[refactor] splits http_target into 4 modules

SoledadHTTPSyncTarget is composed of 4 main groups of responsibility:
* api.py - Public and main methods of a SyncTarget
* fetch.py - Document fetching logic
* send.py - Document sending logic
* support.py - Support functions and patches

Previous single file had ~600 lines with those 4 logic groups mixed,
making it harder to read and understand.

5 files changed, 788 insertions, 0 deletions

diff --git a/client/src/leap/soledad/client/http_target/__init__.py b/client/src/leap/soledad/client/http_target/__init__.py
new file mode 100644
index 00000000..e77d20f5
--- /dev/null
+++ b/client/src/leap/soledad/client/http_target/__init__.py
@@ -0,0 +1,45 @@
+# -*- coding: utf-8 -*-
+# http_target.py
+# Copyright (C) 2015 LEAP
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+
+"""
+A U1DB backend for encrypting data before sending to server and decrypting
+after receiving.
+"""
+
+
+import logging
+
+from leap.soledad.client.http_target.send import HTTPDocSender
+from leap.soledad.client.http_target.api import SyncTargetAPI
+from leap.soledad.client.http_target.fetch import HTTPDocFetcher
+
+
+logger = logging.getLogger(__name__)
+
+
+class SoledadHTTPSyncTarget(SyncTargetAPI, HTTPDocSender, HTTPDocFetcher):
+
+    """
+    A SyncTarget that encrypts data before sending and decrypts data after
+    receiving.
+
+    Normally encryption will have been written to the sync database upon
+    document modification. The sync database is also used to write temporarily
+    the parsed documents that the remote send us, before being decrypted and
+    written to the main database.
+    """
diff --git a/client/src/leap/soledad/client/http_target/api.py b/client/src/leap/soledad/client/http_target/api.py
new file mode 100644
index 00000000..9e677304
--- /dev/null
+++ b/client/src/leap/soledad/client/http_target/api.py
@@ -0,0 +1,251 @@
+import json
+import base64
+
+from uuid import uuid4
+from u1db import SyncTarget
+
+from twisted.web.error import Error
+from twisted.internet import defer
+
+from leap.soledad.common.errors import InvalidAuthTokenError
+from leap.soledad.client.http_target.support import readBody
+
+from leap.common.http import HTTPClient
+
+
+class SyncTargetAPI(SyncTarget):
+
+    def __init__(self, url, source_replica_uid, creds, crypto, cert_file,
+                 sync_db=None, sync_enc_pool=None):
+        """
+        Initialize the sync target.
+
+        :param url: The server sync url.
+        :type url: str
+        :param source_replica_uid: The source replica uid which we use when
+                                   deferring decryption.
+        :type source_replica_uid: str
+        :param creds: A dictionary containing the uuid and token.
+        :type creds: creds
+        :param crypto: An instance of SoledadCrypto so we can encrypt/decrypt
+                        document contents when syncing.
+        :type crypto: soledad.crypto.SoledadCrypto
+        :param cert_file: Path to the certificate of the ca used to validate
+                          the SSL certificate used by the remote soledad
+                          server.
+        :type cert_file: str
+        :param sync_db: Optional. handler for the db with the symmetric
+                        encryption of the syncing documents. If
+                        None, encryption will be done in-place,
+                        instead of retreiving it from the dedicated
+                        database.
+        :type sync_db: Sqlite handler
+        :param sync_enc_pool: The encryption pool to use to defer encryption.
+                              If None is passed the encryption will not be
+                              deferred.
+        :type sync_enc_pool: leap.soledad.client.encdecpool.SyncEncrypterPool
+        """
+        if url.endswith("/"):
+            url = url[:-1]
+        self._url = str(url) + "/sync-from/" + str(source_replica_uid)
+        self.source_replica_uid = source_replica_uid
+        self._auth_header = None
+        self.set_creds(creds)
+        self._crypto = crypto
+        self._sync_db = sync_db
+        self._sync_enc_pool = sync_enc_pool
+        self._insert_doc_cb = None
+        # asynchronous encryption/decryption attributes
+        self._decryption_callback = None
+        self._sync_decr_pool = None
+        self._http = HTTPClient(cert_file)
+
+    def close(self):
+        self._http.close()
+
+    def set_creds(self, creds):
+        """
+        Update credentials.
