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//! Read MCAP files
//!
//! MCAPs are read from a byte slice instead of a [`Read`] trait object.
//! This helps us avoid unnecessary copies, since [`Schema`]s and [`Message`]s
//! can refer directly to their data.
//!
//! Consider [memory-mapping](https://docs.rs/memmap/0.7.0/memmap/struct.Mmap.html)
//! the file - the OS will load (and cache!) it on-demand, without any
//! further system calls.
use std::{
borrow::Cow,
collections::{BTreeMap, HashMap},
fmt,
io::{self, prelude::*, Cursor},
mem::size_of,
sync::Arc,
};
use binrw::prelude::*;
use byteorder::{ReadBytesExt, LE};
use crc32fast::hash as crc32;
use enumset::{enum_set, EnumSet, EnumSetType};
use log::*;
use crate::{
io_utils::CountingCrcReader,
records::{self, op, Record},
Attachment, Channel, McapError, McapResult, Message, Schema, MAGIC,
};
/// Nonstandard reading options, e.g.,
/// to be more lenient when trying to recover incomplete/damaged files.
///
/// More may be added in future releases.
#[derive(EnumSetType, Debug)]
pub enum Options {
/// Don't require the MCAP file to end with its magic bytes.
IgnoreEndMagic,
}
/// Scans a mapped MCAP file from start to end, returning each record.
///
/// You probably want a [MessageStream] instead - this yields the raw records
/// from the file without any postprocessing (decompressing chunks, etc.)
/// and is mostly meant as a building block for higher-level readers.
pub struct LinearReader<'a> {
buf: &'a [u8],
malformed: bool,
}
impl<'a> LinearReader<'a> {
/// Create a reader for the given file,
/// checking [`MAGIC`] bytes on both ends.
pub fn new(buf: &'a [u8]) -> McapResult<Self> {
Self::new_with_options(buf, enum_set!())
}
/// Create a reader for the given file with special options.
pub fn new_with_options(buf: &'a [u8], options: EnumSet<Options>) -> McapResult<Self> {
if !buf.starts_with(MAGIC)
|| (!options.contains(Options::IgnoreEndMagic)
&& (!buf.ends_with(MAGIC) || buf.len() < 2 * MAGIC.len()))
{
return Err(McapError::BadMagic);
}
let buf = &buf[MAGIC.len()..];
if buf.ends_with(MAGIC) {
Ok(Self::sans_magic(&buf[0..buf.len() - MAGIC.len()]))
} else {
Ok(Self::sans_magic(buf))
}
}
/// Like [`new()`](Self::new), but assumes `buf` has the magic bytes sliced off.
///
/// Useful for iterating through slices of an MCAP file instead of the whole thing.
pub fn sans_magic(buf: &'a [u8]) -> Self {
Self {
buf,
malformed: false,
}
}
/// Returns the number of unprocessed bytes
/// (sans the file's starting and ending magic)
///
/// Used to calculate offsets for the data section et al.
fn bytes_remaining(&self) -> usize {
self.buf.len()
}
}
impl<'a> Iterator for LinearReader<'a> {
type Item = McapResult<records::Record<'a>>;
fn next(&mut self) -> Option<Self::Item> {
if self.buf.is_empty() {
return None;
}
// After an unrecoverable error (due to something wonky in the file),
// don't keep trying to walk it.
