_pylibmcmodule.c

/**
 * _pylibmc: hand-made libmemcached bindings for Python
 *
 * Copyright (c) 2008, Ludvig Ericson
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 *  - Redistributions of source code must retain the above copyright notice,
 *  this list of conditions and the following disclaimer.
 * 
 *  - Redistributions in binary form must reproduce the above copyright notice,
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 * 
 *  - Neither the name of the author nor the names of the contributors may be
 *  used to endorse or promote products derived from this software without
 *  specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "_pylibmcmodule.h"
#ifdef USE_ZLIB
#  include <zlib.h>
#  define ZLIB_BUFSZ (1 << 14)
/* only callable while holding the GIL */
#  define _ZLIB_ERR(s, rc) \
  PyErr_Format(PylibMCExc_MemcachedError, "zlib error %d in " s, rc);
#endif

#define PyBool_TEST(t) ((t) ? Py_True : Py_False)

#define PyModule_ADD_REF(mod, nam, obj) \
    { Py_INCREF(obj); \
      PyModule_AddObject(mod, nam, obj); }


/* {{{ Type methods */
static PylibMC_Client *PylibMC_ClientType_new(PyTypeObject *type,
        PyObject *args, PyObject *kwds) {
    PylibMC_Client *self;

    /* GenericNew calls GenericAlloc (via the indirection type->tp_alloc) which
     * adds GC tracking if flagged for, and also calls PyObject_Init. */
    self = (PylibMC_Client *)PyType_GenericNew(type, args, kwds);

    if (self != NULL) {
        self->mc = memcached_create(NULL);
        self->sasl_set = false;
    }

    return self;
}

static void PylibMC_ClientType_dealloc(PylibMC_Client *self) {
    if (self->mc != NULL) {
#if LIBMEMCACHED_WITH_SASL_SUPPORT
        if (self->sasl_set) {
            memcached_destroy_sasl_auth_data(self->mc);
        }
#endif
        memcached_free(self->mc);
    }

    self->ob_type->tp_free(self);
}
/* }}} */

static int PylibMC_Client_init(PylibMC_Client *self, PyObject *args,
        PyObject *kwds) {
    PyObject *srvs, *srvs_it, *c_srv;
    unsigned char set_stype = 0, bin = 0, got_server = 0;
    const char *user = NULL, *pass = NULL;
    memcached_return rc;

    static char *kws[] = { "servers", "binary", "username", "password", NULL };

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|bzz", kws,
                                     &srvs, &bin, &user, &pass)) {
        return -1;
    }

    if ((srvs_it = PyObject_GetIter(srvs)) == NULL) {
        return -1;
    }

    /* setup sasl */
    if (user != NULL || pass != NULL) {

#if LIBMEMCACHED_WITH_SASL_SUPPORT
        if (user == NULL || pass == NULL) {
            PyErr_SetString(PyExc_TypeError, "SASL requires both username and password");
            goto error;
        }

        if (!bin) {
            PyErr_SetString(PyExc_TypeError, "SASL requires the memcached binary protocol");
            goto error;
        }

        rc = memcached_set_sasl_auth_data(self->mc, user, pass);
        if (rc != MEMCACHED_SUCCESS) {
            PylibMC_ErrFromMemcached(self, "memcached_set_sasl_auth_data", rc);
            goto error;
        }

        /* Can't just look at the memcached_st->sasl data, because then it
         * breaks in libmemcached 0.43 and potentially earlier. */
        self->sasl_set = true;

#else
        PyErr_SetString(PyExc_TypeError, "libmemcached does not support SASL");
        goto error;

#endif
    }

    memcached_behavior_set(self->mc, MEMCACHED_BEHAVIOR_BINARY_PROTOCOL, bin);

    while ((c_srv = PyIter_Next(srvs_it)) != NULL) {
        unsigned char stype;
        char *hostname;
        unsigned short int port;

        got_server |= 1;
        port = 0;
        if (PyString_Check(c_srv)) {
            memcached_server_st *list;

            list = memcached_servers_parse(PyString_AS_STRING(c_srv));
            if (list == NULL) {
                PyErr_SetString(PylibMCExc_MemcachedError,
                        "memcached_servers_parse returned NULL");
                goto it_error;
            }

            rc = memcached_server_push(self->mc, list);
            free(list);
            if (rc != MEMCACHED_SUCCESS) {
                PylibMC_ErrFromMemcached(self, "memcached_server_push", rc);
                goto it_error;
            }
        } else if (PyArg_ParseTuple(c_srv, "Bs|H", &stype, &hostname, &port)) {
            if (set_stype && set_stype != stype) {
                PyErr_SetString(PyExc_ValueError, "can't mix transport types");
                goto it_error;
            } else {
                set_stype = stype;
                if (stype == PYLIBMC_SERVER_UDP) {
                    memcached_behavior_set(self->mc,
                        MEMCACHED_BEHAVIOR_USE_UDP, 1);
                }
            }

            switch (stype) {
                case PYLIBMC_SERVER_TCP:
                    rc = memcached_server_add(self->mc, hostname, port);
                    break;
                case PYLIBMC_SERVER_UDP:
                    rc = memcached_server_add_udp(self->mc, hostname, port);
                    break;
                case PYLIBMC_SERVER_UNIX:
                    if (port) {
                        PyErr_SetString(PyExc_ValueError,
                                "can't set port on unix sockets");
                        goto it_error;
                    }
                    rc = memcached_server_add_unix_socket(self->mc, hostname);
                    break;
                default:
                    PyErr_Format(PyExc_ValueError, "bad type: %u", stype);
                    goto it_error;
            }
            if (rc != MEMCACHED_SUCCESS) {
                PylibMC_ErrFromMemcached(self, "memcached_server_add_*", rc);
                goto it_error;
            }
        }
        Py_DECREF(c_srv);
        continue;

it_error:
        Py_DECREF(c_srv);
        goto error;
    }

    if (!got_server) {
        PyErr_SetString(PylibMCExc_MemcachedError, "empty server list");
        goto error;
    }

    Py_DECREF(srvs_it);
    return 0;
error:
    Py_DECREF(srvs_it);
    return -1;
}

/* {{{ Compression helpers */
#ifdef USE_ZLIB
static int _PylibMC_Deflate(char *value, size_t value_len,
                    char **result, size_t *result_len) {
    /* FIXME Failures are entirely silent. */
    int rc;

    z_stream strm;
    *result = NULL;
    *result_len = 0;

    /* Don't ask me about this one. Got it from zlibmodule.c in Python 2.6. */
    ssize_t out_sz = value_len + value_len / 1000 + 12 + 1;

    if ((*result = malloc(out_sz)) == NULL) {
      goto error;
    }

    /* TODO Should break up next_in into blocks of max 0xffffffff in length. */
    assert(value_len < 0xffffffffU);
    assert(out_sz < 0xffffffffU);

    strm.avail_in = (uInt)value_len;
    strm.avail_out = (uInt)out_sz;
    strm.next_in = (Bytef *)value;
    strm.next_out = (Bytef *)*result;

    /* we just pre-allocated all of it up front */
    strm.zalloc = (alloc_func)NULL;
    strm.zfree = (free_func)Z_NULL;

    /* TODO Expose compression level somehow. */
    if (deflateInit((z_streamp)&strm, Z_BEST_SPEED) != Z_OK) {
        goto error;
    }

    Py_BEGIN_ALLOW_THREADS;
    rc = deflate((z_streamp)&strm, Z_FINISH);
    Py_END_ALLOW_THREADS;

    if (rc != Z_STREAM_END) {
        _ZLIB_ERR("deflate", rc);
        goto error;
    }

    if (deflateEnd((z_streamp)&strm) != Z_OK) {
        goto error;
    }

    if(strm.total_out >= value_len) {
      /* if we didn't actually save anything, don't bother storing it
         compressed */
      goto error;
    }

    /* *result should already be populated since that's the address we
       passed into the z_stream */
    *result_len = strm.total_out;

    return 1;
error:
    /* if any error occurred, we'll just use the original value
       instead of trying to compress it */
    if(*result != NULL) {
      free(*result);
      *result = NULL;
    }
    return 0;
}

static PyObject *_PylibMC_Inflate(char *value, size_t size) {
    int rc;
    char *out;
    PyObject *out_obj;
    Py_ssize_t rvalsz;
    z_stream strm;

    /* Output buffer */
    rvalsz = ZLIB_BUFSZ;
    out_obj = PyString_FromStringAndSize(NULL, rvalsz);
    if (out_obj == NULL) {
        return NULL;
    }
    out = PyString_AS_STRING(out_obj);

