tahoe-lafs/src/allmydata/codec.py

# -*- test-case-name: allmydata.test.test_encode_share -*-

from zope.interface import implements
from twisted.internet import defer
from allmydata.util import mathutil
from allmydata.util.assertutil import precondition
from allmydata.interfaces import ICodecEncoder, ICodecDecoder
import zfec


class ReplicatingEncoder(object):
    implements(ICodecEncoder)
    ENCODER_TYPE = "rep"

    def set_params(self, data_size, required_shares, max_shares):
        assert data_size % required_shares == 0
        assert required_shares <= max_shares
        self.data_size = data_size
        self.required_shares = required_shares
        self.max_shares = max_shares

    def get_encoder_type(self):
        return self.ENCODER_TYPE

    def get_serialized_params(self):
        return "%d" % self.required_shares

    def get_block_size(self):
        return self.data_size

    def encode(self, inshares, desired_shareids=None):
        assert isinstance(inshares, list)
        for inshare in inshares:
            assert isinstance(inshare, str)
            assert self.required_shares * len(inshare) == self.data_size
        data = "".join(inshares)
        if desired_shareids is None:
            desired_shareids = range(self.max_shares)
        shares = [data for i in desired_shareids]
        return defer.succeed((shares, desired_shareids))

class ReplicatingDecoder(object):
    implements(ICodecDecoder)

    def set_serialized_params(self, params):
        self.required_shares = int(params)

    def get_needed_shares(self):
        return self.required_shares

    def decode(self, some_shares, their_shareids):
        assert len(some_shares) == self.required_shares
        assert len(some_shares) == len(their_shareids)
        data = some_shares[0]

        chunksize = mathutil.div_ceil(len(data), self.required_shares)
        numchunks = mathutil.div_ceil(len(data), chunksize)
        l = [ data[i:i+chunksize] for i in range(0, len(data), chunksize) ]

        return defer.succeed(l)


class CRSEncoder(object):
    implements(ICodecEncoder)
    ENCODER_TYPE = "crs"

    def set_params(self, data_size, required_shares, max_shares):
        assert required_shares <= max_shares
        self.data_size = data_size
        self.required_shares = required_shares
        self.max_shares = max_shares
        self.share_size = mathutil.div_ceil(data_size, required_shares)
        self.last_share_padding = mathutil.pad_size(self.share_size, required_shares)
        self.encoder = zfec.Encoder(required_shares, max_shares)

    def get_encoder_type(self):
        return self.ENCODER_TYPE

    def get_serialized_params(self):
        return "%d-%d-%d" % (self.data_size, self.required_shares,
                             self.max_shares)

    def get_block_size(self):
        return self.share_size

    def encode(self, inshares, desired_share_ids=None):
        precondition(desired_share_ids is None or len(desired_share_ids) <= self.max_shares, desired_share_ids, self.max_shares)

        if desired_share_ids is None:
            desired_share_ids = range(self.max_shares)

        for inshare in inshares:
            assert len(inshare) == self.share_size, (len(inshare), self.share_size, self.data_size, self.required_shares)
        shares = self.encoder.encode(inshares, desired_share_ids)

        return defer.succeed((shares, desired_share_ids))

class CRSDecoder(object):
    implements(ICodecDecoder)

    def set_serialized_params(self, params):
        pieces = params.split("-")
        self.data_size = int(pieces[0])
        self.required_shares = int(pieces[1])
        self.max_shares = int(pieces[2])

        self.chunk_size = self.required_shares
        self.num_chunks = mathutil.div_ceil(self.data_size, self.chunk_size)
        self.share_size = self.num_chunks
        self.decoder = zfec.Decoder(self.required_shares, self.max_shares)

    def get_needed_shares(self):
        return self.required_shares

    def decode(self, some_shares, their_shareids):
        precondition(len(some_shares) == len(their_shareids),
                     len(some_shares), len(their_shareids))
        precondition(len(some_shares) == self.required_shares,
                     len(some_shares), self.required_shares)
        data = self.decoder.decode(some_shares,
                                   [int(s) for s in their_shareids])
        return defer.succeed(data)


all_encoders = {
    ReplicatingEncoder.ENCODER_TYPE: (ReplicatingEncoder, ReplicatingDecoder),
    CRSEncoder.ENCODER_TYPE: (CRSEncoder, CRSDecoder),
    }

def get_decoder_by_name(name):
    decoder_class = all_encoders[name][1]
    return decoder_class()