increment can't bigger than 4294967295

[eibisee]

$o = new Memcached();
$o->addServers( array(
array('127.0.0.1', 11211, 100)
));
$o->set('ddd', 0, 0);

$x = $o->increment('ddd', 4294967295); //OK
$x = $o->increment('ddd', 4294967296); //Error.

system is 64Bit.

[mhagstrand]

This is the result of an overflow. The value of 4294967296 (2^32) is just overflowing to 0. Incrementing by 4294967297 will result in an increment by 1.

PHP-memcached is casting the offset value of the increment and decrement function to an unsigned int. This can be seen in the php_memcached.c file with the code below:

if (incr) {
     status = memcached_increment(m_obj->memc, key, key_len, (unsigned int)offset, &value);
} else {

Fixing this is NOT as simple as just removing the cast from php_memcached.c. The memcached_increment function in libmemcached has a parameter called offset which is a uint32_t. This can be seen in the libmemcached file libmemcached/auto.cc with the code below:

memcached_return_t memcached_increment(memcached_st *memc,
                                       const char *key, size_t key_length,
                                       uint32_t offset,
                                       uint64_t *value)
{
      return memcached_increment_by_key(memc, key, key_length, key, key_length, offset, value);
} 

You should probably file this issue with libmemcached. The function memcached_increment_by_key uses a uint64_t for the offset. It could be used by PHP-memcached instead but the API docs for libmemcached still list the offset parameter in memcached_increment_by_key as uint32_t. That can be seen here:
http://docs.libmemcached.org/memcached_auto.html

[sodabrew]

Confirmed this is still a bug in 3.0.0 with PHP 7.0 and PHP 7.1.

[sodabrew]

Ah, the value can be 64-bit, but the increment is limited to 32-bits per API call. The protocol does allow 64-bit increments, so it might only be an API issue in libmemcached: https://github.com/memcached/memcached/blob/master/doc/protocol.txt#L274

[mhagstrand]

The problem still exists in the libmemcached:
http://bazaar.launchpad.net/~tangent-trunk/libmemcached/1.2/view/head:/libmemcached/auto.cc#L149

It is possible to work around this problem by replacing memcached_increment with memcached_increment_by_key in the code below.
https://github.com/php-memcached-dev/php-memcached/blob/master/php_memcached.c#L2224

That would look something like this:

    if (by_key) {
      if (incr) {
        status = memcached_increment_by_key(intern->memc, ZSTR_VAL(server_key), ZSTR_LEN(server_key), ZSTR_VAL(key), ZSTR_LEN(key), offset, &value);
      } else {
        status = memcached_decrement_by_key(intern->memc, ZSTR_VAL(server_key), ZSTR_LEN(server_key), ZSTR_VAL(key), ZSTR_LEN(key), offset, &value);
      }
    } else {
      if (incr) {
        status = memcached_increment_by_key(intern->memc, ZSTR_VAL(key), ZSTR_LEN(key), ZSTR_VAL(key), ZSTR_LEN(key), offset, &value);
      } else {
        status = memcached_decrement_by_key(intern->memc, ZSTR_VAL(key), ZSTR_LEN(key), ZSTR_VAL(key), ZSTR_LEN(key), offset, &value);
      }
    }

[sodabrew]

The documentation is mis-matched to the actual code! Yes, memcached_increment_by_key accepts a 64-bit offset. This should be straightforward to fix in the master branch.

[mhagstrand]

I can put together a PR if you want or you can take care of it if you want.

[sodabrew]

Thanks for the offer! I've got it going in #306