/* This Source Code Form is subject to the terms of the Mozilla Public *License,v.2.0.IfacopyoftheMPLwasnotdistributedwiththis
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
//! This crate implements a prefs file parser. //! //! Pref files have the following grammar. Note that there are slight //! differences between the grammar for a default prefs files and a user prefs //! file. //! //! ```text //! <pref-file> = <pref>* //! <pref> = <pref-spec> "(" <pref-name> "," <pref-value> <pref-attrs> ")" ";" //! <pref-spec> = "user_pref" | "pref" | "sticky_pref" // in default pref files //! <pref-spec> = "user_pref" // in user pref files //! <pref-name> = <string-literal> //! <pref-value> = <string-literal> | "true" | "false" | <int-value> //! <int-value> = <sign>? <int-literal> //! <sign> = "+" | "-" //! <int-literal> = [0-9]+ (and cannot be followed by [A-Za-z_]) //! <string-literal> = //! A single or double-quoted string, with the following escape sequences //! allowed: \", \', \\, \n, \r, \xNN, \uNNNN, where \xNN gives a raw byte //! value that is copied directly into an 8-bit string value, and \uNNNN //! gives a UTF-16 code unit that is converted to UTF-8 before being copied //! into an 8-bit string value. \x00 and \u0000 are disallowed because they //! would cause C++ code handling such strings to misbehave. //! <pref-attrs> = ("," <pref-attr>)* // in default pref files //! = <empty> // in user pref files //! <pref-attr> = "sticky" | "locked" // default pref files only //! ``` //! //! Comments can take three forms: //! - `# Python-style comments` //! - `// C++ style comments` //! - `/* C style comments (non-nested) */` //! //! Non-end-of-line whitespace chars are `\t`, `\v`, `\f`, and space. //! //! End-of-line sequences can take three forms, each of which is considered as //! a single EOL: //! - `\n` //! - `\r` (without subsequent `\n`) //! - `\r\n` //! //! The valid range for `<int-value>` is -2,147,483,648..2,147,483,647. Values //! outside that range will result in a parse error. //! //! A `\0` char is interpreted as the end of the file. The use of this character //! in a prefs file is not recommended. Within string literals `\x00` or //! `\u0000` can be used instead. //! //! The parser performs error recovery. On a syntax error, it will scan forward //! to the next `;` token and then continue parsing. If the syntax error occurs //! in the middle of a token, it will first finish obtaining the current token //! in an appropriate fashion.
// This parser uses several important optimizations. // // - Because "`\0` means EOF" is part of the grammar (see above), EOF is // representable by a u8. If EOF was represented by an out-of-band value such // as -1 or 256, we'd have to return a larger type such as `u16` or `i16` // from `get_char()`. // // - When starting a new token, it uses a lookup table with the first char, // which quickly identifies what kind of token it will be. Furthermore, if // that token is an unambiguous single-char token (e.g. `(`, `)`, `+`, `,`, // `-`, `;`), the parser will return the appropriate token kind value at // minimal cost because the single-char tokens have a uniform representation. // // - It has a lookup table that identifies chars in string literals that need // special handling. This means non-special chars (the common case) can be // handled with a single test, rather than testing for the multiple special // cases. // // - It pre-scans string literals for special chars. If none are present, it // bulk copies the string literal into a Vec, which is faster than doing a // char-by-char copy. // // - It reuses Vecs to avoid creating a new one for each string literal.
