Implement bounded Binary LLSD codec

2026-08-09 00:29:07 +00:00
parent d152e80ef9
commit 7a4f1f2fb1
17 changed files with 965 additions and 208 deletions
--- a/crates/libremetaverse-structured-data/src/binary.rs
+++ b/crates/libremetaverse-structured-data/src/binary.rs
@@ -0,0 +1,681 @@
+//! Bounded Binary LLSD codec compatible with `LibreMetaverse`'s marker grammar.
+
+#![allow(clippy::missing_errors_doc)] // Public Result shapes are fixed by the mapped API.
+#![allow(clippy::needless_pass_by_value)] // Owned arguments mirror mapped C# value parameters.
+#![allow(clippy::unnecessary_wraps)] // Result return shapes are fixed by the mapped API.
+#![allow(clippy::unused_self)] // Parser error helpers retain local cursor context call sites.
+
+use crate::{Error, OSD};
+use libremetaverse_types::UUID;
+use libremetaverse_types::compat::{ReadWrite, Uri};
+use std::collections::HashMap;
+use std::io::{Cursor, Read as _, Seek as _, SeekFrom};
+use std::time::{Duration, UNIX_EPOCH};
+
+const HEADER: &[u8] = b"<?llsd/binary?>";
+const ALT_HEADER: &[u8] = b"<? llsd/binary ?>";
+const MAX_INPUT_BYTES: usize = OSD::DEFAULT_MAX_BINARY_BYTES;
+
+const fn is_binary_whitespace(byte: u8) -> bool {
+    matches!(byte, b' ' | b'\t' | b'\n' | b'\r')
+}
+
+pub(crate) fn deserialize_bytes(data: Vec<u8>) -> Result<OSD, Error> {
+    if data.len() > MAX_INPUT_BYTES {
+        return Err(parse_error(0, "binary LLSD input exceeds allocation limit"));
+    }
+    let mut parser = Parser::new(&data);
+    parser.skip_whitespace();
+    if parser.consume_prefix_ignore_ascii_case(ALT_HEADER)
+        || parser.consume_prefix_ignore_ascii_case(HEADER)
+    {
+        parser.skip_whitespace();
+    }
+    let value = parser.parse_value(0)?;
+    value.validate_limits(
+        OSD::DEFAULT_MAX_DEPTH,
+        OSD::DEFAULT_MAX_NODES,
+        OSD::DEFAULT_MAX_BINARY_BYTES,
+    )?;
+    Ok(value)
+}
+
+pub(crate) fn deserialize_stream(mut stream: Box<dyn ReadWrite + Send>) -> Result<OSD, Error> {
+    let mut data = Vec::new();
+    (&mut *stream)
+        .take((MAX_INPUT_BYTES + 1) as u64)
+        .read_to_end(&mut data)
+        .map_err(|_| Error::InvalidOperation)?;
+    deserialize_bytes(data)
+}
+
+pub(crate) fn serialize(value: OSD) -> Result<Vec<u8>, Error> {
+    serialize_with_header(value, true)
+}
+
+pub(crate) fn serialize_with_header(value: OSD, prepend_header: bool) -> Result<Vec<u8>, Error> {
+    value.validate_limits(
+        OSD::DEFAULT_MAX_DEPTH,
+        OSD::DEFAULT_MAX_NODES,
+        OSD::DEFAULT_MAX_BINARY_BYTES,
+    )?;
+    let mut encoder = Encoder::new();
+    if prepend_header {
+        encoder.extend(HEADER)?;
+        encoder.push(b'\n')?;
+    }
+    encoder.write_value(&value, 0)?;
+    Ok(encoder.finish())
+}
+
+pub(crate) fn serialize_stream(value: OSD) -> Result<Cursor<Vec<u8>>, Error> {
+    serialize_stream_with_header(value, true)
+}
+
+pub(crate) fn serialize_stream_with_header(
+    value: OSD,
+    prepend_header: bool,
+) -> Result<Cursor<Vec<u8>>, Error> {
+    let bytes = serialize_with_header(value, prepend_header)?;
+    let position = bytes.len() as u64;
+    let mut cursor = Cursor::new(bytes);
+    cursor.set_position(position);
+    Ok(cursor)
+}
+
+pub(crate) fn consume_bytes(
+    mut stream: Box<dyn ReadWrite + Send>,
+    consume_bytes: i32,
+) -> Result<Vec<u8>, Error> {
+    let length = usize::try_from(consume_bytes).map_err(|_| Error::Argument)?;
+    if length > MAX_INPUT_BYTES {
+        return Err(Error::Argument);
+    }
+    let mut bytes = vec![0_u8; length];
+    stream
+        .read_exact(&mut bytes)
+        .map_err(|_| Error::IndexOutOfRange)?;
+    Ok(bytes)
+}
+
+pub(crate) fn find_byte(mut stream: Box<dyn ReadWrite + Send>, to_find: u8) -> Result<bool, Error> {
+    let start = stream
+        .stream_position()
+        .map_err(|_| Error::InvalidOperation)?;
+    let mut byte = [0_u8; 1];
+    if stream
+        .read(&mut byte)
+        .map_err(|_| Error::InvalidOperation)?
