increment/decrement can erroneously report MEMCACHED_UNKNOWN_READ_FAILURE

[Jason V. Miller]

When calling down into the increment and decrement functions, the response parsing code makes a call to strtoull without resetting errno [1] to zero first. Failing to initialize errno can ultimately cause a value of EINVAL to propagate across the function call, invoke the error handler, and the library will return MEMCACHED_UNKNOWN_READ_FAILURE despite a successful call to the memcached server:

This will be observed by consumers of the library as MEMCACHED_UNKNOWN_READ_FAILURE, followed by the handle becoming unavailable until the retry timeout has expired.

This issue was introduced in libmemcached-1.0.3, and exists in the latest version in the 1.0 branch, libmemcached-1.0.16.

To fix this issue, make sure errno is set to zero before calling strtoull.

To test for this issue, set errno to EINVAL before calling memcached_increment and observe an incorrect return value of MEMCACHED_UNKNOWN_READ_FAILURE.

[1] http://linux.die.net/man/3/strtoull (see Notes)

[Jason V. Miller (jmiller-d)]

Thanks.