// Copyright 2020 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build goexperiment.jsonv2
package jsontext
import (
"bytes"
"errors"
"math"
"strconv"
"encoding/json/internal/jsonflags"
"encoding/json/internal/jsonwire"
)
// NOTE: Token is analogous to v1 json.Token.
const (
maxInt64 = math.MaxInt64
minInt64 = math.MinInt64
maxUint64 = math.MaxUint64
minUint64 = 0 // for consistency and readability purposes
invalidTokenPanic = "invalid jsontext.Token; it has been voided by a subsequent json.Decoder call"
)
var errInvalidToken = errors.New("invalid jsontext.Token")
// Token represents a lexical JSON token, which may be one of the following:
// - a JSON literal (i.e., null, true, or false)
// - a JSON string (e.g., "hello, world!")
// - a JSON number (e.g., 123.456)
// - a begin or end delimiter for a JSON object (i.e., { or } )
// - a begin or end delimiter for a JSON array (i.e., [ or ] )
//
// A Token cannot represent entire array or object values, while a [Value] can.
// There is no Token to represent commas and colons since
// these structural tokens can be inferred from the surrounding context.
type Token struct {
nonComparable
// Tokens can exist in either a "raw" or an "exact" form.
// Tokens produced by the Decoder are in the "raw" form.
// Tokens returned by constructors are usually in the "exact" form.
// The Encoder accepts Tokens in either the "raw" or "exact" form.
//
// The following chart shows the possible values for each Token type:
// ╔═════════════════╦════════════╤════════════╤════════════╗
// ║ Token type ║ raw field │ str field │ num field ║
// ╠═════════════════╬════════════╪════════════╪════════════╣
// ║ null (raw) ║ "null" │ "" │ 0 ║
// ║ false (raw) ║ "false" │ "" │ 0 ║
// ║ true (raw) ║ "true" │ "" │ 0 ║
// ║ string (raw) ║ non-empty │ "" │ offset ║
// ║ string (string) ║ nil │ non-empty │ 0 ║
// ║ number (raw) ║ non-empty │ "" │ offset ║
// ║ number (float) ║ nil │ "f" │ non-zero ║
// ║ number (int64) ║ nil │ "i" │ non-zero ║
// ║ number (uint64) ║ nil │ "u" │ non-zero ║
// ║ object (delim) ║ "{" or "}" │ "" │ 0 ║
// ║ array (delim) ║ "[" or "]" │ "" │ 0 ║
// ╚═════════════════╩════════════╧════════════╧════════════╝
//
// Notes:
// - For tokens stored in "raw" form, the num field contains the
// absolute offset determined by raw.previousOffsetStart().
// The buffer itself is stored in raw.previousBuffer().
// - JSON literals and structural characters are always in the "raw" form.
// - JSON strings and numbers can be in either "raw" or "exact" forms.
// - The exact zero value of JSON strings and numbers in the "exact" forms
// have ambiguous representation. Thus, they are always represented
// in the "raw" form.
// raw contains a reference to the raw decode buffer.
// If non-nil, then its value takes precedence over str and num.
// It is only valid if num == raw.previousOffsetStart().
raw *decodeBuffer
// str is the unescaped JSON string if num is zero.
// Otherwise, it is "f", "i", or "u" if num should be interpreted
// as a float64, int64, or uint64, respectively.
str string
// num is a float64, int64, or uint64 stored as a uint64 value.
// It is non-zero for any JSON number in the "exact" form.
num uint64
}
// TODO: Does representing 1-byte delimiters as *decodeBuffer cause performance issues?
var (
Null Token = rawToken("null")
False Token = rawToken("false")
True Token = rawToken("true")
BeginObject Token = rawToken("{")
EndObject Token = rawToken("}")
BeginArray Token = rawToken("[")
EndArray Token = rawToken("]")
zeroString Token = rawToken(`""`)
zeroNumber Token = rawToken(`0`)
nanString Token = String("NaN")
pinfString Token = String("Infinity")
ninfString Token = String("-Infinity")
)
func rawToken(s string) Token {
return Token{raw: &decodeBuffer{buf: []byte(s), prevStart: 0, prevEnd: len(s)}}
}
// Bool constructs a Token representing a JSON boolean.
func Bool(b bool) Token {
if b {
return True
}
return False
}
// String constructs a Token representing a JSON string.
// The provided string should contain valid UTF-8, otherwise invalid characters
// may be mangled as the Unicode replacement character.
func String(s string) Token {
if len(s) == 0 {
return zeroString
}
return Token{str: s}
}
// Float constructs a Token representing a JSON number.