+        == 0
+    {
+        return Ok(false);
+    }
+    if byte[0] == to_find {
+        Ok(true)
+    } else {
+        stream
+            .seek(SeekFrom::Start(start))
+            .map_err(|_| Error::InvalidOperation)?;
+        Ok(false)
+    }
+}
+
+pub(crate) fn find_string(
+    mut stream: Box<dyn ReadWrite + Send>,
+    to_find: String,
+) -> Result<bool, Error> {
+    let start = stream
+        .stream_position()
+        .map_err(|_| Error::InvalidOperation)?;
+    let expected = to_find.as_bytes();
+    if expected.len() > MAX_INPUT_BYTES {
+        return Err(Error::Argument);
+    }
+    let mut actual = vec![0_u8; expected.len()];
+    let matched = stream.read_exact(&mut actual).is_ok()
+        && actual
+            .iter()
+            .zip(expected)
+            .all(|(left, right)| left.eq_ignore_ascii_case(right));
+    if !matched {
+        stream
+            .seek(SeekFrom::Start(start))
+            .map_err(|_| Error::InvalidOperation)?;
+    }
+    Ok(matched)
+}
+
+pub(crate) fn skip_whitespace(mut stream: Box<dyn ReadWrite + Send>) -> Result<(), Error> {
+    loop {
+        let start = stream
+            .stream_position()
+            .map_err(|_| Error::InvalidOperation)?;
+        let mut byte = [0_u8; 1];
+        if stream
+            .read(&mut byte)
+            .map_err(|_| Error::InvalidOperation)?
+            == 0
+        {
+            return Ok(());
+        }
+        if !is_binary_whitespace(byte[0]) {
+            stream
+                .seek(SeekFrom::Start(start))
+                .map_err(|_| Error::InvalidOperation)?;
+            return Ok(());
+        }
+    }
+}
+
+pub(crate) fn host_to_network_int_bytes(value: i32) -> Result<Vec<u8>, Error> {
+    Ok(value.to_be_bytes().to_vec())
+}
+
+pub(crate) fn network_to_host_int(bytes: Vec<u8>) -> Result<i32, Error> {
+    let bytes: [u8; 4] = bytes
+        .get(..4)
+        .ok_or(Error::IndexOutOfRange)?
+        .try_into()
+        .map_err(|_| Error::IndexOutOfRange)?;
+    Ok(i32::from_be_bytes(bytes))
+}
+
+pub(crate) fn network_to_host_double(bytes: Vec<u8>) -> Result<f64, Error> {
+    let bytes: [u8; 8] = bytes
+        .get(..8)
+        .ok_or(Error::IndexOutOfRange)?
+        .try_into()
+        .map_err(|_| Error::IndexOutOfRange)?;
+    Ok(f64::from_be_bytes(bytes))
+}
+
+struct Parser<'a> {
+    bytes: &'a [u8],
+    position: usize,
+    nodes: usize,
+    allocated: usize,
+}
+
+impl<'a> Parser<'a> {
+    const fn new(bytes: &'a [u8]) -> Self {
+        Self {
+            bytes,
+            position: 0,
+            nodes: 0,
+            allocated: 0,
+        }
+    }
+
+    fn parse_value(&mut self, depth: usize) -> Result<OSD, Error> {
+        if depth > OSD::DEFAULT_MAX_DEPTH {
+            return Err(self.error("binary LLSD nesting depth exceeded"));
+        }
+        self.nodes = self
+            .nodes
+            .checked_add(1)
+            .ok_or_else(|| self.error("binary LLSD node count overflow"))?;
+        if self.nodes > OSD::DEFAULT_MAX_NODES {
+            return Err(self.error("binary LLSD node limit exceeded"));
+        }
+        self.skip_whitespace();
+        let marker_position = self.position;
+        let marker = self.read_byte("missing binary LLSD value marker")?;
+        match marker {
+            b'!' => Ok(OSD::Undefined),
+            b'1' => Ok(OSD::Boolean(true)),
+            b'0' => Ok(OSD::Boolean(false)),
+            b'i' => Ok(OSD::Integer(i32::from_be_bytes(
+                self.read_array("truncated binary LLSD integer")?,
+            ))),
+            b'r' => Ok(OSD::Real(f64::from_be_bytes(
+                self.read_array("truncated binary LLSD real")?,
+            ))),
+            b'u' => {
+                let bytes = self.read_exact(16, "truncated binary LLSD UUID")?;
+                Ok(OSD::UUID(UUID::new_with_bytes_int32(bytes.to_vec(), 0)?))
