import os
from zope.interface import implements
from twisted.python import log, failure
from twisted.internet import defer
from twisted.application import service
from foolscap import Referenceable

from allmydata.util.hashutil import file_renewal_secret_hash, \
     file_cancel_secret_hash, bucket_renewal_secret_hash, \
     bucket_cancel_secret_hash, plaintext_hasher, \
     storage_index_chk_hash, plaintext_segment_hasher, key_hasher
from allmydata import encode, storage, hashtree, uri
from allmydata.util import idlib, mathutil
from allmydata.interfaces import IUploadable, IUploader, IEncryptedUploadable
from allmydata.Crypto.Cipher import AES

from cStringIO import StringIO
import collections, random


class HaveAllPeersError(Exception):
    # we use this to jump out of the loop
    pass

# this wants to live in storage, not here
class TooFullError(Exception):
    pass

# our current uri_extension is 846 bytes for small files, a few bytes
# more for larger ones (since the filesize is encoded in decimal in a
# few places). Ask for a little bit more just in case we need it. If
# the extension changes size, we can change EXTENSION_SIZE to
# allocate a more accurate amount of space.
EXTENSION_SIZE = 1000

class PeerTracker:
    def __init__(self, peerid, permutedid, connection,
                 sharesize, blocksize, num_segments, num_share_hashes,
                 storage_index,
                 bucket_renewal_secret, bucket_cancel_secret):
        self.peerid = peerid
        self.permutedid = permutedid
        self.connection = connection # to an RIClient
        self.buckets = {} # k: shareid, v: IRemoteBucketWriter
        self.sharesize = sharesize
        #print "PeerTracker", peerid, permutedid, sharesize
        as = storage.allocated_size(sharesize,
                                    num_segments,
                                    num_share_hashes,
                                    EXTENSION_SIZE)
        self.allocated_size = as
                                                           
        self.blocksize = blocksize
        self.num_segments = num_segments
        self.num_share_hashes = num_share_hashes
        self.storage_index = storage_index
        self._storageserver = None

        self.renew_secret = bucket_renewal_secret
        self.cancel_secret = bucket_cancel_secret

    def __repr__(self):
        return ("<PeerTracker for peer %s and SI %s>"
                % (idlib.b2a(self.peerid)[:4],
                   idlib.b2a(self.storage_index)[:6]))

    def query(self, sharenums):
        if not self._storageserver:
            d = self.connection.callRemote("get_service", "storageserver")
            d.addCallback(self._got_storageserver)
            d.addCallback(lambda res: self._query(sharenums))
            return d
        return self._query(sharenums)
    def _got_storageserver(self, storageserver):
        self._storageserver = storageserver
    def _query(self, sharenums):
        #print " query", self.peerid, len(sharenums)
        d = self._storageserver.callRemote("allocate_buckets",
                                           self.storage_index,
                                           self.renew_secret,
                                           self.cancel_secret,
                                           sharenums,
                                           self.allocated_size,
                                           canary=Referenceable())
        d.addCallback(self._got_reply)
        return d
        
    def _got_reply(self, (alreadygot, buckets)):
        #log.msg("%s._got_reply(%s)" % (self, (alreadygot, buckets)))
        b = {}
        for sharenum, rref in buckets.iteritems():
            bp = storage.WriteBucketProxy(rref, self.sharesize,
                                          self.blocksize,
                                          self.num_segments,
                                          self.num_share_hashes,
                                          EXTENSION_SIZE)
            b[sharenum] = bp
        self.buckets.update(b)
        return (alreadygot, set(b.keys()))

class Tahoe3PeerSelector:

    def __init__(self, upload_id):
        self.upload_id = upload_id

    def __repr__(self):
        return "<Tahoe3PeerSelector for upload %s>" % self.upload_id

    def get_shareholders(self, client,
                         storage_index, share_size, block_size,
                         num_segments, total_shares, shares_of_happiness,
                         push_to_ourselves):
        """
        @return: a set of PeerTracker instances that have agreed to hold some
            shares for us
        """

        self.total_shares = total_shares
        self.shares_of_happiness = shares_of_happiness

