axel源码中看到的content-length比实际的少一个字节，为啥子？

lylesong

用axel看到的长度比 用httpfox看到的content-length 少一个字节，

比如这个链接，

http://qianqian.baidu.com/download/BaiduMusic-12345630.exe

httpfox看到的是 Content-Length        7421120
‘
而 axel中看到的却是  Content-Length: 7421119

但是从实际下载来看，文件又没有损坏，这个是为啥子啊？

lylesong

哦，请求头里面加了一句

Range: bytes=1-

所以网站返回来的数据就是

1. Content-Range: bytes 1-7421119/7421120

复制代码

对于Range: 这个参数不咋个理解，从1开始，咋个还变少了。

linux_c_py_php

怪怪的。。

OwnWaterloo

断点续传诶。。。因为从1开始所以就不需要第1个字节而只需要后续部分了啊。。。

lylesong

回复 4# OwnWaterloo


    恩，后面查资料看到了，http 1.1 里面对range， content-range的用法了，
但是别人都是从0开始，[中间划分几块] 最后到 length -1 为止。

axel 这个程序里面从1开始，也是到length -1为止，这里看了源码也没看明白，

你说的从1开始，1不要了，第0个字节抛弃了，文件还是完整的啊？

OwnWaterloo

回复 5# lylesong

刚才试了一下：

1. 
   
2. $ curl -sI http://qianqian.baidu.com/download/BaiduMusic-12345630.exe | egrep -i '^(HTTP/|Content|Accept-Ranges)'
   
3. HTTP/1.1 200 OK
   
4. Content-Type: application/octet-stream
   
5. Content-Length: 7421120
   
6. Content-Type: application/octet-stream
   
7. Content-Disposition: attachment; filename=BaiduMusic-12345630.exe
   
8. Accept-Ranges: bytes
   

复制代码

支持Accept-Ranges，并且长度是7421120。

之后用

1. 
   
2. $ axel http://qianqian.baidu.com/download/BaiduMusic-12345630.exe
   

复制代码

下载并且抓到下面一些请求：


GET /download/BaiduMusic-12345630.exe HTTP/1.0
Host: qianqian.baidu.com
Range: bytes=1-
User-Agent: Axel 2.4 (Linux)

HTTP/1.1 206 Partial Content
Server: nginx
Date: Sun, 23 Mar 2014 14:09:26 GMT
Content-Type: application/octet-stream
Content-Length: 7421119
Last-Modified: Wed, 04 Dec 2013 16:05:53 GMT
Connection: close
Content-Type: application/octet-stream
Content-Disposition: attachment; filename=BaiduMusic-12345630.exe
Content-Range: bytes 1-7421119/7421120

GET /download/BaiduMusic-12345630.exe HTTP/1.0
Host: qianqian.baidu.com
Range: bytes=3710561-5565841
User-Agent: Axel 2.4 (Linux)

HTTP/1.1 206 Partial Content
Server: nginx
Date: Sun, 23 Mar 2014 14:09:26 GMT
Content-Type: application/octet-stream
Content-Length: 1855281
Last-Modified: Wed, 04 Dec 2013 16:05:53 GMT
Connection: close
Content-Type: application/octet-stream
Content-Disposition: attachment; filename=BaiduMusic-12345630.exe
Content-Range: bytes 3710561-5565841/7421120

GET /download/BaiduMusic-12345630.exe HTTP/1.0
Host: qianqian.baidu.com
User-Agent: Axel 2.4 (Linux)

HTTP/1.1 200 OK
Server: nginx
Date: Sun, 23 Mar 2014 14:09:26 GMT
Content-Type: application/octet-stream
Content-Length: 7421120
Last-Modified: Wed, 04 Dec 2013 16:05:53 GMT
Connection: close
Content-Type: application/octet-stream
Content-Disposition: attachment; filename=BaiduMusic-12345630.exe
Accept-Ranges: bytes

GET /download/BaiduMusic-12345630.exe HTTP/1.0
Host: qianqian.baidu.com
Range: bytes=5565842-7421119
User-Agent: Axel 2.4 (Linux)

HTTP/1.1 206 Partial Content
Server: nginx
Date: Sun, 23 Mar 2014 14:09:26 GMT
Content-Type: application/octet-stream
Content-Length: 1855278
Last-Modified: Wed, 04 Dec 2013 16:05:53 GMT
Connection: close
Content-Type: application/octet-stream
Content-Disposition: attachment; filename=BaiduMusic-12345630.exe
Content-Range: bytes 5565842-7421119/7421120

GET /download/BaiduMusic-12345630.exe HTTP/1.0
Host: qianqian.baidu.com
Range: bytes=1855280-3710560
User-Agent: Axel 2.4 (Linux)

HTTP/1.1 206 Partial Content
Server: nginx
Date: Sun, 23 Mar 2014 14:09:26 GMT
Content-Type: application/octet-stream
Content-Length: 1855281
Last-Modified: Wed, 04 Dec 2013 16:05:53 GMT
Connection: close
Content-Type: application/octet-stream
Content-Disposition: attachment; filename=BaiduMusic-12345630.exe
Content-Range: bytes 1855280-3710560/7421120

确实第1个请求是Range: bytes=1-。 但后续也有一个没有带Range的请求。
不清楚为什么要这样处理。。。