+            }
+            b'b' => {
+                let length = self.read_length("invalid binary LLSD binary length")?;
+                self.add_allocation(length, "binary LLSD binary allocation limit exceeded")?;
+                Ok(OSD::Binary(
+                    self.read_exact(length, "truncated binary LLSD binary value")?
+                        .to_vec(),
+                ))
+            }
+            b's' => {
+                let bytes = self.read_sized_text("string")?;
+                Ok(OSD::String(String::from_utf8_lossy(bytes).into_owned()))
+            }
+            b'l' => {
+                let bytes = self.read_sized_text("URI")?;
+                let text = String::from_utf8_lossy(bytes).into_owned();
+                let uri = OSD::String(text.clone())
+                    .as_uri()?
+                    .ok_or_else(|| self.error_at(marker_position, "invalid binary LLSD URI"))?;
+                Ok(OSD::Uri(uri))
+            }
+            b'd' => {
+                let timestamp = f64::from_le_bytes(self.read_array("truncated binary LLSD date")?);
+                Ok(OSD::Date(system_time_from_seconds(timestamp).ok_or_else(
+                    || self.error_at(marker_position, "invalid binary LLSD date"),
+                )?))
+            }
+            b'[' => self.parse_array(depth),
+            b'{' => self.parse_map(depth),
+            _ => Err(self.error_at(marker_position, "unknown binary LLSD type marker")),
+        }
+    }
+
+    fn parse_array(&mut self, depth: usize) -> Result<OSD, Error> {
+        let count = self.read_length("invalid binary LLSD array count")?;
+        if count > OSD::DEFAULT_MAX_NODES || count > self.remaining() {
+            return Err(self.error("binary LLSD array count exceeds available input"));
+        }
+        let allocation = count
+            .checked_mul(std::mem::size_of::<OSD>())
+            .ok_or_else(|| self.error("binary LLSD array allocation overflow"))?;
+        self.add_allocation(allocation, "binary LLSD array allocation limit exceeded")?;
+        let mut values = Vec::with_capacity(count);
+        for _ in 0..count {
+            values.push(self.parse_value(depth + 1)?);
+        }
+        self.expect_byte(b']', "missing binary LLSD array end marker")?;
+        Ok(OSD::Array(values))
+    }
+
+    fn parse_map(&mut self, depth: usize) -> Result<OSD, Error> {
+        let count = self.read_length("invalid binary LLSD map count")?;
+        if count > OSD::DEFAULT_MAX_NODES || count > self.remaining() {
+            return Err(self.error("binary LLSD map count exceeds available input"));
+        }
+        let allocation = count
+            .checked_mul(std::mem::size_of::<(String, OSD)>())
+            .ok_or_else(|| self.error("binary LLSD map allocation overflow"))?;
+        self.add_allocation(allocation, "binary LLSD map allocation limit exceeded")?;
+        let mut values = HashMap::with_capacity(count);
+        for _ in 0..count {
+            self.expect_byte(b'k', "missing binary LLSD map key marker")?;
+            let key_bytes = self.read_sized_text("map key")?;
+            let key = String::from_utf8_lossy(key_bytes).into_owned();
+            let value = self.parse_value(depth + 1)?;
+            values.insert(key, value);
+        }
+        self.expect_byte(b'}', "missing binary LLSD map end marker")?;
+        Ok(OSD::Map(values))
+    }
+
+    fn read_sized_text(&mut self, context: &'static str) -> Result<&'a [u8], Error> {
+        let length = self.read_length(match context {
+            "string" => "invalid binary LLSD string length",
+            "URI" => "invalid binary LLSD URI length",
+            _ => "invalid binary LLSD map key length",
+        })?;
+        self.add_allocation(length, "binary LLSD text allocation limit exceeded")?;
+        self.read_exact(
+            length,
+            match context {
+                "string" => "truncated binary LLSD string",
+                "URI" => "truncated binary LLSD URI",
+                _ => "truncated binary LLSD map key",
+            },
+        )
+    }
+
+    fn read_length(&mut self, context: &'static str) -> Result<usize, Error> {
+        let position = self.position;
+        let raw = i32::from_be_bytes(self.read_array(context)?);
+        usize::try_from(raw).map_err(|_| self.error_at(position, context))
+    }
+
+    fn read_array<const N: usize>(&mut self, context: &'static str) -> Result<[u8; N], Error> {
+        self.read_exact(N, context)?
