lbry-sdk/lbrynet/stream/descriptor.py

import os
import json
import binascii
import logging
import typing
import asyncio
from cryptography.hazmat.primitives.ciphers.algorithms import AES
from lbrynet.blob import MAX_BLOB_SIZE
from lbrynet.blob.blob_info import BlobInfo
from lbrynet.blob.blob_file import BlobFile
from lbrynet.cryptoutils import get_lbry_hash_obj
from lbrynet.error import InvalidStreamDescriptorError

log = logging.getLogger(__name__)


def format_sd_info(stream_name: str, key: str, suggested_file_name: str, stream_hash: str,
                   blobs: typing.List[typing.Dict]) -> typing.Dict:
    return {
        "stream_type": "lbryfile",
        "stream_name": stream_name,
        "key": key,
        "suggested_file_name": suggested_file_name,
        "stream_hash": stream_hash,
        "blobs": blobs
    }


def random_iv_generator() -> typing.Generator[bytes, None, None]:
    while 1:
        yield os.urandom(AES.block_size // 8)


def file_reader(file_path: str):
    length = int(os.stat(file_path).st_size)
    offset = 0

    with open(file_path, 'rb') as stream_file:
        while offset < length:
            bytes_to_read = min((length - offset), MAX_BLOB_SIZE - 1)
            if not bytes_to_read:
                break
            blob_bytes = stream_file.read(bytes_to_read)
            yield blob_bytes
            offset += bytes_to_read


class StreamDescriptor:
    def __init__(self, loop: asyncio.BaseEventLoop, blob_dir: str, stream_name: str, key: str,
                 suggested_file_name: str, blobs: typing.List[BlobInfo], stream_hash: typing.Optional[str] = None,
                 sd_hash: typing.Optional[str] = None):
        self.loop = loop
        self.blob_dir = blob_dir
        self.stream_name = stream_name
        self.key = key
        self.suggested_file_name = suggested_file_name
        self.blobs = blobs
        self.stream_hash = stream_hash or self.get_stream_hash()
        self.sd_hash = sd_hash

    def get_stream_hash(self) -> str:
        return self.calculate_stream_hash(
            binascii.hexlify(self.stream_name.encode()), self.key.encode(),
            binascii.hexlify(self.suggested_file_name.encode()),
            [blob_info.as_dict() for blob_info in self.blobs]
        )

    def calculate_sd_hash(self) -> str:
        h = get_lbry_hash_obj()
        h.update(self.as_json())
        return h.hexdigest()

    def as_json(self) -> bytes:
        return json.dumps(
            format_sd_info(binascii.hexlify(self.stream_name.encode()).decode(), self.key,
                           binascii.hexlify(self.suggested_file_name.encode()).decode(),
                           self.stream_hash,
                           [blob_info.as_dict() for blob_info in self.blobs]), sort_keys=True
        ).encode()

    async def make_sd_blob(self):
        sd_hash = self.calculate_sd_hash()
        sd_data = self.as_json()
        sd_blob = BlobFile(self.loop, self.blob_dir, sd_hash, len(sd_data))
        if not sd_blob.get_is_verified():
            writer = sd_blob.open_for_writing()
            writer.write(sd_data)
        await sd_blob.verified.wait()
        await sd_blob.close()
        return sd_blob

