Django接收自定义http header过程详解

add by zhj: Django将所有http header（包括你自定义的http header）都放在了HttpRequest.META这个Python标准字典中，当然HttpRequest.META

中还包含其它一些键值对，这些键值对是Django加进去的，如SERVER_PORT等。对于http header，Django进行了重命名，规则如下

(1) 所有header名大写，将连接符“-”改为下划线“_”

(2) 除CONTENT_TYPE和CONTENT_LENGTH，其它的header名称前加“HTTP_”前缀

参见 https://docs.djangoproject.com/en/1.6/ref/request-response/#django.http.HttpRequest.META

我个人比较喜欢跟踪源代码来查看，源代码如下，

class WSGIRequestHandler(BaseHTTPRequestHandler):

  server_version = "WSGIServer/" + __version__

  def get_environ(self):
    env = self.server.base_environ.copy()
    env['SERVER_PROTOCOL'] = self.request_version
    env['REQUEST_METHOD'] = self.command
    if '?' in self.path:
      path,query = self.path.split('?',1)
    else:
      path,query = self.path,''

    env['PATH_INFO'] = urllib.unquote(path)
    env['QUERY_STRING'] = query

    host = self.address_string()
    if host != self.client_address[0]:
      env['REMOTE_HOST'] = host
    env['REMOTE_ADDR'] = self.client_address[0]

    if self.headers.typeheader is None:
      env['CONTENT_TYPE'] = self.headers.type
    else:
      env['CONTENT_TYPE'] = self.headers.typeheader

    length = self.headers.getheader('content-length')
    if length:
      env['CONTENT_LENGTH'] = length

    for h in self.headers.headers:
      k,v = h.split(':',1)
      k=k.replace('-','_').upper(); v=v.strip()
      if k in env:
        continue          # skip content length, type,etc.
      if 'HTTP_'+k in env:
        env['HTTP_'+k] += ','+v   # comma-separate multiple headers
      else:
        env['HTTP_'+k] = v
    return env

  def get_stderr(self):
    return sys.stderr

  def handle(self):
    """Handle a single HTTP request"""

    self.raw_requestline = self.rfile.readline()
    if not self.parse_request(): # An error code has been sent, just exit
      return

    handler = ServerHandler(
      self.rfile, self.wfile, self.get_stderr(), self.get_environ()
    )
    handler.request_handler = self   # backpointer for logging
    handler.run(self.server.get_app())

class WSGIRequest(http.HttpRequest):
  def __init__(self, environ):
    script_name = base.get_script_name(environ)
    path_info = base.get_path_info(environ)
    if not path_info:
      # Sometimes PATH_INFO exists, but is empty (e.g. accessing
      # the SCRIPT_NAME URL without a trailing slash). We really need to
      # operate as if they'd requested '/'. Not amazingly nice to force
      # the path like this, but should be harmless.
      path_info = '/'
    self.environ = environ
    self.path_info = path_info
    self.path = '%s/%s' % (script_name.rstrip('/'), path_info.lstrip('/'))
    self.META = environ
    self.META['PATH_INFO'] = path_info
    self.META['SCRIPT_NAME'] = script_name
    self.method = environ['REQUEST_METHOD'].upper()
    _, content_params = self._parse_content_type(self.META.get('CONTENT_TYPE', ''))
    if 'charset' in content_params:
      try:
        codecs.lookup(content_params['charset'])
      except LookupError:
        pass
      else:
        self.encoding = content_params['charset']
    self._post_parse_error = False
    try:
      content_length = int(self.environ.get('CONTENT_LENGTH'))
    except (ValueError, TypeError):
      content_length = 0
    self._stream = LimitedStream(self.environ['wsgi.input'], content_length)
    self._read_started = False
    self.resolver_match = None

WSGIRequest类实例化方法__init__(self,environ)中第二个参数就是WSGIRequestHandler.get_environ()方法返回的数据

WSGIRequest.META在environ的基础上加了一些键值对

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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