+            .try_into()
+            .map_err(|_| self.error(context))
+    }
+
+    fn read_exact(&mut self, length: usize, context: &'static str) -> Result<&'a [u8], Error> {
+        let end = self
+            .position
+            .checked_add(length)
+            .ok_or_else(|| self.error(context))?;
+        let value = self
+            .bytes
+            .get(self.position..end)
+            .ok_or_else(|| self.error(context))?;
+        self.position = end;
+        Ok(value)
+    }
+
+    fn read_byte(&mut self, context: &'static str) -> Result<u8, Error> {
+        let byte = *self
+            .bytes
+            .get(self.position)
+            .ok_or_else(|| self.error(context))?;
+        self.position += 1;
+        Ok(byte)
+    }
+
+    fn expect_byte(&mut self, expected: u8, context: &'static str) -> Result<(), Error> {
+        let position = self.position;
+        if self.read_byte(context)? == expected {
+            Ok(())
+        } else {
+            Err(self.error_at(position, context))
+        }
+    }
+
+    fn add_allocation(&mut self, amount: usize, context: &'static str) -> Result<(), Error> {
+        self.allocated = self
+            .allocated
+            .checked_add(amount)
+            .ok_or_else(|| self.error(context))?;
+        if self.allocated > OSD::DEFAULT_MAX_BINARY_BYTES {
+            Err(self.error(context))
+        } else {
+            Ok(())
+        }
+    }
+
+    fn skip_whitespace(&mut self) {
+        while self
+            .bytes
+            .get(self.position)
+            .is_some_and(|byte| is_binary_whitespace(*byte))
+        {
+            self.position += 1;
+        }
+    }
+
+    fn consume_prefix_ignore_ascii_case(&mut self, prefix: &[u8]) -> bool {
+        let Some(candidate) = self.bytes.get(self.position..self.position + prefix.len()) else {
+            return false;
+        };
+        if candidate.eq_ignore_ascii_case(prefix) {
+            self.position += prefix.len();
+            true
+        } else {
+            false
+        }
+    }
+
+    const fn remaining(&self) -> usize {
+        self.bytes.len() - self.position
+    }
+
+    const fn error(&self, context: &'static str) -> Error {
+        self.error_at(self.position, context)
+    }
+
+    const fn error_at(&self, position: usize, context: &'static str) -> Error {
+        parse_error(position, context)
+    }
+}
+
+struct Encoder {
+    bytes: Vec<u8>,
+}
+
+impl Encoder {
+    fn new() -> Self {
+        Self {
+            bytes: Vec::with_capacity(128),
+        }
+    }
+
+    fn finish(self) -> Vec<u8> {
+        self.bytes
+    }
+
+    fn write_value(&mut self, value: &OSD, depth: usize) -> Result<(), Error> {
+        if depth > OSD::DEFAULT_MAX_DEPTH {
+            return Err(parse_error(
+                self.bytes.len(),
+                "binary LLSD nesting depth exceeded",
+            ));
+        }
+        match value {
+            OSD::Undefined => self.push(b'!'),
+            OSD::Boolean(value) => self.push(if *value { b'1' } else { b'0' }),
+            OSD::Integer(value) => {
+                self.push(b'i')?;
+                self.extend(&value.to_be_bytes())
+            }
+            OSD::Real(value) => {
+                self.push(b'r')?;
+                self.extend(&value.to_be_bytes())
+            }
+            OSD::UUID(value) => {
+                self.push(b'u')?;
+                self.extend(&value.get_bytes()?)