use std::os::raw::{c_char, c_uchar};
//--------------------------------------------------------------------------- // The public interface //---------------------------------------------------------------------------
/// Keep this in sync with PrefType in Preferences.cpp. #[derive(Clone, Copy, Debug, PartialEq)] #[repr(u8)] pubenum PrefType {
None,
String,
Int,
Bool,
}
/// Keep this in sync with PrefValueKind in Preferences.h. #[derive(Clone, Copy, Debug, PartialEq)] #[repr(u8)] pubenum PrefValueKind {
Default,
User,
}
/// Keep this in sync with PrefValue in Preferences.cpp. #[repr(C)] pub union PrefValue { pub string_val: *const c_char, pub int_val: i32, pub bool_val: bool,
}
/// Keep this in sync with PrefsParserPrefFn in Preferences.cpp. type PrefFn = unsafeextern"C"fn(
pref_name: *const c_char,
pref_type: PrefType,
pref_value_kind: PrefValueKind,
pref_value: PrefValue,
is_sticky: bool,
is_locked: bool,
);
/// Keep this in sync with PrefsParserErrorFn in Preferences.cpp. type ErrorFn = unsafeextern"C"fn(msg: *const c_char);
/// Parse the contents of a prefs file. /// /// `buf` is a null-terminated string. `len` is its length, excluding the /// null terminator. /// /// `pref_fn` is called once for each successfully parsed pref. /// /// `error_fn` is called once for each parse error detected. /// /// Keep this in sync with the prefs_parser_parse() declaration in /// Preferences.cpp. #[no_mangle] pubunsafeextern"C"fn prefs_parser_parse(
path: *const c_char,
kind: PrefValueKind,
buf: *const c_char,
len: usize,
pref_fn: PrefFn,
error_fn: ErrorFn,
) -> bool { let path = std::ffi::CStr::from_ptr(path)
.to_string_lossy()
.into_owned();
// Make sure `buf` ends in a '\0', and include that in the length, because // it represents EOF. let buf = std::slice::from_raw_parts(buf as *const c_uchar, len + 1);
assert!(buf.last() == Some(&EOF));
//--------------------------------------------------------------------------- // The implementation //---------------------------------------------------------------------------
// String literal, e.g. '"string"'. The value is stored elsewhere.
String,
// Unsigned integer literal, e.g. '123'. Although libpref uses i32 values, // any '-' and '+' before an integer literal are treated as separate // tokens, so these token values are always positive. Furthermore, we // tokenize int literals as u32 so that 2147483648 (which doesn't fit into // an i32) can be subsequently negated to -2147483648 (which does fit into // an i32) if a '-' token precedes it.
Int(u32),
// Malformed token.
Error(&'static str),
// Malformed token at a particular line number. For use when // Parser::line_num might not be the right line number when the error is // reported. E.g. if a multi-line string has a bad escape sequence on the // first line, we don't report the error until the string's end has been // reached.
ErrorAtLine(&'static str, u32),
}
// We categorize every char by what action should be taken when it appears at // the start of a new token. #[derive(Clone, Copy, PartialEq)] enum CharKind { // These are ordered by frequency. See the comment in GetToken().
SingleChar, // Unambiguous single-char tokens: [()+,-] or EOF
SpaceNL, // [\t\v\f \n]
Keyword, // [A-Za-z_]
Quote, // ["']
Slash, // /
Digit, // [0-9]
Hash, // #
CR, // \r
Other, // Everything else; invalid except within strings and comments.
}
struct Parser<'t> {
path: &'t str, // Path to the file being parsed. Used in error messages.
kind: PrefValueKind, // Default prefs file or user prefs file?
buf: &'t [u8], // Text being parsed.
i: usize, // Index of next char to be read.
line_num: u32, // Current line number within the text.
pref_fn: PrefFn, // Callback for processing each pref.
error_fn: ErrorFn, // Callback for parse errors.
has_errors: bool, // Have we encountered errors?
