RustとPostgreSQLで色々な型をやりとりしてみた(NUMERIC対応)

# はじめに
RustでPostgreSQLを使いたいです。PostgreSQLには様々な型があるので、Rustでそれに合った型で受け取りたいです。
以前[RustとPostgreSQLで色々な型をやりとりしてみた(postgres 0.17対応)](https://qiita.com/aoyagikouhei/items/d2d1fec0d95f4a66cba9)という記事を書きましたが、これの修正版になります。

以前との違いは以下のようになります。
1. Rustのcrateであるpostgresからtokio-postgresに変更し、async/awaitにした
1. PostgreSQLのNUMERIC型に対応

## サポートされている型
[tokio_postgresのドキュメント](https://docs.rs/tokio-postgres/latest/tokio_postgres/types/trait.FromSql.html)にサポートされる型が記述されています。
しかにここにはNUMERIC型の記述がありません。結構使われる重要な型だと思うのですが・・・
RustでPostgreSQLの型をサポートするには、tokio_postgres::types::FromSqlとtokio_postgres::types::ToSqlを実装すれば良いです。
[rust_decimal](https://crates.io/crates/rust_decimal)がfeaturesでサポートしているので、これを使います。

# プログラム
```rust:Cargo.toml
[package]
name = "playground"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
bit-vec = "^0.6"
chrono = "^0.4"
eui48 = "^1.1"
geo-types = "^0.7"
deadpool-postgres = "^0.10"
rust_decimal = { version = "^1.23", features = ["db-tokio-postgres"] }
serde_json = "^1.0"
uuid = { version = "^0.8", features = ["serde", "v4"] }
tokio = { version = "1", features = ["full"] }

[dependencies.tokio-postgres]
version = "^0.7.5"
features = [
    "with-bit-vec-0_6",
    "with-chrono-0_4",
    "with-eui48-1",
    "with-geo-types-0_7",
    "with-serde_json-1",
    "with-uuid-0_8",
]
```

```rust:main.rs
use bit_vec::BitVec;
use chrono::prelude::*;
use deadpool_postgres::{
    Manager,
    ManagerConfig,
    Pool,
    RecyclingMethod,
    tokio_postgres::{
        Config,
        NoTls
    }
};
use eui48::{MacAddress, Eui48};
use geo_types::{
    Coordinate,
    Point,
    Rect,
    LineString,
};
use rust_decimal::Decimal;
use serde_json::Value;
use std::{
    collections::{
        HashMap,
    },
    net::{
        IpAddr,
        Ipv4Addr,
    },
    str::FromStr,
    time::{
        SystemTime,
    },
};
use uuid::Uuid;

#[derive(Debug, PartialEq)]
struct Data {
    bool_val: bool,
    bool_array_val: Vec<bool>,
    bool_option_some_val: Option<bool>,
    bool_option_none_val: Option<bool>,
    char_val: i8,
    smallint_val: i16,
    int_val: i32,
    oid_val: u32,
    bigint_val: i64,
    real_val: f32,
    double_val: f64,
    text_val: String,
    bytes_val: Vec<u8>,
    hstore_val: HashMap<String, Option<String>>,
    system_time_val: SystemTime,
    inet_val: IpAddr,
    timestamp_val: NaiveDateTime,
    timestamptz_val: DateTime<Utc>,
    date_val: NaiveDate,
    time_val: NaiveTime,
    macaddr_val: MacAddress,
    point_val: Point<f64>,
    box_val: Rect<f64>,
    path_val: LineString<f64>,
    jsonb_val: Value,
    uuid_val: Uuid,
    varbit_val: BitVec,
    decimal_val: Decimal,
}

fn make_pool() -> Pool {
    let mut pg_config = Config::new();
    pg_config.host("db");
    pg_config.user("user");
    pg_config.password("pass");
    pg_config.dbname("web");
    let mgr_config = ManagerConfig {
        recycling_method: RecyclingMethod::Fast
    };
    let mgr = Manager::from_config(pg_config, NoTls, mgr_config);
    let pool = Pool::builder(mgr).max_size(16).build().unwrap();
    pool
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let pool = make_pool();
    let client = pool.get().await.unwrap();
    let sql = r#"
        SELECT
            $1::BOOL AS bool_val
            ,$2::BOOL[] AS bool_array_val
            ,$3::BOOL AS bool_option_some_val
            ,$4::BOOL AS bool_option_none_val
            ,$5::"char" AS char_val
            ,$6::SMALLINT AS smallint_val
            ,$7::INT AS int_val
            ,$8::OID AS oid_val
            ,$9::BIGINT AS bigint_val
            ,$10::REAL AS real_val
            ,$11::DOUBLE PRECISION AS double_val
            ,$12::TEXT AS text_val
            ,$13::BYTEA AS bytes_val
            ,$14::HSTORE AS hstore_val
            ,$15::TIMESTAMPTZ AS system_time_val
            ,$16::INET AS inet_val
            ,$17::TIMESTAMP AS timestamp_val
            ,$18::TIMESTAMPTZ AS timestamptz_val
            ,$19::DATE AS date_val
            ,$20::TIME AS time_val
            ,$21::MACADDR AS macaddr_val
            ,$22::POINT AS point_val
            ,$23::BOX AS box_val
            ,$24::PATH AS path_val
            ,$25::JSONB AS jsonb_val
            ,$26::UUID AS uuid_val