+
+        :param creds: A dictionary containing the uuid and token.
+        :type creds: dict
+        """
+        uuid = creds['token']['uuid']
+        token = creds['token']['token']
+        auth = '%s:%s' % (uuid, token)
+        b64_token = base64.b64encode(auth)
+        self._auth_header = {'Authorization': ['Token %s' % b64_token]}
+
+    @property
+    def _base_header(self):
+        return self._auth_header.copy() if self._auth_header else {}
+
+    @property
+    def _defer_encryption(self):
+        return self._sync_enc_pool is not None
+
+    def _http_request(self, url, method='GET', body=None, headers=None, content_type=None):
+        headers = headers or self._base_header
+        if content_type:
+            headers.update({'content-type': [content_type]})
+        d = self._http.request(url, method, body, headers, readBody)
+        d.addErrback(_unauth_to_invalid_token_error)
+        return d
+
+    @defer.inlineCallbacks
+    def get_sync_info(self, source_replica_uid):
+        """
+        Return information about known state of remote database.
+
+        Return the replica_uid and the current database generation of the
+        remote database, and its last-seen database generation for the client
+        replica.
+
+        :param source_replica_uid: The client-size replica uid.
+        :type source_replica_uid: str
+
+        :return: A deferred which fires with (target_replica_uid,
+                 target_replica_generation, target_trans_id,
+                 source_replica_last_known_generation,
+                 source_replica_last_known_transaction_id)
+        :rtype: twisted.internet.defer.Deferred
+        """
+        raw = yield self._http_request(self._url)
+        res = json.loads(raw)
+        defer.returnValue([
+            res['target_replica_uid'],
+            res['target_replica_generation'],
+            res['target_replica_transaction_id'],
+            res['source_replica_generation'],
+            res['source_transaction_id']
+        ])
+
+    def record_sync_info(
+            self, source_replica_uid, source_replica_generation,
+            source_replica_transaction_id):
+        """
+        Record tip information for another replica.
+
+        After sync_exchange has been processed, the caller will have
+        received new content from this replica. This call allows the
+        source replica instigating the sync to inform us what their
+        generation became after applying the documents we returned.
+
+        This is used to allow future sync operations to not need to repeat data
+        that we just talked about. It also means that if this is called at the
+        wrong time, there can be database records that will never be
+        synchronized.
+
+        :param source_replica_uid: The identifier for the source replica.
+        :type source_replica_uid: str
+        :param source_replica_generation: The database generation for the
+                                          source replica.
+        :type source_replica_generation: int
+        :param source_replica_transaction_id: The transaction id associated
+                                              with the source replica
+                                              generation.
+        :type source_replica_transaction_id: str
+
+        :return: A deferred which fires with the result of the query.
+        :rtype: twisted.internet.defer.Deferred
+        """
+        data = json.dumps({
+            'generation': source_replica_generation,
+            'transaction_id': source_replica_transaction_id
+        })
+        return self._http_request(
+            self._url,
+            method='PUT',
+            body=data,
+            content_type='application/json')
+
+    @defer.inlineCallbacks
+    def sync_exchange(self, docs_by_generation, source_replica_uid,
+                      last_known_generation, last_known_trans_id,
+                      insert_doc_cb, ensure_callback=None,
+                      defer_decryption=True, sync_id=None):
+        """
+        Find out which documents the remote database does not know about,
+        encrypt and send them. After that, receive documents from the remote
+        database.
+
+        :param docs_by_generations: A list of (doc_id, generation, trans_id)
+                                    of local documents that were changed since
+                                    the last local generation the remote
+                                    replica knows about.
