Appending to Archives

zesven allows adding files to existing archives without full recompression.

Using ArchiveAppender

Open an existing archive for appending:

use zesven::{ArchiveAppender, ArchivePath, Result};

fn main() -> Result<()> {
    let mut appender = ArchiveAppender::open("existing.7z")?;

    // Add new files
    appender.add_bytes(ArchivePath::new("new_file.txt")?, b"New content")?;
    appender.add_path("document.pdf", ArchivePath::new("docs/document.pdf")?)?;

    // Finalize
    appender.finish()?;
    Ok(())
}

How Appending Works

When you append to an archive:

1. The existing archive structure is read
2. New files are compressed as a new folder (block)
3. The archive header is rewritten to include both old and new entries

Original data is not recompressed, making appends efficient.

Append Options

Configure compression for new files:

use zesven::{ArchiveAppender, WriteOptions, ArchivePath, Result};

fn main() -> Result<()> {
    let options = WriteOptions::new()
        .level(7)?
        .solid();

    let mut appender = ArchiveAppender::open("archive.7z")?
        .with_options(options);

    appender.add_bytes(ArchivePath::new("data.txt")?, b"Compressed data")?;
    appender.finish()?;
    Ok(())
}

Appending with Custom Options

Configure compression options for appended files:

use zesven::{ArchiveAppender, WriteOptions, ArchivePath, Result};

fn main() -> Result<()> {
    let options = WriteOptions::new()
        .level(9)?;

    let mut appender = ArchiveAppender::open("archive.7z")?
        .with_options(options);

    appender.add_bytes(ArchivePath::new("new_file.txt")?, b"New data")?;
    appender.finish()?;
    Ok(())
}

Limitations

• No duplicate handling: Files with the same path create duplicates
• No solid merging: New files form a separate solid block
• Header size grows: Each append adds header overhead

For archives that need frequent updates, consider using ArchiveEditor instead.

When to Append vs. Recreate

Use appending when:

• Adding a few files to a large archive
• Speed is more important than optimal compression
• You don't need to remove or update existing files

Recreate the archive when:

• Many files need to be added
• Existing files need to be updated or removed
• Optimal compression ratio is important
• The archive has accumulated many appends

Append Result

use zesven::{ArchiveAppender, ArchivePath, Result};

fn main() -> Result<()> {
    let mut appender = ArchiveAppender::open("archive.7z")?;
    appender.add_bytes(ArchivePath::new("data.txt")?, b"Data")?;

    let result = appender.finish()?;

    println!("Files added: {}", result.entries_added);
    println!("Total entries: {}", result.total_entries);
    println!("Total bytes: {}", result.total_bytes);

    Ok(())
}

See Also

• Creating Archives - Create new archives
• Editing Archives - Update or remove files