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Rust 实战 – 使用套接字联网API 2

2019-05-27 13:262022-03-01 rust 实战

上一节，我们已经实现了一个最小可运行版本。之所以使用Rust而不是C，是因为Rust具备了必要的抽象能力，还能获得跟C差不多的性能。这一节，我们对上一节的代码做必要的封装，顺便还能把unsafe的代码包装成safe的API。

我将上一节的源码放到了这里，你可以去查看。

还记得上一节，我们把使用到的libc中的函数socket、bind、connect和结构体sockaddr、sockaddr_in、in_addr等，在Rust这边定义了出来。实际上，几乎libc中的函数，libc这个crate都帮我们定义好了。你可以去这里查看。编译器和标准库本身也使用了这个crate，我们也使用这个。

首先在Cargo.toml文件的[dependencies]下面加入libc = "0.2":

[dependencies]
libc = "0.2"

接着在main.rs文件上方加入use libc;，也可以use libc as c;。或者你直接简单粗暴use libc::*，并不推荐这样，除非你明确知道你使用的函数来自哪里。并将我们定义的与libc中对用的常量、函数、结构体删除。再添加libc::或c::到我们使用那些常量、结构体、函数的地方。如果你是直接use libc::*，除了直接删除那部分代码外，几乎什么都不用做。目前的代码：

Rust 实战 – 使用套接字联网API 1

2019-05-27 03:302019-05-27 rust 实战

虽然标准库已经封装好了 TcpListener 和TcpStream 等基础api，但作为Rust 的爱好者，我们可以去一探究竟。本文假设你已经对 Rust 和 Linux 操作系统有了一定了解。

在 Linux 上 Rust 默认会链接的系统的 libc 以及一些其他的库，这就意味着，你可以直接使用libc中的函数。比如，你可以使用 gethostname 获取你电脑的 “hostname”:

use std::os::raw::c_char;
use std::ffi::CStr;
extern {
    pub fn gethostname(name: *mut c_char, len: usize) -> i32;
}
fn main() {
    let len = 255;
    let mut buf = Vec::<u8>::with_capacity(len);
    let ptr = buf.as_mut_ptr() as *mut c_char;
    unsafe {
        gethostname(ptr, len);
        println!("{:?}", CStr::from_ptr(ptr));
    }
}

解释一下上面的代码。

extren 表示“外部块（External blocks）”，用来申明外部非 Rust 库中的符号。我们需要使用 Rust 以外的函数，比如 libc ，就需要在 extren 中将需要用到的函数定义出来，然后就可以像使用本地函数一样使用外部函数，编译器会负责帮我们转换，是不是很方便呢。但是，调用一个外部函数是unsafe的，编译器不能提供足够的保证，所以要放到unsafe块中。

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Photos2018-10-09 10:592022-03-01 Photography

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A collection of textile samples lay spread out on the table – Samsa was a travelling salesman – and above it there hung a picture that he had recently cut out of an illustrated magazine and housed in a nice, gilded frame. It showed a lady fitted out with a fur hat and fur boa who sat upright, raising a heavy fur muff that covered the whole of her lower arm towards the viewer.

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Far far away, behind the word mountains, far from the countries Vokalia and Consonantia, there live the blind texts. Separated they live in Bookmarksgrove right at the coast of the Semantics, a large language ocean. A small river named Duden flows by their place and supplies it with the necessary regelialia.

Travel and change of place impart new vigor to the mind.

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A wonderful serenity has taken possession of my entire soul, like these sweet mornings of spring which I enjoy with my whole heart. I am alone, and feel the charm of existence in this spot, which was created for the bliss of souls like mine. I feel the presence of the Almighty, who formed us in his own image, and the breath of that universal love which bears and sustains us.

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She packed her seven versalia, put her initial into the belt and made herself on the way. When she reached the first hills of the Italic Mountains, she had a last view back on the skyline of her hometown Bookmarksgrove, the headline of Alphabet Village and the subline of her own road, the Line Lane.

Life is Either a Daring Adventure or Nothing at All

On her way she met a copy. The copy warned the Little Blind Text, that where it came from it would have been rewritten a thousand times and everything that was left from its origin would be the word “and” and the Little Blind Text should turn around and return to its own, safe country.

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Rust 实战 – 使用套接字联网API 2

Rust 实战 – 使用套接字联网API 1

These Places Tell Their Own Amazing Stories Through Photographs

How Does Travel Impart New Vigor to the Human Mind

The Growing Importance of Honest, Powerful Storytelling

When Things Have to Change: How to Find the Willpower

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