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Feb 14, 2017
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Add comments to justify unsafe blocks. #119

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98 changes: 63 additions & 35 deletions src/tokenizer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -576,6 +576,7 @@ fn consume_string<'a>(tokenizer: &mut Tokenizer<'a>, single_quote: bool) -> Toke
fn consume_quoted_string<'a>(tokenizer: &mut Tokenizer<'a>, single_quote: bool)
-> Result<Cow<'a, str>, ()> {
tokenizer.advance(1); // Skip the initial quote
// start_pos is at code point boundary, after " or '
let start_pos = tokenizer.position();
let mut string_bytes;
loop {
Expand All @@ -598,6 +599,11 @@ fn consume_quoted_string<'a>(tokenizer: &mut Tokenizer<'a>, single_quote: bool)
}
}
b'\\' | b'\0' => {
// * The tokenizer’s input is UTF-8 since it’s `&str`.
// * start_pos is at a code point boundary
// * so is the current position (which is before '\\' or '\0'
//
// So `string_bytes` is well-formed UTF-8.
string_bytes = tokenizer.slice_from(start_pos).as_bytes().to_owned();
break
}
Expand All @@ -611,8 +617,8 @@ fn consume_quoted_string<'a>(tokenizer: &mut Tokenizer<'a>, single_quote: bool)
if matches!(tokenizer.next_byte_unchecked(), b'\n' | b'\r' | b'\x0C') {
return Err(());
}
let c = tokenizer.consume_byte();
match_byte! { c,
let b = tokenizer.consume_byte();
match_byte! { b,
b'"' => {
if !single_quote {
break;
Expand All @@ -634,26 +640,29 @@ fn consume_quoted_string<'a>(tokenizer: &mut Tokenizer<'a>, single_quote: bool)
tokenizer.advance(1);
}
}
// This pushes one well-formed code point
_ => consume_escape_and_write(tokenizer, &mut string_bytes)
}
}
// else: escaped EOF, do nothing.
continue;
}
b'\0' => {
// string.push('\u{FFFD}'),
string_bytes.push(0xef);
string_bytes.push(0xbf);
string_bytes.push(0xbd);
string_bytes.extend("\u{FFFD}".as_bytes());
continue;
}
_ => {},
}

string_bytes.push(c);
// If this byte is part of a multi-byte code point,
// we’ll end up copying the whole code point before this loop does something else.
string_bytes.push(b);
}

Ok(Owned(to_utf8(string_bytes)))
Ok(Owned(
// string_bytes is well-formed UTF-8, see other comments.
unsafe { from_utf8_release_unchecked(string_bytes) }
))
}


Expand Down Expand Up @@ -695,6 +704,7 @@ fn consume_ident_like<'a>(tokenizer: &mut Tokenizer<'a>) -> Token<'a> {
}

fn consume_name<'a>(tokenizer: &mut Tokenizer<'a>) -> Cow<'a, str> {
// start_pos is the end of the previous token, therefore at a code point boundary
let start_pos = tokenizer.position();
let mut value_bytes;
loop {
Expand All @@ -704,11 +714,16 @@ fn consume_name<'a>(tokenizer: &mut Tokenizer<'a>) -> Cow<'a, str> {
match_byte! { tokenizer.next_byte_unchecked(),
b'a'...b'z' | b'A'...b'Z' | b'0'...b'9' | b'_' | b'-' => { tokenizer.advance(1) },
b'\\' | b'\0' => {
// * The tokenizer’s input is UTF-8 since it’s `&str`.
// * start_pos is at a code point boundary
// * so is the current position (which is before '\\' or '\0'
//
// So `value_bytes` is well-formed UTF-8.
value_bytes = tokenizer.slice_from(start_pos).as_bytes().to_owned();
break
}
c => {
if c.is_ascii() {
b => {
if b.is_ascii() {
return Borrowed(tokenizer.slice_from(start_pos));
}
tokenizer.advance(1);
Expand All @@ -717,34 +732,37 @@ fn consume_name<'a>(tokenizer: &mut Tokenizer<'a>) -> Cow<'a, str> {
}

while !tokenizer.is_eof() {
let c = tokenizer.next_byte_unchecked();
match_byte! { c,
let b = tokenizer.next_byte_unchecked();
match_byte! { b,
b'a'...b'z' | b'A'...b'Z' | b'0'...b'9' | b'_' | b'-' => {
tokenizer.advance(1);
value_bytes.push(c)
value_bytes.push(b) // ASCII
}
b'\\' => {
if tokenizer.has_newline_at(1) { break }
tokenizer.advance(1);
// This pushes one well-formed code point
consume_escape_and_write(tokenizer, &mut value_bytes)
}
b'\0' => {
tokenizer.advance(1);
// value.push('\u{FFFD}')
value_bytes.push(0xef);
value_bytes.push(0xbf);
value_bytes.push(0xbd);
value_bytes.extend("\u{FFFD}".as_bytes());
},
_ => {
if c.is_ascii() {
if b.is_ascii() {
break;
}
tokenizer.advance(1);
value_bytes.push(c)
// This byte *is* part of a multi-byte code point,
// we’ll end up copying the whole code point before this loop does something else.
value_bytes.push(b)
}
}
}
Owned(to_utf8(value_bytes))
Owned(
// string_bytes is well-formed UTF-8, see other comments.
unsafe { from_utf8_release_unchecked(value_bytes) }
)
}


