Implement JavaString

Cargo.toml

@@ -179,6 +179,7 @@ valence_generated = { path = "crates/valence_generated", version = "0.2.0-alpha.
 valence_ident = { path = "crates/valence_ident", version = "0.2.0-alpha.1" }
 valence_ident_macros = { path = "crates/valence_ident_macros", version = "0.2.0-alpha.1" }
 valence_inventory = { path = "crates/valence_inventory", version = "0.2.0-alpha.1" }
+valence_java_string = { path = "crates/valence_java_string", version = "0.1.0" }
 valence_lang = { path = "crates/valence_lang", version = "0.2.0-alpha.1" }
 valence_math = { path = "crates/valence_math", version = "0.2.0-alpha.1" }
 valence_nbt = { path = "crates/valence_nbt", features = [

crates/valence_java_string/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "valence_java_string"
+description = "An implementation of Java strings, tolerant of invalid UTF-16 encoding"
+readme = "README.md"
+version = "0.1.0"
+keywords = ["java", "string", "utf16"]
+edition.workspace = true
+repository.workspace = true
+documentation.workspace = true
+license.workspace = true
+
+[features]
+serde = ["dep:serde"]
+
+[dependencies]
+serde = { workspace = true, optional = true }

crates/valence_java_string/README.md

@@ -0,0 +1,17 @@
+# valence_java_string
+
+An implementation of Java strings, tolerant of invalid UTF-16 encoding.
+This allows for round-trip serialization of all Java strings, including those which contain invalid UTF-16, while still
+being able to perform useful operations on those strings. 
+
+These Java strings use the UTF-8 encoding, with the modification that surrogate code points (code points between U+D800 
+and U+DFFF inclusive) are allowed. This allows for zero-cost conversion from Rust strings to Java strings. This modified
+encoding is known as "semi-UTF-8" throughout the codebase. Similarly, this crate introduces a `JavaCodePoint` type which
+is analogous to `char`, except that surrogate code points are allowed.
+
+This crate is mostly undocumented, because most methods are entirely analogous to those of the same name in Rust's
+strings. Please refer to the `std` documentation.
+
+# Features
+
+- `serde` Adds support for [`serde`](https://docs.rs/serde/latest/serde/)

