91 lines
2.7 KiB
Go
91 lines
2.7 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
// Package jsonutil provides utilities to improve JSON performance.
|
|
// It includes an Unmarshal wrapper that amortizes allocated garbage over subsequent runs
|
|
// and a Bytes type to reduce allocations when unmarshalling a non-hex-encoded string into a []byte.
|
|
package jsonutil
|
|
|
|
import (
|
|
"bytes"
|
|
"encoding/json"
|
|
"sync"
|
|
)
|
|
|
|
// decoder is a re-usable json decoder.
|
|
type decoder struct {
|
|
dec *json.Decoder
|
|
r *bytes.Reader
|
|
}
|
|
|
|
var readerPool = sync.Pool{
|
|
New: func() any {
|
|
return bytes.NewReader(nil)
|
|
},
|
|
}
|
|
|
|
var decoderPool = sync.Pool{
|
|
New: func() any {
|
|
var d decoder
|
|
d.r = readerPool.Get().(*bytes.Reader)
|
|
d.dec = json.NewDecoder(d.r)
|
|
return &d
|
|
},
|
|
}
|
|
|
|
// Unmarshal is similar to encoding/json.Unmarshal.
|
|
// There are three major differences:
|
|
//
|
|
// On error, encoding/json.Unmarshal zeros v.
|
|
// This Unmarshal may leave partial data in v.
|
|
// Always check the error before using v!
|
|
// (Future improvements may remove this bug.)
|
|
//
|
|
// The errors they return don't always match perfectly.
|
|
// If you do error matching more precise than err != nil,
|
|
// don't use this Unmarshal.
|
|
//
|
|
// This Unmarshal allocates considerably less memory.
|
|
func Unmarshal(b []byte, v any) error {
|
|
d := decoderPool.Get().(*decoder)
|
|
d.r.Reset(b)
|
|
off := d.dec.InputOffset()
|
|
err := d.dec.Decode(v)
|
|
d.r.Reset(nil) // don't keep a reference to b
|
|
// In case of error, report the offset in this byte slice,
|
|
// instead of in the totality of all bytes this decoder has processed.
|
|
// It is not possible to make all errors match json.Unmarshal exactly,
|
|
// but we can at least try.
|
|
switch jsonerr := err.(type) {
|
|
case *json.SyntaxError:
|
|
jsonerr.Offset -= off
|
|
case *json.UnmarshalTypeError:
|
|
jsonerr.Offset -= off
|
|
case nil:
|
|
// json.Unmarshal fails if there's any extra junk in the input.
|
|
// json.Decoder does not; see https://github.com/golang/go/issues/36225.
|
|
// We need to check for anything left over in the buffer.
|
|
if d.dec.More() {
|
|
// TODO: Provide a better error message.
|
|
// Unfortunately, we can't set the msg field.
|
|
// The offset doesn't perfectly match json:
|
|
// Ours is at the end of the valid data,
|
|
// and theirs is at the beginning of the extra data after whitespace.
|
|
// Close enough, though.
|
|
err = &json.SyntaxError{Offset: d.dec.InputOffset() - off}
|
|
|
|
// TODO: zero v. This is hard; see encoding/json.indirect.
|
|
}
|
|
}
|
|
if err == nil {
|
|
decoderPool.Put(d)
|
|
} else {
|
|
// There might be junk left in the decoder's buffer.
|
|
// There's no way to flush it, no Reset method.
|
|
// Abandoned the decoder but reuse the reader.
|
|
readerPool.Put(d.r)
|
|
}
|
|
return err
|
|
}
|