/rust-anyhow-sample

Primary LanguageRust

rust-anyhow-sample

このPRで、Cargoもfailureからanyhowに移行したらしい。 まずはanyhowを試してみる。

使い方

use anyhow::Resultで使う。

extern crate anyhow;
extern crate serde;
extern crate serde_json;

use anyhow::Result;
use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize, Debug)]
struct ClusterMap {
    name: String,
    group: i32,
}

fn get_cluster_info() -> Result<ClusterMap> {
    let config = std::fs::read_to_string("cluster.json")?;
    let map: ClusterMap = serde_json::from_str(&config)?;
    Ok(map)
}

fn main() {
    let cm = get_cluster_info().unwrap();
    println!("{:?}", cm);
}

正常系

利用するjson

{
  "name": "cluster A",
  "group": 1
}

実行結果

❯ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/myanyhow`
ClusterMap { name: "cluster A", group: 1 }

cluster.jsonがない場合

❯ cargo run
   Compiling myanyhow v0.1.0 (/Users/cipepser/.go/src/github.com/cipepser/rust-anyhow-sample/myanyhow)
    Finished dev [unoptimized + debuginfo] target(s) in 0.49s
     Running `target/debug/myanyhow`
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: No such file or directory (os error 2)', src/libcore/result.rs:1165:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

jsonの型が違う場合

groupをstringにしてみる。

{
  "name": "cluster A",
  "group": "1"
}
❯ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/myanyhow`
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: invalid type: string "1", expected i32 at line 3 column 14', src/libcore/result.rs:1165:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

context

mainもpanicさせずに、errを表示させるようにした。

extern crate anyhow;
extern crate serde;
extern crate serde_json;

use anyhow::{Context, Result};
use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize, Debug)]
struct ClusterMap {
    name: String,
    group: i32,
}

fn get_cluster_info() -> Result<ClusterMap> {
    let config = std::fs::read_to_string("cluster.json")
        .context("failed to read config file")?;
    let map: ClusterMap = serde_json::from_str(&config)?;
    Ok(map)
}

fn main() {
    let _ = match get_cluster_info() {
        Ok(cm) => println!("{:?}", cm),
        Err(err) => println!("{:?}", err),
    };
}

cluster.jsonがない場合

❯ cargo run
failed to read config file

Caused by:
    No such file or directory (os error 2)

with_context

extern crate anyhow;
extern crate serde;
extern crate serde_json;

use anyhow::{Context, Result};
use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize, Debug)]
struct ClusterMap {
    name: String,
    group: i32,
}

fn get_cluster_info(path: &str) -> Result<ClusterMap> {
    let config = std::fs::read_to_string(&path)
        .with_context(|| format!("failed to read config file: {}", path))?;
    let map: ClusterMap = serde_json::from_str(&config)?;
    Ok(map)
}

fn main() {
    let _ = match get_cluster_info("cluster.json") {
        Ok(cm) => println!("{:?}", cm),
        Err(err) => println!("{:?}", err),
    };
}

cluster.jsonがない場合

❯ cargo run
failed to read config file: cluster.json

Caused by:
    No such file or directory (os error 2)

独自エラー

thiserrorを追加して、独自エラーとしてClusterMapErrorを定義。

validateでgroupの範囲を0-100とし、範囲外の場合は、InvalidGroup(i32)を返す仕様とした。

extern crate anyhow;
extern crate serde;
extern crate serde_json;
extern crate thiserror;

use anyhow::{Context, Result};
use serde::{Serialize, Deserialize};
use thiserror::Error;
use crate::ClusterMapError::InvalidGroup;

#[derive(Serialize, Deserialize, Debug)]
struct ClusterMap {
    name: String,
    group: i32,
}

#[derive(Error, Debug)]
pub enum ClusterMapError {
    #[error("Invalid range of range (expected in 0-100), got {0}")]
    InvalidGroup(i32),
}

impl ClusterMap {
    fn validate(self) -> Result<Self> {
        if self.group < 0 || self.group > 100 {
            Err(InvalidGroup(self.group).into())
        } else {
            Ok(self)
        }
    }
}

fn get_cluster_info(path: &str) -> Result<ClusterMap> {
    let config = std::fs::read_to_string(&path)
        .with_context(|| format!("failed to read config file: {}", path))?;
    let map: ClusterMap = serde_json::from_str(&config)?;
    let map = map.validate()?;
    Ok(map)
}


fn main() {
    let _ = match get_cluster_info("cluster.json") {
        Ok(cm) => println!("{:?}", cm),
        Err(err) => println!("{:?}", err),
    };
}

groupが101の場合（範囲外）

利用するjson

{
  "name": "cluster A",
  "group": 101
}

実行結果

❯ cargo run
Invalid range of range (expected in 0-100), got 101

この時点のCargo.toml

[dependencies]
anyhow = "1.0"
serde = { version = "1.0", features = ["derive"] }
serde_json = "1.0.44"
thiserror = "1.0"

References