用 Rust 构建爬虫：抓取和解析 HTML

• https://kerkour.com/rust-crawler-scraping-and-parsing-html

Rust 编译器为您捕获的错误

忘记关闭文件或连接：

resp, err := http.Get("http://kerkour.com")
if err != nil {
// ...
}
// defer resp.Body.Close() // DON'T forget this line

let wordlist_file = File::open("wordlist.txt")?;
// do something...

// we don't need to close wordlist_file
// it will be closed when the variable goes out of scope

未释放的互斥锁：

type App struct {
  mutex sync.Mutex
  data  map[string]string
}

func (app *App) DoSomething(input string) {
  app.mutex.Lock()
defer app.mutex.Unlock()
// do something with data and input
}

func (app *App) DoManyThings(input []string) {
for _, item := range input {
      app.mutex.Lock()
defer app.mutex.Unlock()
// do something with data and item
  }
}

for item in input {
  let _guard = mutex.lock().expect("locking mutex");
// do something
// mutex is released here as _guard is dropped
}

缺少 switch case：

假设我们正在跟踪在线商店中产品的状态：

const (
  StatusUnknown   Status = 0
  StatusDraft     Status = 1
  StatusPublished Status = 2
)

switch status {
case StatusUnknown:
// ...
case StatusDraft:
// ...
case StatusPublished:
// ...
}

#[derive(Debug, Clone, Copy)]
enum Platform {
    Linux,
    MacOS,
    Windows,
    Unknown,
}

impl fmt::Display for Platform {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match self {
            Platform::Linux => write!(f, "Linux"),
            Platform::Macos => write!(f, "macOS"),
// Compile time error! We forgot Windows and Unknown
        }
    }
}

无效的指针取消引用：

据我所知，不可能在安全的 Rust 中创建对无效地址的引用。

type User struct {
// ...
    Foo *Bar // is it intended to be used a a pointer, or as an optional field?
}

struct User {
// ...
    foor: Option<Bar>, // it's clear that this field is optional
}

未初始化的变量：

假设我们正在处理用户帐户：

type User struct {
  ID          uuid.UUID
  CreatedAt   time.Time
  UpdatedAt time.Time
  Email       string
}

func (app *App) CreateUser(email string) {
// ...
    now := time.Now().UTC()

    user := User {
      ID: uuid.New(),
      CreatedAt: now,
      UpdatedAt: now,
      Email: email,
    }
    err = app.repository.CreateUser(app.db, user)
// ...
}

struct User {
  id: uuid::Uuid,
  created_at: DateTime<Utc>,
  updated_at: DateTime<Utc>,
  email: String,
  allowed_storage: i64,
}

fn create_user(email: String) {
let user = User {
      id: uuid::new(),
      created_at: now,
      updated_at: now,
      email: email,
// we forgot to update the function to initialize allowed_storage
    };
}

• https://kerkour.com/bugs-rust-compiler-helps-prevent

From 日报小组 侯盛鑫 坏姐姐

• Rust.cc 论坛: 支持 rss
• 微信公众号：Rust 语言中文社区