Noak

A library for reading and writing java bytecode.

Example

```rust use noak::reader::Class;

let mut class = Class::new(&bytes)?;

println!("Major Version: {}", class.version().major); println!(" Access Flags: {:?}", class.accessflags()?); println!(" Class Name: {}", class.thisclass_name()?.display()?); ```

Why should you use noak?

• Reading:
  • You want to parse class files without losing information.
  • You don't want to parse the entire class file.
  • Any valid class file is accepted by noak. Many invalid class files are accepted as well (this can be useful for reading heavily obfuscated code).
• Writing:
  • You want to write your own class files (limitations apply; see below).

Why wouldn't you use noak?

Many of these issues are in the process of being resolved, but that may take some time. - You want more than just a low-level class file reader and writer. - Noak makes heavy use of the type system and macros. This can cause problems with your IDE or make some aspects hard to understand. - Documentation is virtually non-existent. - The API is very unstable. - The code is not heavily tested. - Reading: - Some code may be repetitive (e.g. retrieving values from the constant pool). - Writing: - Modifying existing class files can be very tedious. - Not every attribute can be written at the moment (related issue) - Jumps above 65535 bytes may fail to be written. - The builder API isn't flexible enough for your use case. - Custom errors are quite restricted. - Stack Map Frames are not automatically generated.

Alternatives

This is not an exhaustive list. The statements below may not accurately reflect reality.

Libraries written in Rust: - cafebabe - Parses the entire file at once. - Accesses the constant pool during parsing. No explicit retrieval from the user side required. - classreader-rs - Parses the entire file at once. - Only supports parsing. - Does not support any attributes from version 53.0 and above. - Does not parse strings containing unpaired surrogates. - jbcrs - Parses the entire file at once. - Only supports parsing. - Does not support any attributes from version 53.0 and above. - Does not parse files containing UTF-8 constants with unpaired surrogates. - frappe/classfile - Parses the entire file at once. - Only supports parsing. - Does not support any attributes from version 53.0 and above. - Does not parse files containing UTF-8 constants with surrogates. - classfile-rs - Seems to be very incomplete. - Supports writing as well as parsing. - Parses the entire file at once. - Reads UTF-8 constants lossily. - classfile-parser - Seems to be very incomplete. - Parses the entire file at once. - Only supports parsing. - classfmt - Seems to be very incomplete. - Parses the entire file at once. - Only supports parsing. - javabc - Seems to be very incomplete. - Parses the entire file at once. - Only supports parsing.

A small fraction of libraries written in languages that are not Rust: - ASM (Java) - The most comprehensive and best supported bytecode manipulation and analysis framework. - Use this if noak does not suit your requirements and probably even if it does suit them. - javassist (Java) - A high-level bytecode library. - BCEL (Java)

License

This project is licensed under the MIT license.