A fast json parser for go

Related tags

JSON go golang json ragel
Overview

rjson

godoc ci

rjson is a json parser that relies on Ragel-generated state machines for most parsing. rjson's api is minimal and focussed on efficient parsing.

Ragel state machines

This whole thing is built around a few Ragel-generated state machines. They are defined in .rl files, and the generated code is in .rl.go files. If you peek at the generated code, beware that it doesn't look like anything intended to be read by a human.

Read functions

rjson provides Read functions for simple json values (strings, numbers, booleans and null). They each take a data []byte argument and read the first json value in data. They return a p int value that is the offset of the first byte after the value they read. When used in a handler, this p should be returned as the handler's p.

Read functions return an error for any json type other than the type they are meant to read. This includes null. So if there is a value that could be either a string or null, be sure to use NextTokenType to check which one it is.

ReadString and ReadStringBytes take a buf []byte argument. ReadStringBytes returns the result appended to buf and ReadString uses it as a byte buffer when decoding strings to avoid memory allocations. buf may be nil in both cases.

Handlers

rjson uses handlers to parse complex json values (objects and arrays). The handler will implement either HandleArrayValue(data []byte) (p int, err error) or HandleObjectValue(fieldname, data []byte) (p int, err error). data is the document being parsed from the current position to the end of the document.

The handler has to return p as either 0, or the offset after the last byte of the value it handled. This is important as it is how rjson knows where to resume parsing the document. When the handler returns 0, rjson uses SkipValue to find the next offset, so it is best to write handlers that return the next offset and avoid an extra call to SkipValue.

When your handler returns an error, HandleArrayValues and HandleObjectValues will immediately return the same error. You can use this to stop parsing a document once you have found all values you are after.

See HandleObjectValues's example

Standard Library Compatibility

rjson endeavors to decode json to the same values as the encoding/json functions. In the source code, most of rjson's exported functions are followed by an unexported version that produces the same output using encoding/json instead of rjson. These are used to ensure compatibility.

The RuneError compatibility exception

When decoding strings, encoding/json will replace bytes with values over 127 that aren't part of a valid utf8 rune with utf8.RuneError. I don't think this is correct behavior, and I have not found any other go json parser that does this, so rjson keeps those bytes as-is when decoding strings.

If you need those RuneErrors, you can use StdLibCompatibleString, StdLibCompatibleSlice, and StdLibCompatibleMap.

Differential Fuzz Testing

rjson uses fuzz testing extensively to test compatibility with encoding/json. See fuzzers.go for the fuzz functions and testdata/fuzz/corpus for the increasingly unwieldy corpus.

What rjson doesn't do

  • drop in replacement for "encoding/json" - rjson doesn't aim to be a replacement for "encoding/json". It probably won't ever unmarshal json to a struct, and it definitely won't ever marshal json. It does one thing well, and that one thing is parsing json fast and with minimal memory allocations.

  • import "unsafe" - Not that there is necessarily anything wrong with using unsafe where it is called for. It's just that you are better off avoiding it where possible, and it is possible here.

  • return unchecked strings - Some json parsers use techniques like strings.IndexByte(data, '"') to skip to the end of a string and return the contents uninspected. This can be dangerous when dealing with json from untrusted sources. Those strings can contain control characters and other invalid json.

  • parse from an io.Reader - I would like to implement this in the future, but it's off the table for now.

  • keep a global resource pool - Some json packages have handy Borrow and Return functions that let you borrow resources and avoid new allocations. rjson leaves it up to the user to decide how to do resource pooling.

Performance principles and tricks

Handle each byte once

This is the main guiding principle of rjson performance. Do everything you can to avoid handling the same byte twice.

fp.ParseJSONFloatPrefix

fp.ParseJSONFloatPrefix is a rewrite of strconv.ParseFloat that deals in bytes instead of strings and eliminates everything not needed for parsing json numbers. This reduces the time to read numbers by about 60%. It's an internal package for now, but I encourage anybody who is parsing json numbers to consider copying this code or writing something similar.

Predict object and array size based on previous values

ReadObject and ReadArray can create a lot of nested maps and slices. It would be nice if we knew how big they would be ahead of time so we can make([]interface{}, 0, size), but we can't know that until we reach the end. In place of that, rjson keeps track of how big the values end up being and allocates values that are as big as the previous sibling value of the same type.

Always Be Benchmarking

Running benchmarks for every change keeps me from going too far down bad paths. Also, consistently benchmarking against other parsers shows me where rjson can be improved.

While I'm coding I frequently run benchdiff with script/benchdiff --benchtime 10ms --bench WhateverBenchmark to get a quick comparison with the previous commit. It takes just a couple of seconds to run, and it saves a lot of time down the road.

