Add support of the JSON in Kvrocks

[xiaobiaozhao]

As everyone knows, JSON is more generic data. And it has richer expressions for data structures, I think we can support the JSON data structures in kvrocks.

This is the official website of RedisJSON
https://redis.io/commands/json.arrappend/

I think kvrocks can use jsonjson's commands.

One way is to use cjson as our JSON library since cjson-lua is already available in kvrocks.
Another approach is to introduce a new JSON library, such as rapidjson, simdjson

The tair DB supports two json formats, JSONPath and JSONPointer

I think Kvrocks can also support both formats. Jsonpointer is simple, JSON path is complex.

[git-hulk]

I think we can support the RedisJSON API first. For choosing the JSON library candidates, I think we should list the metrics which we care like supported JSON path or not, performance, maturity and license, and so on...

@PragmaTwice and @ShooterIT also have some experience with this, to see if they have some comments on this topic.

[PragmaTwice]

I dislike the idea to use cjson, which is not a C++ json library and do not provide enough feature for implementing RedisJSON.

[git-hulk]

Totally agreed. We need to implement the entire JSON path features if use the cJSON.

[mapleFU]

The Json Part:

1. JSON is defined in RFC 7159
2. SQL Standard 2016 support JSON. It support storing JSON as string, and parse and reading using JsonPath. PostgreSQL have 2 Json Types: json (storing as text) and jsonb (self-defined json format), there differences can be seen here: https://www.postgresql.org/docs/current/datatype-json.html . To be short, jsonb may occupy more or less space, and has faster field visit. The bson, msgpack or other are similiar.
3. ClickHouse can using Parsing whole JSON using itself's library and SIMDJSON to streaming parse the record.

For our same kind productions:

• RedisJSON using rust to serde the JSON.
• For Alibaba Tail, it using doc to store it: https://help.aliyun.com/document_detail/145940.htm

Personally, we need to pick the library which are widely used, to prevent from library bugs.

[git-hulk]

@ShooterIT @PragmaTwice @mapleFU favor using the jsoncons, so maybe we can try if there is no further objection on this.

[zagzhang]

Has this pull request made any progress?

[git-hulk]

JSON commands have been supported since 2.7.0, please refer to: https://kvrocks.apache.org/docs/supported-commands#json-commands