json

tinywasm/json

A single, platform-agnostic JSON codec for Go that optimizes WebAssembly binary size by using zero reflection. It relies on fmt.Encodable and fmt.Decodable for struct encoding/decoding, which is typically generated by ormc.

Architecture

• Zero Reflection: Uses type switches and visitor pattern instead of the reflect package.
• Platform-Agnostic: Identical behavior on all platforms (WASM, Linux, macOS, etc.).
• TinyGo Compatible: Optimized for minimal binary size and memory usage.
• 0-Allocation: Hot path is allocation-free (reusing fmt.Conv buffers and pooling writers/readers).
• Typed Codec: Only types implementing fmt.Encodable/fmt.Decodable can be directly encoded or decoded.

Usage

Code Generation with ormc

The ormc CLI (from github.com/tinywasm/orm) generates EncodeFields() and DecodeFields() for every struct in the package.

go install github.com/tinywasm/orm/cmd/ormc@latest
ormc   # run at the module root; writes/rewrites *_orm.go

Structs

Structs MUST implement fmt.Encodable and fmt.Decodable to be supported. This is handled by generating code with ormc.

package main

import (
    "github.com/tinywasm/fmt"
    "github.com/tinywasm/json"
)

type User struct {
    Name string
}

func (u *User) IsNil() bool { return u == nil }
func (u *User) EncodeFields(w fmt.FieldWriter) {
    w.String("name", u.Name)
}
func (u *User) DecodeFields(r fmt.FieldReader) error {
    u.Name, _ = r.String("name")
    return nil
}

func main() {
    u := User{Name: "Alice"}

    var out string
    if err := json.Encode(&u, &out); err != nil {
        panic(err)
    }
    // out: {"name":"Alice"}

    var result User
    if err := json.Decode(out, &result); err != nil {
        panic(err)
    }
}

API

Encode(data fmt.Encodable, output any) error

Serializes to JSON. If data is a collection of objects, it is encoded as a JSON array [...]; otherwise as an object {...}.

• data: fmt.Encodable → {...} or [...]
• output: *[]byte, *string, or io.Writer.

Decode(input any, data fmt.Decodable) error

Parses JSON into data.

• input: []byte, string, or io.Reader.
• data: fmt.Decodable → expects {...} or [...]

Benchmarks

tinywasm/json is 77% smaller than encoding/json in WASM (~27 KB vs ~119 KB), zero-reflect, and 0-allocation on the serialization hot path.

See full results and analysis in benchmarks/README.md.

Contributing

License

See LICENSE for details.