XINFO GROUPS will crash

[Sola1Go]

Unable to parse XINFO
XINFO method is not supported yet, and some difficulties have been encountered in parsing it for me.

auto res = redis->command<std::vector<std::vector<OptionalStringPair>>>("xinfo", "groups", "group_name");

I got: terminate called after throwing an instance of 'sw::redis::ProtoError'
what(): Expect ARRAY reply

auto res = redis->command<std::vector<std::vector<OptionalString>>>("xinfo", "groups", "group_name");

I got: terminate called after throwing an instance of 'sw::redis::ProtoError'
what(): Expect STRING reply
And Expect STRING reply means that the type indicated in redis.command<> is expected a string instead of the correct return is expected to be string?

Environment:

• OS: NixOS
• Compiler: clang 11.1.0
• hiredis version: 1.0.0 master
• redis-plus-plus version: 1.3.1 master

By the way
Is there a better way to judge whether a group/consumer exists?
Regards

[sewenew]

XINFO returns an array reply which can be expressed as an array of map. However the value part of the map might be string or integer.

If you are using C++17, you can use std::variant as the type of the value part (the recommended way):

using XInfoRes = std::vector<std::unordered_map<std::string, std::variant<long long, std::string>>>;

auto res = redis->command<XInfoRes>("xinfo", "groups", "group_name");

You can check this for detail.

However, if you are using an older c++ standard, you have to define XInfoRes as an array of tuple that exactly matches the returned result. You can check this for example.

Or, you can make it return a std::unique_ptr<redisReply, sw::redis::ReplyDeleter>, and parse it manually:

auto r = redis.command("xinfo", "groups", "group_name");
// parse *r manually.

Regards

[Sola1Go]

thx~ 😆

[Sola1Go]

@sewenew
Starting with Redis version 7.0.0, returns of the command XINFO GROUPS have been enhanced with entries entries-read and lag.

These two keys are certain to be present in returns, but their values might be NULL.

// code:
using XInfoRes = std::vector<std::unordered_map<std::string, std::variant<long long, std::string>>>;

auto res = redis->command<XInfoRes>("xinfo", "groups", "group_name");

// crash:
// terminate called after throwing an instance of 'sw::redis::ParseError'
// what():  expect STRING or STATUS or VERB or BIGNUM reply, but got NULL reply

This is the document for XINFO GROUPS.

Regards

[sewenew]

If the value of entries-read and lag might be null, you can add optional<long long> to the std::variant definition:

using XInfoRes = std::vector<std::unordered_map<std::string, std::variant<long long, std::string, std::optional<long long>>>>;

You can try the above code, and if you still get problem, feel free to let me know.

Regards

[Sola1Go]

thx again ~
Regards