为什么换行符\n前需要一个回车return\r？

Question

在下面的代码中，HTTP 协议需要两个换行符，但是 \r 需要什么。为什么我们不能只加两个\n然后发送请求呢？

import socket
mysock = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
mysock.connect(("data.pr4e.org",80))
cmd = 'GET http://data.pr4e.org/romeo.txt HTTP/1.0\r\n\r\n'.encode() # here
mysock.send(cmd)
while True:
    data = mysock.recv(512)
    if len(data) > 0:
        print(data.decode())
    else :
        break
mysock.close()

Answer 1

因为这就是 the HTTP protocol is defined. More specifically, HTTP 1.0 defines a request like this:

Request        = Simple-Request | Full-Request

Full-Request   = Request-Line             
                 *( General-Header       
                  | Request-Header      
                  | Entity-Header )    
                 CRLF
                 [ Entity-Body ]
 
Request-Line = Method SP Request-URI SP HTTP-Version CRLF

Full-Request，这是任何 HTTP 1.0 兼容客户端（简单请求是 HTTP 0.9 且已弃用）都应该使用的，需要有两个 CRLF 令牌（一个在 Request-Line). CRLF 标记是两个字节 \r\n。因此需要在您的示例中以 \r\n\r\n.

结束字符串

此设计选择保留在 HTTP 1.1 中。

Answer 2

因为 HTTP 协议就是这样工作的。

The request/status line and headers must all end with (that is, a carriage return followed by a line feed). The empty line must consist of only and no other whitespace.

https://en.wikipedia.org/wiki/HTTP_message_body

为什么换行符\n前需要一个回车return\r？

Why we need a carriage return \r before the new line character \n?

python

python-3.x

networking

newline

carriage-return