用Django做後臺，客戶端向Django請求數據，爲了區分不同的請求，想把每個請求類別加在HTTP頭部（headers）裏面。
先做實驗，就用Python的httplib庫來做模擬客戶端，參考網上寫出模擬代碼如下：
#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/'爲服務器的響應目錄。
然後是服務端的響應代碼，《The Django Book》第七章有個獲取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)正好看過這個例子，就模擬上面的這個寫了一個能夠返回客戶端自定義頭部的模塊：
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)運行結果如下：
$python get.py #輸出: #200 #OK #<html><body>Category is unkown, id is unkown, agent is unkown</body></html>
可以看到服務器成功響應了，但是卻沒有返回自定義的內容。
我以爲是客戶端模擬headers出問題了，查找和試驗了許多次都沒有返回正確的結果。後來去查Django的文檔，發現了相關的描述：
- 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.
其中紅色的部分說明是說除了兩個特例之外，其他的頭部在META字典中的key值都會被加上“HTTP_”的前綴，終於找到問題所在了，趕緊修改服務端代碼：
category = request.META.get('HTTP_CATEGORY', 'unkown')
id = request.META.get('HTTP_ID','unkown')果然，執行後返回了想要的結果：
$python get.py #正確的輸出： #200 #OK #<html><body>Category is Books, id is 21, agent is Super brower</body></html>
得到的經驗就是遇到問題要多查文檔，搜索引擎並不一定比文檔更高效。
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