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This package provides the ability to encode golang structs to a buffer as JSON very quickly.


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This package provides the ability to encode golang structs to a buffer as JSON.

The main take-aways are

  • It's very fast. (We can't find a faster one)
  • Very low allocs, 0 in a lot of cases.
  • Clear API - similar to the stdlib. It just uses struct tags.
  • No other library dependencies.
  • It doesn't require a build step, like go generate.

Another JSON Library...why?

Performance. Check out these numbers - they were generated with the gojay (which is fast) perf data, SmallPayload and LargePayload respectively.

Numbers were generated on a Centos 7 Machine, Quad-core Intel(R) Core(TM) i5-4590 CPU @ 3.30GHz.

Lib Iter ns/op B/op allocs/op +/-
jingo 10000000 208 0 0 4.8x
stdlib encoding/json 1000000 1008 160 1 1x
gojay 2000000 605 512 1 1.6x
json-iterator 2000000 825 168 2 1.2x
Lib Iter ns/op B/op allocs/op +/-
jingo 200000 9748 0 0 3x
stdlib encoding/json 50000 29854 4866 1 1x
gojay 100000 16884 18308 5 1.7x
json-iterator 100000 21033 4873 2 1.4x

These results can be even more pronounced depending on the shape of the struct - these results are based on a struct with a lot of string data in:

Lib Iter ns/op B/op allocs/op +/-
jingo 10000000 212 0 0 11.5x
stdlib encoding/json 500000 2443 720 4 1x
gojay 1000000 1147 512 1 2.1x
json-iterator 500000 2606 744 5 0.9x

Example Usage

The usage is similar to that of the stdlib json.Marshal, but we do most of our work upon instantiation of the encoders.

The encoders you have available to you are

  • jingo.StructEncoder
  • jingo.SliceEncoder

They both reference each other and they work in exactly the same way. You'll see, like the stdlib encode/json, there is very little wire-up involved.

package main

import (

// sample struct we'll encode
type MyPayload struct {
    Name string `json:"name"`
    Age int     `json:"age"`
    ID int      // anything we don't annotate doesn't get emitted. 

// Create an encoder, letting it know which type of struct we're going to be encoding. 
// You only do this once per type!
var enc = jingo.NewStructEncoder(MyPayload{})

func main() {
    // now lets encode something 
    p := MyPayload{
        Name: "Mr Payload",
        Age: 33,

    // pull a buffer from the pool and pass it along with the struct to Marshal
    buf := jingo.NewBufferFromPool()
    enc.Marshal(&p, buf)

    fmt.Println(buf.String()) // {"name":"Mr Payload","age":33}

    // return the buffer to the pool now we're done


Buffer is a simple custom buffer type which complies with io.Writer. Its main benefit being it has pooling built-in. This goes a long way to helping make jingo fast by reducing its allocations and ensuring good write speeds.


There are a couple of subtle ways you can configure the encoders.

  • You can specify a default capacity for buffer using NewBufferFromPoolWithCap(int)*Buffer
  • It supports the same json:"tag,options" syntax as the stdlib, but not the same options. Currently the options you have are
    • ,stringer, which instead of the standard serialization method for a given type, nominates that its .String() function is invoked instead to provide the serialization value.
    • ,raw, which allows byteslice-like items (like []byte and string) to be written to the buffer directly with no conversion, quoting or otherwise. nil or empty fields annotated as raw will output null.
    • ,encoder which instead of the standard serialization method for a given type, nominates that its .JSONEncode(*jingo.Buffer) function or EncodeJSON(io.Writer) function are invoked instead. From there you can manually write to the buffer or writer for that particular field. There are a choice of 2 interfaces you need to comply with depending on your use case, either jingo.JSONEncoder (which introduces a dependency on Buffer), or jingo.JSONMarshaler which allows writing directly to an io.Writer.
    • ,escape, which safely escapes ",\, line feed (\n), carriage return (\r) and tab (\t) characters to valid JSON whilst writing. To get the same functionality when using SliceEncoder on its own, use jingo.EscapeString to initialize the encoder - e.g NewSliceEncoder([]jingo.EscapeString) - instead of string directly. There is obviously a performance impact on the write speed using this option, the benchmarks show it takes twice the time of a standard string write, so whilst it is still faster than using the stdlib, to get the best performance it is recommended to only be used when needed and only then when the escaping work can't be done up-front.

How does it work

When you create an instance of an encoder it recursively generates an instruction set which defines how to iteratively encode your structs. This gives it the ability to provide a clear API but with the same benefits as a build-time optimized encoder. It's almost exclusively able to do all type assertions and reflection activity during the compile, then makes ample use of the unsafe package during the instruction-set execution (the Marshal call) to make reading and writing very fast.

As part of the instruction set compilation it also generates static meta-data, i.e field names, brackets, braces etc. These are then chunked into instructions on demand.


The package is designed to be performant and as such it is not 100% functionally compatible with stdlib. Specifically.

  • 'Omit if empty' isn't supported, due to the nature of the instruction based approach we would be paying a performance price by including this - although it is not impossible with further effort. It isn't something that affects us as it can generally be worked around.
  • The ,string tag option isn't supported, only strings are quoted by default - use ,stringer instead to achieve the same results. This may be added in future releases.
  • Maps are currently not supported. Initial thoughts were given that this is a performance focused library it doesn't make much sense to iterate maps and would advise against doing so for performance sensitive applications - however - maps are being added!

Contribution Guidelines

Contributions are welcome! Fork the repo and submit a pull request to get your change added.

Please take into consideration whether or not the change aligns with the agenda of the project to avoid having them rejected. For example, when adding a new feature, try to make sure you're creating a new instruction/set for the feature being added - don't add logic to existing instructions at the cost of performance for all other code paths currently using them. It's best to have more instructions with no logic than fewer instructions with a few conditionals that execute at runtime.

Feel free to raise an issue here beforehand to discuss anything with others before your implementation.