library/core/src/str/lossy.rs - rust-lang/rust - Git at Google

 use super::from_utf8_unchecked;
 use super::validations::utf8_char_width;
 use crate::fmt;
 use crate::fmt::{Formatter, Write};
 use crate::iter::FusedIterator;

 impl [u8] {
     /// Creates an iterator over the contiguous valid UTF-8 ranges of this
     /// slice, and the non-UTF-8 fragments in between.
     ///
     /// See the [`Utf8Chunk`] type for documentation of the items yielded by this iterator.
     ///
     /// # Examples
     ///
     /// This function formats arbitrary but mostly-UTF-8 bytes into Rust source
     /// code in the form of a C-string literal (`c"..."`).
     ///
     /// ```
     /// use std::fmt::Write as _;
     ///
     /// pub fn cstr_literal(bytes: &[u8]) -> String {
     ///     let mut repr = String::new();
     ///     repr.push_str("c\"");
     ///     for chunk in bytes.utf8_chunks() {
     ///         for ch in chunk.valid().chars() {
     ///             // Escapes \0, \t, \r, \n, \\, \', \", and uses \u{...} for non-printable characters.
     ///             write!(repr, "{}", ch.escape_debug()).unwrap();
     ///         }
     ///         for byte in chunk.invalid() {
     ///             write!(repr, "\\x{:02X}", byte).unwrap();
     ///         }
     ///     }
     ///     repr.push('"');
     ///     repr
     /// }
     ///
     /// fn main() {
     ///     let lit = cstr_literal(b"\xferris the \xf0\x9f\xa6\x80\x07");
     ///     let expected = stringify!(c"\xFErris the 🦀\u{7}");
     ///     assert_eq!(lit, expected);
     /// }
     /// ```
     #[stable(feature = "utf8_chunks", since = "1.79.0")]
     pub fn utf8_chunks(&self) -> Utf8Chunks<'_> {
         Utf8Chunks { source: self }
     }
 }

 /// An item returned by the [`Utf8Chunks`] iterator.
 ///
 /// A `Utf8Chunk` stores a sequence of [`u8`] up to the first broken character
 /// when decoding a UTF-8 string.
 ///
 /// # Examples
 ///
 /// ```
 /// // An invalid UTF-8 string
 /// let bytes = b"foo\xF1\x80bar";
 ///
 /// // Decode the first `Utf8Chunk`
 /// let chunk = bytes.utf8_chunks().next().unwrap();
 ///
 /// // The first three characters are valid UTF-8
 /// assert_eq!("foo", chunk.valid());
 ///
 /// // The fourth character is broken
 /// assert_eq!(b"\xF1\x80", chunk.invalid());
 /// ```
 #[stable(feature = "utf8_chunks", since = "1.79.0")]
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct Utf8Chunk<'a> {
     valid: &'a str,
     invalid: &'a [u8],
 }

 impl<'a> Utf8Chunk<'a> {
     /// Returns the next validated UTF-8 substring.
     ///
     /// This substring can be empty at the start of the string or between
     /// broken UTF-8 characters.
     #[must_use]
     #[stable(feature = "utf8_chunks", since = "1.79.0")]
     pub fn valid(&self) -> &'a str {
         self.valid
     }

     /// Returns the invalid sequence that caused a failure.
     ///
     /// The returned slice will have a maximum length of 3 and starts after the
     /// substring given by [`valid`]. Decoding will resume after this sequence.
     ///
     /// If empty, this is the last chunk in the string. If non-empty, an
     /// unexpected byte was encountered or the end of the input was reached
     /// unexpectedly.
     ///
     /// Lossy decoding would replace this sequence with [`U+FFFD REPLACEMENT
     /// CHARACTER`].
     ///
     /// [`valid`]: Self::valid
     /// [`U+FFFD REPLACEMENT CHARACTER`]: crate::char::REPLACEMENT_CHARACTER
     #[must_use]
     #[stable(feature = "utf8_chunks", since = "1.79.0")]
     pub fn invalid(&self) -> &'a [u8] {
         self.invalid
     }
 }

 #[must_use]
 #[unstable(feature = "str_internals", issue = "none")]
 pub struct Debug<'a>(&'a [u8]);

