feat(runtime): add ByteStream for binary parsing + MIDI example

README.md

@@ -456,6 +456,39 @@ inline at their ATN action/predicate coordinates. This is the mode the
 conformance harness uses after rendering descriptor grammars through
 `Rust.test.stg` (see below).
 
+### Binary and Byte-Oriented Parsing
+
+ANTLR grammars can parse binary formats, not just text. The convention the
+reference runtimes use is to treat each byte as a codepoint in
+`U+0000..=U+00FF` and write lexer rules over that range
+(`BYTE : '\u0000' .. '\u00FF';`). This runtime ships
+[`ByteStream`](src/byte_stream.rs) for exactly that: a `CharStream` backed by
+raw bytes where the stream index is the byte offset and lookahead returns the
+byte value (`0..=255`). It is generic over the
+backing store — `ByteStream::new(vec)` owns, `ByteStream::new(&buf[..])` borrows
+a network buffer zero-copy, and `ByteStream::from_reader(file)?` drains any
+`std::io::Read`. Because the bytes are not text, `text()` renders a matched span
+as lowercase hex.
+
+Length-prefixed formats ("read N, then consume N bytes") are data-dependent, so
+a pure grammar cannot frame them alone — the same constraint ANTLR's `bencoding`
+grammar solves with a lexer `superClass`. Here that role is filled by a
+[`SemanticHooks`](src/parser.rs) implementation: `LexerSemCtx`/`LexerLifecycleCtx`
+expose `push_mode`/`pop_mode`, `enqueue_token` (to synthesize framing tokens),
+and raw `la()` lookbehind, so a small hook struct can count down a declared
+chunk length and emit an end-of-chunk token. A bare `{helper();}` lexer action
+lowers to a typed hook method via a `--sem-patterns` `[[helper]]` entry with
+`kind = "lexer-action"`, `lower = "hook"`.
+
+A complete worked example — a Standard MIDI File grammar (MThd/MTrk chunks,
+variable-length delta-times, note and meta events) with a chunk-framing hook,
+parsed over a `ByteStream` from a real `.mid` fixture — lives in
+[`tests/fixtures/antlr4-rust-gen/midi-binary/`](tests/fixtures/antlr4-rust-gen/midi-binary/)
+and its integration test (`midi_binary_grammar_parses_standard_midi_file_over_byte_stream`
+in [tests/antlr4_rust_gen_cli.rs](tests/antlr4_rust_gen_cli.rs)). The grammar is
+adapted from [milnet2/midi-grammar](https://github.com/milnet2/midi-grammar)
+(Tobias Blaschke, BSD-3-Clause).
+
 ## Runtime Testsuite
 
