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. 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)
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)
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.