}
// As described above, we use 0 to represent EOF. const EOF: u8 = b'\0';
impl<'t> Parser<'t> { fn new(
path: &'t str,
kind: PrefValueKind,
buf: &'t [u8],
pref_fn: PrefFn,
error_fn: ErrorFn,
) -> Parser<'t> { // Make sure these tables take up 1 byte per entry.
assert!(std::mem::size_of_val(&CHAR_KINDS) == 256);
assert!(std::mem::size_of_val(&SPECIAL_STRING_CHARS) == 256);
fn parse(&mutself) -> bool { // These are reused, because allocating a new Vec for every string is slow. letmut name_str = Vec::with_capacity(128); // For pref names. letmut value_str = Vec::with_capacity(512); // For string pref values. letmut none_str = Vec::with_capacity(0); // For tokens that shouldn't be strings.
letmut token = self.get_token(&mut none_str);
// At the top of the loop we already have a token. In a valid input // this will be either the first token of a new pref, or EOF. loop { // <pref-spec> let (pref_value_kind, mut is_sticky) = match token {
Token::Pref ifself.kind == PrefValueKind::Default => {
(PrefValueKind::Default, false)
}
Token::StickyPref ifself.kind == PrefValueKind::Default => {
(PrefValueKind::Default, true)
}
Token::UserPref => (PrefValueKind::User, false),
Token::SingleChar(EOF) => return !self.has_errors,
_ => {
token = self.error_and_recover(
token, ifself.kind == PrefValueKind::Default { "expected pref specifier at start of pref definition"
} else { "expected 'user_pref' at start of pref definition"
},
); continue;
}
};
// If `token` is a Token::{Error,ErrorAtLine}, it's a lexing error and // the error message is within `token`. Otherwise, it's a parsing error // and the error message is in `msg`. let (msg, line_num) = match token {
Token::Error(token_msg) => (token_msg, self.line_num),
Token::ErrorAtLine(token_msg, line_num) => (token_msg, line_num),
_ => (msg, self.line_num),
}; let msg = format!("{}:{}: prefs parse error: {}", self.path, line_num, msg); let msg = std::ffi::CString::new(msg).unwrap(); unsafe { (self.error_fn)(msg.as_ptr() as *const c_char) };
// "Panic-mode" recovery: consume tokens until one of the following // occurs. // - We hit a semicolon, whereupon we return the following token. // - We hit EOF, whereupon we return EOF. // // For this to work, if the lexing functions hit EOF in an error case // they must unget it so we can safely reget it here. // // If the starting token (passed in above) is EOF we must not get // another token otherwise we will read past the end of `self.buf`. letmut dummy_str = Vec::with_capacity(128); letmut token = token; loop { match token {
Token::SingleChar(b';') => returnself.get_token(&mut dummy_str),
Token::SingleChar(EOF) => return token,
_ => {}
}
token = self.get_token(&mut dummy_str);
}
}
#[inline(always)] fn get_char(&mutself) -> u8 { // We do the bounds check ourselves so we can return EOF on failure. // (Although the buffer is guaranteed to end in an EOF char, we might // go one char past that, whereupon we must return EOF again.) ifself.i < self.buf.len() { let c = unsafe { *self.buf.get_unchecked(self.i) }; self.i += 1;
c
} else {
debug_assert!(self.i == self.buf.len());
EOF
}
}
// This function skips the bounds check in optimized builds. Using it at // the hottest two call sites gives a ~15% parsing speed boost. #[inline(always)] unsafefn get_char_unchecked(&mutself) -> u8 {
debug_assert!(self.i < self.buf.len()); let c = *self.buf.get_unchecked(self.i); self.i += 1;
c
}
#[inline(always)] fn match_single_line_comment(&mutself) { loop { // To reach here, the previous char must have been '/' (if this is // the first loop iteration) or non-special (if this is the second // or subsequent iteration), and assertions elsewhere ensure that // there must be at least one subsequent char after those chars // (the '\0' for EOF). let c = unsafe { self.get_char_unchecked() };