+        :type docs_by_generations: list of tuples
+
+        :param source_replica_uid: The uid of the source replica.
+        :type source_replica_uid: str
+
+        :param last_known_generation: Target's last known generation.
+        :type last_known_generation: int
+
+        :param last_known_trans_id: Target's last known transaction id.
+        :type last_known_trans_id: str
+
+        :param insert_doc_cb: A callback for inserting received documents from
+                              target. If not overriden, this will call u1db
+                              insert_doc_from_target in synchronizer, which
+                              implements the TAKE OTHER semantics.
+        :type insert_doc_cb: function
+
+        :param ensure_callback: A callback that ensures we know the target
+                                replica uid if the target replica was just
+                                created.
+        :type ensure_callback: function
+
+        :param defer_decryption: Whether to defer the decryption process using
+                                 the intermediate database. If False,
+                                 decryption will be done inline.
+        :type defer_decryption: bool
+
+        :return: A deferred which fires with the new generation and
+                 transaction id of the target replica.
+        :rtype: twisted.internet.defer.Deferred
+        """
+
+        self._ensure_callback = ensure_callback
+
+        if sync_id is None:
+            sync_id = str(uuid4())
+        self.source_replica_uid = source_replica_uid
+
+        # save a reference to the callback so we can use it after decrypting
+        self._insert_doc_cb = insert_doc_cb
+
+        gen_after_send, trans_id_after_send = yield self._send_docs(
+            docs_by_generation,
+            last_known_generation,
+            last_known_trans_id,
+            sync_id)
+
+        cur_target_gen, cur_target_trans_id = yield self._receive_docs(
+            last_known_generation, last_known_trans_id,
+            ensure_callback, sync_id,
+            defer_decryption=defer_decryption)
+
+        # update gen and trans id info in case we just sent and did not
+        # receive docs.
+        if gen_after_send is not None and gen_after_send > cur_target_gen:
+            cur_target_gen = gen_after_send
+            cur_target_trans_id = trans_id_after_send
+
+        defer.returnValue([cur_target_gen, cur_target_trans_id])
+
+
+def _unauth_to_invalid_token_error(failure):
+    """
+    An errback to translate unauthorized errors to our own invalid token
+    class.
+
+    :param failure: The original failure.
+    :type failure: twisted.python.failure.Failure
+
+    :return: Either the original failure or an invalid auth token error.
+    :rtype: twisted.python.failure.Failure
+    """
+    failure.trap(Error)
+    if failure.getErrorMessage() == "401 Unauthorized":
+        raise InvalidAuthTokenError
+    return failure
diff --git a/client/src/leap/soledad/client/http_target/fetch.py b/client/src/leap/soledad/client/http_target/fetch.py
new file mode 100644
index 00000000..c4bb79a0
--- /dev/null
+++ b/client/src/leap/soledad/client/http_target/fetch.py
@@ -0,0 +1,237 @@
+# -*- coding: utf-8 -*-
+# http_target.py
+# Copyright (C) 2015 LEAP
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+import logging
+import json
+from u1db import errors
+from u1db.remote import utils
+from twisted.internet import defer
+from leap.soledad.common.document import SoledadDocument
+from leap.soledad.client.events import SOLEDAD_SYNC_RECEIVE_STATUS
+from leap.soledad.client.events import emit
+from leap.soledad.client.crypto import is_symmetrically_encrypted
+from leap.soledad.client.encdecpool import SyncDecrypterPool
+from leap.soledad.client.http_target.support import RequestBody
+
+logger = logging.getLogger(__name__)
+
+
+class HTTPDocFetcher(object):
+
+    @defer.inlineCallbacks
+    def _receive_docs(self, last_known_generation, last_known_trans_id,
+                      ensure_callback, sync_id, defer_decryption):
+
+        self._queue_for_decrypt = defer_decryption \
+            and self._sync_db is not None
+
+        new_generation = last_known_generation
+        new_transaction_id = last_known_trans_id
+
+        if self._queue_for_decrypt:
+            logger.debug(
+                "Soledad sync: will queue received docs for decrypting.")
