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213 lines
13 KiB
Markdown
213 lines
13 KiB
Markdown
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[](https://travis-ci.org/valyala/fastjson)
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[](http://godoc.org/github.com/valyala/fastjson)
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[](https://goreportcard.com/report/github.com/valyala/fastjson)
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[](https://codecov.io/gh/valyala/fastjson)
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# fastjson - fast JSON parser and validator for Go
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## Features
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* Fast. As usual, up to 15x faster than the standard [encoding/json](https://golang.org/pkg/encoding/json/).
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See [benchmarks](#benchmarks).
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* Parses arbitrary JSON without schema, reflection, struct magic and code generation
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contrary to [easyjson](https://github.com/mailru/easyjson).
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* Provides simple [API](http://godoc.org/github.com/valyala/fastjson).
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* Outperforms [jsonparser](https://github.com/buger/jsonparser) and [gjson](https://github.com/tidwall/gjson)
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when accessing multiple unrelated fields, since `fastjson` parses the input JSON only once.
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* Validates the parsed JSON unlike [jsonparser](https://github.com/buger/jsonparser)
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and [gjson](https://github.com/tidwall/gjson).
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* May quickly extract a part of the original JSON with `Value.Get(...).MarshalTo` and modify it
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with [Del](https://godoc.org/github.com/valyala/fastjson#Value.Del)
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and [Set](https://godoc.org/github.com/valyala/fastjson#Value.Set) functions.
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* May parse array containing values with distinct types (aka non-homogenous types).
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For instance, `fastjson` easily parses the following JSON array `[123, "foo", [456], {"k": "v"}, null]`.
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* `fastjson` preserves the original order of object items when calling
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[Object.Visit](https://godoc.org/github.com/valyala/fastjson#Object.Visit).
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## Known limitations
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* Requies extra care to work with - references to certain objects recursively
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returned by [Parser](https://godoc.org/github.com/valyala/fastjson#Parser)
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must be released before the next call to [Parse](https://godoc.org/github.com/valyala/fastjson#Parser.Parse).
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Otherwise the program may work improperly. The same applies to objects returned by [Arena](https://godoc.org/github.com/valyala/fastjson#Arena).
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Adhere recommendations from [docs](https://godoc.org/github.com/valyala/fastjson).
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* Cannot parse JSON from `io.Reader`. There is [Scanner](https://godoc.org/github.com/valyala/fastjson#Scanner)
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for parsing stream of JSON values from a string.
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## Usage
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One-liner accessing a single field:
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```go
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s := []byte(`{"foo": [123, "bar"]}`)
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fmt.Printf("foo.0=%d\n", fastjson.GetInt(s, "foo", "0"))
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// Output:
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// foo.0=123
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```
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Accessing multiple fields with error handling:
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```go
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var p fastjson.Parser
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v, err := p.Parse(`{
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"str": "bar",
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"int": 123,
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"float": 1.23,
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"bool": true,
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"arr": [1, "foo", {}]
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}`)
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if err != nil {
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log.Fatal(err)
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}
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fmt.Printf("foo=%s\n", v.GetStringBytes("str"))
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fmt.Printf("int=%d\n", v.GetInt("int"))
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fmt.Printf("float=%f\n", v.GetFloat64("float"))
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fmt.Printf("bool=%v\n", v.GetBool("bool"))
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fmt.Printf("arr.1=%s\n", v.GetStringBytes("arr", "1"))
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// Output:
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// foo=bar
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// int=123
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// float=1.230000
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// bool=true
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// arr.1=foo
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```
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See also [examples](https://godoc.org/github.com/valyala/fastjson#pkg-examples).
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## Security
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* `fastjson` shouldn't crash or panic when parsing input strings specially crafted
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by an attacker. It must return error on invalid input JSON.
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* `fastjson` requires up to `sizeof(Value) * len(inputJSON)` bytes of memory
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for parsing `inputJSON` string. Limit the maximum size of the `inputJSON`
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before parsing it in order to limit the maximum memory usage.
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## Performance optimization tips
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* Re-use [Parser](https://godoc.org/github.com/valyala/fastjson#Parser) and [Scanner](https://godoc.org/github.com/valyala/fastjson#Scanner)
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for parsing many JSONs. This reduces memory allocations overhead.
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[ParserPool](https://godoc.org/github.com/valyala/fastjson#ParserPool) may be useful in this case.
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* Prefer calling `Value.Get*` on the value returned from [Parser](https://godoc.org/github.com/valyala/fastjson#Parser)
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instead of calling `Get*` one-liners when multiple fields
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must be obtained from JSON, since each `Get*` one-liner re-parses
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the input JSON again.
