AnvilASM

A high-level library for reading, modifying, and generating JVM bytecode.

AnvilASM is a modern successor to SharpASM, designed to make JVM bytecode manipulation intuitive and developer-friendly within the .NET ecosystem.

💡 Design Philosophy

Unlike traditional stream-based parsers (such as the Visitor pattern often found in Java libraries), AnvilASM is built around a High-Level Object Model. The library abstracts the complexities of the raw binary format into a structured, easily navigable hierarchy.

The workflow is straightforward:

1. Parse: Converts raw JVM bytecode (.class files) into a rich high-level data structure.
2. Modify: Access and edit class elements (constants, methods, fields, instructions) directly, using standard C# collections like Dictionaries and Arrays.
3. Build: Reconstructs valid JVM bytecode from the modified structure, handling serialization details automatically.

🏗️ Architecture: High-Level vs. Low-Level

AnvilASM bridges the gap between developer usability and raw binary structure through a two-layer object model. The data flow is structured as follows:

graph LR
    HL[High-Level Object] <-->|Convert| LL[Low-Level Object]
    LL <-->|Serialize / Deserialize| Data[Data / Bytecode]

Loading

High-Level Object <---> Low-Level Object (Serialization/Deserialization) <---> Data

• High-Level Objects: These are the user-facing objects you interact with (e.g., ClassNode, MethodNode). They abstract away complexities like Constant Pool indices, turning them into direct references and standard C# types.
• Low-Level Objects: These objects serve as a direct mapping of the JVM ClassFile structure. They represent the raw u1, u2, u4 data types and strict structural layout required by the JVM specification.
• Transformation:
  • Deserialization: Raw Data is read into Low-Level Objects, which are then resolved into High-Level Objects for editing.
  • Serialization: Your modified High-Level Objects are converted back into Low-Level Objects (rebuilding the Constant Pool), which are then serialized into the final binary Data.

⚠️ Important Note

This project is currently under active development and reconstruction.

If you attempt to run the generated bytecode on a JVM during this phase, you may need to disable the bytecode verifier (e.g., using -Xverify:none or -noverify) as the output may not yet fully comply with strict JVM verification constraints. It is not recommended for production use at this stage.

📄 License

This project is licensed under the Apache License 2.0.