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'rget' - range query based on keys
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Command Specification
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rget <start key> <end key> <left openness flag> <right openness flag> <max items>\r\n

- <start key> where the query starts.
- <end key>   where the query ends.
- <left openness flag> indicates the openness of left side, 0 means the result includes <start key>, while 1 means not.
- <right openness flag> indicates the openness of right side, 0 means the result includes <end key>, while 1 means not.
- <max items> how many items at most return, max is 100.

After this command, the client expects zero or more items, each of
which is received as a text line followed by a data block. After all
the items have been transmitted, the server sends the string

"END\r\n"

to indicate the end of response.

Each item sent by the server looks like this:

VALUE <key> <flags> <bytes>\r\n
<data block>\r\n

- <key> is the key for the item being sent

- <flags> is the flags value set by the storage command

- <bytes> is the length of the data block to follow, *not* including
  its delimiting \r\n

- <data block> is the data for this item.

Notice: all keys in MemcacheDB is sorted alphabetically, so is the return of query result.


Sample Code 
============

Notice: Here we use patched libmemcached, please see: http://memcachedb.googlecode.com/svn/clients/

#include <libmemcached/memcached.h>
/* other includes.. */

int main(int argc, char *argv[]){
    memcached_st *memc;
    memcached_server_st *servers;
    memcached_return rc;

    char *hostname[] = {"127.0.0.1"};
    unsigned int port[] = {21201};
    
    char key[MEMCACHED_MAX_KEY];
    char value[1024];

    char return_key[MEMCACHED_MAX_KEY];
    char *return_value;
    size_t return_key_length;
    size_t return_value_length;
    uint32_t flags;

    memc = memcached_create(NULL);
    servers = memcached_server_list_append(NULL, hostname[0], port[0], &rc);
    if (MEMCACHED_SUCCESS != rc){
        /* error */
    }
    rc = memcached_server_push(memc, servers);
    if (MEMCACHED_SUCCESS != rc){
       /* error */
    }

	/* mget-like api */
	rc= memcached_rget(memc, "0", 1, "z", 1, 0, 0, 4);
	assert(rc == MEMCACHED_SUCCESS);

    while ((return_value= memcached_fetch(memc, return_key, &return_key_length, 
                                          &return_value_length, &flags, &rc)))
    {
        assert(rc == MEMCACHED_SUCCESS);
        memcpy(key, return_key, return_key_length);
        key[return_key_length] = '\0';
        memcpy(value, return_value, return_value_length);
        value[return_value_length] = '\0';
        /* other things */
        free(return_value);
    }

    memcached_server_list_free(servers);
    memcached_free(memc);
    exit(EXIT_SUCCESS);
}