    /* TODO 64-bit fix size/rvalsz */
    assert(size < 0xffffffffU);
    assert(rvalsz < 0xffffffffU);

    /* Set up zlib stream. */
    strm.avail_in = (uInt)size;
    strm.avail_out = (uInt)rvalsz;
    strm.next_in = (Byte *)value;
    strm.next_out = (Byte *)out;

    strm.zalloc = (alloc_func)NULL;
    strm.zfree = (free_func)Z_NULL;

    /* TODO Add controlling of windowBits with inflateInit2? */
    if ((rc = inflateInit((z_streamp)&strm)) != Z_OK) {
        _ZLIB_ERR("inflateInit", rc);
        goto error;
    }

    do {
        Py_BEGIN_ALLOW_THREADS;
        rc = inflate((z_streamp)&strm, Z_FINISH);
        Py_END_ALLOW_THREADS;

        switch (rc) {
        case Z_STREAM_END:
            break;
        /* When a Z_BUF_ERROR occurs, we should be out of memory.
         * This is also true for Z_OK, hence the fall-through. */
        case Z_BUF_ERROR:
            if (strm.avail_out) {
                _ZLIB_ERR("inflate", rc);
                inflateEnd(&strm);
                goto error;
            }
        /* Fall-through */
        case Z_OK:
            if (_PyString_Resize(&out_obj, (Py_ssize_t)(rvalsz << 1)) < 0) {
                inflateEnd(&strm);
                goto error;
            }
            /* Wind forward */
            out = PyString_AS_STRING(out_obj);
            strm.next_out = (Byte *)(out + rvalsz);
            strm.avail_out = (uInt)rvalsz;
            rvalsz = rvalsz << 1;
            break;
        default:
            inflateEnd(&strm);
            goto error;
        }
    } while (rc != Z_STREAM_END);

    if ((rc = inflateEnd(&strm)) != Z_OK) {
        _ZLIB_ERR("inflateEnd", rc);
        goto error;
    }

    _PyString_Resize(&out_obj, strm.total_out);
    return out_obj;
error:
    Py_DECREF(out_obj);
    return NULL;
}
#endif
/* }}} */

static PyObject *_PylibMC_parse_memcached_value(char *value, size_t size,
        uint32_t flags) {
    PyObject *retval = NULL;
    PyObject *tmp = NULL;
    uint32_t dtype = flags & PYLIBMC_FLAG_TYPES;

#if USE_ZLIB
    PyObject *inflated = NULL;

    /* Decompress value if necessary. */
    if (flags & PYLIBMC_FLAG_ZLIB) {
        if ((inflated = _PylibMC_Inflate(value, size)) == NULL) {
            return NULL;
        }
        value = PyString_AS_STRING(inflated);
        size = PyString_GET_SIZE(inflated);
    }
#else
    if (flags & PYLIBMC_FLAG_ZLIB) {
        PyErr_SetString(PylibMCExc_MemcachedError,
            "value for key compressed, unable to inflate");
        return NULL;
    }
#endif

    switch (dtype) {
        case PYLIBMC_FLAG_PICKLE:
            retval = _PylibMC_Unpickle(value, size);
            break;
        case PYLIBMC_FLAG_INTEGER:
        case PYLIBMC_FLAG_LONG:
        case PYLIBMC_FLAG_BOOL:
            /* PyInt_FromString doesn't take a length param and we're
               not NULL-terminated, so we'll have to make an
               intermediate Python string out of it */
            tmp = PyString_FromStringAndSize(value, size);
            if(tmp == NULL) {
              goto cleanup;
            }
            retval = PyInt_FromString(PyString_AS_STRING(tmp), NULL, 10);
            if(retval != NULL && dtype == PYLIBMC_FLAG_BOOL) {
              Py_DECREF(tmp);
              tmp = retval;
              retval = PyBool_FromLong(PyInt_AS_LONG(tmp));
            }
            break;
        case PYLIBMC_FLAG_NONE:
            retval = PyString_FromStringAndSize(value, (Py_ssize_t)size);
            break;
        default:
            PyErr_Format(PylibMCExc_MemcachedError,
                    "unknown memcached key flags %u", flags);
    }

cleanup:

#if USE_ZLIB
    Py_XDECREF(inflated);
#endif

    Py_XDECREF(tmp);

    return retval;
}

static PyObject *_PylibMC_parse_memcached_result(memcached_result_st *res) {
        return _PylibMC_parse_memcached_value((char *)memcached_result_value(res),
                                              memcached_result_length(res),
                                              memcached_result_flags(res));
}

static PyObject *PylibMC_Client_get(PylibMC_Client *self, PyObject *arg) {
    char *mc_val;
    size_t val_size;
    uint32_t flags;
    memcached_return error;

    if (!_PylibMC_CheckKey(arg)) {
        return NULL;
    } else if (!PySequence_Length(arg) ) {
        /* Others do this, so... */
        Py_RETURN_NONE;
    }

    Py_BEGIN_ALLOW_THREADS;
    mc_val = memcached_get(self->mc,
            PyString_AS_STRING(arg), PyString_GET_SIZE(arg),
            &val_size, &flags, &error);
    Py_END_ALLOW_THREADS;

    if (mc_val != NULL) {
        PyObject *r = _PylibMC_parse_memcached_value(mc_val, val_size, flags);
        free(mc_val);
        return r;
    } else if (error == MEMCACHED_SUCCESS) {
        /* This happens for empty values, and so we fake an empty string. */
        return PyString_FromStringAndSize("", 0);
    } else if (error == MEMCACHED_NOTFOUND) {
        /* Since python-memcache returns None when the key doesn't exist,
         * so shall we. */
        Py_RETURN_NONE;
    }

    return PylibMC_ErrFromMemcachedWithKey(self, "memcached_get", error,
                                           PyString_AS_STRING(arg),
                                           PyString_GET_SIZE(arg));
}

static PyObject *PylibMC_Client_gets(PylibMC_Client *self, PyObject *arg) {
    const char* keys[2];
    size_t keylengths[2];
    memcached_result_st *res = NULL;
    memcached_return rc;
    PyObject* ret = NULL;

    if (!_PylibMC_CheckKey(arg)) {
        return NULL;
    } else if (!PySequence_Length(arg)) {
        /* Others do this, so... */
        Py_RETURN_NONE;
    } else if (!memcached_behavior_get(self->mc, MEMCACHED_BEHAVIOR_SUPPORT_CAS)) {
        PyErr_SetString(PyExc_ValueError, "gets without cas behavior");
        return NULL;
    }

    /* Use an mget to fetch the key.
     * mget is the only function that returns a memcached_result_st,
     * which is the only way to get at the returned cas value. */
    *keys = PyString_AS_STRING(arg);
    *keylengths = (size_t)PyString_GET_SIZE(arg);

    Py_BEGIN_ALLOW_THREADS;

    rc = memcached_mget(self->mc, keys, keylengths, 1);
    if (rc == MEMCACHED_SUCCESS)
        res = memcached_fetch_result(self->mc, res, &rc);

    Py_END_ALLOW_THREADS;

    if (rc == MEMCACHED_SUCCESS && res != NULL) {
        ret = Py_BuildValue("(NL)",
                            _PylibMC_parse_memcached_result(res),
                            memcached_result_cas(res));

        /* we have to fetch the last result from the mget cursor */
        if (NULL != memcached_fetch_result(self->mc, NULL, &rc)) {
            memcached_quit(self->mc);
            Py_DECREF(ret);
            ret = NULL;
            PyErr_SetString(PyExc_RuntimeError, "fetch not done");
        }
    } else if (rc == MEMCACHED_END) {
        /* Key not found => (None, None) */
        ret = Py_BuildValue("(OO)", Py_None, Py_None);
    } else {
        ret = PylibMC_ErrFromMemcached(self, "memcached_gets", rc);
    }

    if (res != NULL) {
        memcached_result_free(res);
    }

    return ret;
}

/* {{{ Set commands (set, replace, add, prepend, append) */
static PyObject *_PylibMC_RunSetCommandSingle(PylibMC_Client *self,
        _PylibMC_SetCommand f, char *fname, PyObject *args,
        PyObject *kwds) {
    /* function called by the set/add/etc commands */
    static char *kws[] = { "key", "val", "time", "min_compress_len", NULL };
    PyObject *key;
    PyObject *value;
    unsigned int time = 0; /* this will be turned into a time_t */
    unsigned int min_compress = 0;
    bool success = false;

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "SO|II", kws,
                                     &key, &value,
                                     &time, &min_compress)) {
      return NULL;
    }

