Write custom SQL functions (VDFs) for VillageSQL in safe Rust. The SDK handles all FFI marshaling so you work entirely in ordinary Rust types.

Crates

Prerequisites

• Rust toolchain (stable, 1.87+)
• cargo-vsql installed (see cargo-vsql README)
• VillageSQL build directory (for install and test commands)

Quick start

1. Install cargo-vsql

2. Create a new extension crate

The fastest way is the vsql-extension-template-rust template — it scaffolds the Cargo.toml, manifest.json, source layout, and a CI workflow for you:

cargo install cargo-generate
cargo generate --git https://github.com/villagesql/vsql-extension-template-rust

cargo new --lib my-extension
cd my-extension

[lib]
crate-type = ["cdylib"]

[dependencies]
villagesql = "0.0.1"

3. Write your function

use villagesql::{InValue, VdfReturn};

fn my_func(args: &[InValue]) -> VdfReturn {
    match args.first() {
        Some(InValue::String(s)) => VdfReturn::string(s.to_uppercase()),
        Some(InValue::Null) | None => VdfReturn::null(),
        _ => VdfReturn::error("my_func: expected a STRING argument"),
    }
}

villagesql::extension! {
    funcs: [
        villagesql::func!(my_func, "my_func", [villagesql::Type::String] -> villagesql::Type::String),
    ]
}

4. Add a manifest

Create manifest.json next to Cargo.toml:

{
  "name": "my-extension",
  "version": "0.1.0",
  "description": "What your extension does",
  "author": "Your Name",
  "license": "GPL-2.0"
}

5. Package, install, and test

Run cargo vsql commands from inside your extension directory (not the workspace root).

export VillageSQL_BUILD_DIR=/path/to/villagesql/build
cargo vsql install
cargo vsql test

For the full API reference see the villagesql README. For all cargo vsql commands see the cargo-vsql README.

Continuous integration

Reusable GitHub Actions workflows for building, testing, and packaging Rust VillageSQL extensions live in villagesql/extension-actions. The vsql-extension-template-rust template wires them up by default.

Examples

• examples/vsql_rot13 — minimal string function; a good starting template
• examples/vsql_rational — custom type (n/d rational numbers) with arithmetic VDFs, demonstrating custom_type!, InValue::Custom, and VdfReturn::binary