+            }
+            OSD::String(value) => {
+                self.push(b's')?;
+                self.write_sized(value.as_bytes())
+            }
+            OSD::Binary(value) => {
+                self.push(b'b')?;
+                self.write_sized(value)
+            }
+            OSD::Date(value) => {
+                self.push(b'd')?;
+                self.extend(&crate::model::unix_seconds_for_codec(*value).to_le_bytes())
+            }
+            OSD::Uri(Uri(value)) => {
+                self.push(b'l')?;
+                self.write_sized(value.as_bytes())
+            }
+            OSD::Array(values) => {
+                self.push(b'[')?;
+                self.write_length(values.len())?;
+                for value in values {
+                    self.write_value(value, depth + 1)?;
+                }
+                self.push(b']')
+            }
+            OSD::Map(values) => {
+                self.push(b'{')?;
+                self.write_length(values.len())?;
+                let mut entries: Vec<_> = values.iter().collect();
+                entries.sort_unstable_by_key(|(key, _)| *key);
+                for (key, value) in entries {
+                    self.push(b'k')?;
+                    self.write_sized(key.as_bytes())?;
+                    self.write_value(value, depth + 1)?;
+                }
+                self.push(b'}')
+            }
+            OSD::LlsdXml(_) => Err(parse_error(
+                self.bytes.len(),
+                "LLSD XML fragments have no Binary LLSD marker",
+            )),
+        }
+    }
+
+    fn write_sized(&mut self, value: &[u8]) -> Result<(), Error> {
+        self.write_length(value.len())?;
+        self.extend(value)
+    }
+
+    fn write_length(&mut self, length: usize) -> Result<(), Error> {
+        let length = i32::try_from(length).map_err(|_| Error::Argument)?;
+        self.extend(&length.to_be_bytes())
+    }
+
+    fn push(&mut self, value: u8) -> Result<(), Error> {
+        if self.bytes.len() >= MAX_INPUT_BYTES {
+            return Err(Error::Argument);
+        }
+        self.bytes.push(value);
+        Ok(())
+    }
+
+    fn extend(&mut self, value: &[u8]) -> Result<(), Error> {
+        let length = self
+            .bytes
+            .len()
+            .checked_add(value.len())
+            .ok_or(Error::Argument)?;
+        if length > MAX_INPUT_BYTES {
+            return Err(Error::Argument);
+        }
+        self.bytes.extend_from_slice(value);
+        Ok(())
+    }
+}
+
+fn system_time_from_seconds(seconds: f64) -> Option<std::time::SystemTime> {
+    if !seconds.is_finite() {
+        return None;
+    }
+    if seconds >= 0.0 {
+        UNIX_EPOCH.checked_add(Duration::try_from_secs_f64(seconds).ok()?)
+    } else {
+        UNIX_EPOCH.checked_sub(Duration::try_from_secs_f64(-seconds).ok()?)
+    }
+}
+
+const fn parse_error(position: usize, context: &'static str) -> Error {
+    Error::Parse { position, context }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn every_variant_round_trips_with_header_and_nested_values() {
+        let uuid = UUID::new_with_string("97f4aeca-88a1-42a1-b385-b97b18abb255".into()).unwrap();
+        let value = OSD::Array(vec![
+            OSD::Undefined,
+            OSD::Boolean(true),
+            OSD::Integer(-42),
+            OSD::Real(12.5),
+            OSD::String("text 𐄷".into()),
+            OSD::UUID(uuid),
+            OSD::Date(UNIX_EPOCH + Duration::from_millis(1_199_218_231_125)),
+            OSD::Uri(Uri("https://example.test/a".into())),
+            OSD::Binary(vec![0, 1, 255]),
+            OSD::Map(HashMap::from([("nested".into(), OSD::Array(vec![]))])),
+        ]);
+        let encoded = serialize(value.clone()).unwrap();
+        assert!(encoded.starts_with(b"<?llsd/binary?>\n"));
+        assert_eq!(deserialize_bytes(encoded).unwrap(), value);
+        assert_eq!(
+            deserialize_bytes(b" \t\r\n<? LlSd/BiNaRy ?>\r\ni\0\0\0\x07".to_vec()).unwrap(),
+            OSD::Integer(7)
+        );
+        assert!(matches!(
+            deserialize_bytes(b"\x0b!".to_vec()),
+            Err(Error::Parse {
+                position: 0,
+                context: "unknown binary LLSD type marker"
+            })
+        ));
+
+        let mut encoded_stream = serialize_stream_with_header(value.clone(), false).unwrap();
+        assert_eq!(
+            encoded_stream.position(),
+            encoded_stream.get_ref().len() as u64
+        );
+        encoded_stream.set_position(0);
+        assert_eq!(deserialize_stream(Box::new(encoded_stream)).unwrap(), value);
+
+        assert_eq!(
+            host_to_network_int_bytes(-42).unwrap(),
+            (-42_i32).to_be_bytes()
+        );
+        assert_eq!(
+            network_to_host_int((-42_i32).to_be_bytes().to_vec()).unwrap(),
