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.)
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
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 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, RESET, SELECT.