// The values NaN, +Inf, and -Inf will be represented
// as a JSON string with the values "NaN", "Infinity", and "-Infinity".
func Float(n float64) Token {
switch {
case math.Float64bits(n) == 0:
return zeroNumber
case math.IsNaN(n):
return nanString
case math.IsInf(n, +1):
return pinfString
case math.IsInf(n, -1):
return ninfString
}
return Token{str: "f", num: math.Float64bits(n)}
}
// Int constructs a Token representing a JSON number from an int64.
func Int(n int64) Token {
if n == 0 {
return zeroNumber
}
return Token{str: "i", num: uint64(n)}
}
// Uint constructs a Token representing a JSON number from a uint64.
func Uint(n uint64) Token {
if n == 0 {
return zeroNumber
}
return Token{str: "u", num: uint64(n)}
}
// Clone makes a copy of the Token such that its value remains valid
// even after a subsequent [Decoder.Read] call.
func (t Token) Clone() Token {
// TODO: Allow caller to avoid any allocations?
if raw := t.raw; raw != nil {
// Avoid copying globals.
if t.raw.prevStart == 0 {
switch t.raw {
case Null.raw:
return Null
case False.raw:
return False
case True.raw:
return True
case BeginObject.raw:
return BeginObject
case EndObject.raw:
return EndObject
case BeginArray.raw:
return BeginArray
case EndArray.raw:
return EndArray
}
}
if uint64(raw.previousOffsetStart()) != t.num {
panic(invalidTokenPanic)
}
buf := bytes.Clone(raw.previousBuffer())
return Token{raw: &decodeBuffer{buf: buf, prevStart: 0, prevEnd: len(buf)}}
}
return t
}
// Bool returns the value for a JSON boolean.
// It panics if the token kind is not a JSON boolean.
func (t Token) Bool() bool {
switch t.raw {
case True.raw:
return true
case False.raw:
return false
default:
panic("invalid JSON token kind: " + t.Kind().String())
}
}
// appendString appends a JSON string to dst and returns it.
// It panics if t is not a JSON string.
func (t Token) appendString(dst []byte, flags *jsonflags.Flags) ([]byte, error) {
if raw := t.raw; raw != nil {
// Handle raw string value.
buf := raw.previousBuffer()
if Kind(buf[0]) == '"' {
if jsonwire.ConsumeSimpleString(buf) == len(buf) {
return append(dst, buf...), nil
}
dst, _, err := jsonwire.ReformatString(dst, buf, flags)
return dst, err
}
} else if len(t.str) != 0 && t.num == 0 {
// Handle exact string value.
return jsonwire.AppendQuote(dst, t.str, flags)
}
panic("invalid JSON token kind: " + t.Kind().String())
}
// String returns the unescaped string value for a JSON string.
// For other JSON kinds, this returns the raw JSON representation.
func (t Token) String() string {
// This is inlinable to take advantage of "function outlining".
// This avoids an allocation for the string(b) conversion
// if the caller does not use the string in an escaping manner.
// See https://blog.filippo.io/efficient-go-apis-with-the-inliner/
s, b := t.string()
if len(b) > 0 {
return string(b)
}
return s
}
func (t Token) string() (string, []byte) {
if raw := t.raw; raw != nil {
if uint64(raw.previousOffsetStart()) != t.num {
panic(invalidTokenPanic)
}
buf := raw.previousBuffer()
if buf[0] == '"' {
// TODO: Preserve ValueFlags in Token?
isVerbatim := jsonwire.ConsumeSimpleString(buf) == len(buf)
return "", jsonwire.UnquoteMayCopy(buf, isVerbatim)
}
// Handle tokens that are not JSON strings for fmt.Stringer.
return "", buf
}
if len(t.str) != 0 && t.num == 0 {
return t.str, nil
}
// Handle tokens that are not JSON strings for fmt.Stringer.
if t.num > 0 {
switch t.str[0] {
case 'f':
return string(jsonwire.AppendFloat(nil, math.Float64frombits(t.num), 64)), nil
case 'i':
return strconv.FormatInt(int64(t.num), 10), nil
case 'u':
return strconv.FormatUint(uint64(t.num), 10), nil
}
}
return "<invalid jsontext.Token>", nil
}
// appendNumber appends a JSON number to dst and returns it.
// It panics if t is not a JSON number.
func (t Token) appendNumber(dst []byte, flags *jsonflags.Flags) ([]byte, error) {
if raw := t.raw; raw != nil {
// Handle raw number value.
buf := raw.previousBuffer()
if Kind(buf[0]).normalize() == '0' {
dst, _, err := jsonwire.ReformatNumber(dst, buf, flags)
return dst, err
}
} else if t.num != 0 {
// Handle exact number value.
switch t.str[0] {
case 'f':
return jsonwire.AppendFloat(dst, math.Float64frombits(t.num), 64), nil
case 'i':
return strconv.AppendInt(dst, int64(t.num), 10), nil
case 'u':
return strconv.AppendUint(dst, uint64(t.num), 10), nil
}
}
panic("invalid JSON token kind: " + t.Kind().String())
}
// Float returns the floating-point value for a JSON number.
// It returns a NaN, +Inf, or -Inf value for any JSON string
// with the values "NaN", "Infinity", or "-Infinity".