 #[unstable(feature = "str_internals", issue = "none")]
 impl fmt::Debug for Debug<'_> {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         f.write_char('"')?;

         for chunk in self.0.utf8_chunks() {
             // Valid part.
             // Here we partially parse UTF-8 again which is suboptimal.
             {
                 let valid = chunk.valid();
                 let mut from = 0;
                 for (i, c) in valid.char_indices() {
                     let esc = c.escape_debug();
                     // If char needs escaping, flush backlog so far and write, else skip
                     if esc.len() != 1 {
                         f.write_str(&valid[from..i])?;
                         for c in esc {
                             f.write_char(c)?;
                         }
                         from = i + c.len_utf8();
                     }
                 }
                 f.write_str(&valid[from..])?;
             }

             // Broken parts of string as hex escape.
             for &b in chunk.invalid() {
                 write!(f, "\\x{:02X}", b)?;
             }
         }

         f.write_char('"')
     }
 }

 /// An iterator used to decode a slice of mostly UTF-8 bytes to string slices
 /// ([`&str`]) and byte slices ([`&[u8]`][byteslice]).
 ///
 /// This struct is created by the [`utf8_chunks`] method on bytes slices.
 /// If you want a simple conversion from UTF-8 byte slices to string slices,
 /// [`from_utf8`] is easier to use.
 ///
 /// See the [`Utf8Chunk`] type for documentation of the items yielded by this iterator.
 ///
 /// [byteslice]: slice
 /// [`utf8_chunks`]: slice::utf8_chunks
 /// [`from_utf8`]: super::from_utf8
 ///
 /// # Examples
 ///
 /// This can be used to create functionality similar to
 /// [`String::from_utf8_lossy`] without allocating heap memory:
 ///
 /// ```
 /// fn from_utf8_lossy<F>(input: &[u8], mut push: F) where F: FnMut(&str) {
 ///     for chunk in input.utf8_chunks() {
 ///         push(chunk.valid());
 ///
 ///         if !chunk.invalid().is_empty() {
 ///             push("\u{FFFD}");
 ///         }
 ///     }
 /// }
 /// ```
 ///
 /// [`String::from_utf8_lossy`]: ../../std/string/struct.String.html#method.from_utf8_lossy
 #[must_use = "iterators are lazy and do nothing unless consumed"]
 #[stable(feature = "utf8_chunks", since = "1.79.0")]
 #[derive(Clone)]
 pub struct Utf8Chunks<'a> {
     source: &'a [u8],
 }

 impl<'a> Utf8Chunks<'a> {
     #[doc(hidden)]
     #[unstable(feature = "str_internals", issue = "none")]
     pub fn debug(&self) -> Debug<'_> {
         Debug(self.source)
     }
 }

 #[stable(feature = "utf8_chunks", since = "1.79.0")]
 impl<'a> Iterator for Utf8Chunks<'a> {
     type Item = Utf8Chunk<'a>;

     fn next(&mut self) -> Option<Utf8Chunk<'a>> {
         if self.source.is_empty() {
             return None;
         }

         const TAG_CONT_U8: u8 = 128;
         fn safe_get(xs: &[u8], i: usize) -> u8 {
             *xs.get(i).unwrap_or(&0)
         }

         let mut i = 0;
         let mut valid_up_to = 0;
         while i < self.source.len() {
             // SAFETY: `i < self.source.len()` per previous line.
             // For some reason the following are both significantly slower:
             // while let Some(&byte) = self.source.get(i) {
             // while let Some(byte) = self.source.get(i).copied() {
             let byte = unsafe { *self.source.get_unchecked(i) };
             i += 1;

             if byte < 128 {
                 // This could be a `1 => ...` case in the match below, but for
                 // the common case of all-ASCII inputs, we bypass loading the
                 // sizeable UTF8_CHAR_WIDTH table into cache.
             } else {
                 let w = utf8_char_width(byte);

