pebble/python_libs/pulse2/tests/test_framing.py

# Copyright 2024 Google LLC
#
# 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.

from __future__ import absolute_import

import unittest

from pebble.pulse2 import framing


class TestEncodeFrame(unittest.TestCase):

    def test_empty_frame(self):
        # CRC-32 of nothing is 0
        # COBS encoding of b'\0\0\0\0' is b'\x01\x01\x01\x01\x01' (5 bytes)
        self.assertEqual(framing.encode_frame(b''),
                         b'\x55\x01\x01\x01\x01\x01\x55')

    def test_simple_data(self):
        self.assertEqual(framing.encode_frame(b'abcdefg'),
                         b'\x55\x0cabcdefg\xa6\x6a\x2a\x31\x55')

    def test_flag_in_datagram(self):
        # ASCII 'U' is 0x55 hex
        self.assertEqual(framing.encode_frame(b'QUACK'),
                         b'\x55\x0aQ\0ACK\xdf\x8d\x80\x74\x55')

    def test_flag_in_fcs(self):
        # crc32(b'R') -> 0x5767df55
        # Since there is an \x55 byte in the FCS, it must be substituted,
        # just like when that byte value is present in the datagram itself.
        self.assertEqual(framing.encode_frame(b'R'),
                         b'\x55\x06R\0\xdf\x67\x57\x55')


class TestFrameSplitter(unittest.TestCase):

    def setUp(self):
        self.splitter = framing.FrameSplitter()

    def test_basic_functionality(self):
        self.splitter.write(b'\x55abcdefg\x55foobar\x55asdf\x55')
        self.assertEqual(list(self.splitter),
                         [b'abcdefg', b'foobar', b'asdf'])

    def test_wait_for_sync(self):
        self.splitter.write(b'garbage data\x55frame 1\x55')
        self.assertEqual(list(self.splitter), [b'frame 1'])

    def test_doubled_flags(self):
        self.splitter.write(b'\x55abcd\x55\x55efgh\x55')
        self.assertEqual(list(self.splitter), [b'abcd', b'efgh'])

    def test_multiple_writes(self):
        self.splitter.write(b'\x55ab')
        self.assertEqual(list(self.splitter), [])
        self.splitter.write(b'cd\x55')
        self.assertEqual(list(self.splitter), [b'abcd'])

    def test_lots_of_writes(self):
        for char in b'\x55abcd\x55ef':
            self.splitter.write(bytearray([char]))
        self.assertEqual(list(self.splitter), [b'abcd'])

    def test_iteration_pops_frames(self):
        self.splitter.write(b'\x55frame 1\x55frame 2\x55frame 3\x55')
        self.assertEqual(next(iter(self.splitter)), b'frame 1')
        self.assertEqual(list(self.splitter), [b'frame 2', b'frame 3'])

    def test_stopiteration_latches(self):
        # The iterator protocol requires that once an iterator raises
        # StopIteration, it must continue to do so for all subsequent calls
        # to its next() method.
        self.splitter.write(b'\x55frame 1\x55')
        iterator = iter(self.splitter)
        self.assertEqual(next(iterator), b'frame 1')
        with self.assertRaises(StopIteration):
            next(iterator)
            next(iterator)
        self.splitter.write(b'\x55frame 2\x55')
        with self.assertRaises(StopIteration):
            next(iterator)
        self.assertEqual(list(self.splitter), [b'frame 2'])

    def test_max_frame_length(self):
        splitter = framing.FrameSplitter(max_frame_length=6)
        splitter.write(
                b'\x5512345\x55123456\x551234567\x551234\x5512345678\x55')
        self.assertEqual(list(splitter), [b'12345', b'123456', b'1234'])

    def test_dynamic_max_length_1(self):
        self.splitter.write(b'\x5512345')
        self.splitter.max_frame_length = 6
        self.splitter.write(b'6\x551234567\x551234\x55')
        self.assertEqual(list(self.splitter), [b'123456', b'1234'])

    def test_dynamic_max_length_2(self):
        self.splitter.write(b'\x551234567')
        self.splitter.max_frame_length = 6
        self.splitter.write(b'89\x55123456\x55')
        self.assertEqual(list(self.splitter), [b'123456'])


class TestDecodeTransparency(unittest.TestCase):

    def test_easy_decode(self):
        self.assertEqual(framing.decode_transparency(b'\x06abcde'), b'abcde')

    def test_escaped_flag(self):
        self.assertEqual(framing.decode_transparency(b'\x06Q\0ACK'), b'QUACK')

    def test_flag_byte_in_frame(self):
        with self.assertRaises(framing.DecodeError):
            framing.decode_transparency(b'\x06ab\x55de')

    def test_truncated_cobs_block(self):
        with self.assertRaises(framing.DecodeError):
            framing.decode_transparency(b'\x0aabc')


class TestStripFCS(unittest.TestCase):

    def test_frame_too_short(self):
        with self.assertRaises(framing.CorruptFrame):
            framing.strip_fcs(b'abcd')

    def test_good_fcs(self):
        self.assertEqual(framing.strip_fcs(b'abcd\x11\xcd\x82\xed'), b'abcd')

    def test_frame_corrupted(self):
        with self.assertRaises(framing.CorruptFrame):
            framing.strip_fcs(b'abce\x11\xcd\x82\xed')

    def test_fcs_corrupted(self):
        with self.assertRaises(framing.CorruptFrame):
            framing.strip_fcs(b'abcd\x13\xcd\x82\xed')


class TestDecodeFrame(unittest.TestCase):

    def test_it_works(self):
        # Not much to test; decode_frame is just chained decode_transparency
        # with strip_fcs, and both of those have already been tested separately.
        self.assertEqual(framing.decode_frame(b'\x0aQ\0ACK\xdf\x8d\x80t'),
                         b'QUACK')