code: def request_headers(self):
          '''Fill request headers from the environ dictionary and
          modify them via the list of :attr:`headers_middleware`.
          The returned headers will be sent to the target uri.
          '''
          headers = CIMultiDict()
          for k in self.environ:
              if k.startswith('HTTP_'):
                  head = k[5:].replace('_', '-')
                  headers[head] = self.environ[k]
          for head in ENVIRON_HEADERS:
              k = head.replace('-', '_').upper()
              v = self.environ.get(k)
              if v:
                  headers[head] = v
          for middleware in self.wsgi.headers_middleware:
              middleware(self.environ, headers)
          return headerf request_headers(self):
          '''Fill request headers from the environ dictionary and
          modify them via the list of :attr:`headers_middleware`.
          The returned headers will be sent to the target uri.
          '''
          headers = CIMultiDict()
          for k in self.environ:
              if k.startswith('HTTP_'):
                  head = k[5:].replace('_', '-')
                  headers[head] = self.environ[k]
          for head in ENVIRON_HEADERS:
              k = head.replace('-', '_').upper()
              v = self.environ.get(k)
              if v:
                  headers[head] = v
          for middleware in self.wsgi.headers_middleware:
              middleware(self.environ, headers)
          return headers
docs: Fill request headers from the environ dictionary and
          modify them via the list of :attr:`headers_middleware`.
          The returned headers will be sent to the target uri.