v/vlib/x/json2/scanner.v

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// Copyright (c) 2019-2021 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module json2
import strconv
struct Scanner {
mut:
text []byte
pos int
line int
col int
}
enum TokenKind {
none_
error
str_
float
int_
null
bool_
eof
comma = 44
colon = 58
lsbr = 91
rsbr = 93
lcbr = 123
rcbr = 125
}
struct Token {
lit []byte
kind TokenKind
line int
col int
}
const (
// list of characters commonly used in JSON.
char_list = [`{`, `}`, `[`, `]`, `,`, `:`]
// list of newlines to check when moving to a new position.
newlines = [`\r`, `\n`, `\t`]
// list of escapable that needs to be escaped inside a JSON string.
// double quotes and forward slashes are excluded intentionally since
// they have their own separate checks for it in order to pass the
// JSON test suite (https://github.com/nst/JSONTestSuite/).
important_escapable_chars = [`\b`, `\f`, `\n`, `\r`, `\t`]
// list of valid unicode escapes aside from \u{4-hex digits}
valid_unicode_escapes = [`b`, `f`, `n`, `r`, `t`, `\\`, `"`, `/`]
// used for transforming escapes into valid unicode (eg. n => \n)
unicode_transform_escapes = map{
98: `\b`
102: `\f`
110: `\n`
114: `\r`
116: `\t`
92: `\\`
34: `"`
47: `/`
}
exp_signs = [byte(`-`), `+`]
)
// move_pos proceeds to the next position.
fn (mut s Scanner) move() {
s.move_pos(true, true)
}
// move_pos_with_newlines is the same as move_pos but only enables newline checking.
fn (mut s Scanner) move_pos_with_newlines() {
s.move_pos(false, true)
}
fn (mut s Scanner) move_pos(include_space bool, include_newlines bool) {
s.pos++
if s.pos < s.text.len {
if include_newlines && s.text[s.pos] in json2.newlines {
s.line++
s.col = 0
if s.text[s.pos] == `\r` && s.pos + 1 < s.text.len && s.text[s.pos + 1] == `\n` {
s.pos++
}
for s.pos < s.text.len && s.text[s.pos] in json2.newlines {
s.move()
}
} else if include_space && s.text[s.pos] == ` ` {
s.pos++
s.col++
for s.pos < s.text.len && s.text[s.pos] == ` ` {
s.move()
}
}
} else {
s.col++
}
}
// error returns an error token.
fn (s Scanner) error(description string) Token {
return s.tokenize(description.bytes(), .error)
}
// tokenize returns a token based on the given lit and kind.
fn (s Scanner) tokenize(lit []byte, kind TokenKind) Token {
return Token{
lit: lit
kind: kind
col: s.col
line: s.line
}
}
// text_scan scans and returns a string token.
[manualfree]
fn (mut s Scanner) text_scan() Token {
mut has_closed := false
mut chrs := []byte{}
for {
s.pos++
s.col++
if s.pos >= s.text.len {
break
}
ch := s.text[s.pos]
if (s.pos - 1 >= 0 && s.text[s.pos - 1] != `\\`) && ch == `"` {
has_closed = true
break
} else if (s.pos - 1 >= 0 && s.text[s.pos - 1] != `\\`)
&& ch in json2.important_escapable_chars {
return s.error('character must be escaped with a backslash')
} else if (s.pos == s.text.len - 1 && ch == `\\`) || ch == byte(0) {
return s.error('invalid backslash escape')
} else if s.pos + 1 < s.text.len && ch == `\\` {
peek := s.text[s.pos + 1]
if peek in json2.valid_unicode_escapes {
chrs << json2.unicode_transform_escapes[int(peek)]
s.pos++
s.col++
continue
} else if peek == `u` {
if s.pos + 5 < s.text.len {
s.pos++
s.col++
mut codepoint := []byte{}
codepoint_start := s.pos
for s.pos < s.text.len && s.pos < codepoint_start + 4 {
s.pos++
s.col++
if s.text[s.pos] == `"` {
break
} else if !s.text[s.pos].is_hex_digit() {
return s.error('`${s.text[s.pos].ascii_str()}` is not a hex digit')
}
codepoint << s.text[s.pos]
}
if codepoint.len != 4 {
return s.error('unicode escape must have 4 hex digits')
}
val := u32(strconv.parse_uint(codepoint.bytestr(), 16, 32))
converted := utf32_to_str(val)
converted_bytes := converted.bytes()
chrs << converted_bytes
unsafe {
converted.free()
converted_bytes.free()
codepoint.free()
}
continue
} else {
return s.error('incomplete unicode escape')
}
} else if peek == `U` {
return s.error('unicode endpoints must be in lowercase `u`')
} else if peek == byte(229) {
return s.error('unicode endpoint not allowed')
} else {
return s.error('invalid backslash escape')
}
}
chrs << ch
}
tok := s.tokenize(chrs, .str_)
s.move()
if !has_closed {
return s.error('missing double quotes in string closing')
}
return tok
}
// num_scan scans and returns an int/float token.