crates/valence_java_string/src/cesu8.rs

@@ -0,0 +1,251 @@
+use std::borrow::Cow;
+
+use crate::validations::{utf8_char_width, CONT_MASK, TAG_CONT};
+use crate::{JavaStr, JavaString, Utf8Error};
+
+impl JavaStr {
+    /// Converts from Java's [modified UTF-8](https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html#modified-utf-8) format to a `Cow<JavaStr>`.
+    #[inline]
+    pub fn from_modified_utf8(bytes: &[u8]) -> Result<Cow<JavaStr>, Utf8Error> {
+        match JavaStr::from_full_utf8(bytes) {
+            Ok(str) => Ok(Cow::Borrowed(str)),
+            Err(_) => JavaString::from_modified_utf8_iter(bytes.iter().copied()).map(Cow::Owned),
+        }
+    }
+
+    /// Converts to Java's [modified UTF-8](https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html#modified-utf-8) format.
+    #[inline]
+    #[must_use]
+    pub fn to_modified_utf8(&self) -> Cow<[u8]> {
+        if is_valid_cesu8(self) {
+            Cow::Borrowed(self.as_bytes())
+        } else {
+            Cow::Owned(self.to_modified_utf8_internal())
+        }
+    }
+
+    #[inline]
+    fn to_modified_utf8_internal(&self) -> Vec<u8> {
+        let bytes = self.as_bytes();
+        let mut encoded = Vec::with_capacity(bytes.len() + bytes.len() >> 2);
+        let mut i = 0;
+        while i < bytes.len() {
+            let b = bytes[i];
+            if b == 0 {
+                encoded.extend([0xc0, 0x80].into_iter());
+                i += 1;
+            } else if b < 128 {
+                // Pass ASCII through quickly.
+                encoded.push(b);
+                i += 1;
+            } else {
+                // Figure out how many bytes we need for this character.
+                let w = utf8_char_width(b);
+                let char_bytes = unsafe {
+                    // SAFETY: input must be valid semi UTF-8, so there must be at least w more
+                    // bytes from i
+                    bytes.get_unchecked(i..i + w)
+                };
+                if w != 4 {
+                    // Pass through short UTF-8 sequences unmodified.
+                    encoded.extend(char_bytes.iter().copied())
+                } else {
+                    // Encode 4-byte sequences as 6 bytes
+                    let s = unsafe {
+                        // SAFETY: input is valid semi UTF-8
+                        JavaStr::from_semi_utf8_unchecked(bytes)
+                    };
+                    let c = unsafe {
+                        // SAFETY: s contains a single char of width 4
+                        s.chars().next().unwrap_unchecked().as_u32() - 0x10000
+                    };
+                    let s = [((c >> 10) as u16) | 0xd800, ((c & 0x3ff) as u16) | 0xdc00];
+                    encoded.extend(enc_surrogate(s[0]).into_iter());
+                    encoded.extend(enc_surrogate(s[1]).into_iter());
+                }
+                i += w;
+            }
+        }
+        encoded
+    }
+}
+
+impl JavaString {
+    /// Converts from Java's [modified UTF-8](https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html#modified-utf-8) format to a `JavaString`.
+    #[inline]
+    pub fn from_modified_utf8(bytes: Vec<u8>) -> Result<JavaString, Utf8Error> {
+        match JavaString::from_full_utf8(bytes) {
+            Ok(str) => Ok(str),
+            Err(err) => JavaString::from_modified_utf8_iter(err.bytes.into_iter()),
+        }
+    }
+
+    /// Converts from Java's [modified UTF-8](https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html#modified-utf-8) format to a `JavaString`.
+    pub fn from_modified_utf8_iter<I>(mut iter: I) -> Result<JavaString, Utf8Error>
+    where
+        I: Iterator<Item = u8>,
+    {
+        let mut index = 0;
+        let mut decoded = Vec::with_capacity(iter.size_hint().0);
+        let mut surrogate_first: Option<[u8; 3]> = None;
+
+        macro_rules! flush_first_surrogate_half {
+            () => {
+                // append any preceding first half of a surrogate pair
+                if let Some(surrogate_first) = surrogate_first.take() {
+                    decoded.extend(surrogate_first.into_iter());
+                }
+            };
+        }
+
+        while let Some(first) = iter.next() {
+            let old_offset = index;
+
+            macro_rules! err {
+                ($error_len:expr) => {
+                    return Err(Utf8Error {
+                        valid_up_to: old_offset,
+                        error_len: $error_len,
+                    })
+                };
+            }
+
+            macro_rules! next {
+                () => {{
+                    index += 1;
+                    match iter.next() {
+                        Some(a) => a,
+                        None => err!(None),
+                    }
+                }};
+            }
+
+            macro_rules! next_cont {
+                ($error_len:expr) => {{
+                    let byte = next!();
+                    if (byte) & !CONT_MASK == TAG_CONT {
+                        byte