if self.malformed {
return None;
}
let record = match read_record_from_slice(&mut self.buf) {
Ok(k) => k,
Err(e) => {
self.malformed = true;
return Some(Err(e));
}
};
Some(Ok(record))
}
}
/// Read a record and advance the slice
fn read_record_from_slice<'a>(buf: &mut &'a [u8]) -> McapResult<records::Record<'a>> {
if buf.len() < (size_of::<u64>() + size_of::<u8>()) {
warn!("Malformed MCAP - not enough space for record + length!");
return Err(McapError::UnexpectedEof);
}
let op = read_u8(buf);
let len = read_u64(buf);
if buf.len() < len as usize {
warn!(
"Malformed MCAP - record with length {len}, but only {} bytes remain",
buf.len()
);
return Err(McapError::UnexpectedEof);
}
let body = &buf[..len as usize];
debug!("slice: opcode {op:02X}, length {len}");
let record = read_record(op, body)?;
trace!(" {:?}", record);
*buf = &buf[len as usize..];
Ok(record)
}
/// Given a record's opcode and its slice, read it into a [Record]
fn read_record(op: u8, body: &[u8]) -> McapResult<records::Record<'_>> {
macro_rules! record {
($b:ident) => {{
let mut cur = Cursor::new($b);
let res = cur.read_le()?;
res
}};
}
Ok(match op {
op::HEADER => Record::Header(record!(body)),
op::FOOTER => Record::Footer(record!(body)),
op::SCHEMA => {
let mut c = Cursor::new(body);
let header: records::SchemaHeader = c.read_le()?;
let data_len = c.read_u32::<LE>()?;
let mut data = &body[c.position() as usize..];
if data_len > data.len() as u32 {
return Err(McapError::BadSchemaLength {
header: data_len,
available: data.len() as u32,
});
}
data = &data[..data_len as usize];
Record::Schema {
header,
data: Cow::Borrowed(data),
}
}
op::CHANNEL => Record::Channel(record!(body)),
op::MESSAGE => {
let mut c = Cursor::new(body);
let header = c.read_le()?;
let data = Cow::Borrowed(&body[c.position() as usize..]);
Record::Message { header, data }
}
op::CHUNK => {
let mut c = Cursor::new(body);
let header: records::ChunkHeader = c.read_le()?;
let mut data = &body[c.position() as usize..];
if header.compressed_size > data.len() as u64 {
return Err(McapError::BadChunkLength {
header: header.compressed_size,
available: data.len() as u64,
});
}
data = &data[..header.compressed_size as usize];
Record::Chunk {
header,
data: Cow::Borrowed(data),
}
}
op::MESSAGE_INDEX => Record::MessageIndex(record!(body)),
op::CHUNK_INDEX => Record::ChunkIndex(record!(body)),
op::ATTACHMENT => {
let mut c = Cursor::new(body);
let header: records::AttachmentHeader = c.read_le()?;
let data_len = c.read_u64::<LE>()?;
let header_len = c.position() as usize;
let mut data = &body[header_len..body.len() - 4];
if data_len > data.len() as u64 {
return Err(McapError::BadAttachmentLength {
header: data_len,
available: data.len() as u64,
});
}
data = &data[..data_len as usize];
let crc: u32 = Cursor::new(&body[header_len + data.len()..]).read_le()?;
// We usually leave CRCs to higher-level readers -
// (ChunkReader, read_summary(), etc.) - but
//
// 1. We can trivially check it here without checking other records,
// decompressing anything, or doing any other non-trivial work
//
// 2. Since the CRC depends on the serialized header, it doesn't make
// much sense to have users check it.
// (What would they do? lol reserialize the header?)
if crc != 0 {
let calculated = crc32(&body[..header_len + data.len()]);
if crc != calculated {
return Err(McapError::BadAttachmentCrc {
saved: crc,
calculated,
});
}
}
Record::Attachment {
header,
data: Cow::Borrowed(data),
}
}
op::ATTACHMENT_INDEX => Record::AttachmentIndex(record!(body)),
op::STATISTICS => Record::Statistics(record!(body)),
op::METADATA => Record::Metadata(record!(body)),
op::METADATA_INDEX => Record::MetadataIndex(record!(body)),
op::SUMMARY_OFFSET => Record::SummaryOffset(record!(body)),
op::DATA_END => Record::DataEnd(record!(body)),
opcode => Record::Unknown {
opcode,
data: Cow::Borrowed(body),
},
})
}
enum ChunkDecompressor<'a> {
Null(LinearReader<'a>),
/// This is not used when both `zstd` and `lz4` features are disabled.
#[allow(dead_code)]
Compressed(Option<CountingCrcReader<Box<dyn Read + Send + 'a>>>),
}
/// Streams records out of a [Chunk](Record::Chunk), decompressing as needed.
pub struct ChunkReader<'a> {
header: records::ChunkHeader,
decompressor: ChunkDecompressor<'a>,
}
impl<'a> ChunkReader<'a> {
pub fn new(header: records::ChunkHeader, data: &'a [u8]) -> McapResult<Self> {
let decompressor = match header.compression.as_str() {
#[cfg(feature = "zstd")]
"zstd" => ChunkDecompressor::Compressed(Some(CountingCrcReader::new(Box::new(
zstd::Decoder::new(data)?,
)))),
#[cfg(not(feature = "zstd"))]
"zstd" => panic!("Unsupported compression format: zstd"),
#[cfg(feature = "lz4")]
"lz4" => ChunkDecompressor::Compressed(Some(CountingCrcReader::new(Box::new(
lz4_flex::frame::FrameDecoder::new(data),
)))),
#[cfg(not(feature = "lz4"))]
"lz4" => panic!("Unsupported compression format: lz4"),
"" => {
if header.uncompressed_size != header.compressed_size {
warn!(
"Chunk is uncompressed, but claims different compress/uncompressed lengths"
);
}
if header.uncompressed_crc != 0 {
let calculated = crc32(data);
if header.uncompressed_crc != calculated {
return Err(McapError::BadChunkCrc {
saved: header.uncompressed_crc,
calculated,
});
}
}
ChunkDecompressor::Null(LinearReader::sans_magic(data))
}
wat => return Err(McapError::UnsupportedCompression(wat.to_string())),
};
Ok(Self {
header,
decompressor,
})
}
}
impl<'a> Iterator for ChunkReader<'a> {
type Item = McapResult<records::Record<'a>>;
fn next(&mut self) -> Option<Self::Item> {
match &mut self.decompressor {
ChunkDecompressor::Null(r) => r.next(),
ChunkDecompressor::Compressed(stream) => {
// If we consumed the stream last time to get the CRC,
// or because of an error, we're done.