fn (mut s Scanner) num_scan() Token {
// analyze json number structure
// -[digit][?[dot][digit]][?[E/e][?-/+][digit]]
mut is_fl := false
mut dot_index := -1
mut digits := []byte{}
if s.text[s.pos] == `-` {
digits << `-`
if !s.text[s.pos + 1].is_digit() {
return s.invalid_token()
}
s.move_pos_with_newlines()
}
if s.text[s.pos] == `0` && (s.pos + 1 < s.text.len && s.text[s.pos + 1].is_digit()) {
return s.error('leading zeroes in a number are not allowed')
}
for s.pos < s.text.len && (s.text[s.pos].is_digit() || (!is_fl && s.text[s.pos] == `.`)) {
digits << s.text[s.pos]
if s.text[s.pos] == `.` {
is_fl = true
dot_index = digits.len - 1
}
s.move_pos_with_newlines()
}
if dot_index + 1 < s.text.len && digits[dot_index + 1..].len == 0 {
return s.error('invalid float')
}
if s.pos < s.text.len && (s.text[s.pos] == `e` || s.text[s.pos] == `E`) {
digits << s.text[s.pos]
s.move_pos_with_newlines()
if s.pos < s.text.len && s.text[s.pos] in json2.exp_signs {
digits << s.text[s.pos]
s.move_pos_with_newlines()
}
mut exp_digits_count := 0
for s.pos < s.text.len && s.text[s.pos].is_digit() {
digits << s.text[s.pos]
exp_digits_count++
s.move_pos_with_newlines()
}
if exp_digits_count == 0 {
return s.error('invalid exponent')
}
}
kind := if is_fl { TokenKind.float } else { TokenKind.int_ }
return s.tokenize(digits, kind)
}
// invalid_token returns an error token with the invalid token message.
fn (s Scanner) invalid_token() Token {
if s.text[s.pos] >= 32 && s.text[s.pos] <= 126 {
return s.error('invalid token `${s.text[s.pos].ascii_str()}`')
} else {
return s.error('invalid token ${s.text[s.pos].str_escaped()}')
}
}
// scan returns a token based on the scanner's current position.
[manualfree]
fn (mut s Scanner) scan() Token {
if s.pos < s.text.len && (s.text[s.pos] == ` ` || s.text[s.pos] in json2.newlines) {
s.move()
}
if s.pos >= s.text.len {
return s.tokenize([]byte{}, .eof)
} else if s.pos + 3 < s.text.len && (s.text[s.pos] == `t` || s.text[s.pos] == `n`) {
ident := s.text[s.pos..s.pos + 4].bytestr()
if ident == 'true' || ident == 'null' {
mut kind := TokenKind.null
if ident == 'true' {
kind = .bool_
}
unsafe { ident.free() }
val := s.text[s.pos..s.pos + 4]
tok := s.tokenize(val, kind)
s.move() // n / t
s.move() // u / r
s.move() // l / u
s.move() // l / e
return tok
}
unsafe { ident.free() }
return s.invalid_token()
} else if s.pos + 4 < s.text.len && s.text[s.pos] == `f` {
ident := s.text[s.pos..s.pos + 5].bytestr()
if ident == 'false' {
unsafe { ident.free() }
val := s.text[s.pos..s.pos + 5]
tok := s.tokenize(val, .bool_)
s.move() // f
s.move() // a
s.move() // l
s.move() // s
s.move() // e
return tok
}
unsafe { ident.free() }
return s.invalid_token()
} else if s.text[s.pos] in json2.char_list {
chr := s.text[s.pos]
tok := s.tokenize([]byte{}, TokenKind(int(chr)))
s.move()
return tok
} else if s.text[s.pos] == `"` {
return s.text_scan()
} else if s.text[s.pos].is_digit() || s.text[s.pos] == `-` {
return s.num_scan()
} else {
return s.invalid_token()
}
}