Benchmarks

Benchmarks are in ./benchmarks and run with script/compbench. Each package that is benchmarked has its own file that implements the various benchmarks.

JSON data

With the exception of github_repo.json, this is all taken from nativejson-benchmark

All tested JSON data are in UTF-8.

JSON file Size Description
canada.json source 2199KB Contour of Canada border in GeoJSON format. Contains a lot of real numbers.
citm_catalog.json source 1737KB A big benchmark file with indentation used in several Java JSON parser benchmarks.
twitter.json 632KB Search "一" (character of "one" in Japanese and Chinese) in Twitter public time line for gathering some tweets with CJK characters.
github_repo.json 6KB The golang/go repository from GitHub's API. curl https://api.github.com/repos/golang/go

Compared packages

The go community is fortunate to have multiple high-performance options for parsing JSON. The benchmarks include some better known packages. They don't all have the same features, so not all the compared packages are represented in every benchmark. There are also some packages with incorrect Valid() functions. Those are excluded until they are fixed.

Every package should be able to put their best foot forward in the benchmarks. I have tried to write the best code for each package in the benchmark. If anybody sees a way to improve the benchmarks for any package, please create an issue to let me know.

This import statement has all the players seen in the benchmarks below:

import (
encoding_json "encoding/json"

jsonparser "github.com/buger/jsonparser"
jsoniter "github.com/json-iterator/go"
gjson "github.com/tidwall/gjson"
fastjson "github.com/valyala/fastjson"
rjson "github.com/willabides/rjson"
goccyjson "github.com/goccy/go-json"
)

Benchmarks

GetRepoValues

GetRepoValues gets three values of different types from github_repo.json and writes them to a struct. The same as running json.Unmarshal with this struct:

type repoData struct {
Archived bool   `json:"archived"`
Forks    int64  `json:"forks"`
FullName string `json:"full_name"`
}

Valid

Valid runs checks whether json data is valid. It's the equivalent of json.Valid(data)

ReadObject

ReadObject decodes json data to a map[string]interface{}.

ReadFloat64

ReadFloat64 parses a json number and returns its value as a float64.

ReadInt64

ReadInt64 parses a json number and returns its value as an int64.

ReadString

ReadString decodes a json string and returns its value as a string.

ReadBool

ReadBool decodes a json true or false and returns the value.

Results

These are the results from running the benchmarks 10x and using benchstat to compare each package to rjson. You can run them yourself by running script/compbench.

encoding_json

name encoding_json (ns/op) rjson (ns/op) delta
GetRepoValues 38913.3 2056.6 -94.71%
Valid_canada 6484170 2206670 -65.97%
Valid_citm_catalog 5185540 1563420 -69.85%
Valid_github_repo 20420.8 5276.7 -74.16%
Valid_twitter 2160090 566341 -73.78%
ReadObject_canada 45105700 25741500 -42.93%
ReadObject_citm_catalog 17937000 11083500 -38.21%
ReadObject_github_repo 93517 32133.7 -65.64%
ReadObject_twitter 7811660 4160820 -46.74%
name encoding_json (B/op) rjson (B/op) delta
GetRepoValues 250 16 -93.60%
Valid_canada 140837 44592.4 -68.34%
Valid_citm_catalog 82338 23178.2 -71.85%
Valid_github_repo 1 0 -100.00%
Valid_twitter 12751.9 3207.3 -74.85%
ReadObject_canada 11695000 8433900 -27.88%
ReadObject_citm_catalog 5411520 5114650 -5.49%
ReadObject_github_repo 25698.7 17038.1 -33.70%
ReadObject_twitter 2194880 2690170 +22.57%

fastjson

name fastjson (ns/op) rjson (ns/op) delta
GetRepoValues 4693.56 2056.6 -56.18%
ReadFloat64_zero 27.3833 13.686 -50.02%
ReadFloat64_smallInt 27.99 16.733 -40.22%
ReadFloat64_negExp 40.5811 25.7811 -36.47%
ReadInt64_zero 27.284 11.0838 -59.38%
ReadInt64_small 27.883 13.504 -51.57%
ReadInt64_big_negative 83.9378 26.88 -67.98%
ReadString_short_ascii 58.306 32.86 -43.64%
ReadString_medium_ascii 635.23 1746.2 +174.89%
ReadString_medium 317.56 738.61 +132.59%
ReadBool 18.936 8.0014 -57.75%
name fastjson (B/op) rjson (B/op) delta
GetRepoValues 18 16 -11.11%
ReadFloat64_zero 0 0 ~
ReadFloat64_smallInt 0 0 ~
ReadFloat64_negExp 0 0 ~
ReadInt64_zero 0 0 ~
ReadInt64_small 0 0 ~
ReadInt64_big_negative 0 0 ~
ReadString_short_ascii 5 5 ~
ReadString_medium_ascii 896 896 ~
ReadString_medium 384 384 ~
ReadBool 0 0 ~

