348 lines
12 KiB
Rust
348 lines
12 KiB
Rust
use bytes::{BigEndian, ByteOrder};
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pub const EBML_HEAD_ID: u64 = 0x0A45DFA3;
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pub const VOID_ID: u64 = 0x6C;
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#[derive(Debug, PartialEq)]
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pub enum Error {
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CorruptVarint,
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UnknownElementId,
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UnknownElementLength,
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CorruptPayload,
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}
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#[derive(Debug, PartialEq)]
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pub enum WriteError {
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BufferTooSmall,
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OutOfRange,
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}
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#[derive(Debug, PartialEq)]
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pub enum Varint {
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/// a numeric value
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Value(u64),
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/// the reserved "unknown" value
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Unknown
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}
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/// Try to parse an EBML varint at the start of the given slice.
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/// Returns an Err() if the format is corrupt.
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/// Returns Ok(None) if more bytes are needed to get a result.
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/// Returns Ok(Some((varint, size))) to return a varint value and
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/// the size of the parsed varint.
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pub fn decode_varint(bytes: &[u8]) -> Result<Option<(Varint, usize)>, Error> {
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let mut value: u64 = 0;
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let mut value_length = 1;
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let mut mask: u8 = 0x80;
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let mut unknown_marker: u64 = !0;
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if bytes.len() == 0 {
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return Ok(None)
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}
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// get length marker bit from first byte & parse first byte
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while mask > 0 {
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if (mask & bytes[0]) != 0 {
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value = (bytes[0] & !mask) as u64;
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unknown_marker = (mask - 1) as u64;
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break
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}
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value_length += 1;
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mask = mask >> 1;
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}
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if mask == 0 {
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return Err(Error::CorruptVarint)
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}
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// check we have enough data to parse
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if value_length > bytes.len() {
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return Ok(None)
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}
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// decode remaining bytes
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for i in 1..value_length {
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value = (value << 8) + (bytes[i] as u64);
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unknown_marker = (unknown_marker << 8) + 0xFF;
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}
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// determine result
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if value == unknown_marker {
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Ok(Some((Varint::Unknown, value_length)))
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} else {
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Ok(Some((Varint::Value(value), value_length)))
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}
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}
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/// Try to parse an EBML element header at the start of the given slice.
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/// Returns an Err() if the format is corrupt.
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/// Returns Ok(None) if more bytes are needed to get a result.
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/// Returns Ok(Some((id, varint, size))) to return the element id,
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/// the size of the payload, and the size of the parsed header.
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pub fn decode_tag(bytes: &[u8]) -> Result<Option<(u64, Varint, usize)>, Error> {
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// parse element ID
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match decode_varint(bytes) {
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Ok(None) => Ok(None),
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Err(err) => Err(err),
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Ok(Some((Varint::Unknown, _))) => Err(Error::UnknownElementId),
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Ok(Some((Varint::Value(element_id), id_size))) => {
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// parse payload size
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match decode_varint(&bytes[id_size..]) {
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Ok(None) => Ok(None),
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Err(err) => Err(err),
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Ok(Some((element_length, length_size))) =>
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Ok(Some((
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element_id,
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element_length,
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id_size + length_size
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)))
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}
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}
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}
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}
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pub fn decode_uint(bytes: &[u8]) -> Result<u64, Error> {
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if bytes.len() < 1 || bytes.len() > 8 {
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return Err(Error::CorruptPayload);
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}
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Ok(BigEndian::read_uint(bytes, bytes.len()))
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}
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const SMALL_FLAG: u64 = 0x80;
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const EIGHT_FLAG: u64 = 0x01 << (8*7);
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const EIGHT_MAX: u64 = EIGHT_FLAG - 2;
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/// Tries to write an EBML varint to the buffer
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pub fn encode_varint(varint: Varint, buffer: &mut [u8]) -> Result<usize, WriteError> {
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let (size, number) = match varint {
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Varint::Unknown => (1, 0xFF),
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Varint::Value(too_big) if too_big > EIGHT_MAX => {
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return Err(WriteError::OutOfRange)
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},