if stream.is_none() {
return None;
}
let s = stream.as_mut().unwrap();
let record = match read_record_from_chunk_stream(s) {
Ok(k) => k,
Err(e) => {
*stream = None; // Don't try to recover.
return Some(Err(e));
}
};
// If we've read all there is to read...
if s.position() >= self.header.uncompressed_size {
// Get the CRC.
let calculated = stream.take().unwrap().finalize();
// If the header stored a CRC
// and it doesn't match what we have, complain.
if self.header.uncompressed_crc != 0
&& self.header.uncompressed_crc != calculated
{
return Some(Err(McapError::BadChunkCrc {
saved: self.header.uncompressed_crc,
calculated,
}));
}
// All good!
}
Some(Ok(record))
}
}
}
}
/// Like [read_record_from_slice], but for a decompression stream
fn read_record_from_chunk_stream<'a, R: Read>(r: &mut R) -> McapResult<records::Record<'a>> {
let op = r.read_u8()?;
let len = r.read_u64::<LE>()?;
debug!("chunk: opcode {op:02X}, length {len}");
let record = match op {
op::SCHEMA => {
let mut record = Vec::new();
r.take(len).read_to_end(&mut record)?;
if len as usize != record.len() {
return Err(McapError::UnexpectedEoc);
}
let mut c = Cursor::new(&record);
let header: records::SchemaHeader = c.read_le()?;
let data_len = c.read_u32::<LE>()?;
let header_end = c.position();
// Should we rotate and shrink instead?
let mut data = record.split_off(header_end as usize);
if data_len > data.len() as u32 {
return Err(McapError::BadSchemaLength {
header: data_len,
available: data.len() as u32,
});
}
data.truncate(data_len as usize);
Record::Schema {
header,
data: Cow::Owned(data),
}
}
op::CHANNEL => {
let mut record = Vec::new();
r.take(len).read_to_end(&mut record)?;
if len as usize != record.len() {
return Err(McapError::UnexpectedEoc);
}
let mut c = Cursor::new(&record);
let channel: records::Channel = c.read_le()?;
if c.position() != record.len() as u64 {
warn!(
"Channel {}'s length doesn't match its record length",
channel.topic
);
}
Record::Channel(channel)
}
op::MESSAGE => {
// Optimization: messages are the mainstay of the file,
// so allocate the header and the data separately to avoid having
// to split them up or move them around later.
// Fortunately, message headers are fixed length.
const HEADER_LEN: u64 = 22;
let mut header_buf = Vec::new();
r.take(HEADER_LEN).read_to_end(&mut header_buf)?;
if header_buf.len() as u64 != HEADER_LEN {
return Err(McapError::UnexpectedEoc);
}
let header: records::MessageHeader = Cursor::new(header_buf).read_le()?;
let mut data = Vec::new();
r.take(len - HEADER_LEN).read_to_end(&mut data)?;
if data.len() as u64 != len - HEADER_LEN {
return Err(McapError::UnexpectedEoc);
}
Record::Message {
header,
data: Cow::Owned(data),
}
}
wut => return Err(McapError::UnexpectedChunkRecord(wut)),
};
trace!(" {:?}", record);
Ok(record)
}
/// Like [`LinearReader`], but unpacks chunks' records into its stream
pub struct ChunkFlattener<'a> {
top_level: LinearReader<'a>,
dechunk: Option<ChunkReader<'a>>,
malformed: bool,
}
impl<'a> ChunkFlattener<'a> {
pub fn new(buf: &'a [u8]) -> McapResult<Self> {
Self::new_with_options(buf, enum_set!())
}
pub fn new_with_options(buf: &'a [u8], options: EnumSet<Options>) -> McapResult<Self> {
let top_level = LinearReader::new_with_options(buf, options)?;
Ok(Self {
top_level,
dechunk: None,
malformed: false,
})
}
fn bytes_remaining(&self) -> usize {
self.top_level.bytes_remaining()
}
}
impl<'a> Iterator for ChunkFlattener<'a> {
type Item = McapResult<records::Record<'a>>;
fn next(&mut self) -> Option<Self::Item> {
if self.malformed {
return None;
}
let n: Option<Self::Item> = loop {
// If we're reading from a chunk, do that until it returns None.
if let Some(d) = &mut self.dechunk {
match d.next() {
Some(d) => break Some(d),
None => self.dechunk = None,
}
}
// Fall through - if we didn't extract a record from a chunk
// (or that chunk ended), move on to the next top-level record.
match self.top_level.next() {
// If it's a chunk, get a new chunk reader going...
