ZooKeeper
  1. ZooKeeper
  2. ZOOKEEPER-311

handle small path lengths in zoo_create()

    Details

    • Type: Improvement Improvement
    • Status: Closed
    • Priority: Minor Minor
    • Resolution: Fixed
    • Affects Version/s: 3.0.0, 3.0.1, 3.1.0, 3.1.1, 3.2.0
    • Fix Version/s: 3.2.1, 3.3.0
    • Component/s: c client
    • Labels:
      None
    • Hadoop Flags:
      Incompatible change
    • Release Note:
      Hide
      The zoo_create() function is revised to take path_buffer and path_buffer_len arguments. The path_buffer will be filled with as much of the actual path of the new node fits into the buffer, including a null terminator. Unlike previous behavior, if path_buffer_len (formerly max_realpath_len) is 1, the buffer will be filled with a single null terminator.
      Show
      The zoo_create() function is revised to take path_buffer and path_buffer_len arguments. The path_buffer will be filled with as much of the actual path of the new node fits into the buffer, including a null terminator. Unlike previous behavior, if path_buffer_len (formerly max_realpath_len) is 1, the buffer will be filled with a single null terminator.

      Description

      The synchronous completion for zoo_create() contains the following code:

      if (sc->u.str.str_len > strlen(res.path)) {
          len = strlen(res.path);
      } else {
          len = sc->u.str.str_len-1;
      }
      if (len > 0) {
          memcpy(sc->u.str.str, res.path, len);
          sc->u.str.str[len] = '\0';
      }
      

      In the case where the max_realpath_len argument to zoo_create() is 0, none of this code executes, which is OK. In the case where max_realpath_len is 1, a user might expect their buffer to be filled with a null terminator, but again, nothing will happen (even if strlen(res.path) is 0, which is unlikely since new node's will have paths longer than "/").

      The name of the argument to zoo_create() is also a little misleading, as is its description ("the maximum length of real path you would want") in zookeeper.h, and the example usage in the Programmer's Guide:

      int rc = zoo_create(zh,"/xyz","value", 5, &CREATE_ONLY, ZOO_EPHEMERAL, buffer, sizeof(buffer)-1);
      

      In fact this value should be the actual length of the buffer, including space for the null terminator. If the user supplies a max_realpath_len of 10 and a buffer of 11 bytes, and strlen(res.path) is 10, the code will truncate the returned value to 9 bytes and put the null terminator in the second-last byte, leaving the final byte of the buffer unused.

      It would be better, I think, to rename the realpath and max_realpath_len arguments to something like path_buffer and path_buffer_len, akin to zoo_set(). The path_buffer_len would be treated as the full length of the buffer (as the code does now, in fact, but the docs suggest otherwise).

      The code in the synchronous completion could then be changed as per the attached patch.

      Since this would change, slightly, the behaviour or "contract" of the API, I would be inclined to suggest waiting until 4.0.0 to implement this change.

      1. ZOOKEEPER-311.patch
        3 kB
        Chris Darroch
      2. ZOOKEEPER-311.patch
        6 kB
        Chris Darroch

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          • Assignee:
            Chris Darroch
            Reporter:
            Chris Darroch
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            Dates

            • Created:
              Updated:
              Resolved:

              Development