+
+        if defer_decryption:
+            self._setup_sync_decr_pool()
+
+        # ---------------------------------------------------------------------
+        # maybe receive the first document
+        # ---------------------------------------------------------------------
+
+        # we fetch the first document before fetching the rest because we need
+        # to know the total number of documents to be received, and this
+        # information comes as metadata to each request.
+
+        doc = yield self._receive_one_doc(
+            last_known_generation, last_known_trans_id,
+            sync_id, 0)
+        self._received_docs = 0
+        number_of_changes, ngen, ntrans = self._insert_received_doc(doc, 1, 1)
+
+        if defer_decryption:
+            self._sync_decr_pool.start(number_of_changes)
+
+        # ---------------------------------------------------------------------
+        # maybe receive the rest of the documents
+        # ---------------------------------------------------------------------
+
+        # launch many asynchronous fetches and inserts of received documents
+        # in the temporary sync db. Will wait for all results before
+        # continuing.
+
+        received = 1
+        deferreds = []
+        while received < number_of_changes:
+            d = self._receive_one_doc(
+                last_known_generation,
+                last_known_trans_id, sync_id, received)
+            d.addCallback(
+                self._insert_received_doc,
+                received + 1,  # the index of the current received doc
+                number_of_changes)
+            deferreds.append(d)
+            received += 1
+        results = yield defer.gatherResults(deferreds)
+
+        # get generation and transaction id of target after insertions
+        if deferreds:
+            _, new_generation, new_transaction_id = results.pop()
+
+        # ---------------------------------------------------------------------
+        # wait for async decryption to finish
+        # ---------------------------------------------------------------------
+
+        if defer_decryption:
+            yield self._sync_decr_pool.deferred
+            self._sync_decr_pool.stop()
+
+        defer.returnValue([new_generation, new_transaction_id])
+
+    def _receive_one_doc(self, last_known_generation,
+                         last_known_trans_id, sync_id, received):
+        # add remote replica metadata to the request
+        body = RequestBody(
+            last_known_generation=last_known_generation,
+            last_known_trans_id=last_known_trans_id,
+            sync_id=sync_id,
+            ensure=self._ensure_callback is not None)
+        # inform server of how many documents have already been received
+        body.insert_info(received=received)
+        # send headers
+        return self._http_request(
+            self._url,
+            method='POST',
+            body=str(body),
+            content_type='application/x-soledad-sync-get')
+
+    def _insert_received_doc(self, response, idx, total):
+        """
+        Insert a received document into the local replica.
+
+        :param response: The body and headers of the response.
+        :type response: tuple(str, dict)
+        :param idx: The index count of the current operation.
+        :type idx: int
+        :param total: The total number of operations.
+        :type total: int
+        """
+        new_generation, new_transaction_id, number_of_changes, doc_id, \
+            rev, content, gen, trans_id = \
+            self._parse_received_doc_response(response)
+        if doc_id is not None:
+            # decrypt incoming document and insert into local database
+            # -------------------------------------------------------------
+            # symmetric decryption of document's contents
+            # -------------------------------------------------------------
+            # If arriving content was symmetrically encrypted, we decrypt it.
+            # We do it inline if defer_decryption flag is False or no sync_db
+            # was defined, otherwise we defer it writing it to the received
+            # docs table.
+            doc = SoledadDocument(doc_id, rev, content)
+            if is_symmetrically_encrypted(doc):
+                if self._queue_for_decrypt:
+                    self._sync_decr_pool.insert_encrypted_received_doc(
+                        doc.doc_id, doc.rev, doc.content, gen, trans_id,
+                        idx)
+                else:
+                    # defer_decryption is False or no-sync-db fallback
+                    doc.set_json(self._crypto.decrypt_doc(doc))
+                    self._insert_doc_cb(doc, gen, trans_id)
+            else:
+                # not symmetrically encrypted doc, insert it directly
+                # or save it in the decrypted stage.
