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|
// Copyright (C) 2022-2023 Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later
package lowmemjson
import (
"bytes"
"fmt"
"io"
"unicode/utf8"
"git.lukeshu.com/go/lowmemjson/internal"
)
// A ReEncoderConfig controls how a ReEncoder should behave.
type ReEncoderConfig struct {
// A JSON document is specified to be a single JSON element;
// but it is often desirable to handle streams of multiple
// JSON elements.
AllowMultipleValues bool
// Whether to minify the JSON.
//
// Trims all whitespace, except that it emits a newline
// between two *number* top-level values (or puts a newline
// after all top-level values if ForceTrailingNewlines).
//
// Trims superflous 0s from numbers.
Compact bool
// CompactIfUnder causes the *ReEncoder to behave as if
// Compact=true for individual elements if doing so would
// cause that element to be under this number of bytes.
//
// Has no affect if Compact is true or Indent is empty.
//
// his has O(2^min(CompactIfUnder, depth)) time overhead, so
// set with caution.
CompactIfUnder int
// String to use to indent; ignored if Compact is true.
//
// Newlines are emitted *between* top-level values; a newline is
// not emitted after the *last* top-level value (unless
// ForceTrailingNewlines is on).
Indent string
// String to put before indents.
Prefix string
// Whether to emit a newline after each top-level value. See
// the comments on Compact and Indent for discussion of how
// this is different than the usual behavior.
ForceTrailingNewlines bool
// Returns whether a given character in a string should be
// backslash-escaped. The bool argument is whether it was
// \u-escaped in the input. This does not affect characters
// that must or must-not be escaped to be valid JSON.
//
// If not set, then EscapeDefault is used.
BackslashEscape BackslashEscaper
}
// NewReEncoder returns a new ReEncoder instance.
//
// A ReEncoder tends to make many small writes; if Out.Write
// calls are syscalls, then you may want to wrap Out in a
// bufio.Writer.
func NewReEncoder(out io.Writer, cfg ReEncoderConfig) *ReEncoder {
return &ReEncoder{
ReEncoderConfig: cfg,
out: internal.NewAllWriter(out),
specu: new(speculation),
}
}
// A ReEncoder takes a stream of JSON elements (by way of implementing
// io.Writer and WriteRune), and re-encodes the JSON, writing it to
// the .Out member.
//
// This is useful for prettifying, minifying, sanitizing, and/or
// validating JSON.
//
// The memory use of a ReEncoder is O(CompactIfUnder+depth).
type ReEncoder struct {
ReEncoderConfig
out internal.AllWriter
// state: .Write's and .WriteString's utf8-decoding buffer
buf [utf8.UTFMax]byte
bufLen int
// state: .WriteRune
err error
par internal.Parser
written int
inputPos int64
// state: .handleRune
lastNonSpace internal.RuneType
lastNonSpaceNonEOF internal.RuneType
wasNumber bool
curIndent int
uhex [4]byte // "\uABCD"-encoded characters in strings
fracZeros int64
expZero bool
specu *speculation
// state: .pushWriteBarrier and .popWriteBarrier
barriers []barrier
}
type barrier struct {
inputPos int64
stackSize int
}
type speculation struct {
speculating bool
endWhenStackSize int
fmt ReEncoder
compact bytes.Buffer
buf []inputTuple
}
func (specu *speculation) Reset() {
specu.speculating = false
specu.endWhenStackSize = 0
specu.fmt = ReEncoder{}
specu.compact.Reset()
specu.buf = specu.buf[:0]
}
type inputTuple struct {
c rune
t internal.RuneType
stackSize int
}
// public API //////////////////////////////////////////////////////////////////
var (
_ internal.AllWriter = (*ReEncoder)(nil)
_ io.Closer = (*ReEncoder)(nil)
)
// Write implements io.Writer; it does what you'd expect.
