gtsocial-umbx

decode.go (8820B)

---

 // Copyright 2018 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.
 
 package json
 
 import (
 	"bytes"
 	"fmt"
 	"io"
 	"regexp"
 	"unicode/utf8"
 
 	"google.golang.org/protobuf/internal/errors"
 )
 
 // call specifies which Decoder method was invoked.
 type call uint8
 
 const (
 	readCall call = iota
 	peekCall
 )
 
 const unexpectedFmt = "unexpected token %s"
 
 // ErrUnexpectedEOF means that EOF was encountered in the middle of the input.
 var ErrUnexpectedEOF = errors.New("%v", io.ErrUnexpectedEOF)
 
 // Decoder is a token-based JSON decoder.
 type Decoder struct {
 	// lastCall is last method called, either readCall or peekCall.
 	// Initial value is readCall.
 	lastCall call
 
 	// lastToken contains the last read token.
 	lastToken Token
 
 	// lastErr contains the last read error.
 	lastErr error
 
 	// openStack is a stack containing ObjectOpen and ArrayOpen values. The
 	// top of stack represents the object or the array the current value is
 	// directly located in.
 	openStack []Kind
 
 	// orig is used in reporting line and column.
 	orig []byte
 	// in contains the unconsumed input.
 	in []byte
 }
 
 // NewDecoder returns a Decoder to read the given []byte.
 func NewDecoder(b []byte) *Decoder {
 	return &Decoder{orig: b, in: b}
 }
 
 // Peek looks ahead and returns the next token kind without advancing a read.
 func (d *Decoder) Peek() (Token, error) {
 	defer func() { d.lastCall = peekCall }()
 	if d.lastCall == readCall {
 		d.lastToken, d.lastErr = d.Read()
 	}
 	return d.lastToken, d.lastErr
 }
 
 // Read returns the next JSON token.
 // It will return an error if there is no valid token.
 func (d *Decoder) Read() (Token, error) {
 	const scalar = Null | Bool | Number | String
 
 	defer func() { d.lastCall = readCall }()
 	if d.lastCall == peekCall {
 		return d.lastToken, d.lastErr
 	}
 
 	tok, err := d.parseNext()
 	if err != nil {
 		return Token{}, err
 	}
 
 	switch tok.kind {
 	case EOF:
 		if len(d.openStack) != 0 ||
 			d.lastToken.kind&scalar|ObjectClose|ArrayClose == 0 {
 			return Token{}, ErrUnexpectedEOF
 		}
 
 	case Null:
 		if !d.isValueNext() {
 			return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
 		}
 
 	case Bool, Number:
 		if !d.isValueNext() {
 			return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
 		}
 
 	case String:
 		if d.isValueNext() {
 			break
 		}
 		// This string token should only be for a field name.
 		if d.lastToken.kind&(ObjectOpen|comma) == 0 {
 			return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
 		}
 		if len(d.in) == 0 {
 			return Token{}, ErrUnexpectedEOF
 		}
 		if c := d.in[0]; c != ':' {
 			return Token{}, d.newSyntaxError(d.currPos(), `unexpected character %s, missing ":" after field name`, string(c))
 		}
 		tok.kind = Name
 		d.consume(1)
 
 	case ObjectOpen, ArrayOpen:
 		if !d.isValueNext() {
 			return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
 		}
 		d.openStack = append(d.openStack, tok.kind)
 
 	case ObjectClose:
 		if len(d.openStack) == 0 ||
 			d.lastToken.kind == comma ||
 			d.openStack[len(d.openStack)-1] != ObjectOpen {
 			return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
 		}
 		d.openStack = d.openStack[:len(d.openStack)-1]
 
 	case ArrayClose:
 		if len(d.openStack) == 0 ||
 			d.lastToken.kind == comma ||
 			d.openStack[len(d.openStack)-1] != ArrayOpen {
 			return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
 		}
 		d.openStack = d.openStack[:len(d.openStack)-1]
 
 	case comma:
 		if len(d.openStack) == 0 ||
 			d.lastToken.kind&(scalar|ObjectClose|ArrayClose) == 0 {
 			return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
 		}
 	}
 
 	// Update d.lastToken only after validating token to be in the right sequence.
 	d.lastToken = tok
 
 	if d.lastToken.kind == comma {
 		return d.Read()
 	}
 	return tok, nil
 }
 
 // Any sequence that looks like a non-delimiter (for error reporting).
 var errRegexp = regexp.MustCompile(`^([-+._a-zA-Z0-9]{1,32}|.)`)
 
