4\r\n" in order to specify that four bulk
write will follow. Then every bulk write is transmitted.
If the specified key does not exist instead of the number of elements in the
-list, the special value 'nil' is sent. Example:
+list, the special value -1 is sent as count. Example:
C: LRANGE nokey 0 1
-S: nil
+S: *-1
A client library API SHOULD return a nil object and not an empty list when this
-happens. This makes possible to distinguish between empty list and non existing ones.Single elements of a multi bulk reply may have -1 length, in order to signal that this elements are missing and not empty strings. This can happen with the SORT command when used with the GET pattern option when the specified key is missing. Example of a multi bulk reply containing an empty element:
-S: 3
-S: 3
+happens. This makes possible to distinguish between empty list and non existing ones.Single elements of a multi bulk reply may have -1 length, in order to signal that this elements are missing and not empty strings. This can happen with the SORT command when used with the GET pattern option when the specified key is missing. Example of a multi bulk reply containing an empty element:
+S: *3
+S: $3
S: foo
-S: -1
-S: 3
+S: $-1
+S: $3
S: bar
-
The second element is nul. The client library should return something like this:
+
The second element is nul. The client library should return something like this:
["foo",nil,"bar"]
-
Like bulk reply errors Multi-bulk reply errors are reported using a negative
-count. Example:
-C: LRANGE stringkey 0 1
-S: -38
-S: -ERR Requested element is not a string
-
The following commands reply with a multi-bulk reply: LRANGE, LINTER
Check the Bulk replies errors section for more information.As already seen a status code reply is in the form of a single line string
-terminated by "\r\n". For example:
+
As already seen a single line reply is in the form of a single line string
+starting with "+" terminated by "\r\n". For example:
+OK
-
and
--ERR no suck key
-
are two examples of status code replies. The first character of a status code reply is always "+" or "-".
The following commands reply with a status code reply:
-PING, SET, SELECT, SAVE, BGSAVE, SHUTDOWN, RENAME, LPUSH, RPUSH, LSET, LTRIMThis type of reply is just a CRLF terminated string representing an integer. For example "0\r\n", or "1000\r\n" are integer replies.
With commands like INCR or LASTSAVE using the integer reply to actually return a value there is no special meaning for the returned integer. It is just an incremental number for INCR, a UNIX time for LASTSAVE and so on.
Some commands like EXISTS will return 1 for true and 0 for false.
Other commands like SADD, SREM and SETNX will return 1 if the operation was actually done, 0 otherwise, and a negative value if the operation is invalid (for example SADD against a non-set value), accordingly to this table:
-
--1 no such key
--2 operation against the a key holding a value of the wrong type
--3 source and destiantion objects/dbs are the same
--4 argument out of range
-
-In all this cases it is mandatory that the client raises an error instead to pass the negative value to the caller. Please check the commands documentation for the exact behaviour.
The following commands will reply with an integer reply: SETNX, DEL, EXISTS, INCR, INCRBY, DECR, DECRBY, DBSIZE, LASTSAVE, RENAMENX, MOVE, LLEN, SADD, SREM, SISMEMBER, SCARD
The commands that will never return a negative integer (commands that can't fail) are: INCR, DECR, INCRBY, DECRBY, LASTSAVE, EXISTS, SETNX, DEL, DBSIZE.This replies are just single line strings terminated by CRLF. Only two commands reply in this way currently, RANDOMKEY and TYPE.A client can use the same connection in order to issue multiple commands.
+
The client library should return everything after the "+", that is, the string "OK" in the example.
The following commands reply with a status code reply:
+PING, SET, SELECT, SAVE, BGSAVE, SHUTDOWN, RENAME, LPUSH, RPUSH, LSET, LTRIMThis type of reply is just a CRLF terminated string representing an integer, prefixed by a ":" byte. For example ":0\r\n", or ":1000\r\n" are integer replies.
With commands like INCR or LASTSAVE using the integer reply to actually return a value there is no special meaning for the returned integer. It is just an incremental number for INCR, a UNIX time for LASTSAVE and so on.
Some commands like EXISTS will return 1 for true and 0 for false.
Other commands like SADD, SREM and SETNX will return 1 if the operation was actually done, 0 otherwise.
The following commands will reply with an integer reply: SETNX, DEL, EXISTS, INCR, INCRBY, DECR, DECRBY, DBSIZE, LASTSAVE, RENAMENX, MOVE, LLEN, SADD, SREM, SISMEMBER, SCARDA client can use the same connection in order to issue multiple commands.
Pipelining is supported so multiple commands can be sent with a single
write operation by the client, it is not needed to read the server reply
in order to issue the next command. All the replies can be read at the end.
Usually Redis server and client will have a very fast link so this is not
very important to support this feature in a client implementation, still
if an application needs to issue a very large number of commands in short
-time to use pipelining can be much faster.
+time to use pipelining can be much faster.
+