//
// It is worth noting that Write returns the number of bytes consumed
// from p, not number of bytes written to the output stream. This
// distinction that most io.Writer implementations don't need to make,
// but *ReEncoder does because it transforms the data written to it,
// and the number of bytes written may be wildly different than the
// number of bytes handled.
func (enc *ReEncoder) Write(p []byte) (int, error) {
if len(p) == 0 {
return 0, nil
}
var n int
if enc.bufLen > 0 {
copy(enc.buf[enc.bufLen:], p)
c, size := utf8.DecodeRune(enc.buf[:])
n += size - enc.bufLen
enc.bufLen = 0
if _, err := enc.WriteRune(c); err != nil {
return 0, err
}
}
for utf8.FullRune(p[n:]) {
c, size := utf8.DecodeRune(p[n:])
if _, err := enc.WriteRune(c); err != nil {
return n, err
}
n += size
}
enc.bufLen = copy(enc.buf[:], p[n:])
return len(p), nil
}
// WriteString implements io.StringWriter; it does what you'd expect,
// but see the notes on the Write method.
func (enc *ReEncoder) WriteString(p string) (int, error) {
if len(p) == 0 {
return 0, nil
}
var n int
if enc.bufLen > 0 {
copy(enc.buf[enc.bufLen:], p)
c, size := utf8.DecodeRune(enc.buf[:])
n += size - enc.bufLen
enc.bufLen = 0
if _, err := enc.WriteRune(c); err != nil {
return 0, err
}
}
for utf8.FullRuneInString(p[n:]) {
c, size := utf8.DecodeRuneInString(p[n:])
if _, err := enc.WriteRune(c); err != nil {
return n, err
}
n += size
}
enc.bufLen = copy(enc.buf[:], p[n:])
return len(p), nil
}
// WriteByte implements io.ByteWriter; it does what you'd expect.
func (enc *ReEncoder) WriteByte(b byte) error {
return internal.WriteByte(enc, b)
}
// Close implements io.Closer; it does what you'd expect, mostly.
//
// The *ReEncoder may continue to be written to with new JSON values
// if enc.AllowMultipleValues is set.
func (enc *ReEncoder) Close() error {
if enc.bufLen > 0 {
return &ReEncodeSyntaxError{
Offset: enc.inputPos,
Err: fmt.Errorf("%w: unflushed unicode garbage: %q", io.ErrUnexpectedEOF, enc.buf[:enc.bufLen]),
}
}
if _, err := enc.par.HandleEOF(); err != nil {
enc.err = &ReEncodeSyntaxError{
Err: err,
Offset: enc.inputPos,
}
return enc.err
}
if len(enc.barriers) == 0 {
if err := enc.handleRune(0, internal.RuneTypeError, enc.stackSize()); err != nil {
enc.err = &ReEncodeSyntaxError{
Err: err,
Offset: enc.inputPos,
}
return enc.err
}
if enc.AllowMultipleValues {
enc.par.Reset()
}
}
return nil
}
// WriteRune writes a single Unicode code point, returning the number
// of bytes written to the output stream and any error.
//
// Even when there is no error, the number of bytes written may be
// zero (for example, when the rune is whitespace and the ReEncoder is
// minifying the JSON), or it may be substantially longer than one
// code point's worth (for example, when `\uXXXX` escaping a character
// in a string, or when outputing extra whitespace when the ReEncoder
// is prettifying the JSON).
func (enc *ReEncoder) WriteRune(c rune) (n int, err error) {
if enc.err != nil {
return 0, enc.err
}
if enc.bufLen > 0 {
enc.err = fmt.Errorf("lowmemjson.ReEncoder: cannot .WriteRune() when there is a partial rune that has been .Write()en: %q", enc.buf[:enc.bufLen])
return 0, enc.err
}
enc.written = 0
rehandle:
t, err := enc.par.HandleRune(c)
if err != nil {
enc.err = &ReEncodeSyntaxError{
Err: err,
Offset: enc.inputPos,
}
return enc.written, enc.err
}
enc.err = enc.handleRune(c, t, enc.stackSize())
if enc.err == nil && t == internal.RuneTypeEOF {
if enc.AllowMultipleValues && len(enc.barriers) == 0 {
enc.par.Reset()
goto rehandle
} else {
enc.err = &ReEncodeSyntaxError{
Err: fmt.Errorf("invalid character %q after top-level value", c),
Offset: enc.inputPos,
}
return enc.written, enc.err
}
}
enc.inputPos += int64(utf8.RuneLen(c))
return enc.written, enc.err
}
// semi-public API /////////////////////////////////////////////////////////////
func (enc *ReEncoder) pushWriteBarrier() {
enc.barriers = append(enc.barriers, barrier{
inputPos: enc.inputPos,
stackSize: enc.stackSize(),
})
enc.par.PushWriteBarrier()
enc.inputPos = 0
}
func (enc *ReEncoder) popWriteBarrier() {
enc.par.PopBarrier()
enc.inputPos += enc.barriers[len(enc.barriers)-1].inputPos
enc.barriers = enc.barriers[:len(enc.barriers)-1]
enc.lastNonSpace = enc.lastNonSpaceNonEOF
}
// internal ////////////////////////////////////////////////////////////////////