 On the maintainer checkout, where the ANTLR jar and upstream runtime-testsuite

src/byte_stream.rs

@@ -0,0 +1,282 @@
+//! A byte-oriented [`CharStream`] for parsing binary formats.
+//!
+//! ANTLR grammars normally consume Unicode text, but many real-world formats
+//! are raw bytes: chunk containers (RIFF/WAV), fixed-width records (tar), and
+//! self-describing tag streams (CBOR, Standard MIDI). The reference runtimes
+//! parse these by treating each byte as a codepoint in `U+0000..=U+00FF` (a
+//! "Latin-1" view) and writing lexer rules over `' '..'ÿ'`.
+//!
+//! [`InputStream`](crate::InputStream) can do this too, but only after decoding
+//! the bytes into a `String`: any byte `>= 0x80` is not valid UTF-8 on its own,
+//! so the whole input takes the non-ASCII path and is materialized into a
+//! `Vec<char>` plus a byte-offset table — roughly 12 bytes of heap per input
+//! byte, and the compiled-DFA ASCII scanner is disabled.
+//!
+//! `ByteStream` avoids all of that. It is generic over any `AsRef<[u8]>`
+//! backing store, so stream index equals byte offset, lookahead is a single
+//! array read, and there is no transcoding or auxiliary allocation.
+//!
+//! # Mapping to Rust IO primitives
+//!
+//! ANTLR parsing needs random access — the lexer and parser `seek`, look
+//! behind with `la(-1)`, and `mark`/`release` for prediction — so the bytes
+//! must live fully in memory; `ByteStream` cannot lazily pull from a socket
+//! mid-parse. The design instead meets the two IO shapes that matter:
+//!
+//! - **Bytes you already hold** (a network read buffer, an `mmap`, a slice of a
+//!   larger frame): borrow them zero-copy with `ByteStream::new(&buf[..])`.
+//!   Nothing is copied; the stream lives as long as the borrow.
+//! - **A reader** (`File`, `TcpStream`, `Stdin`, `Cursor`): drain it into an
+//!   owned buffer with [`ByteStream::from_reader`], which is just a thin
+//!   wrapper over [`std::io::Read::read_to_end`].
+//! - **An owned `Vec<u8>`**: hand it over with `ByteStream::new(vec)` and the
+//!   stream takes ownership without copying.
+//!
+//! ```ignore
+//! // From a file:
+//! let stream = ByteStream::from_reader(std::fs::File::open(path)?)?;
+//! // Zero-copy from an in-memory buffer (e.g. bytes read off a socket):
+//! let stream = ByteStream::new(&packet[..]);
+//!
+//! let lexer = MidiLexer::new(stream);
+//! let tokens = CommonTokenStream::new(lexer);
+//! let mut parser = MidiParser::new(tokens);
+//! let tree = parser.file()?;
+//! ```
+//!
+//! Write lexer rules against the byte range, e.g. `BYTE : ' ' .. 'ÿ';`.
+//!
+//! # Token text is hex
+//!
+//! Because the bytes are not text, [`CharStream::text`] renders the matched
+//! span as a lowercase hex string with no separators (`[0xDE, 0xAD]` becomes
+//! `"dead"`). Token *positions* are still exact byte offsets; use
+//! [`IntStream::index`](crate::IntStream::index) or a token's byte span when you
+//! need to slice the original bytes.
+
+use std::io;
+
+use crate::char_stream::{CharStream, TextInterval};
+use crate::int_stream::{EOF, IntStream, UNKNOWN_SOURCE_NAME};
+
+/// A [`CharStream`] backed by raw bytes, where each byte is one symbol in
+/// `0..=255` and the stream index is the byte offset.
+///
+/// Generic over the backing store `B: AsRef<[u8]>`: use `Vec<u8>` for owned
+/// bytes or `&[u8]` to borrow an existing buffer zero-copy. See the
+/// [module documentation](self) for how this maps onto Rust IO primitives.
+#[derive(Clone, Debug)]
+pub struct ByteStream<B = Vec<u8>> {
+    bytes: B,
+    cursor: usize,
+    source_name: String,
+}
+
+impl ByteStream<Vec<u8>> {
+    /// Creates a byte stream by draining a [`std::io::Read`] into an owned
+    /// buffer — the bridge for files, sockets, stdin, and [`std::io::Cursor`].
+    ///
+    /// # Errors
+    ///