        # we are responsible for locating the shareholders. self._encoder is
        # responsible for handling the data and sending out the shares.
        peers = client.get_permuted_peers(storage_index, push_to_ourselves)

        assert peers, "peer selection left us with zero peers for our data"

        # this needed_hashes computation should mirror
        # Encoder.send_all_share_hash_trees. We use an IncompleteHashTree
        # (instead of a HashTree) because we don't require actual hashing
        # just to count the levels.
        ht = hashtree.IncompleteHashTree(total_shares)
        num_share_hashes = len(ht.needed_hashes(0, include_leaf=True))

        client_renewal_secret = client.get_renewal_secret()
        client_cancel_secret = client.get_cancel_secret()

        file_renewal_secret = file_renewal_secret_hash(client_renewal_secret,
                                                       storage_index)
        file_cancel_secret = file_cancel_secret_hash(client_cancel_secret,
                                                     storage_index)

        trackers = [ PeerTracker(peerid, permutedid, conn,
                                 share_size, block_size,
                                 num_segments, num_share_hashes,
                                 storage_index,
                                 bucket_renewal_secret_hash(file_renewal_secret,
                                                            peerid),
                                 bucket_cancel_secret_hash(file_cancel_secret,
                                                           peerid),
                                 )
                     for permutedid, peerid, conn in peers ]
        self.all_peers = trackers
        self.usable_peers = set(trackers) # this set shrinks over time
        self.used_peers = set() # while this set grows
        self.unallocated_sharenums = set(range(total_shares)) # this one shrinks

        return self._locate_more_shareholders()

    def _locate_more_shareholders(self):
        d = self._query_peers()
        d.addCallback(self._located_some_shareholders)
        return d

    def _located_some_shareholders(self, res):
        log.msg("_located_some_shareholders")
        log.msg(" still need homes for %d shares, still have %d usable peers"
                % (len(self.unallocated_sharenums), len(self.usable_peers)))
        if not self.unallocated_sharenums:
            # Finished allocating places for all shares.
            log.msg("%s._locate_all_shareholders() "
                    "Finished allocating places for all shares." % self)
            log.msg("used_peers is %s" % (self.used_peers,))
            return self.used_peers
        if not self.usable_peers:
            # Ran out of peers who have space.
            log.msg("%s._locate_all_shareholders() "
                    "Ran out of peers who have space." % self)
            margin = self.total_shares - self.shares_of_happiness
            if len(self.unallocated_sharenums) < margin:
                # But we allocated places for enough shares.
                log.msg("%s._locate_all_shareholders() "
                        "But we allocated places for enough shares.")
                return self.used_peers
            raise encode.NotEnoughPeersError
        # we need to keep trying
        return self._locate_more_shareholders()

    def _create_ring_of_things(self):
        PEER = 1 # must sort later than SHARE, for consistency with download
        SHARE = 0
        # ring_of_things is a list of (position_in_ring, whatami, x) where
        # whatami is SHARE if x is a sharenum or else PEER if x is a
        # PeerTracker instance
        ring_of_things = []
        ring_of_things.extend([ (peer.permutedid, PEER, peer,)
                                for peer in self.usable_peers ])
        shares = [ (i * 2**160 / self.total_shares, SHARE, i)
                   for i in self.unallocated_sharenums]
        ring_of_things.extend(shares)
        ring_of_things.sort()
        ring_of_things = collections.deque(ring_of_things)
        return ring_of_things
        
    def _query_peers(self):
        """
        @return: a deferred that fires when all queries have resolved
        """
        PEER = 1
        SHARE = 0
        ring = self._create_ring_of_things()

        # Choose a random starting point, talk to that peer.
        ring.rotate(random.randrange(0, len(ring)))

        # Walk backwards to find a peer.  We know that we'll eventually find
        # one because we earlier asserted that there was at least one.
        while ring[0][1] != PEER:
            ring.rotate(-1)
        peer = ring[0][2]
        assert isinstance(peer, PeerTracker), peer
        ring.rotate(-1)

