Contract Spec: Experiment with custom sections and if we can store something like XDR in them. See if it is then also easy to extract that section, and strip that section, after compile.

[leighmcculloch]

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[leighmcculloch]

I experimented with custom sections and it looks really promising. There is good support for custom WASM sections in Rust, browsers, wasmi, wasm-opt, and other tools.

The are simple to implement:

#[cfg(target_family = "wasm")]
#[link_section = "scv1"]
pub static SCV1: [u8; 10] = [1, 2, 3, 4, 5, 5, 4, 3, 2, 1];

Ref: #123

I was able to confirm that the bytes could be extracted with the wasm-custom-section tool:

❯ wasm-custom-section target/wasm32-unknown-unknown/release/example_add_i64.wasm show scv1
Section `scv1` (10 bytes):
Length: 10 (0xa) bytes
0000:   01 02 03 04  05 05 04 03  02 01                      ..........

And I was able to confirm that:

• wasm-opt ignores the section and doesn't strip it, so developers are unlikely to accidentally strip their contract specs.
• wasmi is able to run contracts containing a custom section.
• parity_wasm is able to extract custom sections, and strip them. See Export custom sections from Vm rs-soroban-env#103.