                 match w {
                     2 => {
                         if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
                             break;
                         }
                         i += 1;
                     }
                     3 => {
                         match (byte, safe_get(self.source, i)) {
                             (0xE0, 0xA0..=0xBF) => (),
                             (0xE1..=0xEC, 0x80..=0xBF) => (),
                             (0xED, 0x80..=0x9F) => (),
                             (0xEE..=0xEF, 0x80..=0xBF) => (),
                             _ => break,
                         }
                         i += 1;
                         if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
                             break;
                         }
                         i += 1;
                     }
                     4 => {
                         match (byte, safe_get(self.source, i)) {
                             (0xF0, 0x90..=0xBF) => (),
                             (0xF1..=0xF3, 0x80..=0xBF) => (),
                             (0xF4, 0x80..=0x8F) => (),
                             _ => break,
                         }
                         i += 1;
                         if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
                             break;
                         }
                         i += 1;
                         if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
                             break;
                         }
                         i += 1;
                     }
                     _ => break,
                 }
             }

             valid_up_to = i;
         }

         // SAFETY: `i <= self.source.len()` because it is only ever incremented
         // via `i += 1` and in between every single one of those increments, `i`
         // is compared against `self.source.len()`. That happens either
         // literally by `i < self.source.len()` in the while-loop's condition,
         // or indirectly by `safe_get(self.source, i) & 192 != TAG_CONT_U8`. The
         // loop is terminated as soon as the latest `i += 1` has made `i` no
         // longer less than `self.source.len()`, which means it'll be at most
         // equal to `self.source.len()`.
         let (inspected, remaining) = unsafe { self.source.split_at_unchecked(i) };
         self.source = remaining;

         // SAFETY: `valid_up_to <= i` because it is only ever assigned via
         // `valid_up_to = i` and `i` only increases.
         let (valid, invalid) = unsafe { inspected.split_at_unchecked(valid_up_to) };

         Some(Utf8Chunk {
             // SAFETY: All bytes up to `valid_up_to` are valid UTF-8.
             valid: unsafe { from_utf8_unchecked(valid) },
             invalid,
         })
     }
 }

 #[stable(feature = "utf8_chunks", since = "1.79.0")]
 impl FusedIterator for Utf8Chunks<'_> {}

 #[stable(feature = "utf8_chunks", since = "1.79.0")]
 impl fmt::Debug for Utf8Chunks<'_> {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         f.debug_struct("Utf8Chunks").field("source", &self.debug()).finish()
     }
 }
	use super::from_utf8_unchecked;
	use super::validations::utf8_char_width;
	use crate::fmt;
	use crate::fmt::{Formatter, Write};
	use crate::iter::FusedIterator;

	impl [u8] {
	/// Creates an iterator over the contiguous valid UTF-8 ranges of this
	/// slice, and the non-UTF-8 fragments in between.
	///
	/// See the [`Utf8Chunk`] type for documentation of the items yielded by this iterator.
	///
	/// # Examples
	///
	/// This function formats arbitrary but mostly-UTF-8 bytes into Rust source
	/// code in the form of a C-string literal (`c"..."`).
	///
	/// ```
	/// use std::fmt::Write as _;
	///
	/// pub fn cstr_literal(bytes: &[u8]) -> String {
	/// let mut repr = String::new();
	/// repr.push_str("c\"");
	/// for chunk in bytes.utf8_chunks() {
	/// for ch in chunk.valid().chars() {
	/// // Escapes \0, \t, \r, \n, \\, \', \", and uses \u{...} for non-printable characters.
	/// write!(repr, "{}", ch.escape_debug()).unwrap();
	/// }
	/// for byte in chunk.invalid() {
	/// write!(repr, "\\x{:02X}", byte).unwrap();
	/// }
	/// }
	/// repr.push('"');
	/// repr
	/// }
	///
	/// fn main() {
	/// let lit = cstr_literal(b"\xferris the \xf0\x9f\xa6\x80\x07");
	/// let expected = stringify!(c"\xFErris the 🦀\u{7}");
	/// assert_eq!(lit, expected);
	/// }
	/// ```
	#[stable(feature = "utf8_chunks", since = "1.79.0")]
	pub fn utf8_chunks(&self) -> Utf8Chunks<'_> {
	Utf8Chunks { source: self }
	}
	}