gjson

name gjson (ns/op) rjson (ns/op) delta
GetRepoValues 2385.78 2056.6 -13.80%
Valid_canada 2382180 2206670 -7.37%
Valid_citm_catalog 1610320 1563420 ~
Valid_github_repo 7454.2 5276.7 -29.21%
Valid_twitter 761576 566341 -25.64%
ReadObject_canada 57734500 25741500 -55.41%
ReadObject_citm_catalog 17878600 11083500 -38.01%
ReadObject_github_repo 36293.7 32133.7 -11.46%
ReadObject_twitter 6869820 4160820 -39.43%
ReadFloat64_zero 43.645 13.686 -68.64%
ReadFloat64_smallInt 52.223 16.733 -67.96%
ReadFloat64_negExp 85.052 25.7811 -69.69%
ReadInt64_zero 47.348 11.0838 -76.59%
ReadInt64_small 56.248 13.504 -75.99%
ReadInt64_big_negative 147.38 26.88 -81.76%
ReadString_short_ascii 91.589 32.86 -64.12%
ReadString_medium_ascii 3311.4 1746.2 -47.27%
ReadString_medium 1509.4 738.61 -51.07%
ReadBool 47.294 8.0014 -83.08%
name gjson (B/op) rjson (B/op) delta
GetRepoValues 200 16 -92.00%
Valid_canada 48199.9 44592.4 -7.48%
Valid_citm_catalog 25049.3 23178.2 -7.47%
Valid_github_repo 0 0 ~
Valid_twitter 4172.25 3207.3 -23.13%
ReadObject_canada 11677900 8433900 -27.78%
ReadObject_citm_catalog 6693100 5114650 -23.58%
ReadObject_github_repo 22680.3 17038.1 -24.88%
ReadObject_twitter 2429740 2690170 +10.72%
ReadFloat64_zero 0 0 ~
ReadFloat64_smallInt 2 0 -100.00%
ReadFloat64_negExp 16 0 -100.00%
ReadInt64_zero 0 0 ~
ReadInt64_small 2 0 -100.00%
ReadInt64_big_negative 24 0 -100.00%
ReadString_short_ascii 24 5 -79.17%
ReadString_medium_ascii 2960 896 -69.73%
ReadString_medium 1168 384 -67.12%
ReadBool 4 0 -100.00%

jsoniter

name jsoniter (ns/op) rjson (ns/op) delta
GetRepoValues 2447.4 2056.6 -15.97%
ReadObject_canada 62529400 25741500 -58.83%
ReadObject_citm_catalog 12246000 11083500 -9.49%
ReadObject_github_repo 50439.3 32133.7 -36.29%
ReadObject_twitter 5633380 4160820 -26.14%
ReadFloat64_zero 86.41 13.686 -84.16%
ReadFloat64_smallInt 98.254 16.733 -82.97%
ReadFloat64_negExp 131.6 25.7811 -80.41%
ReadInt64_zero 13.726 11.0838 -19.25%
ReadInt64_small 20.3125 13.504 -33.52%
ReadInt64_big_negative 45.837 26.88 -41.36%
ReadString_short_ascii 40.996 32.86 -19.85%
ReadString_medium_ascii 4331.1 1746.2 -59.68%
ReadString_medium 1988.7 738.61 -62.86%
ReadBool 23.4722 8.0014 -65.91%
name jsoniter (B/op) rjson (B/op) delta
GetRepoValues 360 16 -95.56%
ReadObject_canada 17315100 8433900 -51.29%
ReadObject_citm_catalog 5764010 5114650 -11.27%
ReadObject_github_repo 25469.9 17038.1 -33.10%
ReadObject_twitter 2454050 2690170 +9.62%
ReadFloat64_zero 16 0 -100.00%
ReadFloat64_smallInt 16 0 -100.00%
ReadFloat64_negExp 16 0 -100.00%
ReadInt64_zero 0 0 ~
ReadInt64_small 0 0 ~
ReadInt64_big_negative 0 0 ~
ReadString_short_ascii 5 5 ~
ReadString_medium_ascii 2936 896 -69.48%
ReadString_medium 1400 384 -72.57%
ReadBool 0 0 ~

