Crate mcap

A library for manipulating Foxglove MCAP files, both reading:

use std::fs;

use anyhow::{Context, Result};
use camino::Utf8Path;
use memmap2::Mmap;

fn map_mcap<P: AsRef<Utf8Path>>(p: P) -> Result<Mmap> {
    let fd = fs::File::open(p.as_ref()).context("Couldn't open MCAP file")?;
    unsafe { Mmap::map(&fd) }.context("Couldn't map MCAP file")
}

fn read_it() -> Result<()> {
    let mapped = map_mcap("in.mcap")?;

    for message in mcap::MessageStream::new(&mapped)? {
        println!("{:?}", message?);
        // Or whatever else you'd like to do...
    }
    Ok(())
}

or writing:

use std::{collections::BTreeMap, fs, io::BufWriter};

use anyhow::Result;

use mcap::{Channel, records::MessageHeader, Writer};

fn write_it() -> Result<()> {
    // To set the profile or compression options, see mcap::WriteOptions.
    let mut out = Writer::new(
        BufWriter::new(fs::File::create("out.mcap")?)
    )?;

    // Channels and schemas are automatically assigned ID as they're serialized,
    // and automatically deduplicated with `Arc` when deserialized.
    let channel_id = out.add_channel(0, "cool stuff", "application/octet-stream", &BTreeMap::new())?;

    out.write_to_known_channel(
        &MessageHeader {
            channel_id,
            sequence: 25,
            log_time: 6,
            publish_time: 24
        },
        &[1, 2, 3]
    )?;
    out.write_to_known_channel(
        &MessageHeader {
            channel_id,
            sequence: 32,
            log_time: 23,
            publish_time: 25
        },
        &[3, 4, 5]
    )?;

    out.finish()?;

    Ok(())
}

Re-exports

pub use read::parse_record;

pub use read::MessageStream;

pub use read::Summary;

pub use write::WriteOptions;

pub use write::Writer;

Modules

read

Read MCAP data from a memory-mapped file.

records

Raw records parsed from an MCAP file

sans_io

Read MCAP files from any source of bytes

write

Write MCAP files

Structs

Attachment

An attachment and its metadata in an MCAP file

Channel

Describes a channel which Messages are published to in an MCAP file

Message

An event in an MCAP file, published to a Channel

Schema

Describes a schema used by one or more Channels in an MCAP file

Enums

Compression

Compression options for chunks of channels, schemas, and messages in an MCAP file

McapError

Constants

MAGIC

Magic bytes for the MCAP format

Type Aliases

McapResult