	/// An item returned by the [`Utf8Chunks`] iterator.
	///
	/// A `Utf8Chunk` stores a sequence of [`u8`] up to the first broken character
	/// when decoding a UTF-8 string.
	///
	/// # Examples
	///
	/// ```
	/// // An invalid UTF-8 string
	/// let bytes = b"foo\xF1\x80bar";
	///
	/// // Decode the first `Utf8Chunk`
	/// let chunk = bytes.utf8_chunks().next().unwrap();
	///
	/// // The first three characters are valid UTF-8
	/// assert_eq!("foo", chunk.valid());
	///
	/// // The fourth character is broken
	/// assert_eq!(b"\xF1\x80", chunk.invalid());
	/// ```
	#[stable(feature = "utf8_chunks", since = "1.79.0")]
	#[derive(Clone, Debug, PartialEq, Eq)]
	pub struct Utf8Chunk<'a> {
	valid: &'a str,
	invalid: &'a [u8],
	}

	impl<'a> Utf8Chunk<'a> {
	/// Returns the next validated UTF-8 substring.
	///
	/// This substring can be empty at the start of the string or between
	/// broken UTF-8 characters.
	#[must_use]
	#[stable(feature = "utf8_chunks", since = "1.79.0")]
	pub fn valid(&self) -> &'a str {
	self.valid
	}

	/// Returns the invalid sequence that caused a failure.
	///
	/// The returned slice will have a maximum length of 3 and starts after the
	/// substring given by [`valid`]. Decoding will resume after this sequence.
	///
	/// If empty, this is the last chunk in the string. If non-empty, an
	/// unexpected byte was encountered or the end of the input was reached
	/// unexpectedly.
	///
	/// Lossy decoding would replace this sequence with [`U+FFFD REPLACEMENT
	/// CHARACTER`].
	///
	/// [`valid`]: Self::valid
	/// [`U+FFFD REPLACEMENT CHARACTER`]: crate::char::REPLACEMENT_CHARACTER
	#[must_use]
	#[stable(feature = "utf8_chunks", since = "1.79.0")]
	pub fn invalid(&self) -> &'a [u8] {
	self.invalid
	}
	}

	#[must_use]
	#[unstable(feature = "str_internals", issue = "none")]
	pub struct Debug<'a>(&'a [u8]);

	#[unstable(feature = "str_internals", issue = "none")]
	impl fmt::Debug for Debug<'_> {
	fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
	f.write_char('"')?;

	for chunk in self.0.utf8_chunks() {
	// Valid part.
	// Here we partially parse UTF-8 again which is suboptimal.
	{
	let valid = chunk.valid();
	let mut from = 0;
	for (i, c) in valid.char_indices() {
	let esc = c.escape_debug();
	// If char needs escaping, flush backlog so far and write, else skip
	if esc.len() != 1 {
	f.write_str(&valid[from..i])?;
	for c in esc {
	f.write_char(c)?;
	}
	from = i + c.len_utf8();
	}
	}
	f.write_str(&valid[from..])?;
	}

	// Broken parts of string as hex escape.
	for &b in chunk.invalid() {
	write!(f, "\\x{:02X}", b)?;
	}
	}

	f.write_char('"')
	}
	}

	/// An iterator used to decode a slice of mostly UTF-8 bytes to string slices
	/// ([`&str`]) and byte slices ([`&[u8]`][byteslice]).
	///
	/// This struct is created by the [`utf8_chunks`] method on bytes slices.
	/// If you want a simple conversion from UTF-8 byte slices to string slices,
	/// [`from_utf8`] is easier to use.
	///
	/// See the [`Utf8Chunk`] type for documentation of the items yielded by this iterator.
	///
	/// [byteslice]: slice
	/// [`utf8_chunks`]: slice::utf8_chunks
	/// [`from_utf8`]: super::from_utf8
	///
	/// # Examples
	///
	/// This can be used to create functionality similar to
	/// [`String::from_utf8_lossy`] without allocating heap memory:
	///
	/// ```
	/// fn from_utf8_lossy<F>(input: &[u8], mut push: F) where F: FnMut(&str) {
	/// for chunk in input.utf8_chunks() {
	/// push(chunk.valid());
	///
	/// if !chunk.invalid().is_empty() {
	/// push("\u{FFFD}");
	/// }
	/// }
	/// }
	/// ```
	///
	/// [`String::from_utf8_lossy`]: ../../std/string/struct.String.html#method.from_utf8_lossy
	#[must_use = "iterators are lazy and do nothing unless consumed"]
	#[stable(feature = "utf8_chunks", since = "1.79.0")]
	#[derive(Clone)]
	pub struct Utf8Chunks<'a> {
	source: &'a [u8],
	}

	impl<'a> Utf8Chunks<'a> {
	#[doc(hidden)]
	#[unstable(feature = "str_internals", issue = "none")]
	pub fn debug(&self) -> Debug<'_> {
	Debug(self.source)
	}
	}