#ifndef USE_ZLIB
    if (min_compress) {
      PyErr_SetString(PyExc_TypeError, "min_compress_len without zlib");
      return NULL;
    }
#endif

    pylibmc_mset serialized = { NULL };

    success = _PylibMC_SerializeValue(key, NULL, value, time, &serialized);

    if (!success)
        goto cleanup;

    success = _PylibMC_RunSetCommand(self, f, fname,
                                     &serialized, 1,
                                     min_compress);

cleanup:
    _PylibMC_FreeMset(&serialized);

    if(PyErr_Occurred() != NULL) {
        return NULL;
    } else if(success) {
        Py_RETURN_TRUE;
    } else {
        Py_RETURN_FALSE;
    }
}

static PyObject *_PylibMC_RunSetCommandMulti(PylibMC_Client* self,
        _PylibMC_SetCommand f, char *fname, PyObject* args,
        PyObject* kwds) {
    /* function called by the set/add/incr/etc commands */
    PyObject* keys = NULL;
    PyObject* key_prefix = NULL;
    unsigned int time = 0;
    unsigned int min_compress = 0;
    PyObject * retval = NULL;
    size_t idx = 0;

    static char *kws[] = { "keys", "time", "key_prefix", "min_compress_len", NULL };

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O!|ISI", kws,
                                     &PyDict_Type, &keys,
                                     &time, &key_prefix,
                                     &min_compress)) {
        return NULL;
    }

#ifndef USE_ZLIB
    if (min_compress) {
        PyErr_SetString(PyExc_TypeError, "min_compress_len without zlib");
        return NULL;
    }
#endif

    PyObject *curr_key, *curr_value;
    size_t nkeys = (size_t)PyDict_Size(keys);

    pylibmc_mset* serialized = PyMem_New(pylibmc_mset, nkeys);
    if (serialized == NULL) {
        goto cleanup;
    }

    /**
     * We're pointing into existing Python memory with the 'key' members of
     * pylibmc_mset (extracted using PyDict_Next) and during
     * _PylibMC_RunSetCommand (which uses those same 'key' params, and
     * potentially points into value string objects too), so we don't want to
     * go around decrementing any references that risk destroying the pointed
     * objects until we're done, especially since we're going to release the
     * GIL while we do the I/O that accesses that memory. We're assuming that
     * this is safe because Python strings are immutable
     */

    Py_ssize_t pos = 0; /* PyDict_Next's 'pos' isn't an incrementing index */

    for (idx = 0; PyDict_Next(keys, &pos, &curr_key, &curr_value); idx++) {
        int success = _PylibMC_SerializeValue(curr_key, key_prefix,
                                              curr_value, time,
                                              &serialized[idx]);

        if (!success || PyErr_Occurred() != NULL) {
            /* exception should already be on the stack */
            goto cleanup;
        }
    }

    if (PyErr_Occurred() != NULL) {
        /* an iteration error of some sort */
        goto cleanup;
    }

    bool allsuccess = _PylibMC_RunSetCommand(self, f, fname,
                                             serialized, nkeys,
                                             min_compress);

    if (PyErr_Occurred() != NULL) {
        goto cleanup;
    }

    /* Return value for set_multi, which is a list
       of keys which failed to be set */
    if ((retval = PyList_New(0)) == NULL)
        return PyErr_NoMemory();

    for (idx = 0; !allsuccess && idx < nkeys; idx++) {
        if (serialized[idx].success)
            continue;

        if (PyList_Append(retval, serialized[idx].key_obj) != 0) {
            /* Ugh */
            Py_DECREF(retval);
            retval = PyErr_NoMemory();
            goto cleanup;
        }
    }

cleanup:
    if (serialized != NULL) {
        for (pos = 0; pos < nkeys; pos++) {
            _PylibMC_FreeMset(&serialized[pos]);
        }
        PyMem_Free(serialized);
    }

    return retval;
}

static PyObject *_PylibMC_RunCasCommand(PylibMC_Client *self,
        PyObject *args, PyObject *kwds) {
    /* function called by the set/add/etc commands */
    static char *kws[] = { "key", "val", "cas", "time", NULL };
    PyObject *ret = NULL;
    PyObject *key;
    PyObject *value;
    uint64_t cas = 0;
    unsigned int time = 0; /* this will be turned into a time_t */
    bool success = false;
    memcached_return rc;

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "SOL|I", kws,
                                     &key, &value, &cas,
                                     &time)) {
      return NULL;
    }

    if (!memcached_behavior_get(self->mc, MEMCACHED_BEHAVIOR_SUPPORT_CAS)) {
      PyErr_SetString(PyExc_ValueError, "cas without cas behavior");
      return NULL;
    }

    pylibmc_mset mset = { NULL };

    /* TODO: because it's RunSetCommand that does the zlib
       compression, cas can't currently use compressed values. */
    success = _PylibMC_SerializeValue(key, NULL, value, time, &mset);

    if (!success || PyErr_Occurred() != NULL) {
        goto cleanup;
    }

    Py_BEGIN_ALLOW_THREADS;
    rc = memcached_cas(self->mc,
                       mset.key, mset.key_len,
                       mset.value, mset.value_len,
                       mset.time, mset.flags, cas);
    Py_END_ALLOW_THREADS;

    switch(rc) {
        case MEMCACHED_SUCCESS:
            Py_INCREF(Py_True);
            ret = Py_True;
            break;
        case MEMCACHED_DATA_EXISTS:
            Py_INCREF(Py_False);
            ret = Py_False;
            break;
        default:
            PylibMC_ErrFromMemcachedWithKey(self, "memcached_cas", rc,
                                            mset.key, mset.key_len);
    }

cleanup:
    _PylibMC_FreeMset(&mset);

    return ret;
}

static void _PylibMC_FreeMset(pylibmc_mset *mset) {
      Py_XDECREF(mset->key_obj);
      mset->key_obj = NULL;

      Py_XDECREF(mset->prefixed_key_obj);
      mset->prefixed_key_obj = NULL;

      /* Either a ref we own, or a ref passed to us which we borrowed. */
      Py_XDECREF(mset->value_obj);
      mset->value_obj = NULL;
}

static int _PylibMC_SerializeValue(PyObject* key_obj,
                                   PyObject* key_prefix,
                                   PyObject* value_obj,
                                   time_t time,
                                   pylibmc_mset* serialized) {
    /* first zero the whole structure out */
    memset((void *)serialized, 0x0, sizeof(pylibmc_mset));

    serialized->time = time;
    serialized->success = false;
    serialized->flags = PYLIBMC_FLAG_NONE;

    if(!_PylibMC_CheckKey(key_obj)
       || PyString_AsStringAndSize(key_obj, &serialized->key,
                                   &serialized->key_len) == -1) {
        return false;
    }

    /* We need to incr our reference here so that it's guaranteed to
       exist while we release the GIL. Even if we fail after this it
       should be decremeneted by pylib_mset_free */
    Py_INCREF(key_obj);
    serialized->key_obj = key_obj;

    /* Check the key_prefix */
    if (key_prefix != NULL) {
        if (!_PylibMC_CheckKey(key_prefix)) {
            return false;
        }

        /* Ignore empty prefixes */
        if (!PyString_Size(key_prefix)) {
            key_prefix = NULL;
        }
    }

    /* Make the prefixed key if appropriate */
    if (key_prefix != NULL) {
        PyObject* prefixed_key_obj = NULL; /* freed by _PylibMC_FreeMset */

        prefixed_key_obj = PyString_FromFormat("%s%s",
                PyString_AS_STRING(key_prefix),
                PyString_AS_STRING(key_obj));

        if(prefixed_key_obj == NULL) {
            return false;
        }

        /* check the key and overwrite the C string */
        if(!_PylibMC_CheckKey(prefixed_key_obj)
           || PyString_AsStringAndSize(prefixed_key_obj,
                                       &serialized->key,
                                       &serialized->key_len) == -1) {
            Py_DECREF(prefixed_key_obj);
            return false;
        }

        serialized->prefixed_key_obj = prefixed_key_obj;
    }

    /* Key/key_size should be harmonized, now onto the value */

    PyObject* store_val = NULL;

