Python HTTP functions

Function handler

In Python runtime environments, the signature of a function follows the Python Web Server Gateway Interface (WSGI) specification. You can process requests based on the WSGI specification.

Handler

Python HTTP functions provide two types of handlers:

• Handler 1

  # Method 1: User provide the function. FC call the function to process request and send back response.
  
  HELLO_WORLD = b"Hello world! \n"
  
  def handler(environ, start_response):    
      context = environ['fc.context']    
      request_uri = environ['fc.request_uri']    
      for k, v in environ.items():        
          if k.startswith("HTTP_"):            
              # process custom request headers            
              pass    
  
      # get request_body    
      try:        
          request_body_size = int(environ.get('CONTENT_LENGTH', 0))    
      except (ValueError):        
          request_body_size = 0   
      request_body = environ['wsgi.input'].read(request_body_size)   
  
      # get request_method    
      request_method = environ['REQUEST_METHOD']    
  
      # get path info    
      path_info = environ['PATH_INFO']    
  
      # get server_protocol    
      server_protocol = environ['SERVER_PROTOCOL']    
  
      # get content_type    
      try:        
          content_type = environ['CONTENT_TYPE']    
      except (KeyError):        
          content_type = " "    
  
      # get query_string    
      try:        
          query_string = environ['QUERY_STRING']        
      except (KeyError):        
          query_string = " "   
  
      print 'request_body: {}'.format(request_body)    
      print 'method: {}\n path: {}\n  query_string: {}\n server_protocol: {}\n'.format(request_method, path_info,  query_string, server_protocol)    
      # do something here    
  
      status = '200 OK'    
      response_headers = [('Content-type', 'text/plain')]    
      start_response(status, response_headers)    
      # return value must be iterable    
      return [HELLO_WORLD]

• Handler 2

  # Method 2: User provide the callable class object. FC call the object to process request and send back response.
  
  HELLO_WORLD = b"Hello world! \n"
  
  class AppClass:    
      """Produce the same output, but using a class    
      """    
  
      def __init__(self, environ, start_response):        
          self.environ = environ        
          self.start = start_response    
  
      def __iter__(self):        
          status = '200 OK'        
          response_headers = [('Content-type', 'text/plain')]        
          self.start(status, response_headers)        
          yield HELLO_WORLD
  
  def handler(environ, start_response):    
      return AppClass(environ, start_response)

Paramters

• environ: indicates the Python dictionary that stores all client-related information. For more information, see environ Variables. In addition to the variables included in the dictionary, Function Compute provides two user-defined keys: fc.context and fc.request_uri.
  • fc.context has the same meaning as the context parameter of Python event functions.
  • fc.request_uri indicates the request URL of the string type.
    Note The HTTP_Variables field in the environ parameter contains the request header. For example, if the request header is 'x-Custom-key':'value', the environ parameter is environ['HTTP_X_CUSTOM_KEY']='value'. Based on WSGI, the key in the request header is processed as key = "HTTP_" + k.upper().replace("-","_").
• start_response: indicates a callable provided in runtime environments of Function Compute. For more information, see The start_response() Callable.

  The start_response parameter has two required position parameters and one optional parameter. In the following sample code, the three parameters are named status, response_headers, and exc_info.

  # Provided by FC runtime. 
  # status: a string like '200 OK' or '403 FORBIDDEN'
  # return: must be a write(body_data) callable
  def start_response(status, response_headers, exc_info=None):    
  ...

  • status: indicates the HTTP response status, which is a string.
  • response_headers: indicates the HTTP response headers. It is a list that contains a tuple in the (header_name, header_value) format.
  • exc_info: indicates the information that the server needs to return to the client. This parameter is optional.

After the application object completes executing the business logic based on the environ parameter, the application object must return the result to the server. An HTTP response must contain the status, headers, and body parameters. Therefore, before the application returns the value of body, you must call the start_response() function to return the value of status and headers to the server. In this way, the server knows that the application starts to return the value of body.

Get the request body

You can use WSGI to get the raw body.

The following sample code shows how to get the request body:

# get request_body    
    try:        
        request_body_size = int(environ.get('CONTENT_LENGTH', 0))    
    except (ValueError):        
        request_body_size = 0    
    request_body = environ['wsgi.input'].read(request_body_size)

References

The preceding example of handler function 2 shows that you can run projects that are built by using WSGI-based web frameworks such as Flask and Django in Python runtime environments of Function Compute. For more information, see Deploy Python projects based on WSGI-based web frameworks to Function Compute.