    @classmethod
    def _from_stream_descriptor_blob(cls, loop: asyncio.BaseEventLoop, blob_dir: str,
                                     blob: BlobFile) -> 'StreamDescriptor':
        assert os.path.isfile(blob.file_path)
        with open(blob.file_path, 'rb') as f:
            json_bytes = f.read()
        decoded = json.loads(json_bytes.decode())
        if decoded['blobs'][-1]['length'] != 0:
            raise InvalidStreamDescriptorError("Does not end with a zero-length blob.")
        if any([blob_info['length'] == 0 for blob_info in decoded['blobs'][:-1]]):
            raise InvalidStreamDescriptorError("Contains zero-length data blob")
        if 'blob_hash' in decoded['blobs'][-1]:
            raise InvalidStreamDescriptorError("Stream terminator blob should not have a hash")
        if any([i != blob_info['blob_num'] for i, blob_info in enumerate(decoded['blobs'])]):
            raise InvalidStreamDescriptorError("Stream contains out of order or skipped blobs")
        descriptor = cls(
            loop, blob_dir,
            binascii.unhexlify(decoded['stream_name']).decode(),
            decoded['key'],
            binascii.unhexlify(decoded['suggested_file_name']).decode(),
            [BlobInfo(info['blob_num'], info['length'], info['iv'], info.get('blob_hash'))
             for info in decoded['blobs']],
            decoded['stream_hash'],
            blob.blob_hash
        )
        if descriptor.get_stream_hash() != decoded['stream_hash']:
            raise InvalidStreamDescriptorError("Stream hash does not match stream metadata")
        return descriptor

    @classmethod
    async def from_stream_descriptor_blob(cls, loop: asyncio.BaseEventLoop, blob_dir: str,
                                          blob: BlobFile) -> 'StreamDescriptor':
        return await loop.run_in_executor(None, lambda: cls._from_stream_descriptor_blob(loop, blob_dir, blob))

    @staticmethod
    def get_blob_hashsum(b: typing.Dict):
        length = b['length']
        if length != 0:
            blob_hash = b['blob_hash']
        else:
            blob_hash = None
        blob_num = b['blob_num']
        iv = b['iv']
        blob_hashsum = get_lbry_hash_obj()
        if length != 0:
            blob_hashsum.update(blob_hash.encode())
        blob_hashsum.update(str(blob_num).encode())
        blob_hashsum.update(iv.encode())
        blob_hashsum.update(str(length).encode())
        return blob_hashsum.digest()

    @staticmethod
    def calculate_stream_hash(hex_stream_name: bytes, key: bytes, hex_suggested_file_name: bytes,
                              blob_infos: typing.List[typing.Dict]) -> str:
        h = get_lbry_hash_obj()
        h.update(hex_stream_name)
        h.update(key)
        h.update(hex_suggested_file_name)
        blobs_hashsum = get_lbry_hash_obj()
        for blob in blob_infos:
            blobs_hashsum.update(StreamDescriptor.get_blob_hashsum(blob))
        h.update(blobs_hashsum.digest())
        return h.hexdigest()

    @classmethod
    async def create_stream(cls, loop: asyncio.BaseEventLoop, blob_dir: str,
                            file_path: str, key: typing.Optional[bytes] = None,
                            iv_generator: typing.Optional[typing.Generator[bytes, None, None]] = None
                            ) -> 'StreamDescriptor':

        blobs: typing.List[BlobInfo] = []

        iv_generator = iv_generator or random_iv_generator()
        key = key or os.urandom(AES.block_size // 8)
        blob_num = -1
        for blob_bytes in file_reader(file_path):
            blob_num += 1
            blob_info = await BlobFile.create_from_unencrypted(
                    loop, blob_dir, key, next(iv_generator), blob_bytes, blob_num
                )
            blobs.append(blob_info)
        blobs.append(
            BlobInfo(len(blobs), 0, binascii.hexlify(next(iv_generator)).decode()))  # add the stream terminator
        descriptor = cls(
            loop, blob_dir, os.path.basename(file_path), binascii.hexlify(key).decode(), os.path.basename(file_path),
            blobs
        )
        sd_blob = await descriptor.make_sd_blob()
        descriptor.sd_hash = sd_blob.blob_hash
        return descriptor

    def lower_bound_decrypted_length(self) -> int:
        length = sum((blob.length - 1 for blob in self.blobs[:-2]))
        return length + self.blobs[-2].length - (AES.block_size // 8)

    def upper_bound_decrypted_length(self) -> int:
        return self.lower_bound_decrypted_length() + (AES.block_size // 8)