func (enc *ReEncoder) stackSize() int {
sz := enc.par.StackSize()
for _, barrier := range enc.barriers {
sz += barrier.stackSize
}
return sz
}
func (enc *ReEncoder) handleRune(c rune, t internal.RuneType, stackSize int) error {
if enc.CompactIfUnder == 0 || enc.Compact || enc.Indent == "" {
return enc.handleRuneNoSpeculation(c, t)
}
// main
if !enc.specu.speculating { // not speculating
switch t {
case internal.RuneTypeObjectBeg, internal.RuneTypeArrayBeg: // start speculating
if err, _ := enc.handleRunePre(c, t); err != nil {
return err
}
enc.specu.speculating = true
enc.specu.endWhenStackSize = stackSize - 1
enc.specu.fmt = ReEncoder{
ReEncoderConfig: enc.ReEncoderConfig,
out: &enc.specu.compact,
}
enc.specu.fmt.Compact = true
enc.specu.buf = append(enc.specu.buf, inputTuple{
c: c,
t: t,
stackSize: stackSize,
})
if err := enc.specu.fmt.handleRuneMain(c, t); err != nil {
return err
}
default:
if err := enc.handleRuneNoSpeculation(c, t); err != nil {
return err
}
}
} else { // speculating
enc.specu.buf = append(enc.specu.buf, inputTuple{
c: c,
t: t,
stackSize: stackSize,
})
if err := enc.specu.fmt.handleRune(c, t, stackSize); err != nil {
return err
}
switch {
case enc.specu.compact.Len() >= enc.CompactIfUnder: // stop speculating; use indent
buf := append([]inputTuple(nil), enc.specu.buf...)
enc.specu.Reset()
if err := enc.handleRuneMain(buf[0].c, buf[0].t); err != nil {
return err
}
for _, tuple := range buf[1:] {
if err := enc.handleRune(tuple.c, tuple.t, tuple.stackSize); err != nil {
return err
}
}
case stackSize == enc.specu.endWhenStackSize: // stop speculating; use compact
if _, err := enc.specu.compact.WriteTo(enc.out); err != nil {
return err
}
enc.specu.Reset()
enc.lastNonSpace = t
enc.curIndent--
}
}
return nil
}
func (enc *ReEncoder) handleRuneNoSpeculation(c rune, t internal.RuneType) error {
err, shouldHandle := enc.handleRunePre(c, t)
if err != nil {
return err
}
if !shouldHandle {
return nil
}
return enc.handleRuneMain(c, t)
}
// handleRunePre handles buffered things that need to happen before
// the new rune itself is handled.
func (enc *ReEncoder) handleRunePre(c rune, t internal.RuneType) (error, bool) {
// emit newlines between top-level values
if enc.lastNonSpace == internal.RuneTypeEOF {
switch {
case enc.wasNumber && t.IsNumber():
if err := enc.emitByte('\n'); err != nil {
return err, false
}
case enc.Indent != "" && !enc.Compact:
if err := enc.emitByte('\n'); err != nil {
return err, false
}
}
}
// shorten numbers
switch t { // trim trailing '0's from the fraction-part, but don't remove all digits
case internal.RuneTypeNumberFracDot:
enc.fracZeros = 0
case internal.RuneTypeNumberFracDig:
if c == '0' && enc.lastNonSpace == internal.RuneTypeNumberFracDig {
enc.fracZeros++
return nil, false
}
fallthrough
default:
for enc.fracZeros > 0 {
if err := enc.emitByte('0'); err != nil {
return err, false
}
enc.fracZeros--
}
}
switch t { // trim leading '0's from the exponent-part, but don't remove all digits
case internal.RuneTypeNumberExpE, internal.RuneTypeNumberExpSign:
enc.expZero = true
case internal.RuneTypeNumberExpDig:
if c == '0' && enc.expZero {
return nil, false
}
enc.expZero = false
default:
if enc.expZero {
if err := enc.emitByte('0'); err != nil {
return err, false
}
enc.expZero = false
}
}
// whitespace
switch {
case enc.Compact:
if t == internal.RuneTypeSpace {
return nil, false
}
case enc.Indent != "":
switch t {
case internal.RuneTypeSpace:
// let us manage whitespace, don't pass it through
return nil, false
case internal.RuneTypeObjectEnd, internal.RuneTypeArrayEnd:
enc.curIndent--
switch enc.lastNonSpace {
case internal.RuneTypeObjectBeg, internal.RuneTypeArrayBeg:
// collapse
default:
if err := enc.emitNlIndent(); err != nil {
return err, false
}
}
default:
switch enc.lastNonSpace {
case internal.RuneTypeObjectBeg, internal.RuneTypeObjectComma, internal.RuneTypeArrayBeg, internal.RuneTypeArrayComma:
if err := enc.emitNlIndent(); err != nil {
return err, false
}
case internal.RuneTypeObjectColon:
if err := enc.emitByte(' '); err != nil {
return err, false
}
}
switch t {
case internal.RuneTypeObjectBeg, internal.RuneTypeArrayBeg:
enc.curIndent++
}
}
}
return nil, true
}
// handleRuneMain handles the new rune itself, not buffered things.