        # loop invariant: at the top of the loop, we are always one step to
        # the left of a peer, which is stored in the peer variable.
        outstanding_queries = []
        sharenums_to_query = set()
        for i in range(len(ring)):
            if ring[0][1] == SHARE:
                sharenums_to_query.add(ring[0][2])
            else:
                if True or sharenums_to_query:
                    d = peer.query(sharenums_to_query)
                    d.addCallbacks(self._got_response, self._got_error, callbackArgs=(peer, sharenums_to_query), errbackArgs=(peer,))
                    outstanding_queries.append(d)
                    d.addErrback(log.err)
                peer = ring[0][2]
                sharenums_to_query = set()
            ring.rotate(-1)
        
        return defer.DeferredList(outstanding_queries)

    def _got_response(self, (alreadygot, allocated), peer, shares_we_requested):
        """
        @type alreadygot: a set of sharenums
        @type allocated: a set of sharenums
        """
        # TODO: some future version of Foolscap might not convert inbound
        # sets into sets.Set on us, even when we're using 2.4
        alreadygot = set(alreadygot)
        allocated = set(allocated)
        #log.msg("%s._got_response(%s, %s, %s): "
        #        "self.unallocated_sharenums: %s, unhandled: %s"
        #        % (self, (alreadygot, allocated), peer, shares_we_requested,
        #           self.unallocated_sharenums,
        #           shares_we_requested - alreadygot - allocated))
        self.unallocated_sharenums -= alreadygot
        self.unallocated_sharenums -= allocated

        if allocated:
            self.used_peers.add(peer)

        if shares_we_requested - alreadygot - allocated:
            # Then he didn't accept some of the shares, so he's full.

            #log.msg("%s._got_response(%s, %s, %s): "
            #        "self.unallocated_sharenums: %s, unhandled: %s HE'S FULL"
            #        % (self,
            #           (alreadygot, allocated), peer, shares_we_requested,
            #           self.unallocated_sharenums,
            #           shares_we_requested - alreadygot - allocated))
            self.usable_peers.remove(peer)

    def _got_error(self, f, peer):
        log.msg("%s._got_error(%s, %s)" % (self, f, peer,))
        self.usable_peers.remove(peer)

class Tahoe2PeerSelector:

    def __init__(self, upload_id):
        self.upload_id = upload_id
        self.query_count, self.good_query_count, self.bad_query_count = 0,0,0
        self.error_count = 0
        self.num_peers_contacted = 0
        self.last_failure_msg = None

    def __repr__(self):
        return "<Tahoe2PeerSelector for upload %s>" % self.upload_id

    def get_shareholders(self, client,
                         storage_index, share_size, block_size,
                         num_segments, total_shares, shares_of_happiness,
                         push_to_ourselves):
        """
        @return: a set of PeerTracker instances that have agreed to hold some
                 shares for us
        """

        self.total_shares = total_shares
        self.shares_of_happiness = shares_of_happiness

        self.homeless_shares = range(total_shares)
        # self.uncontacted_peers = list() # peers we haven't asked yet
        self.contacted_peers = list() # peers worth asking again
        self.use_peers = set() # PeerTrackers that have shares assigned to them
        self.preexisting_shares = {} # sharenum -> PeerTracker holding the share

        peers = client.get_permuted_peers(storage_index, push_to_ourselves)
        if not peers:
            raise encode.NotEnoughPeersError("client gave us zero peers")

        # figure out how much space to ask for

        # this needed_hashes computation should mirror
        # Encoder.send_all_share_hash_trees. We use an IncompleteHashTree
        # (instead of a HashTree) because we don't require actual hashing
        # just to count the levels.
        ht = hashtree.IncompleteHashTree(total_shares)
        num_share_hashes = len(ht.needed_hashes(0, include_leaf=True))

