Max nesting level for json parser

[bazzilio]

Is your feature request related to a problem? Please describe.
I want to have option for the json parser plugin to limit nesting level for the parsing.
My developers send huge metadata json, after parsing it "eats" elasticsearch fields.

curl --progress-bar "http://127.0.0.1:9200/index-logs1/_field_caps?fields=*" | jq '.fields'  | grep -E '^  "' 2>/dev/null | grep metadata | awk -F. '{print NF}' | sort -n | wc -l 
733

curl --progress-bar "http://127.0.0.1:9200/index-logs1/_field_caps?fields=*" | jq '.fields'  | grep -E '^  "' 2>/dev/null | grep context | awk -F. '{print NF}' | sort -n | wc -l 
218

But if i could limit nesting level for parsing, it would dramatically decreased fields count:

curl --progress-bar "http://127.0.0.1:9200/index-logs1/_field_caps?fields=*" | jq '.fields'  | grep -E '^  "' 2>/dev/null | grep metadata | awk -F. 'NF>5 {print NF}' | sort -n | wc -l 
101

curl --progress-bar "http://127.0.0.1:9200/index-logs1/_field_caps?fields=*" | jq '.fields'  | grep -E '^  "' 2>/dev/null | grep context | awk -F. 'NF>5 {print NF}' | sort -n | wc -l 
25

Describe the solution you'd like
Set parameter to json parser section - max_nesting(int)
So the parser would leave unparsed json after the nesting is reacher.

Describe alternatives you've considered

Additional context
As i can see, parameter support with main json ruby libraries:

• oj
• yajl
• json

[bazzilio]

One more question:
is there a way to change DEFAULT_OJ_OPTIONS variable ?
If i correct understang login in sources - looks like oj is the default parser.
But as i see, for parse_io method fluentd uses yajl, so i am confused - which parser is using by default.

[ashie]

is there a way to change DEFAULT_OJ_OPTIONS variable ?

It seems there is no way to do it (pull request is welcome 😄)

If i correct understang login in sources - looks like oj is the default parser.
But as i see, for parse_io method fluentd uses yajl, so i am confused - which parser is using by default.

It seems that oj is optional, it ensures to use oj if it's available but not required mandatory.
On the other hand yajl is madatory required. If oj isn't installed, fall back to yajl.

fluentd/fluentd.gemspec

Line 23 in 6a2852a

gem.add_runtime_dependency("yajl-ruby", ["~> 1.0"])

fluentd/fluentd.gemspec

Line 52 in 6a2852a

gem.add_development_dependency("oj", [">= 2.14", "< 4"])

fluentd/lib/fluent/plugin/parser_json.rb

Lines 61 to 71 in 6a2852a

	rescue LoadError => ex
	name = :yajl
	if log
	if /\boj\z/ =~ ex.message
	log.info "Oj is not installed, and failing back to Yajl for json parser"
	else
	log.warn ex.message
	end
	end
	retry
	end

In addition, there is the following description about yajl in the document of this plugin:

yajl: Mainly for stream parsing

[ashie]

It seems that oj is optional, it ensures to use oj if it's installed but not required mandatory.
On the other hand yajl is madatory required. If oj isn't installed, fall back to yajl.

However, it surely confusing. Because it's not documented, users can't understand such behavior.
We should update the document: https://github.com/fluent/fluentd-docs-gitbook/blob/1.0/parser/json.md

[ashie]

We should update the document: https://github.com/fluent/fluentd-docs-gitbook/blob/1.0/parser/json.md

fluent/fluentd-docs-gitbook#298

[ashie]

Fixed by #3315
You can use FLUENT_OJ_OPTION_MAX_NESTING for it.

[ashie]

Now I've noticed that Oj.default_options doesn't accept :max_nesting: https://www.rubydoc.info/github/ohler55/oj/Oj.default_options

It's reported at https://app.slack.com/client/T0CSKNZLK/C0CTT63EE/thread/C0CTT63EE-1631532462.067500

We should consider other way to apply it.

[vishalmamidi1]

Does FLUENT_OJ_OPTION_MAX_NESTING still doesn't work?

[ashie]

Does FLUENT_OJ_OPTION_MAX_NESTING still doesn't work?

Yes, it doesn't work. Because now I notice that Oj.default_options doesn't support it, I'll remove it.
Instead, I'm considering to add max_nesting parameter to parser_json.

[ashie]

The implementation of Oj:

• https://github.com/ohler55/oj/blob/e2c0fbde9cf13e149ae6b16d0e83ce23f47bb256/ext/oj/oj.c#L171-L233
• https://github.com/ohler55/oj/blob/e2c0fbde9cf13e149ae6b16d0e83ce23f47bb256/ext/oj/oj.c#L607-L955

max_nesting isn't supported by Oj.default_options.