magic-embed: Compile-time Magic Database Embedding

A procedural macro crate for embedding compiled pure_magic databases directly into your Rust binary. This crate provides a convenient way to bundle file type detection rules with your application, eliminating the need for external rule files at runtime.

Features

• Compile-time Embedding: Magic rule files are compiled and embedded during build
• Zero Runtime Dependencies: No need to distribute separate rule files
• Flexible Configuration: Include/exclude specific rule files or directories
• Seamless Integration: Works with the pure_magic

Installation

Add magic-embed to your Cargo.toml:

[dependencies]
magic-embed = "0.1"  # Replace with the latest version
pure-magic = "0.1"     # Required peer dependency

Usage

Apply the #[magic_embed] attribute to a struct to embed a compiled magic database:

use magic_embed::magic_embed;
use pure_magic::MagicDb;

#[magic_embed(include=["../../magic-db/src/magdir"], exclude=["../../magic-db/src/magdir/der"])]
struct MyMagicDb;

fn main() -> Result<(), pure_magic::Error> {
    let db = MyMagicDb::open()?;
    // Use the database as you would with pure_magic
    Ok(())
}

Attributes

Complete Example

use magic_embed::magic_embed;
use pure_magic::MagicDb;
use std::fs::File;
use std::env::current_exe;

#[magic_embed(
    include=["../../magic-db/src/magdir"],
    exclude=["../../magic-db/src/magdir/der"]
)]
struct AppMagicDb;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Open the embedded database
    let db = AppMagicDb::open()?;

    // Use it to detect file types
    let mut file = File::open(current_exe()?)?;
    let magic = db.first_magic(&mut file, None)?;

    println!("Detected: {} (MIME: {})", magic.message(), magic.mime_type());
    Ok(())
}

Build Configuration

To ensure your database is rebuilt when rule files change, create a build.rs file:

// build.rs
fn main() {
    println!("cargo:rerun-if-changed=magic/rules/");
}

Replace magic/rules/ with the path to your actual rule files.

How It Works

1. Compile Time: The macro compiles all specified magic rule files into a binary database
2. Embedding: The compiled database is embedded in your binary as a byte array
3. Runtime: The open() method deserializes the embedded database

The compiled database is stored in target/magic-db/db.bin and will be automatically rebuilt when any included rule file is modified (considering you've added a build.rs script).

Performance Considerations

• The database is compiled only when source files change
• Embedded databases increase binary size but eliminate runtime file I/O
• Database deserialization happens once at runtime when open() is called

License

This project is licensed under the GPL-3.0 License.