Variable-length pipeline response

[cssivision]

Cargo.toml

redis = "0.16"

current API allow us to use pipeline

let (k1, k2) : (i32, i32) = redis::pipe()
    .cmd("zcard").arg("key_1")
    .cmd("zcard").arg("key_2").query(&con).unwrap();

but sometimes we don't know the length of a pipeline's response.

for example, we have x zcard command, we don't know the explicit value of x.

I try to write code like this:

let result: Vec<Option<isize>> = redis::pipe()
    .cmd("zcard").arg("key_1")
    .cmd("zcard").arg("key_2")
    .cmd("zcard").arg("key_3")
    .cmd("zcard").arg("key_4")
    .cmd("zcard").arg("key_5")
    .cmd("zcard").arg("key_6")
    .......
    .cmd("zcard").arg("key_x").query(&con).unwrap();

most time, it works fine, but the length of response not equal to the length of pipeline commands occasionally.

I guess that, current API don't support this usage?

any idea to fix this problem?

[weihanglo]

FromRedisValue is implmented for Vec as following:
https://github.com/mitsuhiko/redis-rs/blob/4d8501b8a9fac6763afdafccb8dc1f80f8cbb739/src/types.rs#L909-L917

I guess some of the responses cannot deserialize to Option<isize> and then be filtered out. Could you please modify the type to Vec<redis::Value> and inspect lengths of commands and result again? 🙇🏽‍♂️

[weihanglo]

BTW, just incidentally spotted a counter-intuitive behavior for redis::pipe (to me). Supposed sending pipeline commands via redis-cli would get array of all command responses no matter failed or not, as below:

$  echo -e 'zcard key_1\nzcard key_2\nzcard key_3' | redis-cli
(error) WRONGTYPE Operation against a key holding the wrong kind of value
(error) WRONGTYPE Operation against a key holding the wrong kind of value
(integer) 0

These behavior also matches what transaction in redis-cli does:

127.0.0.1:6379> MULTI
OK
127.0.0.1:6379> ZCARD key_1
QUEUED
127.0.0.1:6379> ZCARD key_2
QUEUED
127.0.0.1:6379> ZCARD key_3
QUEUED
127.0.0.1:6379> EXEC
1) (error) WRONGTYPE Operation against a key holding the wrong kind of value
2) (error) WRONGTYPE Operation against a key holding the wrong kind of value
3) (integer) 0

However, all of the req_packed_commands implementations return only ONE Err if there is one. Perhaps returning an Vec<RedisResult> is more appropriate when pipelining.

https://github.com/mitsuhiko/redis-rs/blob/1e12518573d00ceed85a23c6574411098e0c3fce/src/connection.rs#L793-L798

Just FYI. Not sure did you also encounter the same problem.

[nihohit]

@cssivision is this issue still present? can you provide sample code to recreate it?