Some(Ok(Record::Chunk { header, data })) => {
// Chunks from the LinearReader will always borrow from the file.
// (Getting a normal reference to the underlying data back
// frees us from returning things that reference this local Cow.)
let data: &'a [u8] = match data {
Cow::Borrowed(b) => b,
Cow::Owned(_) => unreachable!(),
};
self.dechunk = match ChunkReader::new(header, data) {
Ok(d) => Some(d),
Err(e) => break Some(Err(e)),
};
// ...then continue the loop to get the first item from the chunk.
}
// If it's not a chunk, just yield it.
not_a_chunk => break not_a_chunk,
}
};
// Give up on errors
if matches!(n, Some(Err(_))) {
self.malformed = true;
}
n
}
}
/// Parses schemas and channels and wires them together
#[derive(Debug, Default)]
struct ChannelAccumulator<'a> {
schemas: HashMap<u16, Arc<Schema<'a>>>,
channels: HashMap<u16, Arc<Channel<'a>>>,
}
impl<'a> ChannelAccumulator<'a> {
fn add_schema(&mut self, header: records::SchemaHeader, data: Cow<'a, [u8]>) -> McapResult<()> {
if header.id == 0 {
return Err(McapError::InvalidSchemaId);
}
let schema = Arc::new(Schema {
name: header.name.clone(),
encoding: header.encoding,
data,
});
if let Some(preexisting) = self.schemas.insert(header.id, schema.clone()) {
// Oh boy, we have this schema already.
// It had better be identital.
if schema != preexisting {
return Err(McapError::ConflictingSchemas(header.name));
}
}
Ok(())
}
fn add_channel(&mut self, chan: records::Channel) -> McapResult<()> {
// The schema ID can be 0 for "no schema",
// Or must reference some previously-read schema.
let schema = if chan.schema_id == 0 {
None
} else {
match self.schemas.get(&chan.schema_id) {
Some(s) => Some(s.clone()),
None => {
return Err(McapError::UnknownSchema(chan.topic, chan.schema_id));
}
}
};
let channel = Arc::new(Channel {
topic: chan.topic.clone(),
schema,
message_encoding: chan.message_encoding,
metadata: chan.metadata,
});
if let Some(preexisting) = self.channels.insert(chan.id, channel.clone()) {
// Oh boy, we have this channel already.
// It had better be identital.
if preexisting != channel {
return Err(McapError::ConflictingChannels(chan.topic));
}
}
Ok(())
}
fn get(&self, chan_id: u16) -> Option<Arc<Channel<'a>>> {
self.channels.get(&chan_id).cloned()
}
}
/// Reads all messages from the MCAP file---in the order they were written---and
/// perform needed validation (CRCs, etc.) as we go.
///
/// Unlike [`MessageStream`], this iterator returns the raw [`MessageHeader`](records::MessageHeader)
/// and message data instead of constructing a [`Message`].
/// This can be useful for situations where you don't need the specifics of each
/// message's [`Channel`], but just want to be able to discriminate them _by_ their channel
/// (e.g., build some map of `Channel -> Vec<Message>`).
///
/// This stops at the end of the data section and does not read the summary.
pub struct RawMessageStream<'a> {
full_file: &'a [u8],
records: ChunkFlattener<'a>,
done: bool,
channeler: ChannelAccumulator<'static>,
}
impl<'a> RawMessageStream<'a> {
pub fn new(buf: &'a [u8]) -> McapResult<Self> {
Self::new_with_options(buf, enum_set!())
}
pub fn new_with_options(buf: &'a [u8], options: EnumSet<Options>) -> McapResult<Self> {
let full_file = buf;
let records = ChunkFlattener::new_with_options(buf, options)?;
Ok(Self {
full_file,
records,
done: false,
channeler: ChannelAccumulator::default(),
})
}
/// Gets the channel with the given ID (presumably from a [`MessageHeader`](records::MessageHeader))
pub fn get_channel(&self, channel_id: u16) -> Option<Arc<Channel<'a>>> {
self.channeler.get(channel_id)
}
}
pub struct RawMessage<'a> {
header: records::MessageHeader,
data: Cow<'a, [u8]>,
}
impl<'a> Iterator for RawMessageStream<'a> {
type Item = McapResult<RawMessage<'a>>;
fn next(&mut self) -> Option<Self::Item> {
if self.done {
return None;
}
let n = loop {
// Let's start with a working record.
let record = match self.records.next() {
Some(Ok(rec)) => rec,
Some(Err(e)) => break Some(Err(e)),
None => break None,
};
match record {
// Insert schemas into self so we know when subsequent channels reference them.
