> ## Documentation Index > Fetch the complete documentation index at: https://villagesql.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # Rust 扩展示例 > 通过 vsql_rot13 和 vsql_rational 参考实现学习使用 Rust SDK Rust SDK 仓库中随附了两个参考扩展——一个仅包含函数的最小示例，以及一个包含算术运算、排序和哈希的完整自定义类型。 **源码：** [vsql-rust-sdk](https://github.com/villagesql/vsql-rust-sdk/tree/main/examples) 中的 `examples/` *** ## vsql\_rot13 — 仅包含函数的扩展 最简单的 Rust 扩展：一个接受 STRING 并返回 STRING 的 VDF。 **用法：** ```sql theme={null} INSTALL EXTENSION vsql_rot13; SELECT rot13('Hello, World!'); -- 'Uryyb, Jbeyq!' SELECT rot13(rot13('Hello, World!')); -- 'Hello, World!' (rot13 is its own inverse) SELECT rot13(NULL); -- NULL ``` ### 目录结构 ``` vsql_rot13/ ├── Cargo.toml # cdylib crate, depends on villagesql ├── manifest.json # Extension metadata ├── src/ │ └── lib.rs # Implementation + extension! registration └── mysql-test/ └── t/*.test # MTR test cases ``` ### 实现 **文件：`src/lib.rs`** ```rust theme={null} use villagesql::{InValue, VdfReturn}; /// SQL: rot13(s STRING) -> STRING fn rot13_impl(args: &[InValue]) -> VdfReturn { match args.first() { Some(InValue::String(s)) => VdfReturn::string(rot13(s)), Some(InValue::Null) | None => VdfReturn::null(), _ => VdfReturn::error("rot13: expected a STRING argument"), } } fn rot13(s: &str) -> String { s.chars() .map(|c| match c { 'a'..='m' | 'A'..='M' => (c as u8 + 13) as char, 'n'..='z' | 'N'..='Z' => (c as u8 - 13) as char, _ => c, }) .collect() } villagesql::extension! { funcs: [ villagesql::func!(rot13_impl, "rot13", [villagesql::Type::String] -> villagesql::Type::String), ] } ``` **关键模式：** * VDF 接收 `&[InValue]` 并返回 `VdfReturn`——两者都是安全的 Rust 枚举 * NULL 在两端都是一等变体；直接对其进行模式匹配 * `extension!` 宏生成服务器在加载时调用的 C 入口点 * `func!` 声明 SQL 签名；参数和返回类型使用 `villagesql::Type::*` ### 清单 **文件：`manifest.json`** ```json theme={null} { "name": "vsql_rot13", "version": "0.1.0", "description": "Example VillageSQL extension: provides vsql_rot13(STRING) -> STRING", "author": "VillageSQL Community", "license": "GPL-2.0" } ``` *** ## vsql\_rational — 带算术运算的自定义类型 一个完整的自定义类型：以约分形式 `(numerator, denominator)` 存储有理数，并带有算术函数、排序和哈希。 **用法：** ```sql theme={null} INSTALL EXTENSION vsql_rational; CREATE TABLE measurements (id INT, ratio rational); INSERT INTO measurements VALUES (1, '1/2'), (2, '2/4'), -- normalizes to '1/2' on storage (3, '-3/6'), -- normalizes to '-1/2' (4, '0/1'); SELECT id, ratio FROM measurements ORDER BY ratio; SELECT rational_add('1/2', '1/3'); -- '5/6' SELECT rational_mul('2/3', '3/4'); -- '1/2' SELECT rational_to_real('22/7'); -- 3.142857... ``` ### 二进制存储格式 `rational` 存储 **16 字节**（小端序）： * 字节 0–7：分子（`i64`） * 字节 8–15：分母（`i64`） 值始终以约分形式（GCD = 1）存储，且分母为正。 ### 类型系统函数 **文件：`src/lib.rs`** 该类型注册了四个操作：编码（字符串 → 字节）、解码（字节 → 字符串）、比较（用于 ORDER BY）和哈希（用于索引）。 ```rust theme={null} pub fn rational_encode(s: &str) -> Result, String> { let (num_s, den_s) = s .split_once('/') .ok_or_else(|| format!("rational: expected 'n/d', got {s:?}"))?; let num: i64 = num_s.trim().parse().map_err(|e| format!("numerator: {e}"))?; let den: i64 = den_s.trim().parse().map_err(|e| format!("denominator: {e}"))?; let (n, d) = normalize(i128::from(num), i128::from(den)) .ok_or_else(|| "rational: zero or overflowing denominator".to_string())?; Ok(to_bytes(n, d)) } pub fn rational_decode(b: &[u8]) -> Result { if b.len() < BYTES { return Err(format!("rational: expected {} bytes, got {}", BYTES, b.len())); } let (n, d) = from_bytes(b); Ok(format!