    /* First build store_val, a Python String object, out of the object
       we were passed */
    if (PyString_Check(value_obj)) {
        store_val = value_obj;
        Py_INCREF(store_val); /* because we'll be decring it again in
                                 pylibmc_mset_free*/
    } else if (PyBool_Check(value_obj)) {
        serialized->flags |= PYLIBMC_FLAG_BOOL;
        PyObject* tmp = PyNumber_Int(value_obj);
        store_val = PyObject_Str(tmp);
        Py_DECREF(tmp);
    } else if (PyInt_Check(value_obj)) {
        serialized->flags |= PYLIBMC_FLAG_INTEGER;
        PyObject* tmp = PyNumber_Int(value_obj);
        store_val = PyObject_Str(tmp);
        Py_DECREF(tmp);
    } else if (PyLong_Check(value_obj)) {
        serialized->flags |= PYLIBMC_FLAG_LONG;
        PyObject* tmp = PyNumber_Long(value_obj);
        store_val = PyObject_Str(tmp);
        Py_DECREF(tmp);
    } else if(value_obj != NULL) {
        /* we have no idea what it is, so we'll store it pickled */
        Py_INCREF(value_obj);
        serialized->flags |= PYLIBMC_FLAG_PICKLE;
        store_val = _PylibMC_Pickle(value_obj);
        Py_DECREF(value_obj);
    }

    if (store_val == NULL) {
        return false;
    }

    if (PyString_AsStringAndSize(store_val, &serialized->value,
                                 &serialized->value_len) == -1) {
        if (serialized->flags == PYLIBMC_FLAG_NONE) {
            /* For some reason we weren't able to extract the value/size
               from a string that we were explicitly passed, that we
               INCREF'd above */
            Py_DECREF(store_val);
        }
        return false;
    }

    /* So now we have a reference to a string that we may have
       created. we need that to keep existing while we release the GIL,
       so we need to hold the reference, but we need to free it up when
       we're done */
    serialized->value_obj = store_val;

    return true;
}

/* {{{ Set commands (set, replace, add, prepend, append) */
static bool _PylibMC_RunSetCommand(PylibMC_Client* self,
                                   _PylibMC_SetCommand f, char *fname,
                                   pylibmc_mset* msets, size_t nkeys,
                                   size_t min_compress) {
    memcached_st *mc = self->mc;
    memcached_return rc = MEMCACHED_SUCCESS;
    int pos;
    bool error = false;
    bool allsuccess = true;

    Py_BEGIN_ALLOW_THREADS;

    for (pos=0; pos < nkeys && !error; pos++) {
        pylibmc_mset *mset = &msets[pos];

        char *value = mset->value;
        size_t value_len = (size_t)mset->value_len;
        uint32_t flags = mset->flags;

#ifdef USE_ZLIB
        char *compressed_value = NULL;
        size_t compressed_len = 0;

        if (min_compress && value_len >= min_compress) {
            Py_BLOCK_THREADS;
            _PylibMC_Deflate(value, value_len,
                             &compressed_value, &compressed_len);
            Py_UNBLOCK_THREADS;
        }

        if (compressed_value != NULL) {
            /* Will want to change this if this function
             * needs to get back at the old *value at some point */
            value = compressed_value;
            value_len = compressed_len;
            flags |= PYLIBMC_FLAG_ZLIB;
        }
#endif

        /* Finally go and call the actual libmemcached function */
        if (mset->key_len == 0) {
            /* Most other implementations ignore zero-length keys, so
               we'll just do that */
            rc = MEMCACHED_NOTSTORED;
        } else {
            rc = f(mc, mset->key, mset->key_len,
                   value, value_len, mset->time, flags);
        }

#ifdef USE_ZLIB
        if (compressed_value != NULL) {
            free(compressed_value);
        }
#endif

      switch (rc) {
          case MEMCACHED_SUCCESS:
              mset->success = true;
              break;
          case MEMCACHED_FAILURE:
          case MEMCACHED_NO_KEY_PROVIDED:
          case MEMCACHED_BAD_KEY_PROVIDED:
          case MEMCACHED_MEMORY_ALLOCATION_FAILURE:
          case MEMCACHED_DATA_EXISTS:
          case MEMCACHED_NOTSTORED:
              mset->success = false;
              allsuccess = false;
              break;
          default:
              mset->success = false;
              allsuccess = false;
              error = true; /* will break the for loop */
      } /* switch */

    } /* end for each mset */

    Py_END_ALLOW_THREADS;

    /* We only return the last return value, even for a _multi
       operation, but we do set the success on the mset */
    if (error) {
        PylibMC_ErrFromMemcached(self, fname, rc);
        return false;
    } else {
        return allsuccess;
    }
}

/* These all just call _PylibMC_RunSetCommand with the appropriate
 * arguments.  In other words: bulk. */
static PyObject *PylibMC_Client_set(PylibMC_Client *self, PyObject *args,
        PyObject *kwds) {
    PyObject* retval = _PylibMC_RunSetCommandSingle(
            self, memcached_set, "memcached_set", args, kwds);
    return retval;
}

static PyObject *PylibMC_Client_replace(PylibMC_Client *self, PyObject *args,
        PyObject *kwds) {
    return _PylibMC_RunSetCommandSingle(
            self, memcached_replace, "memcached_replace", args, kwds);
}

static PyObject *PylibMC_Client_add(PylibMC_Client *self, PyObject *args,
        PyObject *kwds) {
    return _PylibMC_RunSetCommandSingle(
            self, memcached_add, "memcached_add", args, kwds);
}

static PyObject *PylibMC_Client_prepend(PylibMC_Client *self, PyObject *args,
        PyObject *kwds) {
    return _PylibMC_RunSetCommandSingle(
            self, memcached_prepend, "memcached_prepend", args, kwds);
}

static PyObject *PylibMC_Client_append(PylibMC_Client *self, PyObject *args,
        PyObject *kwds) {
    return _PylibMC_RunSetCommandSingle(
            self, memcached_append, "memcached_append", args, kwds);
}
/* }}} */

static PyObject *PylibMC_Client_cas(PylibMC_Client *self, PyObject *args,
        PyObject *kwds) {
  return _PylibMC_RunCasCommand(self, args, kwds);
}

static PyObject *PylibMC_Client_delete(PylibMC_Client *self, PyObject *args) {
    char *key;
    Py_ssize_t key_len = 0;
    memcached_return rc;

    if (PyArg_ParseTuple(args, "s#:delete", &key, &key_len)
            && _PylibMC_CheckKeyStringAndSize(key, key_len)) {
        Py_BEGIN_ALLOW_THREADS;
        rc = memcached_delete(self->mc, key, key_len, 0);
        Py_END_ALLOW_THREADS;
        switch (rc) {
            case MEMCACHED_SUCCESS:
                Py_RETURN_TRUE;
            case MEMCACHED_FAILURE:
            case MEMCACHED_NOTFOUND:
            case MEMCACHED_NO_KEY_PROVIDED:
            case MEMCACHED_BAD_KEY_PROVIDED:
                Py_RETURN_FALSE;
            default:
                return PylibMC_ErrFromMemcachedWithKey(self, "memcached_delete",
                                                       rc, key, key_len);
        }
    }

    return NULL;
}

/* {{{ Increment & decrement */
static PyObject *_PylibMC_IncrSingle(PylibMC_Client *self,
                                     _PylibMC_IncrCommand incr_func,
                                     PyObject *args) {
    char *key;
    Py_ssize_t key_len = 0;
    unsigned int delta = 1;

    if (!PyArg_ParseTuple(args, "s#|I", &key, &key_len, &delta)) {
        return NULL;
    } else if (!_PylibMC_CheckKeyStringAndSize(key, key_len)) {
        return NULL;
    }

    pylibmc_incr incr = { key, key_len,
                          incr_func, delta,
                          0 };

    _PylibMC_IncrDecr(self, &incr, 1);

    if(PyErr_Occurred() != NULL) {
      /* exception already on the stack */
      return NULL;
    }

    /* might be NULL, but if that's true then it's the right return value */
    return PyLong_FromUnsignedLong((unsigned long)incr.result);
}

static PyObject *_PylibMC_IncrMulti(PylibMC_Client *self,
                                    _PylibMC_IncrCommand incr_func,
                                    PyObject *args, PyObject *kwds) {
    PyObject *key = NULL;
    PyObject *keys = NULL;
    PyObject *keys_tmp = NULL;
    PyObject *key_prefix = NULL;
    PyObject *retval = NULL;
    PyObject *iterator = NULL;
    unsigned int delta = 1;
    size_t nkeys = 0, i = 0;

    static char *kws[] = { "keys", "key_prefix", "delta", NULL };

