Add getHashTag() to JedisClusterCRC16 for future use #728
Description
The redis cluster spec. specifically allows multi-key operation like MSET as long as the same hashtag is specified for all keys. Currently there is no MSET defined in JedisCluster (and other multi-key functions).
For future development CRC16 should be modified to allow the hashtag to be obtained. Using this, operations like MSET can be implemented with a check for consistent hashtag definitions on the keys and then pipe-lined as a single operation maintaining atomicity.
Here's a suggested implementation:
public class JedisClusterCRC16 {
public final static int polynomial = 0x1021; // Represents x^16+x^12+x^5+1
public static String getHashTag(String key) {
int s = key.indexOf("{");
if (s > -1) {
int e = key.indexOf("}", s + 1);
if (e > -1 && e != s + 1) {
key = key.substring(s + 1, e);
}
}
return key;
}
public static int getSlot(String key) {
return getCRC16(getHashTag(key)) % 16384;
}
private static int getCRC16(String key) {
int crc = 0x0000;
for (byte b : key.getBytes()) {
for (int i = 0; i < 8; i++) {
boolean bit = ((b >> (7 - i) & 1) == 1);
boolean c15 = ((crc >> 15 & 1) == 1);
crc <<= 1;
// If coefficient of bit and remainder polynomial = 1 xor crc
// with polynomial
if (c15 ^ bit)
crc ^= polynomial;
}
}
return crc &= 0xffff;
}
}