        # decide upon the renewal/cancel secrets, to include them in the
        # allocat_buckets query.
        client_renewal_secret = client.get_renewal_secret()
        client_cancel_secret = client.get_cancel_secret()

        file_renewal_secret = file_renewal_secret_hash(client_renewal_secret,
                                                       storage_index)
        file_cancel_secret = file_cancel_secret_hash(client_cancel_secret,
                                                     storage_index)

        trackers = [ PeerTracker(peerid, permutedid, conn,
                                 share_size, block_size,
                                 num_segments, num_share_hashes,
                                 storage_index,
                                 bucket_renewal_secret_hash(file_renewal_secret,
                                                            peerid),
                                 bucket_cancel_secret_hash(file_cancel_secret,
                                                           peerid),
                                 )
                     for permutedid, peerid, conn in peers ]
        self.uncontacted_peers = trackers

        d = defer.maybeDeferred(self._loop)
        return d

    def _loop(self):
        if not self.homeless_shares:
            # all done
            msg = ("placed all %d shares, "
                   "sent %d queries to %d peers, "
                   "%d queries placed some shares, %d placed none, "
                   "got %d errors" %
                   (self.total_shares,
                    self.query_count, self.num_peers_contacted,
                    self.good_query_count, self.bad_query_count,
                    self.error_count))
            log.msg("peer selection successful for %s: %s" % (self, msg))
            return self.use_peers

        if self.uncontacted_peers:
            peer = self.uncontacted_peers.pop(0)
            # TODO: don't pre-convert all peerids to PeerTrackers
            assert isinstance(peer, PeerTracker)

            shares_to_ask = set([self.homeless_shares.pop(0)])
            self.query_count += 1
            self.num_peers_contacted += 1
            d = peer.query(shares_to_ask)
            d.addBoth(self._got_response, peer, shares_to_ask)
            return d
        elif self.contacted_peers:
            # ask a peer that we've already asked.
            num_shares = mathutil.div_ceil(len(self.homeless_shares),
                                           len(self.contacted_peers))
            shares_to_ask = set(self.homeless_shares[:num_shares])
            self.homeless_shares[:num_shares] = []
            peer = self.contacted_peers.pop(0)
            self.query_count += 1
            d = peer.query(shares_to_ask)
            d.addBoth(self._got_response, peer, shares_to_ask)
            return d
        else:
            # no more peers. If we haven't placed enough shares, we fail.
            placed_shares = self.total_shares - len(self.homeless_shares)
            if placed_shares < self.shares_of_happiness:
                msg = ("placed %d shares out of %d total (%d homeless), "
                       "sent %d queries to %d peers, "
                       "%d queries placed some shares, %d placed none, "
                       "got %d errors" %
                       (self.total_shares - len(self.homeless_shares),
                        self.total_shares, len(self.homeless_shares),
                        self.query_count, self.num_peers_contacted,
                        self.good_query_count, self.bad_query_count,
                        self.error_count))
                msg = "peer selection failed for %s: %s" % (self, msg)
                if self.last_failure_msg:
                    msg += " (%s)" % (self.last_failure_msg,)
                log.msg(msg)
                raise encode.NotEnoughPeersError(msg)
            else:
                # we placed enough to be happy, so we're done
                return self.use_peers

    def _got_response(self, res, peer, shares_to_ask):
        if isinstance(res, failure.Failure):
            # This is unusual, and probably indicates a bug or a network
            # problem.
            log.msg("%s got error during peer selection: %s" % (peer, res))
            self.error_count += 1
            self.homeless_shares = list(shares_to_ask) + self.homeless_shares
            if self.uncontacted_peers or self.contacted_peers:
                # there is still hope, so just loop
                pass
            else:
                # No more peers, so this upload might fail (it depends upon
                # whether we've hit shares_of_happiness or not). Log the last
                # failure we got: if a coding error causes all peers to fail
                # in the same way, this allows the common failure to be seen
                # by the uploader and should help with debugging
                msg = ("last failure (from %s) was: %s" % (peer, res))
                self.last_failure_msg = msg
        else:
            (alreadygot, allocated) = res
            progress = False
            for s in alreadygot:
                self.preexisting_shares[s] = peer
                if s in self.homeless_shares:
                    self.homeless_shares.remove(s)
                    progress = True

