ftp: prevent server from hanging on closed data connection

Some FTP servers (e.g. Pure-ftpd) end up hanging if we close the data
connection before transferring all the requested data.  If we send ABOR
in that case, it prevents the server from hanging.

Bug: https://bugzilla.redhat.com/643656
Reported by: Pasi Karkkainen, Patrick Monnerat

lib/ftp.c

@@ -3083,6 +3083,11 @@ static CURLcode ftp_done(struct connectdata *conn, CURLcode status,
 #endif
 
   if(conn->sock[SECONDARYSOCKET] != CURL_SOCKET_BAD) {
+    if(!result && ftpc->dont_check)
+      /* prevent some FTP servers (namely Pure-ftpd) from hanging if we close
+       * the data channel before transferring all data */
+      result = Curl_pp_sendf(&ftpc->pp, "ABOR");
+
     if(conn->ssl[SECONDARYSOCKET].use) {
       /* The secondary socket is using SSL so we must close down that part
          first before we close the socket for real */
@@ -3097,7 +3102,7 @@ static CURLcode ftp_done(struct connectdata *conn, CURLcode status,
     }
   }
 
-  if((ftp->transfer == FTPTRANSFER_BODY) && ftpc->ctl_valid &&
+  if(!result && (ftp->transfer == FTPTRANSFER_BODY) && ftpc->ctl_valid &&
      pp->pending_resp && !premature) {
     /*
      * Let's see what the server says about the transfer we just performed,

tests/data/test1036

@@ -50,6 +50,7 @@ TYPE I
 SIZE 1036
 REST 20
 RETR 1036
+ABOR
 QUIT
 </protocol>
 <file name="log/curl1036.out">

tests/data/test1057

@@ -45,6 +45,7 @@ TYPE I
 SIZE 1057
 REST 52
 RETR 1057
+ABOR
 QUIT
 </protocol>
 </verify>

tests/data/test110

@@ -46,6 +46,7 @@ TYPE I
 SIZE 110
 REST 20
 RETR 110
+ABOR
 QUIT
 </protocol>
 </verify>

tests/data/test122

@@ -39,6 +39,7 @@ EPSV
 PASV
 TYPE I
 SIZE 122
+ABOR
 QUIT
 </protocol>
 </verify>

tests/data/test135

@@ -47,6 +47,7 @@ TYPE I
 SIZE 135
 REST 4
 RETR 135
+ABOR
 QUIT
 </protocol>
 </verify>