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* Prefer calling once [Value.Get](https://godoc.org/github.com/valyala/fastjson#Value.Get)
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for common prefix paths and then calling `Value.Get*` on the returned value
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for distinct suffix paths.
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* Prefer iterating over array returned from [Value.GetArray](https://godoc.org/github.com/valyala/fastjson#Object.Visit)
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with a range loop instead of calling `Value.Get*` for each array item.
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## Benchmarks
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Go 1.12 has been used for benchmarking.
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Legend:
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* `small` - parse [small.json](testdata/small.json) (190 bytes).
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* `medium` - parse [medium.json](testdata/medium.json) (2.3KB).
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* `large` - parse [large.json](testdata/large.json) (28KB).
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* `canada` - parse [canada.json](testdata/canada.json) (2.2MB).
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* `citm` - parse [citm_catalog.json](testdata/citm_catalog.json) (1.7MB).
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* `twitter` - parse [twitter.json](testdata/twitter.json) (617KB).
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* `stdjson-map` - parse into a `map[string]interface{}` using `encoding/json`.
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* `stdjson-struct` - parse into a struct containing
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a subset of fields of the parsed JSON, using `encoding/json`.
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* `stdjson-empty-struct` - parse into an empty struct using `encoding/json`.
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This is the fastest possible solution for `encoding/json`, may be used
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for json validation. See also benchmark results for json validation.
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* `fastjson` - parse using `fastjson` without fields access.
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* `fastjson-get` - parse using `fastjson` with fields access similar to `stdjson-struct`.
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```
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$ GOMAXPROCS=1 go test github.com/valyala/fastjson -bench='Parse$'
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goos: linux
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goarch: amd64
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pkg: github.com/valyala/fastjson
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BenchmarkParse/small/stdjson-map 200000 7305 ns/op 26.01 MB/s 960 B/op 51 allocs/op
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BenchmarkParse/small/stdjson-struct 500000 3431 ns/op 55.37 MB/s 224 B/op 4 allocs/op
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BenchmarkParse/small/stdjson-empty-struct 500000 2273 ns/op 83.58 MB/s 168 B/op 2 allocs/op
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BenchmarkParse/small/fastjson 5000000 347 ns/op 547.53 MB/s 0 B/op 0 allocs/op
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BenchmarkParse/small/fastjson-get 2000000 620 ns/op 306.39 MB/s 0 B/op 0 allocs/op
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BenchmarkParse/medium/stdjson-map 30000 40672 ns/op 57.26 MB/s 10196 B/op 208 allocs/op
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BenchmarkParse/medium/stdjson-struct 30000 47792 ns/op 48.73 MB/s 9174 B/op 258 allocs/op
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BenchmarkParse/medium/stdjson-empty-struct 100000 22096 ns/op 105.40 MB/s 280 B/op 5 allocs/op
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BenchmarkParse/medium/fastjson 500000 3025 ns/op 769.90 MB/s 0 B/op 0 allocs/op
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BenchmarkParse/medium/fastjson-get 500000 3211 ns/op 725.20 MB/s 0 B/op 0 allocs/op
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BenchmarkParse/large/stdjson-map 2000 614079 ns/op 45.79 MB/s 210734 B/op 2785 allocs/op
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BenchmarkParse/large/stdjson-struct 5000 298554 ns/op 94.18 MB/s 15616 B/op 353 allocs/op
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BenchmarkParse/large/stdjson-empty-struct 5000 268577 ns/op 104.69 MB/s 280 B/op 5 allocs/op
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BenchmarkParse/large/fastjson 50000 35210 ns/op 798.56 MB/s 5 B/op 0 allocs/op
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BenchmarkParse/large/fastjson-get 50000 35171 ns/op 799.46 MB/s 5 B/op 0 allocs/op
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BenchmarkParse/canada/stdjson-map 20 68147307 ns/op 33.03 MB/s 12260502 B/op 392539 allocs/op
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BenchmarkParse/canada/stdjson-struct 20 68044518 ns/op 33.08 MB/s 12260123 B/op 392534 allocs/op
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BenchmarkParse/canada/stdjson-empty-struct 100 17709250 ns/op 127.11 MB/s 280 B/op 5 allocs/op
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BenchmarkParse/canada/fastjson 300 4182404 ns/op 538.22 MB/s 254902 B/op 381 allocs/op
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BenchmarkParse/canada/fastjson-get 300 4274744 ns/op 526.60 MB/s 254902 B/op 381 allocs/op
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BenchmarkParse/citm/stdjson-map 50 27772612 ns/op 62.19 MB/s 5214163 B/op 95402 allocs/op
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BenchmarkParse/citm/stdjson-struct 100 14936191 ns/op 115.64 MB/s 1989 B/op 75 allocs/op
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BenchmarkParse/citm/stdjson-empty-struct 100 14946034 ns/op 115.56 MB/s 280 B/op 5 allocs/op