jsonparser

name jsonparser (ns/op) rjson (ns/op) delta
GetRepoValues 2289 2056.6 -10.15%
ReadFloat64_zero 42.007 13.686 -67.42%
ReadFloat64_smallInt 44.6211 16.733 -62.50%
ReadFloat64_negExp 64.07 25.7811 -59.76%
ReadInt64_zero 24.623 11.0838 -54.99%
ReadInt64_small 26.106 13.504 -48.27%
ReadInt64_big_negative 55.663 26.88 -51.71%
ReadString_short_ascii 46.104 32.86 -28.73%
ReadString_medium_ascii 1960.9 1746.2 -10.95%
ReadString_medium 800.74 738.61 -7.76%
ReadBool 27.761 8.0014 -71.18%
name jsonparser (B/op) rjson (B/op) delta
GetRepoValues 16 16 ~
ReadFloat64_zero 0 0 ~
ReadFloat64_smallInt 0 0 ~
ReadFloat64_negExp 0 0 ~
ReadInt64_zero 0 0 ~
ReadInt64_small 0 0 ~
ReadInt64_big_negative 0 0 ~
ReadString_short_ascii 5 5 ~
ReadString_medium_ascii 1920 896 -53.33%
ReadString_medium 768 384 -50.00%
ReadBool 0 0 ~

goccyjson

name goccyjson (ns/op) rjson (ns/op) delta
GetRepoValues 6780.2 2056.6 -69.67%
ReadObject_canada 31277700 25741500 -17.70%
ReadObject_citm_catalog 13470600 11083500 -17.72%
ReadObject_github_repo 48540.7 32133.7 -33.80%
ReadObject_twitter 13315800 4160820 -68.75%
name goccyjson (B/op) rjson (B/op) delta
GetRepoValues 6152 16 -99.74%
ReadObject_canada 7767430 8433900 +8.58%
ReadObject_citm_catalog 7140020 5114650 -28.37%
ReadObject_github_repo 26588.8 17038.1 -35.92%
ReadObject_twitter 2798680 2690170 -3.88%

simdjson

name simdjson (ns/op) rjson (ns/op) delta
GetRepoValues 10905.3 2056.6 -81.14%
ReadObject_canada 33910400 25741500 -24.09%
ReadObject_citm_catalog 10772800 11083500 +2.88%
ReadObject_github_repo 42289.4 32133.7 -24.01%
ReadObject_twitter 4343340 4160820 -4.20%
name simdjson (B/op) rjson (B/op) delta
GetRepoValues 821 16 -98.05%
ReadObject_canada 16547900 8433900 -49.03%
ReadObject_citm_catalog 8735790 5114650 -41.45%
ReadObject_github_repo 23466.8 17038.1 -27.39%
ReadObject_twitter 2732290 2690170 -1.54%
Issues
  • Benchmark code is wrong

    Benchmark code is wrong

    The following benchmark code is wrong . https://github.com/WillAbides/rjson/blob/main/benchmarks/goccyjson.go#L24

    Must fix package from encoding/json to goccy/go-json and update result on README.md

    opened by goccy 3
  • faster skipping long numbers

    faster skipping long numbers

    This speeds up skipping long numbers at the expense of double reading the token after a number. This will slightly slow skipping objects and arrays with a lot of short number values.

    opened by WillAbides 0
  • It may be better to review the benchmark data

    It may be better to review the benchmark data

    When I read the benchmark code of json-iterator/go in the benchmark of BenchmarkGetRepoValues, I noticed that it uses the feature that can stop the decoding process in the middle. ( https://github.com/WillAbides/rjson/blob/main/benchmarks/jsoniter.go#L100-L102 )

    Of course, it is correct to use the specific feature to improve performance, but this optimization is highly dependent on the input data, so for example, if the key name of full_name is the end of the input data, benchmark results so different.

    Therefore, when measuring using the best case, it is better to consider the worst case as well, or to use a benchmark that does not depend on the input data.

    BEST

    If archived , full_name , forks are in the top of input data .

    $ go test -bench BenchmarkGetRepoValues/jsoniter
    goos: darwin
    goarch: amd64
    pkg: github.com/willabides/rjson/benchmarks
    BenchmarkGetRepoValues/jsoniter-16               5982798               192 ns/op              48 B/op          4 allocs/op
    PASS
    ok      github.com/willabides/rjson/benchmarks  1.655s
    

    WORST

    If full_name is in the end of input data .

    $ go test -bench BenchmarkGetRepoValues/jsoniter
    goos: darwin
    goarch: amd64
    pkg: github.com/willabides/rjson/benchmarks
    BenchmarkGetRepoValues/jsoniter-16                117582              9576 ns/op            1680 B/op        123 allocs/op
    PASS
    ok      github.com/willabides/rjson/benchmarks  2.846s
    
    opened by goccy 1
Owner
WillAbides
WillAbides
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