            # the PeerTracker will remember which shares were allocated on
            # that peer. We just have to remember to use them.
            if allocated:
                self.use_peers.add(peer)
                progress = True

            not_yet_present = set(shares_to_ask) - set(alreadygot)
            still_homeless = not_yet_present - set(allocated)

            if progress:
                # they accepted or already had at least one share, so
                # progress has been made
                self.good_query_count += 1
            else:
                self.bad_query_count += 1

            if still_homeless:
                # In networks with lots of space, this is very unusual and
                # probably indicates an error. In networks with peers that
                # are full, it is merely unusual. In networks that are very
                # full, it is common, and many uploads will fail. In most
                # cases, this is obviously not fatal, and we'll just use some
                # other peers.

                # some shares are still homeless, keep trying to find them a
                # home. The ones that were rejected get first priority.
                self.homeless_shares = (list(still_homeless)
                                        + self.homeless_shares)
                # Since they were unable to accept all of our requests, so it
                # is safe to assume that asking them again won't help.
            else:
                # if they *were* able to accept everything, they might be
                # willing to accept even more.
                self.contacted_peers.append(peer)

        # now loop
        return self._loop()


class EncryptAnUploadable:
    """This is a wrapper that takes an IUploadable and provides
    IEncryptedUploadable."""
    implements(IEncryptedUploadable)

    def __init__(self, original):
        self.original = original
        self._encryptor = None
        self._plaintext_hasher = plaintext_hasher()
        self._plaintext_segment_hasher = None
        self._plaintext_segment_hashes = []
        self._params = None

    def get_size(self):
        return self.original.get_size()

    def set_serialized_encoding_parameters(self, params):
        self._params = params

    def _get_encryptor(self):
        if self._encryptor:
            return defer.succeed(self._encryptor)

        if self._params is not None:
            self.original.set_serialized_encoding_parameters(self._params)

        d = self.original.get_encryption_key()
        def _got(key):
            e = AES.new(key=key, mode=AES.MODE_CTR, counterstart="\x00"*16)
            self._encryptor = e

            storage_index = storage_index_chk_hash(key)
            assert isinstance(storage_index, str)
            # There's no point to having the SI be longer than the key, so we
            # specify that it is truncated to the same 128 bits as the AES key.
            assert len(storage_index) == 16  # SHA-256 truncated to 128b
            self._storage_index = storage_index

            return e
        d.addCallback(_got)
        return d

    def get_storage_index(self):
        d = self._get_encryptor()
        d.addCallback(lambda res: self._storage_index)
        return d

    def set_segment_size(self, segsize):
        self._segment_size = segsize

    def _get_segment_hasher(self):
        p = self._plaintext_segment_hasher
        if p:
            left = self._segment_size - self._plaintext_segment_hashed_bytes
            return p, left
        p = plaintext_segment_hasher()
        self._plaintext_segment_hasher = p
        self._plaintext_segment_hashed_bytes = 0
        return p, self._segment_size

    def _update_segment_hash(self, chunk):
        offset = 0
        while offset < len(chunk):
            p, segment_left = self._get_segment_hasher()
            chunk_left = len(chunk) - offset
            this_segment = min(chunk_left, segment_left)
            p.update(chunk[offset:offset+this_segment])
            self._plaintext_segment_hashed_bytes += this_segment

            if self._plaintext_segment_hashed_bytes == self._segment_size:
                # we've filled this segment
                self._plaintext_segment_hashes.append(p.digest())
                self._plaintext_segment_hasher = None

            offset += this_segment

    def read_encrypted(self, length):
        d = self._get_encryptor()
        d.addCallback(lambda res: self.original.read(length))
        def _got(data):
            assert isinstance(data, (tuple, list)), type(data)
            data = list(data)
            cryptdata = []
            # we use data.pop(0) instead of 'for chunk in data' to save
            # memory: each chunk is destroyed as soon as we're done with it.
            while data:
                chunk = data.pop(0)
                self._plaintext_hasher.update(chunk)
                self._update_segment_hash(chunk)
                cryptdata.append(self._encryptor.encrypt(chunk))
                del chunk
            return cryptdata
        d.addCallback(_got)
        return d

