eventfold 0.2.0

Lightweight, append-only event log with derived views — your application state is a fold over an event log
Documentation 
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use std::fs::{File, OpenOptions};
use std::io::{self, BufRead, BufReader, Write};
use std::path::Path;

/// Compress data and append as a new zstd frame to the archive file.
/// Creates the archive file if it doesn't exist.
///
/// # Errors
///
/// Returns an error if creating/opening the archive file fails, or if
/// compression or writing fails.
pub fn append_compressed_frame(archive_path: &Path, data: &[u8]) -> io::Result<()> {
    let file = OpenOptions::new()
        .create(true)
        .append(true)
        .open(archive_path)?;
    let mut encoder = zstd::Encoder::new(file, 3)?;
    encoder.write_all(data)?;
    let file = encoder.finish()?;
    file.sync_data()?;
    Ok(())
}

/// Open the archive and return a streaming decompressor that reads through
/// all concatenated frames as one continuous byte stream.
/// Returns `Ok(None)` if the archive doesn't exist.
///
/// # Errors
///
/// Returns an error if opening the file or initializing the zstd
/// decoder fails.
pub fn open_archive_reader(archive_path: &Path) -> io::Result<Option<Box<dyn BufRead>>> {
    let file = match File::open(archive_path) {
        Ok(f) => f,
        Err(e) if e.kind() == io::ErrorKind::NotFound => return Ok(None),
        Err(e) => return Err(e),
    };
    let decoder = zstd::Decoder::new(file)?;
    Ok(Some(Box::new(BufReader::new(decoder))))
}