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HELLO [protover [AUTH username password] [SETNAME clientname]]

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.

Dragonfly supports two protocols: RESP2 and RESP3.

Connections start in RESP2 mode, so clients implementing RESP2 do not need to updated or changed.

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 reply looks like this:

dragonfly> HELLO
1) "server"
2) "redis"
3) "version"
4) "6.2.11"
5) "dfly_version"
6) "df-dev"
7) "proto"
8) (integer) 2
9) "id"
10) (integer) 1
11) "mode"
12) "standalone"
13) "role"
14) "master"

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:

dragonfly> HELLO 3
1# "server" => "redis"
2# "version" => "6.2.11"
3# "dfly_version" => "df-dev"
4# "proto" => (integer) 3
5# "id" => (integer) 1
6# "mode" => "standalone"
7# "role" => "master"

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 authenticates 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 default username is default as Dragonfly has built in support for ACLs. SETNAME <clientname>: this is the equivalent of calling CLIENT SETNAME.


Array reply: a list of server properties. The reply is a map instead of an array when RESP3 is selected. The command returns an error if the protover requested does not exist.