Crate mcap

source · []
Expand description

A library for manipulating Foxglove MCAP files, both reading:

use std::fs;

use anyhow::{Context, Result};
use camino::Utf8Path;
use memmap::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 my_channel = Channel {
        topic: String::from("cool stuff"),
        schema: None,
        message_encoding: String::from("application/octet-stream"),
        metadata: BTreeMap::default()
    };

    let channel_id = out.add_channel(&my_channel)?;

    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::MessageStream;
pub use read::Summary;
pub use write::WriteOptions;
pub use write::Writer;

Modules

Read MCAP files
Raw records parsed from an MCAP file
Write MCAP files

Structs

An attachment and its metadata in an MCAP file
Describes a channel which Messages are published to in an MCAP file
An event in an MCAP file, published to a Channel
Describes a schema used by one or more Channels in an MCAP file

Enums

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

Constants

Magic bytes for the MCAP format

Type Definitions