Simple "carrot" contract for ckb

This contract aims to reveal some problems with a simple Rust ckb contract.

• Some compilation options will ruin the binary.
• Contract does not work as expected.

Overview

To slim the size of contract binary in Rust, I use two groups of compilation optimization options. While one group of options will cause failure of contract execution.

What does this contract (should) do?

The contract examines the output data. if data starts with bytes “carrot”, the contract will immediately return a non-zero value, and the validation fails.

2020-05-14 18:45:24.766 +08:00 GlobalRuntime-3 DEBUG ckb-script  script group: Byte32(0x17cdd44f05902b124ba1f1d56ea5f2b89bc9d72b26dd60639d3fff43129d9922) DEBUG OUTPUT: Let's see if you are carrying carrots.
2020-05-14 18:45:24.767 +08:00 GlobalRuntime-3 DEBUG ckb-script  script group: Byte32(0x17cdd44f05902b124ba1f1d56ea5f2b89bc9d72b26dd60639d3fff43129d9922) DEBUG OUTPUT: No!!! You have a carrot!

Binary Size

During compilation, two groups of options are used with different combination. Above all, the --release flag is always used.

The first group of options is write in Cargo.toml:

[profile.release]
lto = true
opt-level = 'z'
codegen-units = 1

Command for compilation:

cargo build --release

The other is used as env arg with cargo build:

RUSTFLAGS='-C link-arg=-s'

# Usage
RUSTFLAGS='-C link-arg=-s' cargo build --release

Use [profile.release]	Use RUSTFLAGS	Binary Size
✗	✗	891408
✓	✗	145816
✗	✓	29352
✓	✓	25176

What happens?

All the contract binary are patched with ckb-binary-patcher.

[profile.release] will mess up the binary

When I compile the contract using the option group [profile.release] (with RUSTFLAGS), the binary breaks down. Any call to the broken contract results to the below vm error:

Internal: VM(InvalidEcall(90112))

“carrots” will pass the examination

If I fill the output data field with byte string carrot, the contract will complain as expected. However, when output data is carrots, the contract will not complain.