

rsp = card.Transaction({'req': 'card.binary', 'delete': True})

if 'err' in rsp:

raise Exception(

f'Error in response to card.binary delete request: {rsp["err"]}.')

def binary_store_transmit(card: Notecard, data: bytearray, offset: int):

"""Write bytes to index `offset` of the binary data store."""

# Make a copy of the data to transmit. We do not modify the user's passed in

# `data` object.

tx_data = bytearray(data)

rsp = card.Transaction({'req': 'card.binary'})

# Ignore `{bad-bin}` errors, because we intend to overwrite the data.

if 'err' in rsp and '{bad-bin}' not in rsp['err']:

raise Exception(rsp['err'])

if 'max' not in rsp or rsp['max'] == 0:

raise Exception(('Unexpected card.binary response: max is zero or not '

'present.'))

curr_len = rsp['length'] if 'length' in rsp else 0

if offset != curr_len:

raise Exception('Notecard data length is misaligned with offset.')

max_len = rsp['max']

remaining = max_len - curr_len if offset > 0 else max_len

if len(tx_data) > remaining:

raise Exception(('Data to transmit won\'t fit in the Notecard\'s binary'

' store.'))

encoded = cobs_encode(tx_data, ord('\n'))

req = {

'req': 'card.binary.put',

'cobs': len(encoded),

'status': _md5_hash(tx_data)

}

encoded.append(ord('\n'))

if offset > 0:

req['offset'] = offset

tries = 1 + BINARY_RETRIES

while tries > 0:

try:

# We need to hold the lock for both the card.binary.put transaction

# and the subsequent transmission of the binary data.

card.lock()

# Pass lock=false because we're already locked.

rsp = card.Transaction(req, lock=False)

if 'err' in rsp:

raise Exception(rsp['err'])

# Send the binary data.

card.transmit(encoded, delay=False)

finally:

card.unlock()

rsp = card.Transaction({'req': 'card.binary'})

if 'err' in rsp:

# Retry on {bad-bin} errors.

if '{bad-bin}' in rsp['err']:

tries -= 1

if card._debug and tries > 0:

print('Error during binary transmission, retrying...')

# Fail on all other error types.

else:

raise Exception(rsp['err'])

else:

break

if tries == 0:

raise Exception('Failed to transmit binary data.')

def binary_store_receive(card, offset: int, length: int):

"""Receive `length' bytes from index `offset` of the binary data store."""

req = {

'req': 'card.binary.get',

'offset': offset,

'length': length

}

try:

# We need to hold the lock for both the card.binary.get transaction

# and the subsequent receipt of the binary data.

card.lock()

# Pass lock=false because we're already locked.

rsp = card.Transaction(req, lock=False)

if 'err' in rsp:

raise Exception(rsp['err'])

# Receive the binary data, keeping everything except the last byte,

# which is a newline.

try:

encoded = card.receive(delay=False)[:-1]

except Exception as e:

# Queue up a reset if there was an issue receiving the binary data.

# The reset will attempt to drain the binary data from the Notecard

# so that the comms channel with the Notecard is clean before the

# next transaction.

card._reset_required = True

raise e

finally:

card.unlock()

decoded = cobs_decode(encoded, ord('\n'))

if _md5_hash(decoded) != rsp['status']:

raise Exception('Computed MD5 does not match received MD5.')

return decoded

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