23.5.3.2. 使用 HTTP range 请求头进行部分下载
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。
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(()) }