	#[stable(feature = "utf8_chunks", since = "1.79.0")]
	impl<'a> Iterator for Utf8Chunks<'a> {
	type Item = Utf8Chunk<'a>;

	fn next(&mut self) -> Option<Utf8Chunk<'a>> {
	if self.source.is_empty() {
	return None;
	}

	const TAG_CONT_U8: u8 = 128;
	fn safe_get(xs: &[u8], i: usize) -> u8 {
	*xs.get(i).unwrap_or(&0)
	}

	let mut i = 0;
	let mut valid_up_to = 0;
	while i < self.source.len() {
	// SAFETY: `i < self.source.len()` per previous line.
	// For some reason the following are both significantly slower:
	// while let Some(&byte) = self.source.get(i) {
	// while let Some(byte) = self.source.get(i).copied() {
	let byte = unsafe { *self.source.get_unchecked(i) };
	i += 1;

	if byte < 128 {
	// This could be a `1 => ...` case in the match below, but for
	// the common case of all-ASCII inputs, we bypass loading the
	// sizeable UTF8_CHAR_WIDTH table into cache.
	} else {
	let w = utf8_char_width(byte);

	match w {
	2 => {
	if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
	break;
	}
	i += 1;
	}
	3 => {
	match (byte, safe_get(self.source, i)) {
	(0xE0, 0xA0..=0xBF) => (),
	(0xE1..=0xEC, 0x80..=0xBF) => (),
	(0xED, 0x80..=0x9F) => (),
	(0xEE..=0xEF, 0x80..=0xBF) => (),
	_ => break,
	}
	i += 1;
	if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
	break;
	}
	i += 1;
	}
	4 => {
	match (byte, safe_get(self.source, i)) {
	(0xF0, 0x90..=0xBF) => (),
	(0xF1..=0xF3, 0x80..=0xBF) => (),
	(0xF4, 0x80..=0x8F) => (),
	_ => break,
	}
	i += 1;
	if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
	break;
	}
	i += 1;
	if safe_get(self.source, i) & 192 != TAG_CONT_U8 {
	break;
	}
	i += 1;
	}
	_ => break,
	}
	}

	valid_up_to = i;
	}

	// SAFETY: `i <= self.source.len()` because it is only ever incremented
	// via `i += 1` and in between every single one of those increments, `i`
	// is compared against `self.source.len()`. That happens either
	// literally by `i < self.source.len()` in the while-loop's condition,
	// or indirectly by `safe_get(self.source, i) & 192 != TAG_CONT_U8`. The
	// loop is terminated as soon as the latest `i += 1` has made `i` no
	// longer less than `self.source.len()`, which means it'll be at most
	// equal to `self.source.len()`.
	let (inspected, remaining) = unsafe { self.source.split_at_unchecked(i) };
	self.source = remaining;

	// SAFETY: `valid_up_to <= i` because it is only ever assigned via
	// `valid_up_to = i` and `i` only increases.
	let (valid, invalid) = unsafe { inspected.split_at_unchecked(valid_up_to) };

	Some(Utf8Chunk {
	// SAFETY: All bytes up to `valid_up_to` are valid UTF-8.
	valid: unsafe { from_utf8_unchecked(valid) },
	invalid,
	})
	}
	}

	#[stable(feature = "utf8_chunks", since = "1.79.0")]
	impl FusedIterator for Utf8Chunks<'_> {}

	#[stable(feature = "utf8_chunks", since = "1.79.0")]
	impl fmt::Debug for Utf8Chunks<'_> {
	fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
	f.debug_struct("Utf8Chunks").field("source", &self.debug()).finish()
	}
	}