+                if self._queue_for_decrypt:
+                    self._sync_decr_pool.insert_received_doc(
+                        doc.doc_id, doc.rev, doc.content, gen, trans_id,
+                        idx)
+                else:
+                    self._insert_doc_cb(doc, gen, trans_id)
+            # -------------------------------------------------------------
+            # end of symmetric decryption
+            # -------------------------------------------------------------
+        self._received_docs += 1
+        _emit_received(self._received_docs, total)
+        return number_of_changes, new_generation, new_transaction_id
+
+    def _parse_received_doc_response(self, response):
+        """
+        Parse the response from the server containing the received document.
+
+        :param response: The body and headers of the response.
+        :type response: tuple(str, dict)
+
+        :return: (new_gen, new_trans_id, number_of_changes, doc_id, rev,
+                 content, gen, trans_id)
+        :rtype: tuple
+        """
+        # decode incoming stream
+        parts = response.splitlines()
+        if not parts or parts[0] != '[' or parts[-1] != ']':
+            raise errors.BrokenSyncStream
+        data = parts[1:-1]
+        # decode metadata
+        try:
+            line, comma = utils.check_and_strip_comma(data[0])
+            metadata = None
+        except (IndexError):
+            raise errors.BrokenSyncStream
+        try:
+            metadata = json.loads(line)
+            new_generation = metadata['new_generation']
+            new_transaction_id = metadata['new_transaction_id']
+            number_of_changes = metadata['number_of_changes']
+        except (ValueError, KeyError):
+            raise errors.BrokenSyncStream
+        # make sure we have replica_uid from fresh new dbs
+        if self._ensure_callback and 'replica_uid' in metadata:
+            self._ensure_callback(metadata['replica_uid'])
+        # parse incoming document info
+        doc_id = None
+        rev = None
+        content = None
+        gen = None
+        trans_id = None
+        if number_of_changes > 0:
+            try:
+                entry = json.loads(data[1])
+                doc_id = entry['id']
+                rev = entry['rev']
+                content = entry['content']
+                gen = entry['gen']
+                trans_id = entry['trans_id']
+            except (IndexError, KeyError):
+                raise errors.BrokenSyncStream
+        return new_generation, new_transaction_id, number_of_changes, \
+            doc_id, rev, content, gen, trans_id
+
+    def _setup_sync_decr_pool(self):
+        """
+        Set up the SyncDecrypterPool for deferred decryption.
+        """
+        if self._sync_decr_pool is None and self._sync_db is not None:
+            # initialize syncing queue decryption pool
+            self._sync_decr_pool = SyncDecrypterPool(
+                self._crypto,
+                self._sync_db,
+                insert_doc_cb=self._insert_doc_cb,
+                source_replica_uid=self.source_replica_uid)
+
+
+def _emit_received(received_docs, total):
+    msg = "%d/%d" % (received_docs, total)
+    emit(SOLEDAD_SYNC_RECEIVE_STATUS, msg)
+    logger.debug("Sync receive status: %s" % msg)
diff --git a/client/src/leap/soledad/client/http_target/send.py b/client/src/leap/soledad/client/http_target/send.py
new file mode 100644
index 00000000..de18df8b
--- /dev/null
+++ b/client/src/leap/soledad/client/http_target/send.py
@@ -0,0 +1,101 @@
+# -*- coding: utf-8 -*-
+# http_target.py
+# Copyright (C) 2015 LEAP
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+import json
+import logging
+from twisted.internet import defer
+from leap.soledad.client.events import emit
+from leap.soledad.client.events import SOLEDAD_SYNC_SEND_STATUS
+from leap.soledad.client.http_target.support import RequestBody
+logger = logging.getLogger(__name__)
+
+
+class HTTPDocSender(object):
+
