用Django做后台，客户端向Django请求数据，为了区分不同的请求，想把每个请求类别加在HTTP头部（headers）里面。
先做实验，就用Python的httplib库来做模拟客户端，参考网上写出模拟代码如下：
#coding=utf8
import httplib
httpClient = None
try:
myheaders = { "category": "Books",
"id": "21",
'My-Agent': "Super brower"
}
httpClient = httplib.HTTPConnection('10.14.1XX.XXX',8086,timeout=30)
httpClient.request('GET','/headinfo/',headers=myheaders)
response = httpClient.getresponse()
print response.status
print response.reason
print response.read()
except Exception, e:
print e
finally:
if httpClient:
httpClient.close()其中'/headinfo/'为服务器的响应目录。
然后是服务端的响应代码，《The Django Book》第七章有个获取META的例子：
# GOOD (VERSION 2)
def ua_display_good2(request):
ua = request.META.get('HTTP_USER_AGENT', 'unknown')
return HttpResponse("Your browser is %s" % ua)正好看过这个例子，就模拟上面的这个写了一个能够返回客户端自定义头部的模块：
from django.http import HttpResponse
def headinfo(request):
category = request.META.get('CATEGORY', 'unkown')
id = request.META.get('ID','unkown')
agent = request.META.get('MY-AGENT','unkown')
html = "<html><body>Category is %s, id is %s, agent is %s</body></html>" % (category, id, agent)
return HttpResponse(html)运行结果如下：
$python get.py #输出: #200 #OK #<html><body>Category is unkown, id is unkown, agent is unkown</body></html>
可以看到服务器成功响应了，但是却没有返回自定义的内容。
我以为是客户端模拟headers出问题了，查找和试验了许多次都没有返回正确的结果。后来去查Django的文档，发现了相关的描述：
- HttpRequest.META
A standard Python dictionary containing all available HTTP headers. Available headers depend on the client and server, but here are some examples:
CONTENT_LENGTH – the length of the request body (as a string).
CONTENT_TYPE – the MIME type of the request body.
HTTP_ACCEPT_ENCODING – Acceptable encodings for the response.
HTTP_ACCEPT_LANGUAGE – Acceptable languages for the response.
HTTP_HOST – The HTTP Host header sent by the client.
HTTP_REFERER – The referring page, if any.
HTTP_USER_AGENT – The client’s user-agent string.
QUERY_STRING – The query string, as a single (unparsed) string.
REMOTE_ADDR – The IP address of the client.
REMOTE_HOST – The hostname of the client.
REMOTE_USER – The user authenticated by the Web server, if any.
REQUEST_METHOD – A string such as "GET" or "POST".
SERVER_NAME – The hostname of the server.
SERVER_PORT – The port of the server (as a string).
With the exception of CONTENT_LENGTH and CONTENT_TYPE, as given above, any HTTP headers in the request are converted toMETA keys by converting all characters to uppercase, replacing any hyphens with underscores and adding an HTTP_ prefix to the name. So, for example, a header called X-Bender would be mapped to the META key HTTP_X_BENDER.
其中红色的部分说明是说除了两个特例之外，其他的头部在META字典中的key值都会被加上“HTTP_”的前缀，终于找到问题所在了，赶紧修改服务端代码：
category = request.META.get('HTTP_CATEGORY', 'unkown')
id = request.META.get('HTTP_ID','unkown')果然，执行后返回了想要的结果：
$python get.py #正确的输出： #200 #OK #<html><body>Category is Books, id is 21, agent is Super brower</body></html>
得到的经验就是遇到问题要多查文档，搜索引擎并不一定比文档更高效。
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