Django 响应数据response的返回源码详解

# 下面的函数都在 ServerHandler 的继承链上方法, 有些方法父类只定义了空方法, 具体逻辑交由子类实现. 有关继承链请参看: http://daoluan.net/blog/decode-django-wsgi/
def run(self, application):
 """Invoke the application"""
 try:
  self.setup_environ()
  # application 在 django 中就是 WSGIHandler 类, 他实现了 __call__ 方法, 所以行为和函数一样.
  self.result = application(self.environ, self.start_response)
  self.finish_response()
 except:
  # handle error
 
def finish_response(self):
 try:
  if not self.result_is_file() or not self.sendfile():
   for data in self.result:
    # 向套接字写数据, 将数据返回给客户端
    self.write(data)
   self.finish_content()
 finally:
  self.close()
 
def write(self, data):
 """'write()' callable as specified by PEP 333""" 
 # 必须是都是字符
 assert type(data) is StringType,"write() argument must be string" 
 if not self.status:
  raise AssertionError("write() before start_response()") 
 # 需要先发送 HTTP 头
 elif not self.headers_sent:
  # Before the first output, send the stored headers
  self.bytes_sent = len(data) # make sure we know content-length
  self.send_headers()
 # 再发送实体
 else:
  self.bytes_sent += len(data)
 
 # XXX check Content-Length and truncate if too many bytes written?
 self._write(data)
 self._flush()
 
def write(self, data):
 """'write()' callable as specified by PEP 3333"""
 
 assert isinstance(data, bytes), "write() argument must be bytestring"
 
 # 必须先调用 self.start_response() 设置状态码
 if not self.status:
  raise AssertionError("write() before start_response()")
 
 # 需要先发送 HTTP 头
 elif not self.headers_sent:
  # Before the first output, send the stored headers
  self.bytes_sent = len(data) # make sure we know content-length
  self.send_headers()
 # 再发送实体
 else:
  self.bytes_sent += len(data)
 
 # XXX check Content-Length and truncate if too many bytes written? 是否需要分段发送过大的数据?
 
 # If data is too large, socket will choke, 窒息死掉 so write chunks no larger
 # than 32MB at a time.
 
 # 分片发送
 length = len(data)
 if length > 33554432:
  offset = 0
  while offset < length:
   chunk_size = min(33554432, length)
   self._write(data[offset:offset+chunk_size])
   self._flush()
   offset += chunk_size
 else:
  self._write(data)
  self._flush()
 
def _write(self,data):
 # 如果是第一次调用, 则调用 stdout.write(), 理解为一个套接字对象
 self.stdout.write(data) 
 # 第二次调用就是直接调用 stdout.write() 了
 self._write = self.stdout.write