new readline test passes

Changed file.py readline() to always check for a newline. Had to make a
few changes for what went into self._rbuffer in the case where buffer
size was met or exceeded and we found a newline.

paramiko/file.py

@@ -204,6 +204,7 @@ def readline(self, size=None):
         if not (self._flags & self.FLAG_READ):
             raise IOError('File not open for reading')
         line = self._rbuffer
+        truncated = False;
         while True:
             if self._at_trailing_cr and (self._flags & self.FLAG_UNIVERSAL_NEWLINE) and (len(line) > 0):
                 # edge case: the newline may be '\r\n' and we may have read
@@ -218,11 +219,11 @@ def readline(self, size=None):
             # enough.
             if (size is not None) and (size >= 0):
                 if len(line) >= size:
-                    # truncate line and return
+                    # truncate line
                     self._rbuffer = line[size:]
                     line = line[:size]
-                    #self._pos += len(line)
-                    break#return line if self._flags & self.FLAG_BINARY else u(line)
+                    truncated = True
+                    break
                 n = size - len(line)
             else:
                 n = self._bufsize
@@ -245,14 +246,13 @@ def readline(self, size=None):
             if (rpos >= 0) and (rpos < pos or pos < 0):
                 pos = rpos
         if pos == -1:
-            #self._rbuffer = line[size:]
-            #line = line[:size]
             self._pos += len(line)
             return line if self._flags & self.FLAG_BINARY else u(line)
         xpos = pos + 1
         if (line[pos] == cr_byte_value) and (xpos < len(line)) and (line[xpos] == linefeed_byte_value):
             xpos += 1
-        self._rbuffer = line[xpos:]
+
+        self._rbuffer = line[xpos:] + self._rbuffer if truncated else line[xpos:]
         lf = line[pos:xpos]
         line = line[:pos] + linefeed_byte
         if (len(self._rbuffer) == 0) and (lf == cr_byte):

tests/test_file.py

@@ -77,6 +77,7 @@ def test_2_readline(self):
         # truncated line:
         self.assertEqual(f.readline(7), 'Third l')
         self.assertEqual(f.readline(), 'ine.\n')
+        # readline should not read past the fourth line
         self.assertEqual(f.readline(25), 'Fourth line.\n')
         self.assertEqual(f.readline(), 'Fifth line.\n')
         self.assertEqual(f.readline(), 'Final line non-terminated.')