epub-wasm

A Rust crate that compiles to WebAssembly for parsing EPUB files into structured JSON format. This crate provides the core EPUB parsing logic that powers the epub-wasm npm package.

Overview

This crate leverages the rbook to parse EPUB files and extract their content into a clean JSON structure with chapters, headings, and paragraphs. The parsed data is then exposed via WebAssembly bindings for use in web applications.

Features

• EPUB parsing: Extracts text content from EPUB files
• Structured output: Organizes content into books, chapters, and blocks
• WebAssembly compatible: Designed for compilation to WASM
• Fast: Leverages Rust's performance for efficient parsing (parse times typically range from ~20 ms to ~60 ms)

Building

Prerequisites

• Rust (latest stable)
• wasm-pack

Build for WebAssembly

# Install wasm-pack if not installed
cargo install wasm-pack

# Build for bundler (recommended for Vite/SvelteKit)
wasm-pack build --release --target bundler

# Or build for web (serves WASM from URL)
# use this to test with the index.html
wasm-pack build --release --target web

Build for Native (Testing)

cargo build --release

Optimization Levels

You can adjust the opt-level in Cargo.toml to balance between performance and binary size:

| Value | Meaning | | ----- | ---------------------------------------------- | | 0 | No optimization (fast compile, slow binary) | | 1 | Basic optimizations | | 2 | Good balance (default for release) | | 3 | Maximum performance | | "s" | Optimize for small binary size | | "z" | Optimize for smallest possible binary size |

For WebAssembly, you might want to use "z" for minimal size or "s" for a balance. The current setting is opt-level = 3 for maximum performance.

Usage

This crate is primarily designed to be compiled to WebAssembly. The main entry point is the parse_epub function:

use epub_wasm::parse_epub;

// Parse EPUB bytes into JSON string
let epub_data: &[u8] = // ... load EPUB file
let json_result = parse_epub(epub_data);
let book: serde_json::Value = serde_json::from_str(&json_result).unwrap();

API

parse_epub(data: &[u8]) -> String

Parses an EPUB file from raw bytes and returns a JSON string representation.

Parameters:

• data: Raw bytes of the EPUB file

Returns: JSON string with the following structure:

{
  "id": "550e8400-e29b-41d4-a716-446655440000",
  "title": "Book Title",
  "chapters": [
    {
      "title": "Chapter Title",
      "id": "6ba7b810-9dad-11d1-80b4-00c04fd430c8",
      "blocks": [
        {
          "type": "heading",
          "text": "Heading Text",
          "position": "0"
        },
        {
          "type": "paragraph",
          "text": "Paragraph text...",
          "position": "1"
        }
      ]
    }
  ]
}

Each block in the parsed output includes a position field, a lexicographically sortable string that defines its stable reading order within the document. eg sequence: "0", "1", "2", ..., "9", "A", "B", ..., "z", "10", "11", ...

Dependencies

• rbook: EPUB parsing library
• serde: Serialization framework
• wasm-bindgen: WebAssembly bindings
• uuid: Id

Development

Running the Web Example

After building with wasm-pack, you can test the generated package:

cd pkg
# Serve locally (requires a web server)
python3 -m http.server 8000
# Then open index.html in browser