// It panics for all other cases.
func (t Token) Float() float64 {
if raw := t.raw; raw != nil {
// Handle raw number value.
if uint64(raw.previousOffsetStart()) != t.num {
panic(invalidTokenPanic)
}
buf := raw.previousBuffer()
if Kind(buf[0]).normalize() == '0' {
fv, _ := jsonwire.ParseFloat(buf, 64)
return fv
}
} else if t.num != 0 {
// Handle exact number value.
switch t.str[0] {
case 'f':
return math.Float64frombits(t.num)
case 'i':
return float64(int64(t.num))
case 'u':
return float64(uint64(t.num))
}
}
// Handle string values with "NaN", "Infinity", or "-Infinity".
if t.Kind() == '"' {
switch t.String() {
case "NaN":
return math.NaN()
case "Infinity":
return math.Inf(+1)
case "-Infinity":
return math.Inf(-1)
}
}
panic("invalid JSON token kind: " + t.Kind().String())
}
// Int returns the signed integer value for a JSON number.
// The fractional component of any number is ignored (truncation toward zero).
// Any number beyond the representation of an int64 will be saturated
// to the closest representable value.
// It panics if the token kind is not a JSON number.
func (t Token) Int() int64 {
if raw := t.raw; raw != nil {
// Handle raw integer value.
if uint64(raw.previousOffsetStart()) != t.num {
panic(invalidTokenPanic)
}
neg := false
buf := raw.previousBuffer()
if len(buf) > 0 && buf[0] == '-' {
neg, buf = true, buf[1:]
}
if numAbs, ok := jsonwire.ParseUint(buf); ok {
if neg {
if numAbs > -minInt64 {
return minInt64
}
return -1 * int64(numAbs)
} else {
if numAbs > +maxInt64 {
return maxInt64
}
return +1 * int64(numAbs)
}
}
} else if t.num != 0 {
// Handle exact integer value.
switch t.str[0] {
case 'i':
return int64(t.num)
case 'u':
if t.num > maxInt64 {
return maxInt64
}
return int64(t.num)
}
}
// Handle JSON number that is a floating-point value.
if t.Kind() == '0' {
switch fv := t.Float(); {
case fv >= maxInt64:
return maxInt64
case fv <= minInt64:
return minInt64
default:
return int64(fv) // truncation toward zero
}
}
panic("invalid JSON token kind: " + t.Kind().String())
}
// Uint returns the unsigned integer value for a JSON number.
// The fractional component of any number is ignored (truncation toward zero).
// Any number beyond the representation of an uint64 will be saturated
// to the closest representable value.
// It panics if the token kind is not a JSON number.
func (t Token) Uint() uint64 {
// NOTE: This accessor returns 0 for any negative JSON number,
// which might be surprising, but is at least consistent with the behavior
// of saturating out-of-bounds numbers to the closest representable number.
if raw := t.raw; raw != nil {
// Handle raw integer value.
if uint64(raw.previousOffsetStart()) != t.num {
panic(invalidTokenPanic)
}
neg := false
buf := raw.previousBuffer()
if len(buf) > 0 && buf[0] == '-' {
neg, buf = true, buf[1:]
}
if num, ok := jsonwire.ParseUint(buf); ok {
if neg {
return minUint64
}
return num
}
} else if t.num != 0 {
// Handle exact integer value.
switch t.str[0] {
case 'u':
return t.num
case 'i':
if int64(t.num) < minUint64 {
return minUint64
}
return uint64(int64(t.num))
}
}
// Handle JSON number that is a floating-point value.
if t.Kind() == '0' {
switch fv := t.Float(); {
case fv >= maxUint64:
return maxUint64
case fv <= minUint64:
return minUint64
default:
return uint64(fv) // truncation toward zero
}
}
panic("invalid JSON token kind: " + t.Kind().String())
}
// Kind returns the token kind.
func (t Token) Kind() Kind {
switch {
case t.raw != nil:
raw := t.raw
if uint64(raw.previousOffsetStart()) != t.num {
panic(invalidTokenPanic)
}
return Kind(t.raw.buf[raw.prevStart]).normalize()
case t.num != 0:
return '0'
case len(t.str) != 0:
return '"'
default:
return invalidKind
}
}
// Kind represents each possible JSON token kind with a single byte,
// which is conveniently the first byte of that kind's grammar
// with the restriction that numbers always be represented with '0':
//
// - 'n': null
// - 'f': false
// - 't': true
// - '"': string
// - '0': number
// - '{': object begin
// - '}': object end
// - '[': array begin
// - ']': array end
//
// An invalid kind is usually represented using 0,
// but may be non-zero due to invalid JSON data.
type Kind byte
const invalidKind Kind = 0
// String prints the kind in a humanly readable fashion.
func (k Kind) String() string {
switch k {
case 'n':
return "null"
case 'f':
return "false"
case 't':
return "true"
case '"':
return "string"
case '0':
return "number"
case '{':
return "{"
case '}':
return "}"
case '[':
return "["
case ']':
return "]"
default:
return "<invalid jsontext.Kind: " + jsonwire.QuoteRune(string(k)) + ">"
}
}
// normalize coalesces all possible starting characters of a number as just '0'.
func (k Kind) normalize() Kind {
if k == '-' || ('0' <= k && k <= '9') {
return '0'
}
return k
}
