Fix JSON parser handling for certain objects (#7162)

This PR also adds some comments and simplifies
the code. Primary handling is done to ensure
that we make sure to honor cached buffer.

Added unit tests as well

Fixes #7141

vendor/github.com/bcicen/jstream/README.md

@@ -0,0 +1,93 @@
+<p align="center"><img width="350px" src="jstream.png" alt="jstream"/></p>
+
+#
+
+[![GoDoc](https://godoc.org/github.com/bcicen/jstream?status.svg)](https://godoc.org/github.com/bcicen/jstream)
+
+
+`jstream` is a streaming JSON parser and value extraction library for Go.
+
+Unlike most JSON parsers, `jstream` is document position- and depth-aware -- this enables the extraction of values at a specified depth, eliminating the overhead of allocating encompassing arrays or objects; e.g:
+
+Using the below example document:
+<img width="85%" src="https://bradley.codes/static/img/jstream-levels.gif" alt="jstream"/>
+
+we can choose to extract and act only the objects within the top-level array:
+```go
+f, _ := os.Open("input.json")
+decoder := jstream.NewDecoder(f, 1) // extract JSON values at a depth level of 1
+for mv := range decoder.Stream() {
+  fmt.Printf("%v\n ", mv.Value)
+}
+```
+
+output:
+```
+map[desc:RGB colors:[red green blue]]
+map[desc:CMYK colors:[cyan magenta yellow black]]
+```
+
+likewise, increasing depth level to `3` yields:
+```
+red
+green
+blue
+cyan
+magenta
+yellow
+black
+```
+
+optionally, kev:value pairs can be emitted as an individual struct:
+```go
+decoder := jstream.NewDecoder(f, 2).EmitKV() // enable KV streaming at a depth level of 2
+```
+
+```
+jstream.KV{desc RGB}
+jstream.KV{colors [red green blue]}
+jstream.KV{desc CMYK}
+jstream.KV{colors [cyan magenta yellow black]}
+```
+
+## Installing 
+
+```bash
+go get github.com/bcicen/jstream
+```
+
+## Commandline
+
+`jstream` comes with a cli tool for quick viewing of parsed values from JSON input:
+
+```bash
+cat input.json | jstream -v -d 1
+depth	start	end	type   | value
+
+1	004	069	object | {"colors":["red","green","blue"],"desc":"RGB"}
+1	073	153	object | {"colors":["cyan","magenta","yellow","black"],"desc":"CMYK"}
+```
+
+### Options
+
+Opt | Description
+--- | ---
+-d \<n\> | emit values at depth n. if n < 0, all values will be emitted
+-v | output depth and offset details for each value
+-h | display help dialog
+
+## Benchmarks
+
+Obligatory benchmarks performed on files with arrays of objects, where the decoded objects are to be extracted.
+
+Two file sizes are used -- regular (1.6mb, 1000 objects) and large (128mb, 100000 objects)
+
+input size | lib | MB/s | Allocated
+--- | --- | --- | ---
+regular | standard | 97 | 3.6MB
+regular | jstream | 175 | 2.1MB
+large | standard | 92 | 305MB
+large | jstream | 404 | 69MB
+
+In a real world scenario, including initialization and reader overhead from varying blob sizes, performance can be expected as below:
+<img src="https://bradley.codes/static/img/bench.svg" alt="jstream"/>