Fix socket leaks (#351)

* Fix socket leaks

* Fixed sockets leak

Lib/ftplib.py

@@ -412,11 +412,13 @@ class FTP:
         """
         self.voidcmd('TYPE I')
         conn = self.transfercmd(cmd, rest)
+        try:
             while 1:
                 data = conn.recv(blocksize)
                 if not data:
                     break
                 callback(data)
+        finally:
             conn.close()
         return self.voidresp()
 
@@ -435,6 +437,8 @@ class FTP:
         if callback is None: callback = print_line
         resp = self.sendcmd('TYPE A')
         conn = self.transfercmd(cmd)
+        fp = None
+        try:
             fp = conn.makefile('rb')
             while 1:
                 line = fp.readline(self.maxline + 1)
@@ -448,6 +452,8 @@ class FTP:
                 elif line[-1:] == '\n':
                     line = line[:-1]
                 callback(line)
+        finally:
+            if fp:
                 fp.close()
             conn.close()
         return self.voidresp()
@@ -469,11 +475,13 @@ class FTP:
         """
         self.voidcmd('TYPE I')
         conn = self.transfercmd(cmd, rest)
+        try:
             while 1:
                 buf = fp.read(blocksize)
                 if not buf: break
                 conn.sendall(buf)
                 if callback: callback(buf)
+        finally:
             conn.close()
         return self.voidresp()
 
@@ -491,6 +499,7 @@ class FTP:
         """
         self.voidcmd('TYPE A')
         conn = self.transfercmd(cmd)
+        try:
             while 1:
                 buf = fp.readline(self.maxline + 1)
                 if len(buf) > self.maxline:
@@ -501,6 +510,7 @@ class FTP:
                     buf = buf + CRLF
                 conn.sendall(buf)
                 if callback: callback(buf)
+        finally:
             conn.close()
         return self.voidresp()