下载

下载文件到临时目录

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使用 tempfile::Builder 创建一个临时目录，并使用 reqwest::get 通过 HTTP 协议异步下载文件。

使用 Response::url 方法内部的 tempdir() 方法获取文件名字，使用 File 结构体创建目标文件，并使用 io::copy 将下载的数据复制到文件中。程序退出时，会自动删除临时目录。

use error_chain::error_chain;
use std::io::copy;
use std::fs::File;
use tempfile::Builder;

error_chain! {
     foreign_links {
         Io(std::io::Error);
         HttpRequest(reqwest::Error);
     }
}

#[tokio::main]
async fn main() -> Result<()> {
    let tmp_dir = Builder::new().prefix("example").tempdir()?;
    let target = "https://www.rust-lang.org/logos/rust-logo-512x512.png";
    let response = reqwest::get(target).await?;

    let mut dest = {
        let fname = response
            .url()
            .path_segments()
            .and_then(|segments| segments.last())
            .and_then(|name| if name.is_empty() { None } else { Some(name) })
            .unwrap_or("tmp.bin");

        println!("file to download: '{}'", fname);
        let fname = tmp_dir.path().join(fname);
        println!("will be located under: '{:?}'", fname);
        File::create(fname)?
    };
    let content =  response.text().await?;
    copy(&mut content.as_bytes(), &mut dest)?;
    Ok(())
}

使用 HTTP range 请求头进行部分下载

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使用 reqwest::blocking::Client::head 获取响应的消息主体的大小（即消息主体内容长度）。

然后，使用 reqwest::blocking::Client::get 下载 10240 字节的内容，同时打印进度消息。本实例使用同步的 reqwest 模块，消息范围标头指定响应的消息块大小和位置。

RFC7233 中定义了消息范围标头。

译者注：RFC（Request For Comments）是一系列以编号排定的文件。文件收集了有关互联网相关信息，以及 UNIX 和互联网社区的软件文件。

use error_chain::error_chain;
use reqwest::header::{HeaderValue, CONTENT_LENGTH, RANGE};
use reqwest::StatusCode;
use std::fs::File;
use std::str::FromStr;

error_chain! {
    foreign_links {
        Io(std::io::Error);
        Reqwest(reqwest::Error);
        Header(reqwest::header::ToStrError);
    }
}

struct PartialRangeIter {
  start: u64,
  end: u64,
  buffer_size: u32,
}

impl PartialRangeIter {
  pub fn new(start: u64, end: u64, buffer_size: u32) -> Result<Self> {
    if buffer_size == 0 {
      Err("invalid buffer_size, give a value greater than zero.")?;
    }
    Ok(PartialRangeIter {
      start,
      end,
      buffer_size,
    })
  }
}

impl Iterator for PartialRangeIter {
  type Item = HeaderValue;
  fn next(&mut self) -> Option<Self::Item> {
    if self.start > self.end {
      None
    } else {
      let prev_start = self.start;
      self.start += std::cmp::min(self.buffer_size as u64, self.end - self.start + 1);
      Some(HeaderValue::from_str(&format!("bytes={}-{}", prev_start, self.start - 1)).expect("string provided by format!"))
    }
  }
}

fn main() -> Result<()> {
  let url = "https://httpbin.org/range/102400?duration=2";
  const CHUNK_SIZE: u32 = 10240;
    
  let client = reqwest::blocking::Client::new();
  let response = client.head(url).send()?;
  let length = response
    .headers()
    .get(CONTENT_LENGTH)
    .ok_or("response doesn't include the content length")?;
  let length = u64::from_str(length.to_str()?).map_err(|_| "invalid Content-Length header")?;
    
  let mut output_file = File::create("download.bin")?;
    
  println!("starting download...");
  for range in PartialRangeIter::new(0, length - 1, CHUNK_SIZE)? {
    println!("range {:?}", range);
    let mut response = client.get(url).header(RANGE, range).send()?;
    
    let status = response.status();
    if !(status == StatusCode::OK || status == StatusCode::PARTIAL_CONTENT) {
      error_chain::bail!("Unexpected server response: {}", status)
    }
    std::io::copy(&mut response, &mut output_file)?;
  }
    
  let content = response.text()?;
  std::io::copy(&mut content.as_bytes(), &mut output_file)?;

  println!("Finished with success!");
  Ok(())
}

POST 文件到 paste-rs

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本实例使用 reqwest::Client 建立与 https://paste.rs 的连接，遵循 reqwest::RequestBuilder 结构体模式。调用 Client::post 方法，以 URL 为参数连接目标，RequestBuilder::body 通过读取文件设置要发送的内容，RequestBuilder::send 方法在文件上传过程中将一直阻塞，直到返回响应消息。最后，read_to_string 返回响应消息并显示在控制台中。

use error_chain::error_chain;
use std::fs::File;
use std::io::Read;

 error_chain! {
     foreign_links {
         HttpRequest(reqwest::Error);
         IoError(::std::io::Error);
     }
 }
 #[tokio::main]

async fn main() -> Result<()> {
    let paste_api = "https://paste.rs";
    let mut file = File::open("message")?;

    let mut contents = String::new();
    file.read_to_string(&mut contents)?;

    let client = reqwest::Client::new();
    let res = client.post(paste_api)
        .body(contents)
        .send()
        .await?;
    let response_text = res.text().await?;
    println!("Your paste is located at: {}",response_text );
    Ok(())
}