Expand Down Expand Up @@ -867,17 +885,16 @@ fn consume_numeric<'a>(tokenizer: &mut Tokenizer<'a>) -> Token<'a> {


#[inline]
fn to_utf8(string_bytes: Vec<u8>) -> String {
unsafe fn from_utf8_release_unchecked(string_bytes: Vec<u8>) -> String {
if cfg!(debug_assertions) {
String::from_utf8(string_bytes).unwrap()
} else {
unsafe {
String::from_utf8_unchecked(string_bytes)
}
String::from_utf8_unchecked(string_bytes)
}
}

fn consume_unquoted_url<'a>(tokenizer: &mut Tokenizer<'a>) -> Result<Token<'a>, ()> {
// This is only called after "url(", so the current position is a code point boundary.
for (offset, c) in tokenizer.input[tokenizer.position..].bytes().enumerate() {
match_byte! { c,
b' ' | b'\t' | b'\n' | b'\r' | b'\x0C' => {},
Expand All @@ -888,6 +905,8 @@ fn consume_unquoted_url<'a>(tokenizer: &mut Tokenizer<'a>) -> Result<Token<'a>,
}
_ => {
tokenizer.advance(offset);
// This function only consumed ASCII (whitespace) bytes,
// so the current position is a code point boundary.
return Ok(consume_unquoted_url_internal(tokenizer))
}
}
Expand All @@ -896,6 +915,7 @@ fn consume_unquoted_url<'a>(tokenizer: &mut Tokenizer<'a>) -> Result<Token<'a>,
return Ok(UnquotedUrl(Borrowed("")));

fn consume_unquoted_url_internal<'a>(tokenizer: &mut Tokenizer<'a>) -> Token<'a> {
// This function is only called with start_pos at a code point boundary.
let start_pos = tokenizer.position();
let mut string_bytes: Vec<u8>;
loop {
Expand All @@ -919,6 +939,11 @@ fn consume_unquoted_url<'a>(tokenizer: &mut Tokenizer<'a>) -> Result<Token<'a>,
return consume_bad_url(tokenizer)
},
b'\\' | b'\0' => {
// * The tokenizer’s input is UTF-8 since it’s `&str`.
// * start_pos is at a code point boundary
// * so is the current position (which is before '\\' or '\0'
//
// So `string_bytes` is well-formed UTF-8.
string_bytes = tokenizer.slice_from(start_pos).as_bytes().to_owned();
break
}
Expand All @@ -930,7 +955,10 @@ fn consume_unquoted_url<'a>(tokenizer: &mut Tokenizer<'a>) -> Result<Token<'a>,
while !tokenizer.is_eof() {
match_byte! { tokenizer.consume_byte(),
b' ' | b'\t' | b'\n' | b'\r' | b'\x0C' => {
return consume_url_end(tokenizer, Owned(to_utf8(string_bytes)));
return consume_url_end(tokenizer, Owned(
// string_bytes is well-formed UTF-8, see other comments.
unsafe { from_utf8_release_unchecked(string_bytes) }
))
}
b')' => {
break;
Expand All @@ -944,18 +972,21 @@ fn consume_unquoted_url<'a>(tokenizer: &mut Tokenizer<'a>) -> Result<Token<'a>,
return consume_bad_url(tokenizer)
}

// This pushes one well-formed code point to string_bytes
consume_escape_and_write(tokenizer, &mut string_bytes)
},
b'\0' => {
// string.push('\u{FFFD}');
string_bytes.push(0xef);
string_bytes.push(0xbf);
string_bytes.push(0xbd);
string_bytes.extend("\u{FFFD}".as_bytes());
}
c => { string_bytes.push(c) }
// If this byte is part of a multi-byte code point,
// we’ll end up copying the whole code point before this loop does something else.
b => { string_bytes.push(b) }
}
}
UnquotedUrl(Owned(to_utf8(string_bytes)))
UnquotedUrl(Owned(
// string_bytes is well-formed UTF-8, see other comments.
unsafe { from_utf8_release_unchecked(string_bytes) }
))
}

fn consume_url_end<'a>(tokenizer: &mut Tokenizer<'a>, string: Cow<'a, str>) -> Token<'a> {
Expand Down Expand Up @@ -1039,11 +1070,8 @@ fn consume_hex_digits<'a>(tokenizer: &mut Tokenizer<'a>) -> (u32, u32) {

// Same constraints as consume_escape except it writes into `bytes` the result
// instead of returning it.
//
// TODO: This could be made more efficient with char::encode_utf8, I guess.
fn consume_escape_and_write(tokenizer: &mut Tokenizer, bytes: &mut Vec<u8>) {
use std::io::Write;
write!(bytes, "{}", consume_escape(tokenizer)).unwrap();
bytes.extend(consume_escape(tokenizer).encode_utf8(&mut [0; 4]).as_bytes())
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Note that encode_utf8 is stable since Rust 1.15.

I’m not convinced this requires a breaking version number increment, but regardless so we’re doing one in #118.

}

// Assumes that the U+005C REVERSE SOLIDUS (\) has already been consumed
Expand Down