HTTP中确定报文结束的方法

HTTP中,确定报文结束有几种不同方法,较为常见的是:

  • 关闭TCP连接
  • 通过Content-Length检测

若不关闭TCP连接,也不在HTTP头部加上Content-Length字段,则无法正确确定HTTP报文是否结束,对于浏览器来说,此时就会一直处于加载状态。

这几天学习Python Socket编程时就遇到了这个问题,下面是一段最简单的HTTP服务器代码,无论收到什么请求都返回一个Hello World!

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from socket import socket, AF_INET, SOCK_STREAM

HTTPResponse ='HTTP/1.1 200 OK\r\n\r\n<html>Hello World!</html>'

WebSocket = socket(AF_INET, SOCK_STREAM)
WebSocket.bind(('localhost', 80))
WebSocket.listen(1)

HTTPSocket, addr = WebSocket.accept() # Wait Connection

while True:
print 'Waiting HTTP Request...'
Request = HTTPSocket.recv(1024)

print 'Send HTTP Response!'
HTTPSocket.sendall(HTTPResponse)

然而,这段代码是无法正常工作的,运行之后使用浏览器访问http://localhost/,得到的结果是这样的:

从Shell的输出结果来看,HTTP响应报文已经发送成功了,此时服务器已经在等待下一次请求了,而浏览器却始终处于Connecting状态中。

可以通过由服务器主动关闭TCP连接来解决这一问题,修改后的代码是这样的:

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from socket import socket, AF_INET, SOCK_STREAM

HTTPResponse ='HTTP/1.1 200 OK\r\n\r\n<html>Hello World!</html>'

WebSocket = socket(AF_INET, SOCK_STREAM)
WebSocket.bind(('localhost', 80))
WebSocket.listen(1)

while True:
print 'Waiting HTTP Request...'
HTTPSocket, addr = WebSocket.accept() # Wait Connection
Request = HTTPSocket.recv(1024)

print 'Send HTTP Response!'
HTTPSocket.sendall(HTTPResponse)

HTTPSocket.close() # Close Connection

修改后就可以正常运行了:

如果不关闭TCP连接,也可以通过加上Content-Length字段来解决这一问题,代码如下:

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from socket import socket, AF_INET, SOCK_STREAM

# Add Content-Length
HTTPResponse ='HTTP/1.1 200 OK\r\nContent-Length: 25\r\n\r\n<html>Hello World!</html>'

WebSocket = socket(AF_INET, SOCK_STREAM)
WebSocket.bind(('localhost', 80))
WebSocket.listen(1)

HTTPSocket, addr = WebSocket.accept() # Wait Connection

while True:
print 'Waiting HTTP Request...'
Request = HTTPSocket.recv(1024)

print 'Send HTTP Response!'
HTTPSocket.sendall(HTTPResponse)

这样浏览器也可以正常访问服务器,运行结果和之前关闭TCP连接完全相同。

一般来说,没有必要始终维持着一个TCP连接,所以最佳的解决方案是:使用Content-Length字段,并且在每次响应之后关闭TCP连接,即以下代码:

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from socket import socket, AF_INET, SOCK_STREAM

# Add Content-Length
HTTPResponse ='HTTP/1.1 200 OK\r\nContent-Length: 25\r\n\r\n<html>Hello World!</html>'

WebSocket = socket(AF_INET, SOCK_STREAM)
WebSocket.bind(('localhost', 80))
WebSocket.listen(1)

while True:
print 'Waiting HTTP Request...'
HTTPSocket, addr = WebSocket.accept() # Wait Connection
Request = HTTPSocket.recv(1024)

print 'Send HTTP Response!'
HTTPSocket.sendall(HTTPResponse)

HTTPSocket.close() # Close Connection
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