// All the special chars have value <= b'\r'. if c > b'\r' { continue;
} match c {
b'\n' => { self.line_num += 1; break;
}
b'\r' => { self.line_num += 1; self.match_char(b'\n'); break;
}
EOF => { break;
}
_ => continue,
}
}
}
fn match_hex_digits(&mutself, ndigits: i32) -> Option<u16> {
debug_assert!(ndigits == 2 || ndigits == 4); letmut value: u16 = 0; for _ in0..ndigits {
value = value << 4; matchself.get_char() {
c @ b'0'..=b'9' => value += (c - b'0') as u16,
c @ b'A'..=b'F' => value += (c - b'A') as u16 + 10,
c @ b'a'..=b'f' => value += (c - b'a') as u16 + 10,
_ => { self.unget_char(); return None;
}
}
}
Some(value)
}
#[inline(always)] fn char_kind(c: u8) -> CharKind { // Use get_unchecked() because a u8 index cannot exceed this table's // bounds. unsafe { *CHAR_KINDS.get_unchecked(c as usize) }
}
#[inline(always)] fn is_special_string_char(c: u8) -> bool { // Use get_unchecked() because a u8 index cannot exceed this table's // bounds. unsafe { *SPECIAL_STRING_CHARS.get_unchecked(c as usize) }
}
// If the obtained Token has a value, it is put within the Token, unless // it's a string, in which case it's put in `str_buf`. This avoids // allocating a new Vec for every string, which is slow. fn get_token(&mutself, str_buf: &mut Vec<u8>) -> Token { loop { // Note: the following tests are ordered by frequency when parsing // greprefs.js: // - SingleChar 36.7% // - SpaceNL 27.7% (14.9% for spaces, 12.8% for NL) // - Keyword 13.4% // - Quote 11.4% // - Slash 8.1% // - Digit 2.7% // - Hash, CR, Other 0.0%
let c = self.get_char(); match Parser::char_kind(c) {
CharKind::SingleChar => { return Token::SingleChar(c);
}
CharKind::SpaceNL => { // It's slightly faster to combine the handling of the // space chars with NL than to handle them separately; we // have an extra test for this case, but one fewer test for // all the subsequent CharKinds. if c == b'\n' { self.line_num += 1;
} continue;
}
CharKind::Keyword => { let start = self.i - 1; loop { let c = self.get_char(); if Parser::char_kind(c) != CharKind::Keyword { self.unget_char(); break;
}
} for info in KEYWORD_INFOS.iter() { if &self.buf[start..self.i] == info.string { return info.token;
}
} return Token::Error("unknown keyword");
}
CharKind::Quote => { returnself.get_string_token(c, str_buf);
}
CharKind::Slash => { matchself.get_char() {
b'/' => { self.match_single_line_comment();
}
b'*' => { if !self.match_multi_line_comment() { return Token::Error("unterminated /* comment");
}
}
c @ _ => { if c == b'\n' || c == b'\r' { // Unget the newline char; the outer loop will // reget it and adjust self.line_num // appropriately. self.unget_char();
} return Token::Error("expected '/' or '*' after '/'");
}
} continue;
}
CharKind::Digit => { letmut value = Some((c - b'0') as u32); loop { let c = self.get_char(); match Parser::char_kind(c) {
CharKind::Digit => { fn add_digit(value: Option<u32>, c: u8) -> Option<u32> {
value?.checked_mul(10)?.checked_add((c - b'0') as u32)
}
value = add_digit(value, c);
}
CharKind::Keyword => { // Reject things like "123foo". Error recovery // will retokenize from "foo" onward. self.unget_char(); return Token::Error("unexpected character in integer literal");
}
_ => { self.unget_char(); break;
}
}
} returnmatch value {
Some(v) => Token::Int(v),
None => Token::Error("integer literal overflowed"),
};
}
CharKind::Hash => { self.match_single_line_comment(); continue;
}
CharKind::CR => { self.match_char(b'\n'); self.line_num += 1; continue;
} // Error recovery will retokenize from the next character.