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Varint::Value(value) => {
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let mut flag = SMALL_FLAG;
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let mut size = 1;
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// flag bit - 1 = UNKNOWN representation once OR'd with the flag;
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// if we're less than that, we can OR with the flag bit to get a valid Varint
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while value >= (flag - 1) {
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// right shift length bit by 1 to indicate adding a new byte;
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// left shift by 8 because there's a new byte at the end
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flag = flag << (8 - 1);
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size += 1;
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};
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(size, flag | value)
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}
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};
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if buffer.len() < size {
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Err(WriteError::BufferTooSmall)
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} else {
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BigEndian::write_uint(buffer, number, size);
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Ok(size)
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}
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}
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#[derive(Debug, PartialEq)]
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pub struct Ebml<S, T>(pub S, pub T);
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pub trait Schema<'a> {
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type Element: 'a;
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fn should_unwrap(&self, element_id: u64) -> bool;
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fn decode<'b: 'a>(&self, element_id: u64, bytes: &'b[u8]) -> Result<Self::Element, Error>;
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fn decode_element<'b: 'a>(&self, bytes: &'b[u8]) -> Result<Option<(Self::Element, usize)>, Error> {
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match decode_tag(bytes) {
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Ok(None) => Ok(None),
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Err(err) => Err(err),
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Ok(Some((element_id, payload_size_tag, tag_size))) => {
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let should_unwrap = self.should_unwrap(element_id);
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let payload_size = match (should_unwrap, payload_size_tag) {
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(true, _) => 0,
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(false, Varint::Unknown) => return Err(Error::UnknownElementLength),
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(false, Varint::Value(size)) => size as usize
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};
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let element_size = tag_size + payload_size;
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if element_size > bytes.len() {
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// need to read more still
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return Ok(None);
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}
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match self.decode(element_id, &bytes[tag_size..element_size]) {
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Ok(element) => Ok(Some((element, element_size))),
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Err(error) => Err(error)
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}
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}
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}
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}
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fn parse<T>(self, source: T) -> Ebml<Self, T> where Self: Sized {
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Ebml(self, source)
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}
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}
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#[cfg(test)]
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mod tests {
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use ebml::*;
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use ebml::Error::{CorruptVarint, UnknownElementId};
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use ebml::Varint::{Unknown, Value};
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use tests::TEST_FILE;
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#[test]
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fn fail_corrupted_varints() {
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assert_eq!(decode_varint(&[0]), Err(CorruptVarint));
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assert_eq!(decode_varint(&[0, 0, 0]), Err(CorruptVarint));
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}
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#[test]
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fn incomplete_varints() {
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assert_eq!(decode_varint(&[]), Ok(None));
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assert_eq!(decode_varint(&[0x40]), Ok(None));
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assert_eq!(decode_varint(&[0x01, 0, 0]), Ok(None));
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}
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#[test]
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fn parse_varints() {
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assert_eq!(decode_varint(&[0xFF]), Ok(Some((Unknown, 1))));
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assert_eq!(decode_varint(&[0x7F, 0xFF]), Ok(Some((Unknown, 2))));
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assert_eq!(decode_varint(&[0x80]), Ok(Some((Value(0), 1))));
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assert_eq!(decode_varint(&[0x81]), Ok(Some((Value(1), 1))));
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assert_eq!(decode_varint(&[0x40, 52]), Ok(Some((Value(52), 2))));
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// test extra data in buffer
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assert_eq!(decode_varint(&[0x83, 0x11]), Ok(Some((Value(3), 1))));
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}
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#[test]
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fn encode_varints() {
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let mut buffer = [0; 10];
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let mut no_space = [0; 0];
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// 1 byte
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assert_eq!(encode_varint(Varint::Unknown, &mut buffer), Ok(1));
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assert_eq!(buffer[0], 0xFF);
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assert_eq!(encode_varint(Varint::Unknown, &mut no_space), Err(WriteError::BufferTooSmall));
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assert_eq!(encode_varint(Varint::Value(0), &mut buffer), Ok(1));
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assert_eq!(buffer[0], 0x80 | 0);
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assert_eq!(encode_varint(Varint::Value(0), &mut no_space), Err(WriteError::BufferTooSmall));
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assert_eq!(encode_varint(Varint::Value(1), &mut buffer), Ok(1));
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assert_eq!(buffer[0], 0x80 | 1);
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assert_eq!(encode_varint(Varint::Value(1), &mut no_space), Err(WriteError::BufferTooSmall));
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assert_eq!(encode_varint(Varint::Value(126), &mut buffer), Ok(1));
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assert_eq!(buffer[0], 0xF0 | 126);
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assert_eq!(encode_varint(Varint::Value(126), &mut no_space), Err(WriteError::BufferTooSmall));