func (enc *ReEncoder) handleRuneMain(c rune, t internal.RuneType) error {
var err error
switch t {
case internal.RuneTypeStringChar:
err = enc.emit(writeStringChar(enc.out, c, BackslashEscapeNone, enc.BackslashEscape))
case internal.RuneTypeStringEsc, internal.RuneTypeStringEscU:
// do nothing
case internal.RuneTypeStringEsc1:
switch c {
case '"':
err = enc.emit(writeStringChar(enc.out, '"', BackslashEscapeShort, enc.BackslashEscape))
case '\\':
err = enc.emit(writeStringChar(enc.out, '\\', BackslashEscapeShort, enc.BackslashEscape))
case '/':
err = enc.emit(writeStringChar(enc.out, '/', BackslashEscapeShort, enc.BackslashEscape))
case 'b':
err = enc.emit(writeStringChar(enc.out, '\b', BackslashEscapeShort, enc.BackslashEscape))
case 'f':
err = enc.emit(writeStringChar(enc.out, '\f', BackslashEscapeShort, enc.BackslashEscape))
case 'n':
err = enc.emit(writeStringChar(enc.out, '\n', BackslashEscapeShort, enc.BackslashEscape))
case 'r':
err = enc.emit(writeStringChar(enc.out, '\r', BackslashEscapeShort, enc.BackslashEscape))
case 't':
err = enc.emit(writeStringChar(enc.out, '\t', BackslashEscapeShort, enc.BackslashEscape))
default:
panic("should not happen")
}
case internal.RuneTypeStringEscUA:
enc.uhex[0], _ = internal.HexToInt(c)
case internal.RuneTypeStringEscUB:
enc.uhex[1], _ = internal.HexToInt(c)
case internal.RuneTypeStringEscUC:
enc.uhex[2], _ = internal.HexToInt(c)
case internal.RuneTypeStringEscUD:
enc.uhex[3], _ = internal.HexToInt(c)
c := 0 |
rune(enc.uhex[0])<<12 |
rune(enc.uhex[1])<<8 |
rune(enc.uhex[2])<<4 |
rune(enc.uhex[3])<<0
err = enc.emit(writeStringChar(enc.out, c, BackslashEscapeUnicode, enc.BackslashEscape))
case internal.RuneTypeError: // EOF explicitly stated by .Close()
fallthrough
case internal.RuneTypeEOF: // EOF implied by the start of the next top-level value
enc.wasNumber = enc.lastNonSpace.IsNumber()
switch {
case enc.ForceTrailingNewlines && len(enc.barriers) == 0:
t = internal.RuneTypeError // enc.lastNonSpace : an NL isn't needed (we already printed one)
err = enc.emitByte('\n')
default:
t = internal.RuneTypeEOF // enc.lastNonSpace : an NL *might* be needed
}
default:
err = enc.emitByte(byte(c))
}
if t != internal.RuneTypeSpace {
enc.lastNonSpace = t
if t != internal.RuneTypeEOF {
enc.lastNonSpaceNonEOF = t
}
}
return err
}
func (enc *ReEncoder) emitByte(c byte) error {
err := enc.out.WriteByte(c)
if err == nil {
enc.written++
}
return err
}
func (enc *ReEncoder) emit(n int, err error) error {
enc.written += n
return err
}
func (enc *ReEncoder) emitNlIndent() error {
if err := enc.emitByte('\n'); err != nil {
return err
}
if enc.Prefix != "" {
if err := enc.emit(enc.out.WriteString(enc.Prefix)); err != nil {
return err
}
}
for i := 0; i < enc.curIndent; i++ {
if err := enc.emit(enc.out.WriteString(enc.Indent)); err != nil {
return err
}
}
return nil
}
|