[refactor] extracts tail logic into TruncatedTailPipe

2 files changed, 59 insertions, 15 deletions

diff --git a/client/src/leap/soledad/client/_blobs.py b/client/src/leap/soledad/client/_blobs.py
index 0d25702c..c64c2bb2 100644
--- a/client/src/leap/soledad/client/_blobs.py
+++ b/client/src/leap/soledad/client/_blobs.py
@@ -36,6 +36,7 @@ import treq
 
 from leap.soledad.client.sqlcipher import SQLCipherOptions
 from leap.soledad.client import pragmas
+from leap.soledad.client._pipes import TruncatedTailPipe
 from leap.soledad.common.errors import SoledadError
 
 from _crypto import DocInfo, BlobEncryptor, BlobDecryptor
@@ -106,7 +107,7 @@ class DecrypterBuffer(object):
 
     def __init__(self, doc_id, rev, secret, tag):
         self.decrypter = None
-        self.buffer = BytesIO()
+        self.preamble = BytesIO()
         self.doc_info = DocInfo(doc_id, rev)
         self.secret = secret
         self.tag = tag
@@ -116,30 +117,22 @@ class DecrypterBuffer(object):
         if not self.decrypter:
             return self.prepare_decrypter(data)
 
-        self.buffer.write(data)
-        if self.buffer.tell() > 16:
-            overflow_size = self.buffer.tell() - 16
-            self.buffer.seek(0)
-            self.decrypter.write(self.buffer.read(overflow_size))
-            remaining = self.buffer.read()
-            self.buffer.seek(0)
-            self.buffer.write(remaining)
-            self.buffer.truncate()
+        self.output.write(data)
 
     def prepare_decrypter(self, data):
         if ' ' not in data:
-            self.buffer.write(data)
+            self.preamble.write(data)
             return
         preamble_chunk, remaining = data.split(' ', 1)
-        self.buffer.write(preamble_chunk)
+        self.preamble.write(preamble_chunk)
         self.decrypter = BlobDecryptor(
-            self.doc_info, BytesIO(self.buffer.getvalue()),
+            self.doc_info, BytesIO(self.preamble.getvalue()),
             secret=self.secret,
             armor=False,
             start_stream=False,
             tag=self.tag)
-        self.buffer = BytesIO()
-        self.write(remaining)
+        self.output = TruncatedTailPipe(self.decrypter, tail_size=16)
+        self.output.write(remaining)
 
     def close(self):
         return self.decrypter._end_stream(), self.decrypter.size
diff --git a/client/src/leap/soledad/client/_pipes.py b/client/src/leap/soledad/client/_pipes.py
new file mode 100644
index 00000000..ed89e14d
--- /dev/null
+++ b/client/src/leap/soledad/client/_pipes.py
@@ -0,0 +1,51 @@
+# -*- coding: utf-8 -*-
+# _pipes.py
+# Copyright (C) 2017 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/>.
+"""
+Components for piping data on streams.
+"""
+from io import BytesIO
+
+
+__all__ = ['TruncatedTailPipe']
+
+
+class TruncatedTailPipe(object):
+    """
+    Truncate the last `tail_size` bytes from the stream.
+    """
+
+    def __init__(self, output=None, tail_size=16):
+        self.tail_size = tail_size
+        self.output = output or BytesIO()
+        self.buffer = BytesIO()
+
+    def write(self, data):
+        self.buffer.write(data)
+        if self.buffer.tell() > self.tail_size:
+            self._truncate_tail()
+
+    def _truncate_tail(self):
+            overflow_size = self.buffer.tell() - self.tail_size
+            self.buffer.seek(0)
+            self.output.write(self.buffer.read(overflow_size))
+            remaining = self.buffer.read()
+            self.buffer.seek(0)
+            self.buffer.write(remaining)
+            self.buffer.truncate()
+
+    def close(self):
+        return self.output