发信人: kenmlee()
整理人: kenmlee(2000-07-08 16:49:34), 站内信件
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8 Connections
#8 连接 /#
8.1 Persistent Connections
#8.1 永久连接 /#
8.1.1 Purpose
#8.1.1 目的 /#
Prior to persistent connections, a separate TCP connection was
established to fetch each URL, increasing the load on HTTP servers
and causing congestion on the Internet. The use of inline images an
d
other associated data often requires a client to make multiple
requests of the same server in a short amount of time. Analyses of
these performance problems are available [30][27]; analysis and
results from a prototype implementation are in [26].
# 在使用永久连接以前，每个URL的获取是通过分别建立TCP连接实现的，既加重
了
HTTP服务器的负载又使Internet更加拥挤。内嵌图片的使用和其他关联数据经
常
要求客户程序在短时间内对同一个服务器进行多次请求。这些执行问题的分析
见
[30][27]，一个原型实现的分析和结果见[26]。
/#
Persistent HTTP connections have a number of advantages:
o By opening and closing fewer TCP connections, CPU time is save
d,
and memory used for TCP protocol control blocks is also saved.
o HTTP requests and responses can be pipelined on a connection.
Pipelining allows a client to make multiple requests without
waiting for each response, allowing a single TCP connection to
be
used much more efficiently, with much lower elapsed time.
o Network congestion is reduced by reducing the number of packet
s
caused by TCP opens, and by allowing TCP sufficient time to
determine the congestion state of the network.
o HTTP can evolve more gracefully; since errors can be reported
without the penalty of closing the TCP connection. Clients usi
ng
future versions of HTTP might optimistically try a new feature
, but
if communicating with an older server, retry with old semantic
s
after an error is reported.
# 永久HTTP连接有如下优点：
o 通过减少打开和关闭更少的TCP连接，节约了CPU时间和用于TCP协议控制
块的内存。
o 一个连接中的HTTP请求和响应可以管道化，管道允许客户程序发出多个
请求而无需
等待每个响应，使单个TCP连接可以更加有效的使用，并且减少了公用的
时间。
o 减少了TCP连接的打开就减少了数据包的数量，于是减少了网络拥塞，并
且使TCP有
充分的时间来判断网络的拥塞状态。
o HTTP本身可以得到更好的发展，因为错误报告无需强制关闭TCP连接。客
户应用程序
在使用将来新版本的HTTP时可能通过使用新的特征来优化，但如果和一
个旧的服务器
通讯，当错误发生时使用旧的语法重试。
/#
HTTP implementations SHOULD implement persistent connections.
# HTTP的实现应该实现永久连接。 /#
8.1.2 Overall Operation
#8.1.2 总体运作机制 /#
A significant difference between HTTP/1.1 and earlier versions of
HTTP is that persistent connections are the default behavior of any
HTTP connection. That is, unless otherwise indicated, the client ma
y
assume that the server will maintain a persistent connection.
# HTTP/1.1和以前版本的HTTP之间的一个显著的不同是，永久连接是HTTP的缺省
连接。
也就是说，除非专门指出，客户程序可以假设服务器将维护一个永久连接。
/#
Persistent connections provide a mechanism by which a client and a
server can signal the close of a TCP connection. This signaling tak
es
place using the Connection header field. Once a close has been
signaled, the client MUST not send any more requests on that
connection.
# 永久连接提供客户程序和服务器程序的TCP连接关闭信号机制，这个信号通过
连接头域
（Connection）传递。一旦收到关闭信号，客户程序必须不再通过这个连接发
送任何
请求。
/#
8.1.2.1 Negotiation
#8.1.2.1 协商 /#
An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
maintain a persistent connection unless a Connection header includi
ng
the connection-token "close" was sent in the request. If the server
chooses to close the connection immediately after sending the
response, it SHOULD send a Connection header including the
connection-token close.
# 除非在请求中的连接头域（Connection）包含关闭连接标示“close”，否则
HTTP/1.1
服务器将假设HTTP/1.1的客户程序意图维持一个永久连接。如果服务器选择在
发送
响应后立即关闭连接，它应该发送包含关闭连接标示的连接头域（Connectio
n）。
/#
An HTTP/1.1 client MAY expect a connection to remain open, but woul
d
decide to keep it open based on whether the response from a server
contains a Connection header with the connection-token close. In ca
se
the client does not want to maintain a connection for more than tha
t
request, it SHOULD send a Connection header including the
connection-token close.
# HTTP/1.1客户应用可以认为连接是一直打开的,但是是否保持打开状态决定于
服务器返回的响应中的连接头域(Connection)是否包含连接标示close.一旦
客户应用不想维护这个连接用户其后的请求,它应该发送一个连接(connectio
n)
包含连接标示close的头域.
/#
If either the client or the server sends the close token in the
Connection header, that request becomes the last one for the
connection.
# 如果客户应用或服务器中的任何一个在连接头域(connection)中发送了连接
标示close,这个请求便成了这个连接的最后一个请求.
/#
Clients and servers SHOULD NOT assume that a persistent connection
is
maintained for HTTP versions less than 1.1 unless it is explicitly
signaled. See section 19.7.1 for more information on backwards
compatibility with HTTP/1.0 clients.
# 除非显式指出,客户应用和服务器不应该假设在低于HTTP/1.1版本中将要维护
一个永久连接.见第19.7.1节关于和HTTP/1.0的客户应用的向后兼容信息.
/#
In order to remain persistent, all messages on the connection must
have a self-defined message length (i.e., one not defined by closur
e
of the connection), as described in section 4.4.
# 为了维护永久连接,所有在连接上的信息必须有一个自定义的消息长度(例如:
一个为定义的出现,连接将关闭),如第4.4节描述的.
/#
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※ 修改:．kenmlee 于 Jul 8 16:38:10 修改本文．[FROM: 61.140.188.222]
※ 来源:．月光软件站 http://www.moon-soft.com．[FROM: 61.140.188.222]
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