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BenchmarkParse/citm/fastjson 1000 1879714 ns/op 918.87 MB/s 17628 B/op 30 allocs/op
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BenchmarkParse/citm/fastjson-get 1000 1881598 ns/op 917.94 MB/s 17628 B/op 30 allocs/op
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BenchmarkParse/twitter/stdjson-map 100 11289146 ns/op 55.94 MB/s 2187878 B/op 31266 allocs/op
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BenchmarkParse/twitter/stdjson-struct 300 5779442 ns/op 109.27 MB/s 408 B/op 6 allocs/op
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BenchmarkParse/twitter/stdjson-empty-struct 300 5738504 ns/op 110.05 MB/s 408 B/op 6 allocs/op
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BenchmarkParse/twitter/fastjson 2000 774042 ns/op 815.86 MB/s 2541 B/op 2 allocs/op
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BenchmarkParse/twitter/fastjson-get 2000 777833 ns/op 811.89 MB/s 2541 B/op 2 allocs/op
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```
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Benchmark results for json validation:
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```
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$ GOMAXPROCS=1 go test github.com/valyala/fastjson -bench='Validate$'
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goos: linux
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goarch: amd64
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pkg: github.com/valyala/fastjson
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BenchmarkValidate/small/stdjson 2000000 955 ns/op 198.83 MB/s 72 B/op 2 allocs/op
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BenchmarkValidate/small/fastjson 5000000 384 ns/op 493.60 MB/s 0 B/op 0 allocs/op
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BenchmarkValidate/medium/stdjson 200000 10799 ns/op 215.66 MB/s 184 B/op 5 allocs/op
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BenchmarkValidate/medium/fastjson 300000 3809 ns/op 611.30 MB/s 0 B/op 0 allocs/op
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BenchmarkValidate/large/stdjson 10000 133064 ns/op 211.31 MB/s 184 B/op 5 allocs/op
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BenchmarkValidate/large/fastjson 30000 45268 ns/op 621.14 MB/s 0 B/op 0 allocs/op
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BenchmarkValidate/canada/stdjson 200 8470904 ns/op 265.74 MB/s 184 B/op 5 allocs/op
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BenchmarkValidate/canada/fastjson 500 2973377 ns/op 757.07 MB/s 0 B/op 0 allocs/op
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BenchmarkValidate/citm/stdjson 200 7273172 ns/op 237.48 MB/s 184 B/op 5 allocs/op
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BenchmarkValidate/citm/fastjson 1000 1684430 ns/op 1025.39 MB/s 0 B/op 0 allocs/op
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BenchmarkValidate/twitter/stdjson 500 2849439 ns/op 221.63 MB/s 312 B/op 6 allocs/op
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BenchmarkValidate/twitter/fastjson 2000 1036796 ns/op 609.10 MB/s 0 B/op 0 allocs/op
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```
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## FAQ
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* Q: _There are a ton of other high-perf packages for JSON parsing in Go. Why creating yet another package?_
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A: Because other packages require either rigid JSON schema via struct magic
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and code generation or perform poorly when multiple unrelated fields
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must be obtained from the parsed JSON.
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Additionally, `fastjson` provides nicer [API](http://godoc.org/github.com/valyala/fastjson).
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* Q: _What is the main purpose for `fastjson`?_
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A: High-perf JSON parsing for [RTB](https://www.iab.com/wp-content/uploads/2015/05/OpenRTB_API_Specification_Version_2_3_1.pdf)
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and other [JSON-RPC](https://en.wikipedia.org/wiki/JSON-RPC) services.
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* Q: _Why fastjson doesn't provide fast marshaling (serialization)?_
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A: Actually it provides some sort of marshaling - see [Value.MarshalTo](https://godoc.org/github.com/valyala/fastjson#Value.MarshalTo).
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But I'd recommend using [quicktemplate](https://github.com/valyala/quicktemplate#use-cases)
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for high-performance JSON marshaling :)
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* Q: _`fastjson` crashes my program!_
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A: There is high probability of improper use.
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* Make sure you don't hold references to objects recursively returned by `Parser` / `Scanner`
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beyond the next `Parser.Parse` / `Scanner.Next` call
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if such restriction is mentioned in [docs](https://github.com/valyala/fastjson/issues/new).
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* Make sure you don't access `fastjson` objects from concurrently running goroutines
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if such restriction is mentioned in [docs](https://github.com/valyala/fastjson/issues/new).
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* Build and run your program with [-race](https://golang.org/doc/articles/race_detector.html) flag.
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Make sure the race detector detects zero races.
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* If your program continue crashing after fixing issues mentioned above, [file a bug](https://github.com/valyala/fastjson/issues/new).
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