# 下面的函數(shù)都在 ServerHandler 的繼承鏈上方法, 有些方法父類(lèi)只定義了空方法, 具體邏輯交由子類(lèi)實(shí)現(xiàn). 有關(guān)繼承鏈請(qǐng)參看: 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 類(lèi), 他實(shí)現(xiàn)了 __call__ 方法, 所以行為和函數(shù)一樣.
  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:
    # 向套接字寫(xiě)數(shù)據(jù), 將數(shù)據(jù)返回給客戶(hù)端
    self.write(data)
   self.finish_content()
 finally:
  self.close()
 
def write(self, data):
 """'write()' callable as specified by PEP 333""" 
 # 必須是都是字符
 assert type(data) is StringType,"write() argument must be string" 
 if not self.status:
  raise AssertionError("write() before start_response()") 
 # 需要先發(fā)送 HTTP 頭
 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()
 # 再發(fā)送實(shí)體
 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"
 
 # 必須先調(diào)用 self.start_response() 設(shè)置狀態(tài)碼
 if not self.status:
  raise AssertionError("write() before start_response()")
 
 # 需要先發(fā)送 HTTP 頭
 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()
 # 再發(fā)送實(shí)體
 else:
  self.bytes_sent += len(data)
 
 # XXX check Content-Length and truncate if too many bytes written? 是否需要分段發(fā)送過(guò)大的數(shù)據(jù)?
 
 # If data is too large, socket will choke, 窒息死掉 so write chunks no larger
 # than 32MB at a time.
 
 # 分片發(fā)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):
 # 如果是第一次調(diào)用, 則調(diào)用 stdout.write(), 理解為一個(gè)套接字對(duì)象
 self.stdout.write(data) 
 # 第二次調(diào)用就是直接調(diào)用 stdout.write() 了
 self._write = self.stdout.write