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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:

we can choose to extract and act only the objects within the top-level array:

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:

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

go get github.com/bcicen/jstream

Commandline

jstream comes with a cli tool for quick viewing of parsed values from JSON input:

jstream -d 1 < input.json

{"colors":["red","green","blue"],"desc":"RGB"}
{"colors":["cyan","magenta","yellow","black"],"desc":"CMYK"}

detailed output with -v option:

cat input.json | jstream -v -d -1
depth    start    end    type   | value
2    018    023    string | "RGB"
3    041    046    string | "red"
3    048    055    string | "green"
3    057    063    string | "blue"
2    039    065    array  | ["red","green","blue"]
1    004    069    object | {"colors":["red","green","blue"],"desc":"RGB"}
2    087    093    string | "CMYK"
3    111    117    string | "cyan"
3    119    128    string | "magenta"
3    130    138    string | "yellow"
3    140    147    string | "black"
2    109    149    array  | ["cyan","magenta","yellow","black"]
1    073    153    object | {"colors":["cyan","magenta","yellow","black"],"desc":"CMYK"}
0    000    155    array  | [{"colors":["red","green","blue"],"desc":"RGB"},{"colors":["cyan","magenta","yellow","black"],"desc":"CMYK"}]

Options

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)

In a real world scenario, including initialization and reader overhead from varying blob sizes, performance can be expected as below: