[jira] Commented: (ZOOKEEPER-311) handle small path lengths in zoo_create()

["Benjamin Reed (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12711316#action_12711316 ] 

Benjamin Reed commented on ZOOKEEPER-311:
-----------------------------------------

i think we should commit this patch now. the only change in behavior is when the length of the buffer to receive the name is of length 1. it is a silly corner case, but really the fact that we don't put a null there should be considered a bug.

> handle small path lengths in zoo_create()
> -----------------------------------------
>
>                 Key: ZOOKEEPER-311
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-311
>             Project: Zookeeper
>          Issue Type: Improvement
>          Components: c client
>    Affects Versions: 3.0.0, 3.0.1, 3.1.0
>            Reporter: Chris Darroch
>            Assignee: Chris Darroch
>            Priority: Minor
>             Fix For: 4.0.0
>
>         Attachments: ZOOKEEPER-311.patch, ZOOKEEPER-311.patch
>
>
> The synchronous completion for zoo_create() contains the following code:\\
> {noformat}
> 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';
> }
> {noformat}
> 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:
> {noformat}
> int rc = zoo_create(zh,"/xyz","value", 5, &CREATE_ONLY, ZOO_EPHEMERAL, buffer, sizeof(buffer)-1);
> {noformat}
> 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.

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