[](https://crates.io/crates/jbcrs) [](https://docs.rs/jbcrs)
# JBcRs
**JBcRs is a Library, written in rust, to support reading and writing of java class files.**
This library is not close from being finished,
but certain features have already been implemented:
- **Basic parsing:**
A class file is parsed rather primitive:
- You have access to the constant pool.
Names, Descriptors and more are represented as `u16`,
Indexing into the pool must be done manually.
No validation of indices when parsing will be done.
- Access Flags are decoded using the bitflags crate
to provide a better experience.
- Attributes are always parsed.
This might be changed since it allows attackers
to craft invalid Debug Attributes,
which don't play a serious role in executing the code,
Parsing the entire class file then might not work,
since an error will be returned.
- More will be coming soon™.
---
# Getting Started:
First, add this library as a dependency to your Cargo.toml
```toml
[dependencies]
jbcrs = "0.1.0"
```
Now, you should choose if you want to use `basic` or `advanced`,
but since `advanced` is not yet implemented, `basic` must be used.
# Basic
We want to parse a class from a byte array
and print its version, access flags and name.
Of course you could use std::fs::File or a zip library,
but showing this is not the purpose of this tutorial.
```rust
use jbcrs::basic;
// You got the bytes from any possible source.
let bytes: &[u8] = [0xCA, 0xFE, 0xBA, 0xBE];
// After parsing the class file,
// you will get the constant pool
// and the class itself.
// You don't have to annotate the types here.
let (constant_pool, class): (basic::Pool, basic::Class) = basic::parse(bytes)
.expect("could not parse class file");
// Print its major and minor version:
println!("version: {}.{}", class.major_version, class.minor_version);
// Access Flags can be printed human readable
println!("access: {}", class.access_flags);
// Printing the name requires us to use the constant pool.
println!("name: {}", constant_pool.get_class_name(class.name).expect("could not get class name"));
```
---
# Resources
[Java Virtual Machine Specification (Java SE 9)](https://docs.oracle.com/javase/specs/jvms/se9/jvms9.pdf)