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refactor: extract parse_hex_char function #60

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Merged
merged 1 commit into from
Nov 12, 2025
Merged

refactor: extract parse_hex_char function #60

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225 changes: 101 additions & 124 deletions src/string.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -136,130 +136,10 @@ pub fn parse_string_with_char_provider<'a, T: CharProvider<'a>>(
let text = text.as_mut().unwrap();
text.push_str(previous_text);
if current_char == 'u' {
let mut hex_text = String::new();
// expect four hex values
for _ in 0..4 {
let current_char = chars.move_next_char();
if !is_hex(current_char) {
return Err(ParseStringError {
byte_index: escape_start,
kind: ParseStringErrorKind::ExpectedFourHexDigits,
});
}
if let Some(current_char) = current_char {
hex_text.push(current_char);
}
}

let hex_value = match u32::from_str_radix(&hex_text, 16) {
Ok(v) => v,
Err(_) => {
return Err(ParseStringError {
byte_index: escape_start,
kind: ParseStringErrorKind::InvalidUnicodeEscapeSequence(hex_text),
});
}
};

// Check if this is a high surrogate (0xD800-0xDBFF)
let hex_char = if (0xD800..=0xDBFF).contains(&hex_value) {
// High surrogate - must be followed by low surrogate
// Peek ahead for \uXXXX pattern
let next_char = chars.move_next_char();
if next_char != Some('\\') {
return Err(ParseStringError {
byte_index: escape_start,
kind: ParseStringErrorKind::InvalidUnicodeEscapeSequence(format!(
"{} (unpaired high surrogate)",
hex_text
)),
});
}

let next_char = chars.move_next_char();
if next_char != Some('u') {
return Err(ParseStringError {
byte_index: escape_start,
kind: ParseStringErrorKind::InvalidUnicodeEscapeSequence(format!(
"{} (unpaired high surrogate)",
hex_text
)),
});
}

// Parse the second \uXXXX
let mut hex_text2 = String::new();
for _ in 0..4 {
let current_char = chars.move_next_char();
if !is_hex(current_char) {
return Err(ParseStringError {
byte_index: escape_start,
kind: ParseStringErrorKind::ExpectedFourHexDigits,
});
}
if let Some(current_char) = current_char {
hex_text2.push(current_char);
}
}

let hex_value2 = match u32::from_str_radix(&hex_text2, 16) {
Ok(v) => v,
Err(_) => {
return Err(ParseStringError {
byte_index: escape_start,
kind: ParseStringErrorKind::InvalidUnicodeEscapeSequence(hex_text2),
});
}
};

// Verify it's a low surrogate (0xDC00-0xDFFF)
if !(0xDC00..=0xDFFF).contains(&hex_value2) {
return Err(ParseStringError {
byte_index: escape_start,
kind: ParseStringErrorKind::InvalidUnicodeEscapeSequence(format!(
"{} (high surrogate not followed by low surrogate)",
hex_text
)),
});
}

// Combine surrogate pair using RFC 8259 formula
let code_point = ((hex_value - 0xD800) * 0x400) + (hex_value2 - 0xDC00) + 0x10000;

match std::char::from_u32(code_point) {
Some(c) => c,
None => {
return Err(ParseStringError {
byte_index: escape_start,
kind: ParseStringErrorKind::InvalidUnicodeEscapeSequence(format!(
"{}\\u{} (invalid surrogate pair)",
hex_text, hex_text2
)),
});
}
}
} else if (0xDC00..=0xDFFF).contains(&hex_value) {
// Low surrogate without high surrogate
return Err(ParseStringError {
byte_index: escape_start,
kind: ParseStringErrorKind::InvalidUnicodeEscapeSequence(format!(
"{} (unpaired low surrogate)",
hex_text
)),
});
} else {
// Normal unicode escape
match std::char::from_u32(hex_value) {
Some(hex_char) => hex_char,
None => {
return Err(ParseStringError {
byte_index: escape_start,
kind: ParseStringErrorKind::InvalidUnicodeEscapeSequence(hex_text),
});
}
}
};