_ => return Token::Error("unexpected character"),
}
}
}
fn string_error_token(&self, token: &mut Token, msg: &'static str) { // We only want to capture the first tokenization error within a string. if *token == Token::String {
*token = Token::ErrorAtLine(msg, self.line_num);
}
}
// Always inline this because it has a single call site. #[inline(always)] fn get_string_token(&mutself, quote_char: u8, str_buf: &le='color:red'>mut Vec<u8>) -> Token { // First scan through the string to see if it contains any chars that // need special handling. let start = self.i; let has_special_chars = loop { // To reach here, the previous char must have been a quote // (quote_char), and assertions elsewhere ensure that there must be // at least one subsequent char (the '\0' for EOF). let c = unsafe { self.get_char_unchecked() }; if Parser::is_special_string_char(c) { break c != quote_char;
}
};
// Clear str_buf's contents without changing its capacity.
str_buf.clear();
// If there are no special chars (the common case), we can bulk copy it // to str_buf. This is a lot faster than the char-by-char loop below. if !has_special_chars {
str_buf.extend(&self.buf[start..self.i - 1]);
str_buf.push(b'\0'); return Token::String;
}
// There were special chars. Re-scan the string, filling in str_buf one // char at a time. // // On error, we change `token` to an error token and then keep going to // the end of the string literal. `str_buf` won't be used in that case. self.i = start; letmut token = Token::String;
loop { let c = self.get_char(); let c2 = if !Parser::is_special_string_char(c) {
c
} elseif c == quote_char { break;
} elseif c == b'\\' { matchself.get_char() {
b'\"' => b'\"',
b'\'' => b'\'',
b'\\' => b'\\',
b'n' => b'\n',
b'r' => b'\r',
b'x' => { iflet Some(value) = self.match_hex_digits(2) {
debug_assert!(value <= 0xff); if value != 0 {
value as u8
} else { self.string_error_token(&mut token, "\\x00 is not allowed"); continue;
}
} else { self.string_error_token(&mut token, "malformed \\x escape sequence"); continue;
}
}
b'u' => { iflet Some(value) = self.match_hex_digits(4) { letmut utf16 = vec![value]; if0xd800 == (0xfc00 & value) { // High surrogate value. Look for the low surrogate value. ifself.match_char(b'\\') && self.match_char(b'u') { iflet Some(lo) = self.match_hex_digits(4) { if0xdc00 == (0xfc00 & lo) { // Found a valid low surrogate.
utf16.push(lo);
} else { self.string_error_token(
&mut token, "invalid low surrogate after high surrogate",
); continue;
}
}
} if utf16.len() != 2 { self.string_error_token(
&mut token, "expected low surrogate after high surrogate",
); continue;
}
} elseif0xdc00 == (0xfc00 & value) { // Unaccompanied low surrogate value. self.string_error_token(
&mut token, "expected high surrogate before low surrogate",
); continue;
} elseif value == 0 { self.string_error_token(&mut token, "\\u0000 is not allowed"); continue;
}
// Insert the UTF-16 sequence as UTF-8. let utf8 = String::from_utf16(&utf16).unwrap();
str_buf.extend(utf8.as_bytes());
} else { self.string_error_token(&mut token, "malformed \\u escape sequence"); continue;
} continue; // We don't want to str_buf.push(c2) below.
}
c @ _ => { if c == b'\n' || c == b'\r' { // Unget the newline char; the outer loop will // reget it and adjust self.line_num appropriately. self.unget_char();
} self.string_error_token(
&mut token, "unexpected escape sequence character after '\\'",
); continue;
}
}
} elseif c == b'\n' { self.line_num += 1;
c
} elseif c == b'\r' { self.line_num += 1; ifself.match_char(b'\n') {
str_buf.push(b'\r');
b'\n'
} else {
c
}
} elseif c == EOF { self.string_error_token(&mut token, "unterminated string literal"); break;
} else { // This case is only hit for the non-closing quote char.
debug_assert!((c == b'\'' || c == b'\"') && c != quote_char);
c
};
str_buf.push(c2);
}
str_buf.push(b'\0');
token
}
}
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