+    @defer.inlineCallbacks
+    def _send_docs(self, docs_by_generation, last_known_generation,
+                   last_known_trans_id, sync_id):
+
+        if not docs_by_generation:
+            defer.returnValue([None, None])
+
+        # add remote replica metadata to the request
+        initial_body = RequestBody(
+            last_known_generation=last_known_generation,
+            last_known_trans_id=last_known_trans_id,
+            sync_id=sync_id,
+            ensure=self._ensure_callback is not None)
+        total = len(docs_by_generation)
+        entries = yield self._entries_from_docs(initial_body, docs_by_generation)
+        while len(entries):
+            result = yield self._http_request(
+                self._url,
+                method='POST',
+                body=entries.remove(1),
+                content_type='application/x-soledad-sync-put')
+            idx = total - len(entries)
+            if self._defer_encryption:
+                self._delete_sent(idx, docs_by_generation)
+            _emit_send(idx, total)
+        response_dict = json.loads(result)[0]
+        gen_after_send = response_dict['new_generation']
+        trans_id_after_send = response_dict['new_transaction_id']
+        defer.returnValue([gen_after_send, trans_id_after_send])
+
+    def _delete_sent(self, idx, docs_by_generation):
+        doc = docs_by_generation[idx][0]
+        self._sync_enc_pool.delete_encrypted_doc(
+            doc.doc_id, doc.rev)
+
+    @defer.inlineCallbacks
+    def _entries_from_docs(self, initial_body, docs_by_generation):
+        number_of_docs = len(docs_by_generation)
+        for idx, (doc, gen, trans_id) in enumerate(docs_by_generation, 1):
+            content = yield self._encrypt_doc(doc)
+            initial_body.insert_info(
+                id=doc.doc_id, rev=doc.rev, content=content, gen=gen,
+                trans_id=trans_id, number_of_docs=number_of_docs,
+                doc_idx=idx)
+        defer.returnValue(initial_body)
+
+    def _encrypt_doc(self, doc):
+        d = None
+        if doc.is_tombstone():
+            d = defer.succeed(None)
+        elif not self._defer_encryption:
+            # fallback case, for tests
+            d = defer.succeed(self._crypto.encrypt_doc(doc))
+        else:
+
+            def _maybe_encrypt_doc_inline(doc_json):
+                if doc_json is None:
+                    # the document is not marked as tombstone, but we got
+                    # nothing from the sync db. As it is not encrypted
+                    # yet, we force inline encryption.
+                    return self._crypto.encrypt_doc(doc)
+                return doc_json
+
+            d = self._sync_enc_pool.get_encrypted_doc(doc.doc_id, doc.rev)
+            d.addCallback(_maybe_encrypt_doc_inline)
+        return d
+
+
+def _emit_send(idx, total):
+    msg = "%d/%d" % (idx, total)
+    emit(
+        SOLEDAD_SYNC_SEND_STATUS,
+        "Soledad sync send status: %s" % msg)
+    logger.debug("Sync send status: %s" % msg)
diff --git a/client/src/leap/soledad/client/http_target/support.py b/client/src/leap/soledad/client/http_target/support.py
new file mode 100644
index 00000000..88934636
--- /dev/null
+++ b/client/src/leap/soledad/client/http_target/support.py
@@ -0,0 +1,154 @@
+# -*- coding: utf-8 -*-
+# http_target.py
+# Copyright (C) 2015 LEAP
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+import warnings
+import json
+from u1db import errors
+from u1db.remote import http_errors
+from twisted.internet import defer
+from twisted.web.client import _ReadBodyProtocol
+from twisted.web.client import PartialDownloadError
+from twisted.web._newclient import ResponseDone
+from twisted.web._newclient import PotentialDataLoss
+
+
+# we want to make sure that HTTP errors will raise appropriate u1db errors,
+# that is, fire errbacks with the appropriate failures, in the context of
+# twisted. Because of that, we redefine the http body reader used by the HTTP
+# client below.
