Handshakes with the server.
HELLO [protover
[AUTH username password]
[SETNAME clientname]]
Switch to a different protocol, optionally authenticating and setting the connection’s name, or provide a contextual client report.
Valkey supports two protocols: RESP2 and RESP3. RESP3 has certain
advantages since when the connection is in this mode, Valkey 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.
Valkey 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. The availability_zone field
only shows up when it is set in the configs, see
availability-zone config for more details, added in Valkey
8.1.
When called without any arguments 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)
15) "availability_zone"
16) "us-east-1"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" => "7.2.4"
3# "proto" => (integer) 3
4# "id" => (integer) 10
5# "mode" => "standalone"
6# "role" => "master"
7# "modules" => (empty array)
8# "availability_zone" => "us-east-1"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 calling AUTH before HELLO
unnecessary when setting up a new connection. Note that the
username can be set to “default” to authenticate against a
server that does not use ACLs, but rather the simpler
requirepass mechanism.SETNAME <clientname>: this is the equivalent of
calling CLIENT SETNAME.Map reply: a list of server properties.
Simple error
reply: if the protover requested does not exist.
O(1)
@connection @fast
availability_zone field is added to the
response if the availability-zone config is set.protover made optional; when called without
arguments the command reports the current connection’s context.AUTH, CLIENT, CLIENT CACHING, CLIENT CAPA, CLIENT GETNAME, CLIENT GETREDIR, CLIENT HELP, CLIENT ID, CLIENT IMPORT-SOURCE, CLIENT INFO, CLIENT KILL, CLIENT LIST, CLIENT NO-EVICT, CLIENT NO-TOUCH, CLIENT PAUSE, CLIENT REPLY, CLIENT SETINFO, CLIENT SETNAME, CLIENT TRACKING, CLIENT TRACKINGINFO, CLIENT UNBLOCK, CLIENT UNPAUSE, ECHO, PING, QUIT, RESET, SELECT.