+            -42
+        );
+        assert_eq!(
+            network_to_host_double(12.5_f64.to_be_bytes().to_vec())
+                .unwrap()
+                .to_bits(),
+            12.5_f64.to_bits()
+        );
+    }
+
+    #[test]
+    fn malformed_seed_corpus_is_rejected_with_positions() {
+        let expected: &[(&str, &str)] = &[
+            ("empty", "missing binary LLSD value marker"),
+            ("unknown_marker", "unknown binary LLSD type marker"),
+            ("truncated_integer", "truncated binary LLSD integer"),
+            ("truncated_real", "truncated binary LLSD real"),
+            ("truncated_uuid", "truncated binary LLSD UUID"),
+            (
+                "negative_binary_length",
+                "invalid binary LLSD binary length",
+            ),
+            (
+                "truncated_binary_length",
+                "invalid binary LLSD binary length",
+            ),
+            (
+                "negative_string_length",
+                "invalid binary LLSD string length",
+            ),
+            ("negative_array_count", "invalid binary LLSD array count"),
+            ("negative_map_count", "invalid binary LLSD map count"),
+            (
+                "oversized_string_length",
+                "binary LLSD text allocation limit exceeded",
+            ),
+            ("missing_array_end", "missing binary LLSD array end marker"),
+            (
+                "missing_map_key_marker",
+                "missing binary LLSD map key marker",
+            ),
+            ("missing_map_end", "missing binary LLSD map end marker"),
+            ("non_finite_date", "invalid binary LLSD date"),
+        ];
+        let corpus = include_str!("../../../fuzz/corpus/binary_llsd/malformed.hex");
+        let seeds: HashMap<_, _> = corpus
+            .lines()
+            .map(|line| {
+                let (name, hex) = line.split_once(':').expect("named fuzz seed");
+                (name, decode_hex(hex))
+            })
+            .collect();
+        assert_eq!(seeds.len(), expected.len());
+        for (name, expected_context) in expected {
+            let seed = seeds.get(name).expect("fuzz seed named by test");
+            let Error::Parse { position, context } = deserialize_bytes(seed.clone()).unwrap_err()
+            else {
+                panic!("malformed seed did not return a positional parse error");
+            };
+            assert!(position <= seed.len());
+            assert_eq!(context, *expected_context);
+        }
+    }
+
+    fn decode_hex(value: &str) -> Vec<u8> {
+        assert_eq!(value.len() % 2, 0, "fuzz seed hex must contain byte pairs");
+        value
+            .as_bytes()
+            .chunks_exact(2)
+            .map(|pair| {
+                let text = std::str::from_utf8(pair).expect("ASCII fuzz seed hex");
+                u8::from_str_radix(text, 16).expect("valid fuzz seed hex")
+            })
+            .collect()
+    }
+
+    #[test]
+    fn excessive_depth_is_rejected_before_stack_growth() {
+        let mut bytes = Vec::new();
+        for _ in 0..=OSD::DEFAULT_MAX_DEPTH {
+            bytes.extend_from_slice(b"[\0\0\0\x01");
+        }
+        bytes.push(b'!');
+        bytes.extend(std::iter::repeat_n(b']', OSD::DEFAULT_MAX_DEPTH + 1));
+        assert!(matches!(
+            deserialize_bytes(bytes),
+            Err(Error::Parse {
+                context: "binary LLSD nesting depth exceeded",
+                ..
+            })
+        ));
+    }
+}
--- a/crates/libremetaverse-structured-data/src/dispatch.rs
+++ b/crates/libremetaverse-structured-data/src/dispatch.rs
@@ -156,11 +156,11 @@ mod tests {
            deserialize_bytes(b"Unknown conference".to_vec()),
            Err(Error::Argument)
        );
+        assert_eq!(
+            deserialize_bytes(b"<? llsd/binary ?>i\0\0\0\0".to_vec()),
+            Ok(OSD::Integer(0))
+        );
        let cases: &[(&[u8], &str)] = &[
-            (
-                b"<? llsd/binary ?>i\0\0\0\0",
-                "M:LibreMetaverse.StructuredData.OSDParser.DeserializeLLSDBinary(System.Byte[])",
-            ),
            (
                b"<? llsd/protobuf ?>",
                "M:LibreMetaverse.StructuredData.OSDParser.DeserializeLLSDProtobuf(System.Byte[])",
--- a/crates/libremetaverse-structured-data/src/generated.rs
+++ b/crates/libremetaverse-structured-data/src/generated.rs
@@ -251,9 +251,7 @@ impl OSDParser {
        stream: Box<dyn libremetaverse_types::compat::ReadWrite + Send>,
        consume_bytes: i32,
    ) -> Result<Vec<u8>, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.ConsumeBytes(System.IO.Stream,System.Int32)",
-        )
+        crate::binary::consume_bytes(stream, consume_bytes)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.Deserialize(System.Byte[])`.