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|SI", kws,
                                     &keys, &key_prefix, &delta))
        return NULL;

    nkeys = (size_t)PySequence_Size(keys);
    if (nkeys == -1)
        return NULL;

    if (key_prefix != NULL) {
        if (!_PylibMC_CheckKey(key_prefix))
            return NULL;

        if (PyString_Size(key_prefix) == 0)
            key_prefix = NULL;
    }

    keys_tmp = PyList_New(nkeys);
    if (keys_tmp == NULL)
        return NULL;

    pylibmc_incr *incrs = PyMem_New(pylibmc_incr, nkeys);
    if (incrs == NULL)
        goto cleanup;

    iterator = PyObject_GetIter(keys);
    if (iterator == NULL)
        goto cleanup;

    /* Build pylibmc_incr structs, prefixed as appropriate. */
    for (i = 0; (key = PyIter_Next(iterator)) != NULL; i++) {
        pylibmc_incr *incr = incrs + i;

        if (!_PylibMC_CheckKey(key))
            goto loopcleanup;

        /* prefix `key` with `key_prefix` */
        if (key_prefix != NULL) {
            PyObject* newkey = PyString_FromFormat("%s%s",
                                                   PyString_AS_STRING(key_prefix),
                                                   PyString_AS_STRING(key));
            Py_DECREF(key);
            key = newkey;
        }

        Py_INCREF(key);
        if (PyList_SetItem(keys_tmp, i, key) == -1)
            goto loopcleanup;

        /* Populate pylibmc_incr */
        if (PyString_AsStringAndSize(key, &incr->key, &incr->key_len) == -1)
            goto loopcleanup;
        incr->delta = delta;
        incr->incr_func = incr_func;
        /* After incring we have no way of knowing whether the real result is 0
         * or if the incr wasn't successful (or if noreply is set), but since
         * we're not actually returning the result that's okay for now */
        incr->result = 0;

loopcleanup:
        Py_DECREF(key);
        if (PyErr_Occurred())
            goto cleanup;
    } /* end each key */

    _PylibMC_IncrDecr(self, incrs, nkeys);

    if (!PyErr_Occurred()) {
        retval = Py_None;
        Py_INCREF(retval);
    } else {
        Py_XDECREF(retval);
        retval = NULL;
    }

cleanup:
    if (incrs != NULL)
        PyMem_Free(incrs);
    Py_DECREF(keys_tmp);
    Py_XDECREF(iterator);

    return retval;
}

static PyObject *PylibMC_Client_incr(PylibMC_Client *self, PyObject *args) {
    return _PylibMC_IncrSingle(self, memcached_increment, args);
}

static PyObject *PylibMC_Client_decr(PylibMC_Client *self, PyObject *args) {
    return _PylibMC_IncrSingle(self, memcached_decrement, args);
}

static PyObject *PylibMC_Client_incr_multi(PylibMC_Client *self, PyObject *args,
                                           PyObject *kwds) {
    return _PylibMC_IncrMulti(self, memcached_increment, args, kwds);
}

static bool _PylibMC_IncrDecr(PylibMC_Client *self,
                              pylibmc_incr *incrs, size_t nkeys) {
    memcached_return rc = MEMCACHED_SUCCESS;
    _PylibMC_IncrCommand f = NULL;
    size_t i, notfound = 0, errors = 0;

    Py_BEGIN_ALLOW_THREADS;
    for (i = 0; i < nkeys; i++) {
        pylibmc_incr *incr = &incrs[i];
        uint64_t result = 0;

        f = incr->incr_func;
        rc = f(self->mc, incr->key, incr->key_len, incr->delta, &result);
        /* TODO Signal errors through `incr` */
        if (rc == MEMCACHED_SUCCESS) {
            incr->result = result;
        } else if (rc == MEMCACHED_NOTFOUND) {
            notfound++;
        } else {
            errors++;
        }
    }
    Py_END_ALLOW_THREADS;

    if (errors + notfound) {
        PyObject *exc = PylibMCExc_MemcachedError;

        if (errors == 0)
            exc = _exc_by_rc(MEMCACHED_NOTFOUND);
        else if (errors == 1)
            exc = _exc_by_rc(rc);

        PyErr_Format(exc, "%d keys %s",
                     (int)(notfound + errors),
                     errors ? "failed" : "not found");
    }

    return 0 == (errors + notfound);
}
/* }}} */

memcached_return pylibmc_memcached_fetch_multi(
        memcached_st *mc, char **keys, size_t nkeys, size_t *key_lens,
        memcached_result_st **results, size_t *nresults, char **err_func) {
    /**
     * Completely GIL-free multi getter
     *
     * Takes a set of keys given by *keys*, and stuffs the results into heap
     * memory returned by *results*.
     *
     * If an error occured during retrieval, this function returns
     * non-MEMCACHED_SUCCESS and *err_func* will point to a useful error
     * function name.
     *
     * FIXME *results* is expected to be able to hold one more result than
     * there are keys asked for, because of an implementation detail.
     */

    memcached_return rc;
    *err_func = NULL;

    rc = memcached_mget(mc, (const char **)keys, key_lens, nkeys);

    if (rc != MEMCACHED_SUCCESS) {
        *err_func = "memcached_mget";
        return rc;
    }

    /* Allocate as much as could possibly be needed, and an extra because of
     * how libmemcached signals EOF. */
    *results = PyMem_New(memcached_result_st, nkeys + 1);

    /* Note that nresults will not be off by one with this because the loops
     * runs a half pass after the last key has been fetched, thus bumping the
     * count once. */
    for (*nresults = 0; ; (*nresults)++) {
        memcached_result_st *res = memcached_result_create(mc, *results + *nresults);

        /* if loop spins out of control, this fails */
        assert(nkeys >= (*nresults));

        res = memcached_fetch_result(mc, res, &rc);

        if (res == NULL || rc == MEMCACHED_END) {
            /* This is how libmecached signals EOF. */
            break;
        } else if (rc == MEMCACHED_BAD_KEY_PROVIDED
                || rc == MEMCACHED_NO_KEY_PROVIDED) {
            continue;
        } else if (rc != MEMCACHED_SUCCESS) {
            memcached_quit(mc);  /* Reset fetch state */
            *err_func = "memcached_fetch";

            /* Clean-up procedure */
            do {
                memcached_result_free(*results + *nresults);
            } while ((*nresults)--);

            PyMem_Free(*results);
            *results = NULL;
            *nresults = 0;

            return rc;
        }
    }

    return MEMCACHED_SUCCESS;
}


static PyObject *PylibMC_Client_get_multi(
        PylibMC_Client *self, PyObject *args, PyObject *kwds) {
    PyObject *key_seq, **key_objs, *retval = NULL;
    char **keys, *prefix = NULL;
    char *err_func = NULL;
    memcached_result_st *res, *results = NULL;
    Py_ssize_t prefix_len = 0;
    Py_ssize_t i;
    PyObject *key_it, *ckey;
    size_t *key_lens;
    size_t nkeys, nresults = 0;
    memcached_return rc;

    static char *kws[] = { "keys", "key_prefix", NULL };

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|s#:get_multi", kws,
            &key_seq, &prefix, &prefix_len))
        return NULL;

    if ((nkeys = (size_t)PySequence_Length(key_seq)) == -1)
        return NULL;

    /* Populate keys and key_lens. */
    keys = PyMem_New(char *, nkeys);
    key_lens = PyMem_New(size_t, nkeys);
    key_objs = PyMem_New(PyObject *, nkeys);
    if (!keys || !key_lens || !key_objs) {
        PyMem_Free(keys);
        PyMem_Free(key_lens);
        PyMem_Free(key_objs);
        return PyErr_NoMemory();
    }

    /* Clear potential previous exception, because we explicitly check for
     * exceptions as a loop predicate. */
    PyErr_Clear();

    /* Iterate through all keys and set lengths etc. */
    key_it = PyObject_GetIter(key_seq);
    i = 0;
    while ((ckey = PyIter_Next(key_it)) != NULL) {
        char *key;
        Py_ssize_t key_len;
        PyObject *rkey;

        assert(i < nkeys);

        if (PyErr_Occurred() || !_PylibMC_CheckKey(ckey)) {
            nkeys = i;
            goto earlybird;
        }

        PyString_AsStringAndSize(ckey, &key, &key_len);

        key_lens[i] = (size_t)(key_len + prefix_len);

        /* Skip empty keys */
        if (!key_lens[i])
            continue;

        /* determine rkey, the prefixed ckey */
        if (prefix != NULL) {
            rkey = PyString_FromStringAndSize(prefix, prefix_len);
            PyString_Concat(&rkey, ckey);
            if (rkey == NULL)
                goto earlybird;
            rkey = PyString_FromFormat("%s%s",
                    prefix, PyString_AS_STRING(ckey));
        } else {
            Py_INCREF(ckey);
            rkey = ckey;
        }
        Py_DECREF(ckey);

        keys[i] = PyString_AS_STRING(rkey);
        key_objs[i++] = rkey;
    }
    nkeys = i;
    Py_XDECREF(key_it);

    if (nkeys == 0) {
        retval = PyDict_New();
        goto earlybird;
    } else if (PyErr_Occurred()) {
        nkeys--;
        goto earlybird;
    }