Record::Schema { header, data } => {
let data = Cow::Owned(data.into_owned());
if let Err(e) = self.channeler.add_schema(header, data) {
break Some(Err(e));
}
}
// Insert channels into self so we know when subsequent messages reference them.
Record::Channel(chan) => {
if let Err(e) = self.channeler.add_channel(chan) {
break Some(Err(e));
}
}
Record::Message { header, data } => {
break Some(Ok(RawMessage { header, data }));
}
// If it's EOD, do unholy things to calculate the CRC.
// This would be much easier reading from a seekable Read instead of a buffer.
// (But that would also force us to make copies of schema, message, and attachment
// data! Should we have two APIs?)
Record::DataEnd(end) => {
if end.data_section_crc != 0 {
// op, length, CRC
const DATA_END_SIZE: usize =
size_of::<u8>() + size_of::<u64>() + size_of::<u32>();
let start_of_data_end = self.full_file.len()
- self.records.bytes_remaining() // sans MAGIC!
- MAGIC.len() // MORE MAGIC
- DATA_END_SIZE;
let data_section = &self.full_file[..start_of_data_end];
let calculated = crc32(data_section);
if end.data_section_crc != calculated {
break Some(Err(McapError::BadDataCrc {
saved: end.data_section_crc,
calculated,
}));
}
}
break None; // We're done at any rate.
}
_skip => {}
};
};
if !matches!(n, Some(Ok(_))) {
self.done = true;
}
n
}
}
/// Like [`RawMessageStream`], but constructs a [`Message`]
/// (complete with its [`Channel`]) from the raw header and data.
///
/// This stops at the end of the data section and does not read the summary.
///
/// Because tying the lifetime of each message to the underlying MCAP memory map
/// makes it very difficult to send between threads or use in async land,
/// and because we assume _most_ MCAP files have _most_ messages in compressed chunks,
/// yielded [`Message`]s have unbounded lifetimes.
/// For messages we've decompressed into their own buffers, this is free!
/// For uncompressed messages, we take a copy of the message's data.
pub struct MessageStream<'a> {
inner: RawMessageStream<'a>,
}
impl<'a> MessageStream<'a> {
pub fn new(buf: &'a [u8]) -> McapResult<Self> {
Self::new_with_options(buf, enum_set!())
}
pub fn new_with_options(buf: &'a [u8], options: EnumSet<Options>) -> McapResult<Self> {
RawMessageStream::new_with_options(buf, options).map(|inner| Self { inner })
}
}
impl<'a> Iterator for MessageStream<'a> {
type Item = McapResult<Message<'static>>;
fn next(&mut self) -> Option<Self::Item> {
match self.inner.next() {
Some(Ok(RawMessage { header, data })) => {
// Messages must have a previously-read channel.
let channel = match self.inner.channeler.get(header.channel_id) {
Some(c) => c,
None => {
return Some(Err(McapError::UnknownChannel(
header.sequence,
header.channel_id,
)))
}
};
Some(Ok(Message {
channel,
sequence: header.sequence,
log_time: header.log_time,
publish_time: header.publish_time,
data: Cow::Owned(data.into_owned()),
}))
}
// Coerce Option<McapResult<(header, data)>> into Option<McapResult<Message>>
Some(Err(e)) => Some(Err(e)),
None => None,
}
}
}
const FOOTER_LEN: usize = 20 + 8 + 1; // 20 bytes + 8 byte len + 1 byte opcode
/// Read the MCAP footer.