            ,$27::VARBIT AS varbit_val
            ,$28::NUMERIC AS decimal_val
    "#;
    let stmt = client.prepare_cached(sql).await?;

    let data = Data {
        bool_val: true,
        bool_array_val: vec![true, false],
        bool_option_some_val: Some(true),
        bool_option_none_val: None,
        char_val: 1,
        smallint_val: 2,
        int_val: 3,
        oid_val: 4,
        bigint_val: 5,
        real_val: 6.1,
        double_val: 7.1,
        text_val: "予定表〜①ﾊﾝｶｸだ".to_string(),
        bytes_val: vec![240, 159, 146, 150],
        hstore_val: {
            let mut hstore_val = HashMap::new();
            hstore_val.insert("key".to_string(), Some("value".to_string()));
            hstore_val
        },
        system_time_val: SystemTime::UNIX_EPOCH, // SystemTime::now()は精度の差で一致しないが使える。
        inet_val: IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)),
        timestamp_val: NaiveDate::from_ymd(2001, 2, 3).and_hms(4, 5, 6),
        timestamptz_val: Utc.ymd(2001, 2, 3).and_hms_milli(4, 5, 6, 7),
        date_val: NaiveDate::from_ymd(2002, 3, 4),
        time_val: NaiveTime::from_hms_milli(8, 59, 59, 100),
        macaddr_val: {
            let eui: Eui48 = [ 0x12, 0x34, 0x56, 0xAB, 0xCD, 0xEF ];
            MacAddress::new( eui )
        },
        point_val: Point::new(1.234, 2.345),
        box_val: Rect::new(
            Coordinate { x: 0., y: 0. },
            Coordinate { x: 10., y: 20. },
        ),
        path_val: LineString(vec![
            Coordinate { x: 0., y: 0. },
            Coordinate { x: 10., y: 20. },]),
        jsonb_val: {
            let json_data = r#"{
                "name" : "予定表〜①ﾊﾝｶｸだ",
                "age" : 92233720368547758070
            }"#;
            serde_json::from_str(json_data).unwrap()
        },
        uuid_val: Uuid::new_v4(),
        varbit_val: {
            let mut varbit_val = BitVec::from_elem(10, false);
            varbit_val.set(2, true);
            varbit_val
        },
        decimal_val: Decimal::from_str("1.1").unwrap(),
    };
    let rows = client.query(&stmt, &[
        &data.bool_val,
        &data.bool_array_val,
        &data.bool_option_some_val,
        &data.bool_option_none_val,
        &data.char_val,
        &data.smallint_val,
        &data.int_val,
        &data.oid_val,
        &data.bigint_val,
        &data.real_val,
        &data.double_val,
        &data.text_val,
        &data.bytes_val,
        &data.hstore_val,
        &data.system_time_val,
        &data.inet_val,
        &data.timestamp_val,
        &data.timestamptz_val,
        &data.date_val,
        &data.time_val,
        &data.macaddr_val,
        &data.point_val,
        &data.box_val,
        &data.path_val,
        &data.jsonb_val,
        &data.uuid_val,
        &data.varbit_val,
        &data.decimal_val,
    ]).await?;

    let row = rows.get(0).unwrap();
    let res = Data {
        bool_val: row.get("bool_val"),
        bool_array_val: row.get("bool_array_val"),
        bool_option_some_val: row.get("bool_option_some_val"),
        bool_option_none_val: row.get("bool_option_none_val"),
        char_val: row.get("char_val"),
        smallint_val: row.get("smallint_val"),
        int_val: row.get("int_val"),
        oid_val: row.get("oid_val"),
        bigint_val: row.get("bigint_val"),
        real_val: row.get("real_val"),
        double_val: row.get("double_val"),
        text_val: row.get("text_val"),
        bytes_val: row.get("bytes_val"),
        hstore_val: row.get("hstore_val"),
        system_time_val: row.get("system_time_val"),
        inet_val: row.get("inet_val"),
        timestamp_val: row.get("timestamp_val"),
        timestamptz_val: row.get("timestamptz_val"),
        date_val: row.get("date_val"),
        time_val: row.get("time_val"),
        macaddr_val: row.get("macaddr_val"),
        point_val: row.get("point_val"),
        box_val: row.get("box_val"),
        path_val: row.get("path_val"),
        jsonb_val: row.get("jsonb_val"),
        uuid_val: row.get("uuid_val"),
        varbit_val: row.get("varbit_val"),
        decimal_val: row.get("decimal_val"),
    };
    assert_eq!(data, res);
    println!("{:?}", data);

    Ok(())
}
```