    /* TODO Make an iterator interface for getting each key separately.
     *
     * This would help large retrievals, as a single dictionary containing all
     * the data at once isn't needed. (Should probably look into if it's even
     * worth it.)
     */
    Py_BEGIN_ALLOW_THREADS;
    rc = pylibmc_memcached_fetch_multi(self->mc,
                                       keys, nkeys, key_lens,
                                       &results, &nresults,
                                       &err_func);
    Py_END_ALLOW_THREADS;

    if (rc != MEMCACHED_SUCCESS) {
        PylibMC_ErrFromMemcached(self, err_func, rc);
        goto earlybird;
    }

    retval = PyDict_New();

    for (i = 0; i < nresults; i++) {
        PyObject *val, *key_obj;
        int rc;

        res = results + i;

        /* Long-winded, but this way we can handle NUL-bytes in keys. */
        key_obj = PyString_FromStringAndSize(memcached_result_key_value(res) + prefix_len,
                                             memcached_result_key_length(res) - prefix_len);
        if (key_obj == NULL)
            goto unpack_error;

        /* Parse out value */
        val = _PylibMC_parse_memcached_result(res);
        if (val == NULL)
            goto unpack_error;

        rc = PyDict_SetItem(retval, key_obj, val);
        Py_DECREF(key_obj);
        Py_DECREF(val);

        if (rc != 0)
            goto unpack_error;

        continue;

unpack_error:
        Py_DECREF(retval);
        retval = NULL;
        break;
    }

earlybird:
    PyMem_Free(key_lens);
    PyMem_Free(keys);

    for (i = 0; i < nkeys; i++)
        Py_DECREF(key_objs[i]);
    PyMem_Free(key_objs);

    if (results != NULL) {
        for (i = 0; i < nresults && results != NULL; i++) {
            memcached_result_free(results + i);
        }
        PyMem_Free(results);
    }

    /* Not INCREFing because the only two outcomes are NULL and a new dict.
     * We're the owner of that dict already, so. */
    return retval;
}

/**
 * Run func over every item in value, building arguments of:
 *     *(item + extra_args)
 */
static PyObject *_PylibMC_DoMulti(PyObject *values, PyObject *func,
        PyObject *prefix, PyObject *extra_args) {
    /* TODO: acquire/release the GIL only once per DoMulti rather than
       once per action; fortunately this is only used for
       delete_multi, which isn't used very often */

    PyObject *retval = PyList_New(0);
    PyObject *iter = NULL;
    PyObject *item = NULL;
    int is_mapping = PyMapping_Check(values);

    if (retval == NULL)
        goto error;

    if ((iter = PyObject_GetIter(values)) == NULL)
        goto error;

    while ((item = PyIter_Next(iter)) != NULL) {
        PyObject *args_f = NULL;
        PyObject *args = NULL;
        PyObject *key = NULL;
        PyObject *ro = NULL;

        /* Calculate key. */
        if (prefix == NULL || prefix == Py_None) {
            /* We now have two owned references to item. */
            key = item;
            Py_INCREF(key);
        } else {
            key = PySequence_Concat(prefix, item);
        }
        if (key == NULL || !_PylibMC_CheckKey(key))
            goto iter_error;

        /* Calculate args. */
        if (is_mapping) {
            PyObject *value;
            char *key_str = PyString_AS_STRING(item);

            if ((value = PyMapping_GetItemString(values, key_str)) == NULL)
                goto iter_error;

            args = PyTuple_Pack(2, key, value);
            Py_DECREF(value);
        } else {
            args = PyTuple_Pack(1, key);
        }
        if (args == NULL)
            goto iter_error;

        /* Calculate full argument tuple. */
        if (extra_args == NULL) {
            Py_INCREF(args);
            args_f = args;
        } else {
            if ((args_f = PySequence_Concat(args, extra_args)) == NULL)
                goto iter_error;
        }

        /* Call stuff. */
        ro = PyObject_CallObject(func, args_f);
        /* This is actually safe even if True got deleted because we're
         * only comparing addresses. */
        Py_XDECREF(ro);
        if (ro == NULL) {
            goto iter_error;
        } else if (ro != Py_True) {
            if (PyList_Append(retval, item) != 0)
                goto iter_error;
        }
        Py_DECREF(args_f);
        Py_DECREF(args);
        Py_DECREF(key);
        Py_DECREF(item);
        continue;
iter_error:
        Py_XDECREF(args_f);
        Py_XDECREF(args);
        Py_XDECREF(key);
        Py_DECREF(item);
        goto error;
    }
    Py_DECREF(iter);

    return retval;
error:
    Py_XDECREF(retval);
    Py_XDECREF(iter);
    return NULL;
}

static PyObject *PylibMC_Client_set_multi(PylibMC_Client *self, PyObject *args,
        PyObject *kwds) {
  return _PylibMC_RunSetCommandMulti(self, memcached_set, "memcached_set_multi",
                                     args, kwds);
}

static PyObject *PylibMC_Client_add_multi(PylibMC_Client *self, PyObject *args,
        PyObject *kwds) {
  return _PylibMC_RunSetCommandMulti(self, memcached_add, "memcached_add_multi",
                                     args, kwds);
}

static PyObject *PylibMC_Client_delete_multi(PylibMC_Client *self,
        PyObject *args, PyObject *kwds) {
    PyObject *prefix = NULL;
    PyObject *time = NULL;
    PyObject *delete;
    PyObject *keys;
    PyObject *call_args;
    PyObject *retval;

    static char *kws[] = { "keys", "key_prefix", NULL };

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|S:delete_multi", kws,
                                     &keys, &prefix))
        return NULL;

    /**
     * Because of how DoMulti works, we have to prohibit the use of mappings
     * here. Otherwise, the values of the mapping will be the second argument
     * to the delete function; the time argument will then become a third
     * argument, which delete doesn't take.
     *
     * So a mapping to DoMulti would produce calls like:
     *   DoMulti({"a": 1, "b": 2}, time=3)
     *      delete("a", 1, 3)
     *      delete("b", 2, 3)
     */
    if (PyMapping_Check(keys)) {
        PyErr_SetString(PyExc_TypeError,
            "keys must be a sequence, not a mapping");
        return NULL;
    }

    if ((delete = PyObject_GetAttrString((PyObject *)self, "delete")) == NULL)
        return NULL;

    if (time == NULL) {
        retval = _PylibMC_DoMulti(keys, delete, prefix, NULL);
    } else {
        if ((call_args = PyTuple_Pack(1, time)) == NULL)
            goto error;
        retval = _PylibMC_DoMulti(keys, delete, prefix, call_args);
        Py_DECREF(call_args);
    }
    Py_DECREF(delete);

    if (retval == NULL)
        return NULL;

    if (PyList_Size(retval) == 0) {
        Py_DECREF(retval);
        retval = Py_True;
    } else {
        Py_DECREF(retval);
        retval = Py_False;
    }
    Py_INCREF(retval);

    return retval;
error:
    Py_XDECREF(delete);
    return NULL;
}

static PyObject *PylibMC_Client_get_behaviors(PylibMC_Client *self) {
    PyObject *retval = PyDict_New();
    PylibMC_Behavior *b;

    if (retval == NULL)
        return NULL;

    for (b = PylibMC_behaviors; b->name != NULL; b++) {
        uint64_t bval;
        PyObject *x;

        bval = memcached_behavior_get(self->mc, b->flag);
        x = PyInt_FromLong((long)bval);
        if (x == NULL || PyDict_SetItemString(retval, b->name, x) == -1) {
            Py_XDECREF(x);
            goto error;
        }

        Py_DECREF(x);
    }

    return retval;
error:
    Py_XDECREF(retval);
    return NULL;
}

static PyObject *PylibMC_Client_set_behaviors(PylibMC_Client *self,
        PyObject *behaviors) {
    PylibMC_Behavior *b;

    for (b = PylibMC_behaviors; b->name != NULL; b++) {
        PyObject *py_v;
        uint64_t v;
        memcached_return r;

        if (!PyMapping_HasKeyString(behaviors, b->name)) {
            continue;
        } else if ((py_v = PyMapping_GetItemString(behaviors, b->name)) == NULL) {
            goto error;
        } else if (!PyInt_Check(py_v)) {
            PyErr_Format(PyExc_TypeError, "behavior %.32s must be int", b->name);
            goto error;
        }

        v = (uint64_t)PyInt_AS_LONG(py_v);
        Py_DECREF(py_v);

        r = memcached_behavior_set(self->mc, b->flag, v);
        if (r != MEMCACHED_SUCCESS) {
            PyErr_Format(PylibMCExc_MemcachedError,
                         "memcached_behavior_set returned %d for "
                         "behavior '%.32s' = %u", r, b->name, (unsigned int)v);
            goto error;
        }
    }