    def get_plaintext_segment_hashtree_nodes(self, num_segments):
        if len(self._plaintext_segment_hashes) < num_segments:
            # close out the last one
            assert len(self._plaintext_segment_hashes) == num_segments-1
            p, segment_left = self._get_segment_hasher()
            self._plaintext_segment_hashes.append(p.digest())
            del self._plaintext_segment_hasher
        assert len(self._plaintext_segment_hashes) == num_segments
        ht = hashtree.HashTree(self._plaintext_segment_hashes)
        return defer.succeed(list(ht))

    def get_plaintext_hash(self):
        h = self._plaintext_hasher.digest()
        return defer.succeed(h)


class CHKUploader:
    peer_selector_class = Tahoe3PeerSelector

    def __init__(self, client, options={}):
        self._client = client
        self._options = options

    def set_params(self, encoding_parameters):
        self._encoding_parameters = encoding_parameters

    def start(self, uploadable):
        """Start uploading the file.

        This method returns a Deferred that will fire with the URI (a
        string)."""

        uploadable = IUploadable(uploadable)
        log.msg("starting upload of %s" % uploadable)

        eu = EncryptAnUploadable(uploadable)
        d = self.start_encrypted(eu)
        def _uploaded(res):
            d1 = uploadable.get_encryption_key()
            d1.addCallback(lambda key: self._compute_uri(res, key))
            return d1
        d.addCallback(_uploaded)
        return d

    def start_encrypted(self, encrypted):
        eu = IEncryptedUploadable(encrypted)

        e = encode.Encoder(self._options)
        e.set_params(self._encoding_parameters)
        d = e.set_encrypted_uploadable(eu)
        d.addCallback(self.locate_all_shareholders)
        d.addCallback(self.set_shareholders, e)
        d.addCallback(lambda res: e.start())
        # this fires with the uri_extension_hash and other data
        return d

    def locate_all_shareholders(self, encoder):
        storage_index = encoder.get_param("storage_index")
        upload_id = idlib.b2a(storage_index)[:6]
        peer_selector = self.peer_selector_class(upload_id)

        share_size = encoder.get_param("share_size")
        block_size = encoder.get_param("block_size")
        num_segments = encoder.get_param("num_segments")
        k,desired,n = encoder.get_param("share_counts")
        push_to_ourselves = self._options.get("push_to_ourselves", False)

        gs = peer_selector.get_shareholders
        d = gs(self._client, storage_index, share_size, block_size,
               num_segments, n, desired, push_to_ourselves)
        return d

    def set_shareholders(self, used_peers, encoder):
        """
        @param used_peers: a sequence of PeerTracker objects
        """
        log.msg("_send_shares, used_peers is %s" % (used_peers,))
        for peer in used_peers:
            assert isinstance(peer, PeerTracker)
        buckets = {}
        for peer in used_peers:
            buckets.update(peer.buckets)
        assert len(buckets) == sum([len(peer.buckets) for peer in used_peers])
        encoder.set_shareholders(buckets)

    def _compute_uri(self, (uri_extension_hash,
                            needed_shares, total_shares, size),
                     key):
        u = uri.CHKFileURI(key=key,
                           uri_extension_hash=uri_extension_hash,
                           needed_shares=needed_shares,
                           total_shares=total_shares,
                           size=size,
                           )
        return u.to_string()

def read_this_many_bytes(uploadable, size, prepend_data=[]):
    if size == 0:
        return defer.succeed([])
    d = uploadable.read(size)
    def _got(data):
        assert isinstance(data, list)
        bytes = sum([len(piece) for piece in data])
        assert bytes > 0
        assert bytes <= size
        remaining = size - bytes
        if remaining:
            return read_this_many_bytes(uploadable, remaining,
                                        prepend_data + data)
        return prepend_data + data
    d.addCallback(_got)
    return d

