HELLO
HELLO [protover [AUTH username password] [SETNAME clientname]]
- Available since:
- 6.0.0
- Time complexity:
- O(1)
- ACL categories:
-
@fast
,@connection
,
Switch to a different protocol, optionally authenticating and setting the connection's name, or provide a contextual client report.
Redis version 6 and above supports two protocols: the old protocol, RESP2, and
a new one introduced with Redis 6, RESP3. RESP3 has certain advantages since
when the connection is in this mode, Redis is able to reply with more semantical
replies: for instance, HGETALL
will return a map type, so a client library
implementation no longer requires to know in advance to translate the array into
a hash before returning it to the caller. For a full coverage of RESP3, please
check the RESP3 specification.
In Redis 6 connections start in RESP2 mode, so clients implementing RESP2 do not need to updated or changed. There are no short term plans to drop support for RESP2, although future version may default to RESP3.
HELLO
always replies with a list of current server and connection properties,
such as: versions, modules loaded, client ID, replication role and so forth.
When called without any arguments in Redis 6.2 and its default use of RESP2
protocol, the reply looks like this:
> HELLO
1) "server"
2) "redis"
3) "version"
4) "255.255.255"
5) "proto"
6) (integer) 2
7) "id"
8) (integer) 5
9) "mode"
10) "standalone"
11) "role"
12) "master"
13) "modules"
14) (empty array)
Clients that want to handshake using the RESP3 mode need to call the HELLO
command and specify the value "3" as the protover
argument, like so:
> HELLO 3
1# "server" => "redis"
2# "version" => "6.0.0"
3# "proto" => (integer) 3
4# "id" => (integer) 10
5# "mode" => "standalone"
6# "role" => "master"
7# "modules" => (empty array)
Because HELLO
replies with useful information, and given that protover
is
optional or can be set to "2", client library authors may consider using this
command instead of the canonical PING
when setting up the connection.
When called with the optional protover
argument, this command switches the
protocol to the specified version and also accepts the following options:
AUTH <username> <password>
: directly authenticate the connection in addition to switching to the specified protocol version. This makes callingAUTH
beforeHELLO
unnecessary when setting up a new connection. Note that theusername
can be set to "default" to authenticate against a server that does not use ACLs, but rather the simplerrequirepass
mechanism of Redis prior to version 6.SETNAME <clientname>
: this is the equivalent of callingCLIENT SETNAME
.
RESP2/RESP3 Reply
Map reply: a list of server properties. Simple error reply: if theprotover
requested does not exist.
History
- Starting with Redis version 6.2.0:
protover
made optional; when called without arguments the command reports the current connection's context.