    pub fn deserialize_with_bytes(
@@ -293,17 +291,13 @@ impl OSDParser {
    pub fn deserialize_llsd_binary_with_bytes(
        binary_data: Vec<u8>,
    ) -> Result<libremetaverse_structured_data::OSD, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.DeserializeLLSDBinary(System.Byte[])",
-        )
+        crate::binary::deserialize_bytes(binary_data)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.DeserializeLLSDBinary(System.IO.Stream)`.
    pub fn deserialize_llsd_binary_with_stream(
        stream: Box<dyn libremetaverse_types::compat::ReadWrite + Send>,
    ) -> Result<libremetaverse_structured_data::OSD, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.DeserializeLLSDBinary(System.IO.Stream)",
-        )
+        crate::binary::deserialize_stream(stream)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.DeserializeLLSDNotation(System.IO.StringReader)`.
    pub fn deserialize_llsd_notation_with_string_reader(
@@ -383,18 +377,14 @@ impl OSDParser {
        stream: Box<dyn libremetaverse_types::compat::ReadWrite + Send>,
        to_find: u8,
    ) -> Result<bool, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.FindByte(System.IO.Stream,System.Byte)",
-        )
+        crate::binary::find_byte(stream, to_find)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.FindString(System.IO.Stream,System.String)`.
    pub fn find_string(
        stream: Box<dyn libremetaverse_types::compat::ReadWrite + Send>,
        to_find: String,
    ) -> Result<bool, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.FindString(System.IO.Stream,System.String)",
-        )
+        crate::binary::find_string(stream, to_find)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.GetLengthInBrackets(System.IO.StringReader)`.
    pub fn get_length_in_brackets(
@@ -415,21 +405,15 @@ impl OSDParser {
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.HostToNetworkIntBytes(System.Int32)`.
    pub fn host_to_network_int_bytes(int_host_end: i32) -> Result<Vec<u8>, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.HostToNetworkIntBytes(System.Int32)",
-        )
+        crate::binary::host_to_network_int_bytes(int_host_end)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.NetworkToHostDouble(System.Byte[])`.
    pub fn network_to_host_double(binary_net_end: Vec<u8>) -> Result<f64, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.NetworkToHostDouble(System.Byte[])",
-        )
+        crate::binary::network_to_host_double(binary_net_end)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.NetworkToHostInt(System.Byte[])`.
    pub fn network_to_host_int(binary_net_end: Vec<u8>) -> Result<i32, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.NetworkToHostInt(System.Byte[])",
-        )
+        crate::binary::network_to_host_int(binary_net_end)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.PeekAndSkipWhitespace(System.IO.StringReader)`.
    pub fn peek_and_skip_whitespace(
@@ -460,35 +444,27 @@ impl OSDParser {
    pub fn serialize_llsd_binary_with_osd(
        osd: libremetaverse_structured_data::OSD,
    ) -> Result<Vec<u8>, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.SerializeLLSDBinary(LibreMetaverse.StructuredData.OSD)",
-        )
+        crate::binary::serialize(osd)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.SerializeLLSDBinary(LibreMetaverse.StructuredData.OSD,System.Boolean)`.
    pub fn serialize_llsd_binary_with_osd_boolean(
        osd: libremetaverse_structured_data::OSD,
        prepend_header: bool,
    ) -> Result<Vec<u8>, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.SerializeLLSDBinary(LibreMetaverse.StructuredData.OSD,System.Boolean)",
-        )
+        crate::binary::serialize_with_header(osd, prepend_header)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.SerializeLLSDBinaryStream(LibreMetaverse.StructuredData.OSD)`.
    pub fn serialize_llsd_binary_stream_with_osd(
        data: libremetaverse_structured_data::OSD,
    ) -> Result<std::io::Cursor<Vec<u8>>, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.SerializeLLSDBinaryStream(LibreMetaverse.StructuredData.OSD)",
-        )
+        crate::binary::serialize_stream(data)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.SerializeLLSDBinaryStream(LibreMetaverse.StructuredData.OSD,System.Boolean)`.
    pub fn serialize_llsd_binary_stream_with_osd_boolean(
        data: libremetaverse_structured_data::OSD,
        prepend_header: bool,
    ) -> Result<std::io::Cursor<Vec<u8>>, crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.SerializeLLSDBinaryStream(LibreMetaverse.StructuredData.OSD,System.Boolean)",
-        )
+        crate::binary::serialize_stream_with_header(data, prepend_header)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.SerializeLLSDInnerXmlString(LibreMetaverse.StructuredData.OSD)`.