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// 2 bytes
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assert_eq!(encode_varint(Varint::Value(127), &mut buffer), Ok(2));
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assert_eq!(&buffer[0..2], &[0x40, 127]);
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assert_eq!(encode_varint(Varint::Value(127), &mut no_space), Err(WriteError::BufferTooSmall));
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assert_eq!(encode_varint(Varint::Value(128), &mut buffer), Ok(2));
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assert_eq!(&buffer[0..2], &[0x40, 128]);
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assert_eq!(encode_varint(Varint::Value(128), &mut no_space), Err(WriteError::BufferTooSmall));
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// 6 bytes
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assert_eq!(encode_varint(Varint::Value(0x03FFFFFFFFFE), &mut buffer), Ok(6));
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assert_eq!(&buffer[0..6], &[0x07, 0xFF, 0xFF, 0xFF, 0xFF, 0xFE]);
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// 7 bytes
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assert_eq!(encode_varint(Varint::Value(0x03FFFFFFFFFF), &mut buffer), Ok(7));
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assert_eq!(&buffer[0..7], &[0x02, 0x03, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF]);
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assert_eq!(encode_varint(Varint::Value(0x01000000000000), &mut buffer), Ok(7));
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assert_eq!(&buffer[0..7], &[0x03, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]);
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assert_eq!(encode_varint(Varint::Value(0x01FFFFFFFFFFFE), &mut buffer), Ok(7));
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assert_eq!(&buffer[0..7], &[0x03, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFE]);
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assert_eq!(encode_varint(Varint::Value(0x01FFFFFFFFFFFE), &mut no_space), Err(WriteError::BufferTooSmall));
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assert_eq!(encode_varint(Varint::Value(0x01FFFFFFFFFFFE), &mut buffer[0..6]), Err(WriteError::BufferTooSmall));
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// 8 bytes
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assert_eq!(encode_varint(Varint::Value(0x01FFFFFFFFFFFF), &mut buffer), Ok(8));
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assert_eq!(&buffer[0..8], &[0x01, 0x01, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF]);
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assert_eq!(encode_varint(Varint::Value(0xFFFFFFFFFFFFFE), &mut buffer), Ok(8));
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assert_eq!(&buffer[0..8], &[0x01, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFE]);
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assert_eq!(encode_varint(Varint::Value(0xFFFFFFFFFFFFFF), &mut buffer), Err(WriteError::OutOfRange));
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assert_eq!(encode_varint(Varint::Value(u64::max_value()), &mut buffer), Err(WriteError::OutOfRange));
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}
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#[test]
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fn fail_corrupted_tags() {
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assert_eq!(decode_tag(&[0]), Err(CorruptVarint));
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assert_eq!(decode_tag(&[0x80, 0]), Err(CorruptVarint));
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assert_eq!(decode_tag(&[0xFF, 0x80]), Err(UnknownElementId));
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assert_eq!(decode_tag(&[0x7F, 0xFF, 0x40, 0]), Err(UnknownElementId));
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}
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#[test]
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fn incomplete_tags() {
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assert_eq!(decode_tag(&[]), Ok(None));
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assert_eq!(decode_tag(&[0x80]), Ok(None));
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assert_eq!(decode_tag(&[0x40, 0, 0x40]), Ok(None));
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}
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#[test]
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fn parse_tags() {
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assert_eq!(decode_tag(&[0x80, 0x80]), Ok(Some((0, Value(0), 2))));
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assert_eq!(decode_tag(&[0x81, 0x85]), Ok(Some((1, Value(5), 2))));
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assert_eq!(decode_tag(&[0x80, 0xFF]), Ok(Some((0, Unknown, 2))));
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assert_eq!(decode_tag(&[0x80, 0x7F, 0xFF]), Ok(Some((0, Unknown, 3))));
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assert_eq!(decode_tag(&[0x85, 0x40, 52]), Ok(Some((5, Value(52), 3))));
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}
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#[test]
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fn bad_uints() {
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assert_eq!(decode_uint(&[]), Err(Error::CorruptPayload));
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assert_eq!(decode_uint(&[0; 9]), Err(Error::CorruptPayload));
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}
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#[test]
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fn parse_uints() {
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assert_eq!(decode_uint(&[0]), Ok(0));
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assert_eq!(decode_uint(&[0; 8]), Ok(0));
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assert_eq!(decode_uint(&[1]), Ok(1));
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assert_eq!(decode_uint(&[0,0,0,0,0,0,0,1]), Ok(1));
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assert_eq!(decode_uint(&[38]), Ok(38));
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assert_eq!(decode_uint(&[0,0,0,0,0,0,0,38]), Ok(38));
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assert_eq!(decode_uint(&[0x7F,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF]), Ok(9223372036854775807));
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assert_eq!(decode_uint(&[0x80,0,0,0,0,0,0,0]), Ok(9223372036854775808));
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assert_eq!(decode_uint(&[0x80,0,0,0,0,0,0,1]), Ok(9223372036854775809));
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}
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struct Dummy;
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#[derive(Debug, PartialEq)]
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struct GenericElement(u64, usize);
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impl<'a> Schema<'a> for Dummy {
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type Element = GenericElement;
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fn should_unwrap(&self, element_id: u64) -> bool {
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match element_id {
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_ => false
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}
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}
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fn decode<'b: 'a>(&self, element_id: u64, bytes: &'b[u8]) -> Result<GenericElement, Error> {
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match element_id {
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_ => Ok(GenericElement(element_id, bytes.len()))
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}
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}
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}
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#[test]
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fn decode_sanity_test() {
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let decoded = Dummy.decode_element(TEST_FILE);
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assert_eq!(decoded, Ok(Some((GenericElement(0x0A45DFA3, 31), 43))));
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}
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}
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