("{n}/{d}")) } pub fn rational_compare(a: &[u8], b: &[u8]) -> std::cmp::Ordering { let (n1, d1) = from_bytes(a); let (n2, d2) = from_bytes(b); // Cross-multiply; denominators are always positive after normalization let lhs = i128::from(n1) * i128::from(d2); let rhs = i128::from(n2) * i128::from(d1); lhs.cmp(&rhs) } ``` ### VDF 实现 接受自定义类型的 VDF 会接收 `InValue::Custom(&[u8])`，并自行解码这些字节： ```rust theme={null} fn rational_add_impl(args: &[InValue]) -> VdfReturn { match (arg(args, 0), arg(args, 1)) { (Ok(Some((n1, d1))), Ok(Some((n2, d2)))) => { match normalize( i128::from(n1) * i128::from(d2) + i128::from(n2) * i128::from(d1), i128::from(d1) * i128::from(d2), ) { Some((n, d)) => VdfReturn::Binary(to_bytes(n, d)), None => VdfReturn::error("rational_add: overflow"), } } (Err(e), _) | (_, Err(e)) => VdfReturn::error(format!("rational_add: {e}")), _ => VdfReturn::null(), } } ``` ### 注册 `extension!` 宏在单个声明中同时注册类型及其函数： ```rust theme={null} villagesql::extension! { funcs: [ villagesql::func!(rational_add_impl, "rational_add", [villagesql::custom!("rational"), villagesql::custom!("rational")] -> villagesql::custom!("rational"), deterministic: true), villagesql::func!(rational_sub_impl, "rational_sub", [villagesql::custom!("rational"), villagesql::custom!("rational")] -> villagesql::custom!("rational"), deterministic: true), villagesql::func!(rational_mul_impl, "rational_mul", [villagesql::custom!("rational"), villagesql::custom!("rational")] -> villagesql::custom!("rational"), deterministic: true), villagesql::func!(rational_div_impl, "rational_div", [villagesql::custom!("rational"), villagesql::custom!("rational")] -> villagesql::custom!("rational"), deterministic: true), villagesql::func!(rational_numer_impl, "rational_numer", [villagesql::custom!("rational")] -> villagesql::Type::Int, deterministic: true), villagesql::func!(rational_denom_impl, "rational_denom", [villagesql::custom!("rational")] -> villagesql::Type::Int, deterministic: true), villagesql::func!(rational_to_real_impl, "rational_to_real", [villagesql::custom!("rational")] -> villagesql::Type::Real, deterministic: true), ], types: [ villagesql::custom_type!( type_name: "rational", persisted_length: 16, max_decode_buffer_length: 42, encode: rational_encode, decode: rational_decode, compare: rational_compare, hash: rational_hash, default: "0/1", ), ] } ``` **关键模式：** * `villagesql::custom!("name")` 用于以参数或返回值的形式引用自定义类型 * `custom_type!` 注册类型及其 encode/decode/compare/hash 函数 * `default: "0/1"` 是内建默认值——服务器在类型初始化时会对该字符串调用 `encode()`，因此它必须是一个有效值 * `persisted_length` 必须与 `encode()` 返回的字节长度匹配 * `deterministic: true` 让优化器可以折叠常量调用 *** ## 关键实现模式 | 模式 | 用法 | | ---------------- | ------------------------------------------- | | **VDF 签名** | `fn impl(args: &[InValue]) -> VdfReturn` | | **NULL 处理** | 显式匹配 `InValue::Null` 和 `None` | | **错误报告** | `VdfReturn::error("message")` 中止语句 | | **自定义类型 encode** | 返回 `Result, String>` | | **自定义类型 decode** | 返回 `Result` | | **类型感知参数** | 在 `func!` 中使用 `villagesql::custom!("name")` | | **注册** | 单个 `extension!` 块声明函数和类型 | *** ## 测试 这两个示例都像 C++ 扩展一样使用 MTR（MySQL Test Runner）： ```bash theme={null} cd /path/to/villagesql/build/mysql-test ./mysql-test-run.pl --suite=vsql_rot13 ./mysql-test-run.pl --suite=vsql_rational ``` 使用 `--record` 生成或更新预期结果。 *** ## 后续步骤 SDK 安装、构建以及 extension! 宏 深入了解 encode、decode、compare 和 hash InValue、VdfReturn 以及宏接口 vsql\_rot13 和 vsql\_rational 的完整源码