    pub fn serialize_llsd_inner_xml_string(
@@ -568,9 +544,7 @@ impl OSDParser {
    pub fn skip_white_space(
        stream: Box<dyn libremetaverse_types::compat::ReadWrite + Send>,
    ) -> Result<(), crate::Error> {
-        libremetaverse_types::not_implemented(
-            "M:LibreMetaverse.StructuredData.OSDParser.SkipWhiteSpace(System.IO.Stream)",
-        )
+        crate::binary::skip_whitespace(stream)
    }
    /// C# member: `M:LibreMetaverse.StructuredData.OSDParser.UnescapeCharacter(System.String,System.Char)`.
    pub fn unescape_character(
--- a/crates/libremetaverse-structured-data/src/lib.rs
+++ b/crates/libremetaverse-structured-data/src/lib.rs
@@ -2,6 +2,7 @@

 extern crate self as libremetaverse_structured_data;

+mod binary;
 mod dispatch;
 mod generated;
 mod model;
--- a/crates/libremetaverse-structured-data/src/model.rs
+++ b/crates/libremetaverse-structured-data/src/model.rs
@@ -188,7 +188,7 @@ impl OSD {
            Self::Real(value) => value.to_be_bytes().to_vec(),
            Self::String(value) | Self::LlsdXml(value) => value.as_bytes().to_vec(),
            Self::UUID(value) => value.get_bytes()?,
-            Self::Date(value) => unix_seconds_f64(*value).to_le_bytes().to_vec(),
+            Self::Date(value) => unix_seconds_for_codec(*value).to_le_bytes().to_vec(),
            Self::Uri(value) => value.0.as_bytes().to_vec(),
            Self::Binary(value) => value.clone(),
            Self::Array(values) => values
@@ -842,7 +842,7 @@ impl OSDUUID {
 scalar_wrapper!(OSDDate, SystemTime, Date, Date);
 impl OSDDate {
    pub fn as_binary(&self) -> Result<Vec<u8>, Error> {
-        Ok(unix_seconds_f64(self.value).to_le_bytes().to_vec())
+        Ok(unix_seconds_for_codec(self.value).to_le_bytes().to_vec())
    }
    pub const fn as_date(&self) -> Result<SystemTime, Error> {
        Ok(self.value)
@@ -1425,7 +1425,7 @@ fn format_real(value: f64) -> String {
        value.to_string()
    }
 }
-fn unix_seconds_f64(value: SystemTime) -> f64 {
+pub(crate) fn unix_seconds_for_codec(value: SystemTime) -> f64 {
    match value.duration_since(UNIX_EPOCH) {
        Ok(duration) => duration.as_secs_f64(),
        Err(error) => -error.duration().as_secs_f64(),
--- a/crates/libremetaverse-types/src/compat.rs
+++ b/crates/libremetaverse-types/src/compat.rs
@@ -16,9 +16,9 @@ use std::sync::{

 pub trait Collection<T> {}

-pub trait ReadWrite: std::io::Read + std::io::Write {}
+pub trait ReadWrite: std::io::Read + std::io::Write + std::io::Seek {}

-impl<T: std::io::Read + std::io::Write> ReadWrite for T {}
+impl<T: std::io::Read + std::io::Write + std::io::Seek> ReadWrite for T {}

 #[derive(Clone, Debug)]
 pub enum Object {
--- a/crates/libremetaverse-types/src/shim.rs
+++ b/crates/libremetaverse-types/src/shim.rs
@@ -55,6 +55,13 @@ pub enum Error {
    InvalidOperation,
    /// An index or destination buffer boundary was exceeded.
    IndexOutOfRange,
+    /// Structured input was malformed at a byte or character position.
+    Parse {
+        /// Zero-based offset at which validation failed.
+        position: usize,
+        /// Static parser context suitable for diagnostics and fuzz triage.
+        context: &'static str,
+    },
    /// An operation observed a requested cancellation.
    Cancelled,
    /// An HTTP request completed with an unsuccessful response.
@@ -73,6 +80,7 @@ impl Error {
            | Self::Argument
            | Self::InvalidOperation
            | Self::IndexOutOfRange
+            | Self::Parse { .. }
            | Self::Cancelled
            | Self::HttpRequest
            | Self::Socket => None,
@@ -96,6 +104,9 @@ impl fmt::Display for Error {
                formatter.write_str("operation was invalid for the current state")
            }
            Self::IndexOutOfRange => formatter.write_str("index was out of range"),
+            Self::Parse { position, context } => {
+                write!(formatter, "parse error at offset {position}: {context}")
+            }
            Self::Cancelled => formatter.write_str("operation was cancelled"),
            Self::HttpRequest => formatter.write_str("HTTP request failed"),
            Self::Socket => formatter.write_str("socket operation failed"),