+    /// Returns any error produced while reading `reader` to end.
+    pub fn from_reader(mut reader: impl io::Read) -> io::Result<Self> {
+        let mut bytes = Vec::new();
+        reader.read_to_end(&mut bytes)?;
+        Ok(Self::new(bytes))
+    }
+}
+
+impl<B: AsRef<[u8]>> ByteStream<B> {
+    /// Creates a byte stream over `bytes`, using ANTLR's unknown source-name
+    /// placeholder.
+    ///
+    /// `bytes` may be an owned `Vec<u8>` or a borrowed `&[u8]` (zero-copy).
+    pub fn new(bytes: B) -> Self {
+        Self::with_source_name(bytes, UNKNOWN_SOURCE_NAME)
+    }
+
+    /// Creates a byte stream with an explicit source name for tokens and
+    /// diagnostics.
+    pub fn with_source_name(bytes: B, source_name: impl Into<String>) -> Self {
+        Self {
+            bytes,
+            cursor: 0,
+            source_name: source_name.into(),
+        }
+    }
+
+    /// Returns the backing bytes.
+    #[must_use]
+    pub fn bytes(&self) -> &[u8] {
+        self.bytes.as_ref()
+    }
+
+    /// Returns true when the cursor has reached or passed the end of input.
+    #[must_use]
+    pub fn is_eof(&self) -> bool {
+        self.cursor >= self.bytes.as_ref().len()
+    }
+}
+
+impl<B: AsRef<[u8]>> IntStream for ByteStream<B> {
+    fn consume(&mut self) {
+        if !self.is_eof() {
+            self.cursor += 1;
+        }
+    }
+
+    fn la(&mut self, offset: isize) -> i32 {
+        if offset == 0 {
+            return 0;
+        }
+
+        // Mirror `InputStream::la`: `+1` is the symbol under the cursor, and
+        // negative offsets look behind. `checked_*` keeps `isize::MIN` and
+        // out-of-range lookahead on the EOF path instead of panicking.
+        let absolute = if offset > 0 {
+            self.cursor.checked_add((offset - 1).cast_unsigned())
+        } else {
+            offset
+                .checked_neg()
+                .and_then(|distance| usize::try_from(distance).ok())
+                .and_then(|distance| self.cursor.checked_sub(distance))
+        };
+
+        absolute.map_or(EOF, |index| self.symbol_at(index).unwrap_or(EOF))
+    }
+
+    fn index(&self) -> usize {
+        self.cursor
+    }
+
+    fn seek(&mut self, index: usize) {
+        self.cursor = index.min(self.bytes.as_ref().len());
+    }
+
+    fn size(&self) -> usize {
+        self.bytes.as_ref().len()
+    }
+
+    fn source_name(&self) -> &str {
+        &self.source_name
+    }
+}
+
+impl<B: AsRef<[u8]>> CharStream for ByteStream<B> {
+    /// Renders the inclusive byte interval as a lowercase, separator-free hex
+    /// string. See the [module documentation](self) for the rationale.
+    fn text(&self, interval: TextInterval) -> String {
+        let bytes = self.bytes.as_ref();
+        if interval.is_empty() {
+            return String::new();
+        }
+        let stop = (interval.stop + 1).min(bytes.len());
+        let start = interval.start.min(stop);
+        use std::fmt::Write as _;
+        bytes[start..stop].iter().fold(
+            String::with_capacity((stop - start) * 2),
+            |mut acc, byte| {
+                // Writing to a String is infallible.
+                let _ = write!(acc, "{byte:02x}");
+                acc
+            },
+        )
+    }
+
+    fn symbol_at(&self, index: usize) -> Option<i32> {
+        Some(
+            self.bytes
+                .as_ref()
+                .get(index)
+                .map_or(EOF, |&byte| i32::from(byte)),
+        )
+    }
+
+    // NOTE: `contiguous_ascii` is deliberately NOT implemented. That fast path
+    // feeds bytes into a 128-wide ASCII DFA row (`ascii_target`), which is only
+    // valid for 7-bit input; bytes `>= 0x80` route correctly through the
+    // generic path's `wide_rows` instead.
+
+    fn byte_interval(&self, interval: TextInterval) -> Option<(usize, usize)> {