 // parseNext parses for the next JSON token. It returns a Token object for
 // different types, except for Name. It does not handle whether the next token
 // is in a valid sequence or not.
 func (d *Decoder) parseNext() (Token, error) {
 	// Trim leading spaces.
 	d.consume(0)
 
 	in := d.in
 	if len(in) == 0 {
 		return d.consumeToken(EOF, 0), nil
 	}
 
 	switch in[0] {
 	case 'n':
 		if n := matchWithDelim("null", in); n != 0 {
 			return d.consumeToken(Null, n), nil
 		}
 
 	case 't':
 		if n := matchWithDelim("true", in); n != 0 {
 			return d.consumeBoolToken(true, n), nil
 		}
 
 	case 'f':
 		if n := matchWithDelim("false", in); n != 0 {
 			return d.consumeBoolToken(false, n), nil
 		}
 
 	case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
 		if n, ok := parseNumber(in); ok {
 			return d.consumeToken(Number, n), nil
 		}
 
 	case '"':
 		s, n, err := d.parseString(in)
 		if err != nil {
 			return Token{}, err
 		}
 		return d.consumeStringToken(s, n), nil
 
 	case '{':
 		return d.consumeToken(ObjectOpen, 1), nil
 
 	case '}':
 		return d.consumeToken(ObjectClose, 1), nil
 
 	case '[':
 		return d.consumeToken(ArrayOpen, 1), nil
 
 	case ']':
 		return d.consumeToken(ArrayClose, 1), nil
 
 	case ',':
 		return d.consumeToken(comma, 1), nil
 	}
 	return Token{}, d.newSyntaxError(d.currPos(), "invalid value %s", errRegexp.Find(in))
 }
 
 // newSyntaxError returns an error with line and column information useful for
 // syntax errors.
 func (d *Decoder) newSyntaxError(pos int, f string, x ...interface{}) error {
 	e := errors.New(f, x...)
 	line, column := d.Position(pos)
 	return errors.New("syntax error (line %d:%d): %v", line, column, e)
 }
 
 // Position returns line and column number of given index of the original input.
 // It will panic if index is out of range.
 func (d *Decoder) Position(idx int) (line int, column int) {
 	b := d.orig[:idx]
 	line = bytes.Count(b, []byte("\n")) + 1
 	if i := bytes.LastIndexByte(b, '\n'); i >= 0 {
 		b = b[i+1:]
 	}
 	column = utf8.RuneCount(b) + 1 // ignore multi-rune characters
 	return line, column
 }
 
 // currPos returns the current index position of d.in from d.orig.
 func (d *Decoder) currPos() int {
 	return len(d.orig) - len(d.in)
 }
 
 // matchWithDelim matches s with the input b and verifies that the match
 // terminates with a delimiter of some form (e.g., r"[^-+_.a-zA-Z0-9]").
 // As a special case, EOF is considered a delimiter. It returns the length of s
 // if there is a match, else 0.
 func matchWithDelim(s string, b []byte) int {
 	if !bytes.HasPrefix(b, []byte(s)) {
 		return 0
 	}
 
 	n := len(s)
 	if n < len(b) && isNotDelim(b[n]) {
 		return 0
 	}
 	return n
 }
 
 // isNotDelim returns true if given byte is a not delimiter character.
 func isNotDelim(c byte) bool {
 	return (c == '-' || c == '+' || c == '.' || c == '_' ||
 		('a' <= c && c <= 'z') ||
 		('A' <= c && c <= 'Z') ||
 		('0' <= c && c <= '9'))
 }
 
 // consume consumes n bytes of input and any subsequent whitespace.
 func (d *Decoder) consume(n int) {
 	d.in = d.in[n:]
 	for len(d.in) > 0 {
 		switch d.in[0] {
 		case ' ', '\n', '\r', '\t':
 			d.in = d.in[1:]
 		default:
 			return
 		}
 	}
 }
 
 // isValueNext returns true if next type should be a JSON value: Null,
 // Number, String or Bool.
 func (d *Decoder) isValueNext() bool {
 	if len(d.openStack) == 0 {
 		return d.lastToken.kind == 0
 	}
 
 	start := d.openStack[len(d.openStack)-1]
 	switch start {
 	case ObjectOpen:
 		return d.lastToken.kind&Name != 0
 	case ArrayOpen:
 		return d.lastToken.kind&(ArrayOpen|comma) != 0
 	}
 	panic(fmt.Sprintf(
 		"unreachable logic in Decoder.isValueNext, lastToken.kind: %v, openStack: %v",
 		d.lastToken.kind, start))
 }
 
 // consumeToken constructs a Token for given Kind with raw value derived from
 // current d.in and given size, and consumes the given size-length of it.
 func (d *Decoder) consumeToken(kind Kind, size int) Token {
 	tok := Token{
 		kind: kind,
 		raw:  d.in[:size],
 		pos:  len(d.orig) - len(d.in),
 	}
 	d.consume(size)
 	return tok
 }
 
 // consumeBoolToken constructs a Token for a Bool kind with raw value derived from
 // current d.in and given size.
 func (d *Decoder) consumeBoolToken(b bool, size int) Token {
 	tok := Token{
 		kind: Bool,
 		raw:  d.in[:size],
 		pos:  len(d.orig) - len(d.in),
 		boo:  b,
 	}
 	d.consume(size)
 	return tok
 }
 
 // consumeStringToken constructs a Token for a String kind with raw value derived
 // from current d.in and given size.
 func (d *Decoder) consumeStringToken(s string, size int) Token {
 	tok := Token{
 		kind: String,
 		raw:  d.in[:size],
 		pos:  len(d.orig) - len(d.in),
 		str:  s,
 	}
 	d.consume(size)
 	return tok
 }
 
 // Clone returns a copy of the Decoder for use in reading ahead the next JSON
 // object, array or other values without affecting current Decoder.
 func (d *Decoder) Clone() *Decoder {
 	ret := *d
 	ret.openStack = append([]Kind(nil), ret.openStack...)
 	return &ret
 }