class LiteralUploader:

    def __init__(self, client, options={}):
        self._client = client
        self._options = options

    def set_params(self, encoding_parameters):
        pass

    def start(self, uploadable):
        uploadable = IUploadable(uploadable)
        d = uploadable.get_size()
        d.addCallback(lambda size: read_this_many_bytes(uploadable, size))
        d.addCallback(lambda data: uri.LiteralFileURI("".join(data)))
        d.addCallback(lambda u: u.to_string())
        return d

    def close(self):
        pass


class ConvergentUploadMixin:
    # to use this, the class it is mixed in to must have a seekable
    # filehandle named self._filehandle
    _params = None
    _key = None

    def set_serialized_encoding_parameters(self, params):
        self._params = params
        # ignored for now

    def get_encryption_key(self):
        if self._key is None:
            f = self._filehandle
            enckey_hasher = key_hasher()
            #enckey_hasher.update(encoding_parameters) # TODO
            f.seek(0)
            BLOCKSIZE = 64*1024
            while True:
                data = f.read(BLOCKSIZE)
                if not data:
                    break
                enckey_hasher.update(data)
            f.seek(0)
            self._key = enckey_hasher.digest()[:16]

        return defer.succeed(self._key)

class NonConvergentUploadMixin:
    _key = None

    def set_serialized_encoding_parameters(self, params):
        pass

    def get_encryption_key(self, encoding_parameters):
        if self._key is None:
            self._key = os.urandom(16)
        return defer.succeed(self._key)


class FileHandle(ConvergentUploadMixin):
    implements(IUploadable)

    def __init__(self, filehandle):
        self._filehandle = filehandle

    def get_size(self):
        self._filehandle.seek(0,2)
        size = self._filehandle.tell()
        self._filehandle.seek(0)
        return defer.succeed(size)

    def read(self, length):
        return defer.succeed([self._filehandle.read(length)])

    def close(self):
        # the originator of the filehandle reserves the right to close it
        pass

class FileName(FileHandle):
    def __init__(self, filename):
        FileHandle.__init__(self, open(filename, "rb"))
    def close(self):
        FileHandle.close(self)
        self._filehandle.close()

class Data(FileHandle):
    def __init__(self, data):
        FileHandle.__init__(self, StringIO(data))

class Uploader(service.MultiService):
    """I am a service that allows file uploading.
    """
    implements(IUploader)
    name = "uploader"
    uploader_class = CHKUploader
    URI_LIT_SIZE_THRESHOLD = 55

    DEFAULT_ENCODING_PARAMETERS = (25, 75, 100)
    # this is a tuple of (needed, desired, total). 'needed' is the number of
    # shares required to reconstruct a file. 'desired' means that we will
    # abort an upload unless we can allocate space for at least this many.
    # 'total' is the total number of shares created by encoding. If everybody
    # has room then this is is how many we will upload.

    def upload(self, uploadable, options={}):
        # this returns the URI
        assert self.parent
        assert self.running
        push_to_ourselves = self.parent.get_push_to_ourselves()
        if push_to_ourselves is not None:
            options["push_to_ourselves"] = push_to_ourselves

        uploadable = IUploadable(uploadable)
        d = uploadable.get_size()
        def _got_size(size):
            uploader_class = self.uploader_class
            if size <= self.URI_LIT_SIZE_THRESHOLD:
                uploader_class = LiteralUploader
            uploader = uploader_class(self.parent, options)
            uploader.set_params(self.parent.get_encoding_parameters()
                                or self.DEFAULT_ENCODING_PARAMETERS)
            return uploader.start(uploadable)
        d.addCallback(_got_size)
        def _done(res):
            uploadable.close()
            return res
        d.addBoth(_done)
        return d

    # utility functions
    def upload_data(self, data, options={}):
        return self.upload(Data(data), options)
    def upload_filename(self, filename, options={}):
        return self.upload(FileName(filename), options)
    def upload_filehandle(self, filehandle, options={}):
        return self.upload(FileHandle(filehandle), options)