+
+class ReadBodyProtocol(_ReadBodyProtocol):
+
+    def __init__(self, response, deferred):
+        """
+        Initialize the protocol, additionally storing the response headers.
+        """
+        _ReadBodyProtocol.__init__(
+            self, response.code, response.phrase, deferred)
+        self.headers = response.headers
+
+    # ---8<--- snippet from u1db.remote.http_client, modified to use errbacks
+    def _error(self, respdic):
+        descr = respdic.get("error")
+        exc_cls = errors.wire_description_to_exc.get(descr)
+        if exc_cls is not None:
+            message = respdic.get("message")
+            self.deferred.errback(exc_cls(message))
+    # ---8<--- end of snippet from u1db.remote.http_client
+
+    def connectionLost(self, reason):
+        """
+        Deliver the accumulated response bytes to the waiting L{Deferred}, if
+        the response body has been completely received without error.
+        """
+        if reason.check(ResponseDone):
+
+            body = b''.join(self.dataBuffer)
+
+            # ---8<--- snippet from u1db.remote.http_client
+            if self.status in (200, 201):
+                self.deferred.callback(body)
+            elif self.status in http_errors.ERROR_STATUSES:
+                try:
+                    respdic = json.loads(body)
+                except ValueError:
+                    self.deferred.errback(
+                        errors.HTTPError(self.status, body, self.headers))
+                else:
+                    self._error(respdic)
+            # special cases
+            elif self.status == 503:
+                self.deferred.errback(errors.Unavailable(body, self.headers))
+            else:
+                self.deferred.errback(
+                    errors.HTTPError(self.status, body, self.headers))
+            # ---8<--- end of snippet from u1db.remote.http_client
+
+        elif reason.check(PotentialDataLoss):
+            self.deferred.errback(
+                PartialDownloadError(self.status, self.message,
+                                     b''.join(self.dataBuffer)))
+        else:
+            self.deferred.errback(reason)
+
+
+def readBody(response):
+    """
+    Get the body of an L{IResponse} and return it as a byte string.
+
+    This is a helper function for clients that don't want to incrementally
+    receive the body of an HTTP response.
+
+    @param response: The HTTP response for which the body will be read.
+    @type response: L{IResponse} provider
+
+    @return: A L{Deferred} which will fire with the body of the response.
+        Cancelling it will close the connection to the server immediately.
+    """
+    def cancel(deferred):
+        """
+        Cancel a L{readBody} call, close the connection to the HTTP server
+        immediately, if it is still open.
+
+        @param deferred: The cancelled L{defer.Deferred}.
+        """
+        abort = getAbort()
+        if abort is not None:
+            abort()
+
+    d = defer.Deferred(cancel)
+    protocol = ReadBodyProtocol(response, d)
+
+    def getAbort():
+        return getattr(protocol.transport, 'abortConnection', None)
+
+    response.deliverBody(protocol)
+
+    if protocol.transport is not None and getAbort() is None:
+        warnings.warn(
+            'Using readBody with a transport that does not have an '
+            'abortConnection method',
+            category=DeprecationWarning,
+            stacklevel=2)
+
+    return d
+
+
+class RequestBody(object):
+
+    def __init__(self, **header_dict):
+        self.headers = header_dict
+        self.entries = []
+
+    def insert_info(self, **entry_dict):
+        entry = json.dumps(entry_dict)
+        self.entries.append(entry)
+        return len(entry)
+
+    def remove(self, number=1):
+        entries = [self.entries.pop(0) for i in xrange(number)]
+        return self.entries_to_str(entries)
+
+    def __str__(self):
+        return self.entries_to_str(self.entries)
+
+    def __len__(self):
+        return len(self.entries)
+
+    def entries_to_str(self, entries=None):
+        data = '[\r\n' + json.dumps(self.headers)
+        data += ''.join(',\r\n' + entry for entry in entries)
+        return data + '\r\n]'