Redigo multi requests

Question

I have previously been using this:

data, err := redis.Bytes(c.Do("GET", key))

to make sure that data returned is a slice of bytes.

However, I now need to add an extra command to the Redis request so I have something like this:

c.Send("MULTI")
c.Send("GET", key)
c.Send("EXPIRE", key)
r, err := c.Do("EXEC")

but now I can't seem to make the GET command return a slice of bytes. I've tried adding redis.Bytes like below but no luck.

c.Send("MULTI")
redis.Bytes(c.Send("GET", key))
c.Send("EXPIRE", key)
r, err := c.Do("EXEC")

Answer 1

MULTI is used to send several commands in an atomic way to Redis, by creating a transaction. This is not a pipeline at all.

None of the commands will be actually executed before the EXEC call so it is impossible to obtain the value when you call GET from within a transaction.

From the docs:

When a Redis connection is in the context of a MULTI request, all commands will reply with the string QUEUED (sent as a Status Reply from the point of view of the Redis protocol). A queued command is simply scheduled for execution when EXEC is called.

In redigo pipelining is done in a different way:

http://godoc.org/github.com/garyburd/redigo/redis#hdr-Pipelining

What you want to do is something like this (untested):

c.Send("GET", key)
c.Send("EXPIRE", key)
c.Flush()
v := redis.Bytes(c.Receive()) // reply from GET
_, err = c.Receive() // reply from EXPIRE

Answer 2

In redis, the EXEC command returns an array containing the results of all the commands in the transaction.

redigo provides a Values function, which converts an array command reply to a []interface{}.

c.Send("MULTI")
c.Send("GET", key)
c.Send("EXPIRE", key)
r, err := redis.Values(c.Do("EXEC"))

r[0] now has the reply from your GET command as a interface{}, so you'll need to do a type assertion to get the slice of bytes you're expecting:

data := r[0].([]byte)

References

• func Values: https://godoc.org/github.com/garyburd/redigo/redis#Values
• Type assertions: https://golang.org/ref/spec#Type_assertions