    Py_RETURN_NONE;
error:
    return NULL;
}

static memcached_return
_PylibMC_AddServerCallback(memcached_st *mc,
                           memcached_server_st *server,
                           void *user) {
    _PylibMC_StatsContext *context = (_PylibMC_StatsContext *)user;
    PylibMC_Client *self = (PylibMC_Client *)context->self;
    memcached_stat_st *stat;
    memcached_return rc;
    PyObject *desc, *val;
    char **stat_keys = NULL;
    char **curr_key;

    stat = context->stats + context->index;

    if ((val = PyDict_New()) == NULL)
        return MEMCACHED_FAILURE;

    stat_keys = memcached_stat_get_keys(mc, stat, &rc);
    if (rc != MEMCACHED_SUCCESS)
        return rc;

    for (curr_key = stat_keys; *curr_key; curr_key++) {
        PyObject *curr_value;
        char *mc_val;
        int fail;

        mc_val = memcached_stat_get_value(mc, stat, *curr_key, &rc);
        if (rc != MEMCACHED_SUCCESS) {
            PylibMC_ErrFromMemcached(self, "get_stats val", rc);
            goto error;
        }

        curr_value = PyString_FromString(mc_val);
        free(mc_val);
        if (curr_value == NULL)
            goto error;

        fail = PyDict_SetItemString(val, *curr_key, curr_value);
        Py_DECREF(curr_value);
        if (fail)
            goto error;
    }

    free(stat_keys);

    desc = PyString_FromFormat("%s:%d (%u)",
            server->hostname, server->port,
            (unsigned int)context->index);

    PyList_SET_ITEM(context->retval, context->index++,
                    Py_BuildValue("NN", desc, val));

    return MEMCACHED_SUCCESS;

error:
    free(stat_keys);
    Py_DECREF(val);
    return MEMCACHED_FAILURE;
}

static PyObject *PylibMC_Client_get_stats(PylibMC_Client *self, PyObject *args) {
    memcached_stat_st *stats;
    memcached_return rc;
    char *mc_args;
    Py_ssize_t nservers;
    _PylibMC_StatsContext context;

    mc_args = NULL;
    if (!PyArg_ParseTuple(args, "|s:get_stats", &mc_args))
        return NULL;

    Py_BEGIN_ALLOW_THREADS;
    stats = memcached_stat(self->mc, mc_args, &rc);
    Py_END_ALLOW_THREADS;
    if (rc != MEMCACHED_SUCCESS)
        return PylibMC_ErrFromMemcached(self, "get_stats", rc);

    /** retval contents:
     * [('<addr, 127.0.0.1:11211> (<num, 1>)', {stat: stat, stat: stat}),
     *  (str, dict),
     *  (str, dict)]
     */
    nservers = (Py_ssize_t)memcached_server_count(self->mc);

    /* Setup stats callback context */
    context.self = (PyObject *)self;
    context.retval = PyList_New(nservers);
    context.stats = stats;
    context.servers = NULL;  /* DEPRECATED */
    context.index = 0;

    /* TODO Remove BC for 0.38 */
#ifndef LIBMEMCACHED_VERSION_HEX
#  define LIBMEMCACHED_VERSION_HEX 0x0
#endif

#if LIBMEMCACHED_VERSION_HEX >= 0x00038000
    memcached_server_function callbacks[] = {
        (memcached_server_function)_PylibMC_AddServerCallback
    };

    rc = memcached_server_cursor(self->mc, callbacks, (void *)&context, 1);
#else /* ver < libmemcached 0.38 */
    context.servers = memcached_server_list(self->mc);

    for (; context.index < nservers; context.index++) {
        memcached_server_st *server = context.servers + context.index;
        memcached_return rc;

        rc = _PylibMC_AddServerCallback(self->mc, server, (void *)&context);
        if (rc != MEMCACHED_SUCCESS)
            break;
    }
#endif

    if (rc != MEMCACHED_SUCCESS) {
        if (!PyErr_Occurred())
            PyErr_SetString(PyExc_RuntimeError, "unknown error occured");
        Py_DECREF(context.retval);
        context.retval = NULL;
    }

    free(context.stats);

    return context.retval;
}

static PyObject *PylibMC_Client_flush_all(PylibMC_Client *self,
        PyObject *args, PyObject *kwds) {
    memcached_return rc;
    time_t expire = 0;
    PyObject *time = NULL;

    static char *kws[] = { "time", NULL };

    if (!PyArg_ParseTupleAndKeywords(args, kwds, "|O!:flush_all", kws,
                                     &PyInt_Type, &time))
        return NULL;

    if (time != NULL)
        expire = PyInt_AS_LONG(time);

    expire = (expire > 0) ? expire : 0;

    Py_BEGIN_ALLOW_THREADS;
    rc = memcached_flush(self->mc, expire);
    Py_END_ALLOW_THREADS;
    if (rc != MEMCACHED_SUCCESS)
        return PylibMC_ErrFromMemcached(self, "flush_all", rc);

    Py_RETURN_TRUE;
}

static PyObject *PylibMC_Client_disconnect_all(PylibMC_Client *self) {
    Py_BEGIN_ALLOW_THREADS;
    memcached_quit(self->mc);
    Py_END_ALLOW_THREADS;
    Py_RETURN_NONE;
}

static PyObject *PylibMC_Client_clone(PylibMC_Client *self) {
    /* Essentially this is a reimplementation of the allocator, only it uses a
     * cloned memcached_st for mc. */
    PylibMC_Client *clone;

    clone = (PylibMC_Client *)PyType_GenericNew(self->ob_type, NULL, NULL);
    if (clone == NULL) {
        return NULL;
    }

    Py_BEGIN_ALLOW_THREADS;
    clone->mc = memcached_clone(NULL, self->mc);
    Py_END_ALLOW_THREADS;
    return (PyObject *)clone;
}
/* }}} */

static PyObject *_exc_by_rc(memcached_return rc) {
    PylibMC_McErr *err;
    for (err = PylibMCExc_mc_errs; err->name != NULL; err++)
        if (err->rc == rc)
            return err->exc;
    return (PyObject *)PylibMCExc_MemcachedError;
}

static char *_get_lead(memcached_st *mc, char *buf, int n, const char *what,
        memcached_return error, const char *key, Py_ssize_t len) {
    int sz = snprintf(buf, n, "error %d from %.32s", error, what);

    if (key != NULL && len) {
        sz += snprintf(buf+sz, n-sz, "(%.32s)", key);
    }

    return buf;
}

static void _set_error(memcached_st *mc, memcached_return error, char *lead) {
    if (error == MEMCACHED_ERRNO) {
        PyErr_Format(PylibMCExc_MemcachedError, "%s: %s",
                     lead, strerror(errno));
    } else if (error == MEMCACHED_SUCCESS) {
        PyErr_Format(PyExc_RuntimeError, "error == MEMCACHED_SUCCESS");
    } else {
        PyObject *exc = _exc_by_rc(error);
#if LIBMEMCACHED_VERSION_HEX >= 0x00049000
        PyErr_Format(exc, "%s: %.200s", lead, memcached_last_error_message(mc));
#else
        PyErr_Format(exc, "%s: %.200s", lead, memcached_strerror(mc, error));
#endif
    }
}

static PyObject *PylibMC_ErrFromMemcachedWithKey(PylibMC_Client *self,
        const char *what, memcached_return error, const char *key, Py_ssize_t len) {
    char lead[128];

    _get_lead(self->mc, lead, sizeof(lead), what, error, key, len);
    _set_error(self->mc, error, lead);

    return NULL;
}

static PyObject *PylibMC_ErrFromMemcached(PylibMC_Client *self,
        const char *what, memcached_return error) {
    char lead[128];

    _get_lead(self->mc, lead, sizeof(lead), what, error, NULL, 0);
    _set_error(self->mc, error, lead);

    return NULL;
}

/* {{{ Pickling */
static PyObject *_PylibMC_GetPickles(const char *attname) {
    PyObject *pickle, *pickle_attr;

    pickle_attr = NULL;
    /* Import cPickle or pickle. */
    pickle = PyImport_ImportModule("cPickle");
    if (pickle == NULL) {
        PyErr_Clear();
        pickle = PyImport_ImportModule("pickle");
    }