///
/// You'd probably prefer to use [`Summary::read`] to parse the whole summary,
/// then index into the rest of the file with
/// [`Summary::stream_chunk`], [`attachment`], [`metadata`], etc.
pub fn footer(mcap: &[u8]) -> McapResult<records::Footer> {
if mcap.len() < MAGIC.len() * 2 + FOOTER_LEN {
return Err(McapError::UnexpectedEof);
}
if !mcap.starts_with(MAGIC) || !mcap.ends_with(MAGIC) {
return Err(McapError::BadMagic);
}
let footer_buf = &mcap[mcap.len() - MAGIC.len() - FOOTER_LEN..];
match LinearReader::sans_magic(footer_buf).next() {
Some(Ok(Record::Footer(f))) => Ok(f),
_ => Err(McapError::BadFooter),
}
}
/// Indexes of an MCAP file parsed from its (optional) summary section
#[derive(Default, Eq, PartialEq)]
pub struct Summary<'a> {
pub stats: Option<records::Statistics>,
/// Maps channel IDs to their channel
pub channels: HashMap<u16, Arc<Channel<'a>>>,
/// Maps schema IDs to their schema
pub schemas: HashMap<u16, Arc<Schema<'a>>>,
pub chunk_indexes: Vec<records::ChunkIndex>,
pub attachment_indexes: Vec<records::AttachmentIndex>,
pub metadata_indexes: Vec<records::MetadataIndex>,
}
impl fmt::Debug for Summary<'_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// Keep the actual maps as HashMaps for constant-time lookups,
// but order everything up before debug printing it here.
let channels = self.channels.iter().collect::<BTreeMap<_, _>>();
let schemas = self.schemas.iter().collect::<BTreeMap<_, _>>();
f.debug_struct("Summary")
.field("stats", &self.stats)
.field("channels", &channels)
.field("schemas", &schemas)
.field("chunk_indexes", &self.chunk_indexes)
.field("attachment_indexes", &self.attachment_indexes)
.field("metadata_indexes", &self.metadata_indexes)
.finish()
}
}
impl<'a> Summary<'a> {
/// Read the summary section of the given mapped MCAP file, if it has one.
pub fn read(mcap: &'a [u8]) -> McapResult<Option<Self>> {
let foot = footer(mcap)?;
// A summary start offset of 0 means there's no summary.
if foot.summary_start == 0 {
return Ok(None);
}
if foot.summary_crc != 0 {
// The checksum covers the entire summary _except_ itself, including other footer bytes.
let calculated =
crc32(&mcap[foot.summary_start as usize..mcap.len() - MAGIC.len() - 4]);
if foot.summary_crc != calculated {
return Err(McapError::BadSummaryCrc {
saved: foot.summary_crc,
calculated,
});
}
}
let mut summary = Summary::default();
let mut channeler = ChannelAccumulator::default();
let summary_end = match foot.summary_offset_start {
0 => MAGIC.len() - FOOTER_LEN,
sos => sos as usize,
};
let summary_buf = &mcap[foot.summary_start as usize..summary_end];
for record in LinearReader::sans_magic(summary_buf) {
match record? {
Record::Statistics(s) => {
if summary.stats.is_some() {
warn!("Multiple statistics records found in summary");
}
summary.stats = Some(s);
}
Record::Schema { header, data } => channeler.add_schema(header, data)?,
Record::Channel(c) => channeler.add_channel(c)?,
Record::ChunkIndex(c) => summary.chunk_indexes.push(c),
Record::AttachmentIndex(a) => summary.attachment_indexes.push(a),
Record::MetadataIndex(i) => summary.metadata_indexes.push(i),
_ => {}
};
}
summary.schemas = channeler.schemas;
summary.channels = channeler.channels;
Ok(Some(summary))
}
/// Stream messages from the chunk with the given index.
///
/// To avoid having to read all preceding chunks first,
/// channels and their schemas are pulled from this summary.
pub fn stream_chunk(
&self,
mcap: &'a [u8],
index: &records::ChunkIndex,
) -> McapResult<impl Iterator<Item = McapResult<Message<'a>>> + '_> {
let end = (index.chunk_start_offset + index.chunk_length) as usize;
if mcap.len() < end {
return Err(McapError::BadIndex);
}
// Get the chunk (as a header and its data) out of the file at the given offset.
let mut reader = LinearReader::sans_magic(&mcap[index.chunk_start_offset as usize..end]);
let (h, d) = match reader.next().ok_or(McapError::BadIndex)? {
Ok(records::Record::Chunk { header, data }) => (header, data),
Ok(_other_record) => return Err(McapError::BadIndex),
Err(e) => return Err(e),
};
// Chunks from the LinearReader will always borrow from the file.
// (Getting a normal reference to the underlying data back
// frees us from returning things that reference this local Cow.)
let d: &'a [u8] = match d {
Cow::Borrowed(b) => b,
Cow::Owned(_) => unreachable!(),
};
if reader.next().is_some() {
// Wut - multiple records in the given slice?
return Err(McapError::BadIndex);
}
// Now let's stream messages out of the chunk.
let messages = ChunkReader::new(h, d)?.filter_map(|record| match record {
Ok(records::Record::Message { header, data }) => {
// Correlate the message to its channel from this summary.
let channel = match self.channels.get(&header.channel_id) {
Some(c) => c.clone(),
None => {
return Some(Err(McapError::UnknownChannel(
header.sequence,
header.channel_id,
)));
}
};
let m = Message {
channel,
sequence: header.sequence,
log_time: header.log_time,
publish_time: header.publish_time,
data,
};
Some(Ok(m))
}
// We don't care about other chunk records (channels, schemas) -
// we should have them from &self already.