let hex_char = parse_hex_char(chars).map_err(|kind| ParseStringError {
byte_index: escape_start,
kind,
})?;
text.push(hex_char);
last_start_byte_index = chars.byte_index() + chars.current_char().map(|c| c.len_utf8()).unwrap_or(0);
} else {
Expand Down Expand Up @@ -308,6 +188,103 @@ pub fn parse_string_with_char_provider<'a, T: CharProvider<'a>>(
}
}

fn parse_hex_char<'a, T: CharProvider<'a>>(chars: &mut T) -> Result<char, ParseStringErrorKind> {
let mut hex_text = String::new();
// expect four hex values
for _ in 0..4 {
let current_char = chars.move_next_char();
if !is_hex(current_char) {
return Err(ParseStringErrorKind::ExpectedFourHexDigits);
}
if let Some(current_char) = current_char {
hex_text.push(current_char);
}
}

let hex_value = match u32::from_str_radix(&hex_text, 16) {
Ok(v) => v,
Err(_) => {
return Err(ParseStringErrorKind::InvalidUnicodeEscapeSequence(hex_text));
}
};

// Check if this is a high surrogate (0xD800-0xDBFF)
let hex_char = if (0xD800..=0xDBFF).contains(&hex_value) {
// High surrogate - must be followed by low surrogate
// Peek ahead for \uXXXX pattern
let next_char = chars.move_next_char();
if next_char != Some('\\') {
return Err(ParseStringErrorKind::InvalidUnicodeEscapeSequence(format!(
"{} (unpaired high surrogate)",
hex_text
)));
}

let next_char = chars.move_next_char();
if next_char != Some('u') {
return Err(ParseStringErrorKind::InvalidUnicodeEscapeSequence(format!(
"{} (unpaired high surrogate)",
hex_text
)));
}

// Parse the second \uXXXX
let mut hex_text2 = String::new();
for _ in 0..4 {
let current_char = chars.move_next_char();
if !is_hex(current_char) {
return Err(ParseStringErrorKind::ExpectedFourHexDigits);
}
if let Some(current_char) = current_char {
hex_text2.push(current_char);
}
}

let hex_value2 = match u32::from_str_radix(&hex_text2, 16) {
Ok(v) => v,
Err(_) => {
return Err(ParseStringErrorKind::InvalidUnicodeEscapeSequence(hex_text2));
}
};

// Verify it's a low surrogate (0xDC00-0xDFFF)
if !(0xDC00..=0xDFFF).contains(&hex_value2) {
return Err(ParseStringErrorKind::InvalidUnicodeEscapeSequence(format!(
"{} (high surrogate not followed by low surrogate)",
hex_text
)));
}

// Combine surrogate pair using RFC 8259 formula
let code_point = ((hex_value - 0xD800) * 0x400) + (hex_value2 - 0xDC00) + 0x10000;

match std::char::from_u32(code_point) {
Some(c) => c,
None => {
return Err(ParseStringErrorKind::InvalidUnicodeEscapeSequence(format!(
"{}\\u{} (invalid surrogate pair)",
hex_text, hex_text2
)));
}
}
} else if (0xDC00..=0xDFFF).contains(&hex_value) {
// Low surrogate without high surrogate
return Err(ParseStringErrorKind::InvalidUnicodeEscapeSequence(format!(
"{} (unpaired low surrogate)",
hex_text
)));
} else {
// Normal unicode escape
match std::char::from_u32(hex_value) {
Some(hex_char) => hex_char,
None => {
return Err(ParseStringErrorKind::InvalidUnicodeEscapeSequence(hex_text));
}
}
};
Ok(hex_char)
}

fn is_hex(c: Option<char>) -> bool {
let Some(c) = c else {
return false;
Expand Down
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