    /* Find attribute and return it. */
    if (pickle != NULL) {
        pickle_attr = PyObject_GetAttrString(pickle, attname);
        Py_DECREF(pickle);
    }

    return pickle_attr;
}

static PyObject *_PylibMC_Unpickle(const char *buff, size_t size) {
    PyObject *pickle_load;
    PyObject *retval = NULL;

    retval = NULL;
    pickle_load = _PylibMC_GetPickles("loads");
    if (pickle_load != NULL) {
        retval = PyObject_CallFunction(pickle_load, "s#", buff, size);
        Py_DECREF(pickle_load);
    }

    return retval;
}

static PyObject *_PylibMC_Pickle(PyObject *val) {
    PyObject *pickle_dump;
    PyObject *retval = NULL;

    pickle_dump = _PylibMC_GetPickles("dumps");
    if (pickle_dump != NULL) {
        retval = PyObject_CallFunction(pickle_dump, "Oi", val, -1);
        Py_DECREF(pickle_dump);
    }

    return retval;
}
/* }}} */

static int _PylibMC_CheckKey(PyObject *key) {
    if (key == NULL) {
        PyErr_SetString(PyExc_ValueError, "key must be given");
        return 0;
    } else if (!PyString_Check(key)) {
        PyErr_SetString(PyExc_TypeError, "key must be an instance of str");
        return 0;
    }

    return _PylibMC_CheckKeyStringAndSize(
            PyString_AS_STRING(key), PyString_GET_SIZE(key));
}

static int _PylibMC_CheckKeyStringAndSize(char *key, Py_ssize_t size) {
    /* libmemcached pads max_key_size with one byte for null termination */
    if (size >= MEMCACHED_MAX_KEY) {
        PyErr_Format(PyExc_ValueError, "key too long, max is %d",
                MEMCACHED_MAX_KEY - 1);
        return 0;
#ifdef NO_EMPTY_KEYS  /* I wish... */
    } else if (size == 0) {
        PyErr_Format(PyExc_ValueError, "key cannot be empty");
#endif
    }
    /* TODO Check key contents here. */

    return key != NULL;
}

static int _init_sasl(void) {
#if LIBMEMCACHED_WITH_SASL_SUPPORT
    int rc;

    /* sasl_client_init needs to be called once before using SASL, and
     * sasl_done after all SASL usage is done (so basically, once per process
     * lifetime). */
    rc = sasl_client_init(NULL);
    if (rc == SASL_NOMEM) {
        PyErr_NoMemory();
    } else if (rc == SASL_BADVERS) {
        PyErr_Format(PyExc_RuntimeError, "SASL: Mechanism version mismatch");
    } else if (rc == SASL_BADPARAM) {
        PyErr_Format(PyExc_RuntimeError, "SASL: Error in config file");
    } else if (rc == SASL_NOMECH) {
        PyErr_Format(PyExc_RuntimeError, "SASL: No mechanisms available");
    } else if (rc != SASL_OK) {
        PyErr_Format(PyExc_RuntimeError, "SASL: Unknown error (rc=%d)", rc);
    }

    if (rc != SASL_OK) {
        return false;
    }

    /* Terrible, terrible hack. Need to call sasl_done, but the Python/C API
     * doesn't provide a hook for when the module is unloaded, so register an
     * atexit handler. This is particularly problematic because
     * "At most 32 cleanup functions can be registered". */
    if (Py_AtExit(sasl_done)) {
        PyErr_Format(PyExc_RuntimeError, "Failed to register atexit handler");
        return false;
    }
#endif

    return true;
}

static int _check_libmemcached_version(void) {
    uint8_t maj, min;
    char *ver, *dot, *tmp;

    ver = dot = strndup(LIBMEMCACHED_VERSION_STRING, 8);
    while ((tmp = strrchr(ver, '.')) != NULL) {
        dot = tmp;
        *dot = 0;
    }

    maj = atoi(ver);
    min = atoi(dot + 1);

    if (maj == 0 && min < 32) {
        PyErr_Format(PyExc_RuntimeError,
            "pylibmc requires >= libmemcached 0.32, was compiled with %s",
            LIBMEMCACHED_VERSION_STRING);
        return false;
    } else {
        return true;
    }
}

static void _make_excs(PyObject *module) {
    PyObject *exc_objs;
    PylibMC_McErr *err;

    PylibMCExc_MemcachedError = PyErr_NewException(
            "_pylibmc.MemcachedError", NULL, NULL);

    exc_objs = PyList_New(0);
    PyList_Append(exc_objs,
        Py_BuildValue("sO", "Error", (PyObject *)PylibMCExc_MemcachedError));

    for (err = PylibMCExc_mc_errs; err->name != NULL; err++) {
        char excnam[64];
        snprintf(excnam, 64, "_pylibmc.%s", err->name);
        err->exc = PyErr_NewException(excnam, PylibMCExc_MemcachedError, NULL);
        PyObject_SetAttrString(err->exc, "retcode", PyInt_FromLong(err->rc));
        PyModule_AddObject(module, err->name, (PyObject *)err->exc);
        PyList_Append(exc_objs,
            Py_BuildValue("sO", err->name, (PyObject *)err->exc));
    }

    PyModule_AddObject(module, "MemcachedError",
                       (PyObject *)PylibMCExc_MemcachedError);
    PyModule_AddObject(module, "exceptions", exc_objs);
}

static void _make_behavior_consts(PyObject *mod) {
    PyObject *behavior_names;
    PylibMC_Behavior *b;
    char name[128];

    /* Add hasher and distribution constants. */
    for (b = PylibMC_hashers; b->name != NULL; b++) {
        sprintf(name, "hash_%s", b->name);
        PyModule_AddIntConstant(mod, name, b->flag);
    }

    for (b = PylibMC_distributions; b->name != NULL; b++) {
        sprintf(name, "distribution_%s", b->name);
        PyModule_AddIntConstant(mod, name, b->flag);
    }

    behavior_names = PyList_New(0);

    for (b = PylibMC_behaviors; b->name != NULL; b++) {
        PyList_Append(behavior_names, PyString_FromString(b->name));
    }

    PyModule_AddObject(mod, "all_behaviors", behavior_names);
}

static PyMethodDef PylibMC_functions[] = {
    {NULL, NULL, 0, NULL}
};

PyMODINIT_FUNC init_pylibmc(void) {
    PyObject *module;

    if (!_check_libmemcached_version())
        return;

    if (!_init_sasl())
        return;

    if (PyType_Ready(&PylibMC_ClientType) < 0) {
        return;
    }

    module = Py_InitModule3("_pylibmc", PylibMC_functions,
            "Hand-made wrapper for libmemcached.\n\
\n\
You should really use the Python wrapper around this library.\n\
\n\
    c = _pylibmc.client([(_pylibmc.server_type_tcp, 'localhost', 11211)])\n\
\n\
Three-tuples of (type, host, port) are used. If type is `server_type_unix`,\n\
no port should be given. libmemcached can parse strings as well::\n\
\n\
   c = _pylibmc.client('localhost')\n\
\n\
See libmemcached's memcached_servers_parse for more info on that. I'm told \n\
you can use UNIX domain sockets by specifying paths, and multiple servers \n\
by using comma-separation. Good luck with that.\n");
    if (module == NULL) {
        return;
    }

    _make_excs(module);

    PyModule_AddStringConstant(module, "__version__", PYLIBMC_VERSION);

    PyModule_ADD_REF(module, "client", (PyObject *)&PylibMC_ClientType);

    PyModule_AddStringConstant(module,
            "libmemcached_version", LIBMEMCACHED_VERSION_STRING);

#if LIBMEMCACHED_WITH_SASL_SUPPORT
    PyModule_ADD_REF(module, "support_sasl", Py_True);
#else
    PyModule_ADD_REF(module, "support_sasl", Py_False);
#endif

#ifdef USE_ZLIB
    PyModule_ADD_REF(module, "support_compression", Py_True);
#else
    PyModule_ADD_REF(module, "support_compression", Py_False);
#endif

    PyModule_AddIntConstant(module, "server_type_tcp", PYLIBMC_SERVER_TCP);
    PyModule_AddIntConstant(module, "server_type_udp", PYLIBMC_SERVER_UDP);
    PyModule_AddIntConstant(module, "server_type_unix", PYLIBMC_SERVER_UNIX);

    _make_behavior_consts(module);
}