Ok(_other_record) => None,
// We do care about errors, though.
Err(e) => Some(Err(e)),
});
Ok(messages)
}
/// Read the mesage indexes for the given indexed chunk.
///
/// Channels and their schemas are pulled from this summary.
/// The offsets in each [`MessageIndexEntry`](records::MessageIndexEntry)
/// is relative to the decompressed contents of the given chunk.
pub fn read_message_indexes(
&self,
mcap: &[u8],
index: &records::ChunkIndex,
) -> McapResult<HashMap<Arc<Channel>, Vec<records::MessageIndexEntry>>> {
if index.message_index_offsets.is_empty() {
// Message indexing is optional... should we be more descriptive here?
return Err(McapError::BadIndex);
}
let mut indexes = HashMap::new();
for (channel_id, offset) in &index.message_index_offsets {
let offset = *offset as usize;
// Message indexes are at least 15 bytes:
// 1 byte opcode, 8 byte length, 2 byte channel ID, 4 byte array len
if mcap.len() < offset + 15 {
return Err(McapError::BadIndex);
}
// Get the MessageIndex out of the file at the given offset.
let mut reader = LinearReader::sans_magic(&mcap[offset..]);
let index = match reader.next().ok_or(McapError::BadIndex)? {
Ok(records::Record::MessageIndex(i)) => i,
Ok(_other_record) => return Err(McapError::BadIndex),
Err(e) => return Err(e),
};
// The channel ID from the chunk index and the message index should match
if *channel_id != index.channel_id {
return Err(McapError::BadIndex);
}
let channel = match self.channels.get(&index.channel_id) {
Some(c) => c,
None => {
return Err(McapError::UnknownChannel(
0, // We don't have a message sequence num yet.
index.channel_id,
));
}
};
if indexes.insert(channel.clone(), index.records).is_some() {
return Err(McapError::ConflictingChannels(channel.topic.clone()));
}
}
Ok(indexes)
}
/// Seek to the given message in the given indexed chunk.
///
/// If you're interested in more than a single message from the chunk,
/// filtering [`Summary::stream_chunk`] is probably a better bet.
/// Compressed chunks aren't random access -
/// this decompresses everything in the chunk before
/// [`message.offset`](records::MessageIndexEntry::offset) and throws it away.
pub fn seek_message(
&self,
mcap: &'a [u8],
index: &records::ChunkIndex,
message: &records::MessageIndexEntry,
) -> McapResult<Message> {
// Get the chunk (as a header and its data) out of the file at the given offset.
let end = (index.chunk_start_offset + index.chunk_length) as usize;
if mcap.len() < end {
return Err(McapError::BadIndex);
}
let mut reader = LinearReader::sans_magic(&mcap[index.chunk_start_offset as usize..end]);
let (h, d) = match reader.next().ok_or(McapError::BadIndex)? {
Ok(records::Record::Chunk { header, data }) => (header, data),
Ok(_other_record) => return Err(McapError::BadIndex),
Err(e) => return Err(e),
};
// Chunks from the LinearReader will always borrow from the file.
// (Getting a normal reference to the underlying data back
// frees us from returning things that reference this local Cow.)
let d: &'a [u8] = match d {
Cow::Borrowed(b) => b,
Cow::Owned(_) => unreachable!(),
};
if reader.next().is_some() {
// Wut - multiple records in the given slice?
return Err(McapError::BadIndex);
}
let mut chunk_reader = ChunkReader::new(h, d)?;
// Do unspeakable things to seek to the message.
match &mut chunk_reader.decompressor {
ChunkDecompressor::Null(reader) => {
// Skip messages until we're at the offset.
while reader.bytes_remaining() as u64 > index.uncompressed_size - message.offset {
match reader.next() {
Some(Ok(_)) => {}
Some(Err(e)) => return Err(e),
None => return Err(McapError::BadIndex),
};
}
// Be exact!
if reader.bytes_remaining() as u64 != index.uncompressed_size - message.offset {
return Err(McapError::BadIndex);
}
}
ChunkDecompressor::Compressed(maybe_read) => {
let reader = maybe_read.as_mut().unwrap();
// Decompress offset bytes, which should put us at the message we want.
io::copy(&mut reader.take(message.offset), &mut io::sink())?;
}
}
// Now let's get our message.
match chunk_reader.next() {
Some(Ok(records::Record::Message { header, data })) => {
// Correlate the message to its channel from this summary.
let channel = match self.channels.get(&header.channel_id) {
Some(c) => c.clone(),
None => {
return Err(McapError::UnknownChannel(
header.sequence,
header.channel_id,
));
}
};
let m = Message {
channel,
sequence: header.sequence,
log_time: header.log_time,
publish_time: header.publish_time,
data,
};
Ok(m)
}
// The index told us this was a message...
