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From "Suhas Dantkale (JIRA)" <j...@apache.org>
Subject [jira] [Created] (ZOOKEEPER-3420) With newer ZK C Client and older ZK server, recv_buffer() could potentially return 0 continuously on non-blocking socket
Date Sat, 08 Jun 2019 01:10:00 GMT
Suhas Dantkale created ZOOKEEPER-3420:
-----------------------------------------

             Summary: With newer ZK C Client and older ZK server, recv_buffer() could potentially
return 0 continuously on non-blocking socket
                 Key: ZOOKEEPER-3420
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3420
             Project: ZooKeeper
          Issue Type: Bug
          Components: c client
    Affects Versions: 3.5.3
            Reporter: Suhas Dantkale


With newer ZK C Client (3.5.*) and older ZK server(3.4.*), recv_buffer() could potentially
return 0 continuously on non-blocking socket.

Following in the recv_buffer() snippet:-
Here, should  the check be:
if (buff == &zh->primer_buffer && buff->curr_offset + rc == buff->len
+ sizeof(buff->len)  - 1) ++rc;
instead of
if (buff == &zh->primer_buffer && rc == buff->len - 1) ++rc;

  if (buff->buffer) {
        /* want off to now represent the offset into the buffer */
        off -= sizeof(buff->len);

        rc = recv(zh->fd, buff->buffer+off, buff->len-off, 0);

        /* dirty hack to make new client work against old server
         * old server sends 40 bytes to finish connection handshake,
         * while we're expecting 41 (1 byte for read-only mode data) */
      if (buff == &zh->primer_buffer && rc == buff->len - 1) ++rc;

        switch(rc) {
        case 0:
            errno = EHOSTDOWN;
        case -1:
#ifdef _WIN32
            if (WSAGetLastError() == WSAEWOULDBLOCK) {
#else
            if (errno == EAGAIN) {
#endif
                break;
            }
            return -1;
        default:
            buff->curr_offset += rc;
        }
    }
    return buff->curr_offset == buff->len + sizeof(buff->len);


Probably the given code assumes that recv() operation will read in one go.
But on non-blocking socket, that assumption doesn't hold true.




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