+        // Index == byte offset, so the byte span is exact.
+        let len = self.bytes.as_ref().len();
+        if interval.is_empty() {
+            let at = self.cursor.min(len);
+            return Some((at, at));
+        }
+        let stop = (interval.stop + 1).min(len);
+        let start = interval.start.min(stop);
+        Some((start, stop))
+    }
+}
+
+#[cfg(test)]
+#[allow(clippy::disallowed_methods)] // insta assertion macros unwrap internal I/O.
+mod tests {
+    use super::*;
+
+    #[test]
+    fn lookahead_reads_bytes_including_high_bytes() {
+        let mut stream = ByteStream::new(vec![0x00, 0x7F, 0x80, 0xFF]);
+        assert_eq!(stream.la(0), 0, "la(0) is the ANTLR sentinel, not EOF");
+        assert_eq!(stream.la(1), 0x00);
+        assert_eq!(stream.la(2), 0x7F);
+        assert_eq!(stream.la(3), 0x80, "high byte is 128, not sign-extended");
+        assert_eq!(stream.la(4), 0xFF);
+        assert_eq!(stream.la(5), EOF);
+        stream.consume();
+        assert_eq!(stream.index(), 1);
+        assert_eq!(stream.la(-1), 0x00);
+        assert_eq!(stream.la(isize::MIN), EOF, "no panic on extreme offset");
+    }
+
+    #[test]
+    fn consume_stops_at_eof_and_seek_clamps() {
+        let mut stream = ByteStream::new(vec![0x01, 0x02]);
+        assert_eq!(stream.size(), 2);
+        stream.consume();
+        stream.consume();
+        stream.consume(); // past EOF is a no-op
+        assert_eq!(stream.index(), 2);
+        assert!(stream.is_eof());
+        stream.seek(99);
+        assert_eq!(stream.index(), 2, "seek clamps to size");
+        stream.seek(1);
+        assert_eq!(stream.la(1), 0x02);
+    }
+
+    #[test]
+    fn text_is_lowercase_hex_and_byte_interval_is_exact() {
+        let stream = ByteStream::new(vec![0xDE, 0xAD, 0xBE, 0xEF]);
+        assert_eq!(stream.text(TextInterval::new(0, 3)), "deadbeef");
+        assert_eq!(stream.text(TextInterval::new(1, 2)), "adbe");
+        assert_eq!(stream.text(TextInterval::empty()), "");
+        // Inclusive char interval [1, 2] -> half-open byte span [1, 3).
+        assert_eq!(stream.byte_interval(TextInterval::new(1, 2)), Some((1, 3)));
+        assert_eq!(stream.symbol_at(0), Some(0xDE));
+        assert_eq!(stream.symbol_at(4), Some(EOF));
+    }
+
+    #[test]
+    fn borrows_bytes_zero_copy() {
+        // The network-buffer case: parse a slice we already hold without
+        // handing ownership to the stream.
+        let buffer: [u8; 4] = [0xCA, 0xFE, 0xBA, 0xBE];
+        let mut stream = ByteStream::new(&buffer[..]);
+        assert_eq!(stream.la(1), 0xCA);
+        assert_eq!(stream.size(), 4);
+        // `buffer` is still ours afterwards.
+        assert_eq!(buffer[0], 0xCA);
+    }
+
+    #[test]
+    fn from_reader_drains_any_read() {
+        // The file/socket case, exercised here with an in-memory Cursor that
+        // implements the same `io::Read` contract as `File`/`TcpStream`.
+        let source = io::Cursor::new(vec![0x4D, 0x54, 0x68, 0x64]); // "MThd"
+        let mut stream = ByteStream::from_reader(source).expect("cursor read is infallible");
+        assert_eq!(stream.size(), 4);
+        assert_eq!(stream.la(1), 0x4D);
+        assert_eq!(stream.text(TextInterval::new(0, 3)), "4d546864");
+    }
+}

src/lib.rs

@@ -3,6 +3,7 @@
 extern crate self as antlr4_runtime;
 
 pub mod atn;
+pub mod byte_stream;
 pub mod char_stream;
 pub mod dfa;
 pub mod errors;
@@ -22,6 +23,7 @@ pub mod vocabulary;
 pub mod xpath;
 
 pub use atn::parser::{ParserAtnPrediction, ParserAtnSimulator, ParserAtnSimulatorError};
+pub use byte_stream::ByteStream;
 pub use char_stream::{CharStream, InputStream, PositionSummary, TextInterval};
 pub use dfa::{DfaStateId, DfaTransition, ParserDfa, ParserDfaStateView, ParserDfaStats};
 pub use errors::{AntlrError, ConsoleErrorListener, ErrorListener};