Some(Ok(_other_record)) => Err(McapError::BadIndex),
Some(Err(e)) => Err(e),
None => Err(McapError::BadIndex),
}
}
}
/// Read the attachment with the given index.
pub fn attachment<'a>(
mcap: &'a [u8],
index: &records::AttachmentIndex,
) -> McapResult<Attachment<'a>> {
let end = (index.offset + index.length) as usize;
if mcap.len() < end {
return Err(McapError::BadIndex);
}
let mut reader = LinearReader::sans_magic(&mcap[index.offset as usize..end]);
let (h, d) = match reader.next().ok_or(McapError::BadIndex)? {
Ok(records::Record::Attachment { header, data }) => (header, data),
Ok(_other_record) => return Err(McapError::BadIndex),
Err(e) => return Err(e),
};
if reader.next().is_some() {
// Wut - multiple records in the given slice?
return Err(McapError::BadIndex);
}
Ok(Attachment {
log_time: h.log_time,
create_time: h.create_time,
name: h.name,
media_type: h.media_type,
data: d,
})
}
/// Read the metadata with the given index.
pub fn metadata(mcap: &[u8], index: &records::MetadataIndex) -> McapResult<records::Metadata> {
let end = (index.offset + index.length) as usize;
if mcap.len() < end {
return Err(McapError::BadIndex);
}
let mut reader = LinearReader::sans_magic(&mcap[index.offset as usize..end]);
let m = match reader.next().ok_or(McapError::BadIndex)? {
Ok(records::Record::Metadata(m)) => m,
Ok(_other_record) => return Err(McapError::BadIndex),
Err(e) => return Err(e),
};
if reader.next().is_some() {
// Wut - multiple records in the given slice?
return Err(McapError::BadIndex);
}
Ok(m)
}
// All of the following panic if they walk off the back of the data block;
// callers are assumed to have made sure they got enoug bytes back with
// `validate_response()`
/// Builds a `read_<type>(&mut buf)` function that reads a given type
/// off the buffer and advances it the appropriate number of bytes.
macro_rules! reader {
($type:ty) => {
paste::paste! {
#[inline]
fn [<read_ $type>](block: &mut &[u8]) -> $type {
const SIZE: usize = size_of::<$type>();
let res = $type::from_le_bytes(
block[0..SIZE].try_into().unwrap()
);
*block = &block[SIZE..];
res
}
}
};
}
reader!(u8);
reader!(u64);
#[cfg(test)]
mod test {
use super::*;
// Can we read a file that's only magic?
// (Probably considered malformed by the spec, but let's not panic on user input)
#[test]
fn only_two_magics() {
let two_magics = MAGIC.repeat(2);
let mut reader = LinearReader::new(&two_magics).unwrap();
assert!(reader.next().is_none());
}
#[test]
fn only_one_magic() {
assert!(matches!(LinearReader::new(MAGIC), Err(McapError::BadMagic)));
}
#[test]
fn only_two_magic_with_ignore_end_magic() {
let two_magics = MAGIC.repeat(2);
let mut reader =
LinearReader::new_with_options(&two_magics, enum_set!(Options::IgnoreEndMagic))
.unwrap();
assert!(reader.next().is_none());
}
#[test]
fn only_one_magic_with_ignore_end_magic() {
let mut reader =
LinearReader::new_with_options(MAGIC, enum_set!(Options::IgnoreEndMagic)).unwrap();
assert!(reader.next().is_none());
}
#[test]
fn test_read_record_from_slice_fails_on_too_short_chunks() {
let res = read_record_from_slice(&mut [0_u8; 4].as_slice());
assert!(matches!(res, Err(McapError::UnexpectedEof)));
let res = read_record_from_slice(&mut [0_u8; 8].as_slice());
assert!(matches!(res, Err(McapError::UnexpectedEof)));
}
#[test]
fn test_read_record_from_slice_parses_for_big_enough_records() {
let res = read_record_from_slice(&mut [0_u8; 9].as_slice());
assert!(res.is_ok());
// Not a very strong test, but we are only testing that it checks the buffer size correctly
assert!(matches!(res, Ok(Record::Unknown { opcode: _, data: _ })));
}
}