+                    } else {
+                        err!($error_len)
+                    }
+                }};
+            }
+
+            if first == 0 {
+                // modified UTF-8 should never contain \0 directly.
+                err!(None);
+            } else if first < 128 {
+                flush_first_surrogate_half!();
+                // Pass ASCII through directly.
+                decoded.push(first);
+            } else if first == 0xc0 {
+                flush_first_surrogate_half!();
+                // modified UTF-8 encoding of null character
+                match next!() {
+                    0x80 => decoded.push(0),
+                    _ => err!(Some(1)),
+                }
+            } else {
+                let w = utf8_char_width(first);
+                let second = next_cont!(Some(1));
+                match w {
+                    // Two-byte sequences can be used directly.
+                    2 => {
+                        flush_first_surrogate_half!();
+                        decoded.extend([first, second].into_iter());
+                    }
+                    3 => {
+                        let third = next_cont!(Some(2));
+                        match (first, second) {
+                            // These are valid UTF-8, so pass them through.
+                            (0xe0, 0xa0..=0xbf)
+                            | (0xe1..=0xec, 0x80..=0xbf)
+                            | (0xed, 0x80..=0x9f)
+                            | (0xee..=0xef, 0x80..=0xbf) => {
+                                flush_first_surrogate_half!();
+                                decoded.extend([first, second, third].into_iter())
+                            }
+                            // First half of a surrogate pair
+                            (0xed, 0xa0..=0xaf) => {
+                                flush_first_surrogate_half!();
+                                surrogate_first = Some([first, second, third]);
+                            }
+                            // Second half of a surrogate pair
+                            (0xed, 0xb0..=0xbf) => {
+                                // try to pair the second half with a preceding first half
+                                if let Some([_, b, c]) = surrogate_first.take() {
+                                    let (fifth, sixth) = (second, third);
+                                    let (second, third) = (b, c);
+                                    let s = dec_surrogates(second, third, fifth, sixth);
+                                    decoded.extend(s.into_iter());
+                                } else {
+                                    // no first half, append the second half directly
+                                    decoded.extend([first, second, third].into_iter());
+                                }
+                            }
+                            _ => err!(Some(1)),
+                        }
+                    }
+                    _ => err!(Some(1)), // modified UTF-8 doesn't allow width 4
+                }
+            }
+        }
+
+        flush_first_surrogate_half!();
+
+        unsafe {
+            // SAFETY: we built a semi UTF-8 encoded string
+            Ok(JavaString::from_semi_utf8_unchecked(decoded))
+        }
+    }
+
+    /// Converts to Java's [modified UTF-8](https://docs.oracle.com/javase/8/docs/api/java/io/DataInput.html#modified-utf-8) format.
+    #[inline]
+    #[must_use]
+    pub fn into_modified_utf8(self) -> Vec<u8> {
+        if is_valid_cesu8(&self) {
+            self.into_bytes()
+        } else {
+            self.to_modified_utf8_internal()
+        }
+    }
+}
+
+#[inline]
+fn dec_surrogate(second: u8, third: u8) -> u32 {
+    0xd000 | ((second & CONT_MASK) as u32) << 6 | (third & CONT_MASK) as u32
+}
+
+#[inline]
+fn dec_surrogates(second: u8, third: u8, fifth: u8, sixth: u8) -> [u8; 4] {
+    // Convert to a 32-bit code point.
+    let s1 = dec_surrogate(second, third);
+    let s2 = dec_surrogate(fifth, sixth);
+    let c = 0x10000 + (((s1 - 0xd800) << 10) | (s2 - 0xdc00));
+    assert!((0x010000..=0x10ffff).contains(&c));
+
+    // Convert to UTF-8.
+    // 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
+    [
+        0b1111_0000u8 | ((c & 0b1_1100_0000_0000_0000_0000) >> 18) as u8,
+        TAG_CONT | ((c & 0b0_0011_1111_0000_0000_0000) >> 12) as u8,
+        TAG_CONT | ((c & 0b0_0000_0000_1111_1100_0000) >> 6) as u8,
+        TAG_CONT | (c & 0b0_0000_0000_0000_0011_1111) as u8,
+    ]
+}
+
+#[inline]
+fn is_valid_cesu8(text: &JavaStr) -> bool {
+    text.bytes()
+        .all(|b| b != 0 && ((b & !CONT_MASK) == TAG_CONT || utf8_char_width(b) <= 3))
+}
+
+#[inline]
+fn enc_surrogate(surrogate: u16) -> [u8; 3] {
+    // 1110xxxx 10xxxxxx 10xxxxxx
+    [
+        0b11100000 | ((surrogate & 0b11110000_00000000) >> 12) as u8,
+        TAG_CONT | ((surrogate & 0b00001111_11000000) >> 6) as u8,
+        TAG_CONT | (surrogate & 0b00000000_00111111) as u8,
+    ]
+}