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HTTP server and request handler built on top of BaseHTTPServer intended for Raspberry Pi projects with a web interface

Project description

HTTP server and request handler built on top of Python standard library’s BaseHTTPServer. Originally intended for Raspberry Pi projects with a web interface, the small web server and the associated request handler add some interesting features to BaseHTTPServer and can be used independently of Raspberry Pi.

The provided example shows how to create a simple web interface to switch ON / OFF a LED via Raspberry GPIO.

Features:

  • config in json file
  • optional multithreaded server
  • static file serving with cache
  • Basic authentication (very basic!)
  • POST parsing
  • QS parsing
  • dynamic routing based on configuration or convention
  • hooks methods to perform differente actions before/after serving a request

Basic usage:

If you are familiar with Python standard library’s BaseHTTPServer and BaseHTTPRequestHandler it should be pretty straightforward: add a method named routed_<request> to your handler class in order to handle a request for the /<request> URL and set the self.content property to the HTML string to be served over HTTP.

class MyHandler(RPiHTTPRequestHandler):
  def routed_whatever:
  # your method definition to serve http://<my_address>:<my_port>/whatever
    # do cool stuff
    self.content = "<html><body>whatever</body></html>"

MyServer = RPiHTTPServer(path_to_config_file, MyHandler)
MyServer.serve_forever()

Default config:

{
  "SERVER_ADDRESS": "0.0.0.0",
  "SERVER_PORT": 8000,
  "SERVER_MULTITHREADED": true,
  "STATIC_URL_PREFIX": "/static",
  "STATIC_FOLDER":  "$CWD/static",
  "STATIC_CACHE": 604800,
  "TEMPLATE_FOLDER": "$CWD/templates",
  "ROUTE": {
    "GET": {
      "": "default_response",
    },
    "POST": {
      "": "default_response",
    }
  }
}

Please note: $CWD stands for “current working directory” but it defaults to the directory of the config file if it exists.

Detailed instructions

Configuration file

Prepare your config file in JSON format following the format of the aforementioned default config. Any missing key will be replaced by the default (e.g.: if you do not specify the port the server will try to start listening on port 80).

Add whatever configuration additional parameter you may need, for instance "GPIO_PIN": 5.

Leave "ROUTE" like it is for the time being (read more about routes below).

Static files

If you want to be able to serve static content, such as images, css, fonts, javascripts, etc., prepare a folder for such files and put the absolute path in the config parameter "STATIC_FOLDER".

You can serve static content directly from a subdir named "static" under the directory where your python script is: in such case, just omit the "STATIC_FOLDER" parameter in the config file.

The config parameter "STATIC_URL_PREFIX" identifies the virtual path to be prepended in the URL to reach static files from HTTP. So, for instance, if you leave the default "STATIC_URL_PREFIX" and you have an image named “foo.png” directly under the configured "STATIC_FOLDER", this will be served via HTTP at

http://<your_server_address>:<your_port>/static/foo.png

Python script

Now in your Python script you need to define the logic by extending the RPiHTTPRequestHandler class. By default every request to the HTTP server is mapped to a method of the extended class with the same name of the request prepended by routed_.

For instance, a request to http://<your_server_address>:<your_port>/switchon, will look for the method routed_switchon of the request handler class. If the method is not available the server will simply give a 404 error.

If you want to specify a custom method for a request, define the method in the "ROUTE" config parameter. One method you would like almost certainly define (or override) is the default_response (request for the / URL).

The mapped method just need to set the self.content variable (as a string) and such content will be served over HTTP with content type text/html; charset=UTF-8 (the default mime type).

In such scenario, your code could look like this:

class MyHandler(RPiHTTPRequestHandler):

  def routed_switchon(self):
    # DO something cool, e.g.: GPIO.output(self.config["GPIO_PIN"], GPIO.HIGH)
    self.content = "<!DOCTYPE html><html><h1>Switch on</h1></html>"

  def routed_switchoff(self):
    # DO something cool, e.g.: GPIO.output(self.config["GPIO_PIN"], GPIO.LOW)
    self.content = "<!DOCTYPE html><html><h1>Switch off</h1></html>"

MyServer = RPiHTTPServer("/path/to/config.json", MyHandler)
MyServer.serve_forever()

From the comments in the above example it should be clear that you can have access to the config parameters via self.config["PARAMETER_NAME"]. You can also add additional properties to the server property of the RPiHTTPServer instance, thus making them available in the request handler class via self.server.PROPERTY_NAME. So for instance, referring to the example above you could write:

MyServer = RPiHTTPServer("/path/to/config.json", MyHandler)
MyServer.server.switch_status = 0
MyServer.serve_forever()

Now in MyHandler you can access to switch_status via self.server.switch_status.

Other properties you can specify/alter before setting self.content:

  • self.content_type: by default set to “text/html; charset=UTF-8”
  • self.response_status: integer, by default set to 200
  • self.response_headers: by default an empty dictionary, it will be automatically filled with Content-Type and Content-Length before sending the response back to the client. Set additional dictionary keys to serve additional headers.

Other useful properties accessible in the request handler class:

At the current stage the library does not offer support for parametric routes.

Hooks

Available hook methods that can be implemented in your extended class:

  • pre_handle_request: gets executed before handling the HTTP request, that is, before evaluating the route and authentication, but after evaluating GET, POST method and parameters sent from the client. It doesn’t get executed in case of requests to static files.
  • pre_call_controller: gets executed after the controller has been established and authentication has been verified, but before calling the actual controller method
  • pre_serve_response: gets executed after the controller has been executed but before sending any response content back to the client. It doesn’t get executed in case of 404 error, static files or failed authentication.
  • post_serve_response: gets executed after the response has been sent back to the client. It doesn’t get executed in case of static files or failed authentication (but it gets for 404 errors).

HTML templates

The library does only offer a very basic template handling. The method render_template of the RPiHTTPRequestHandler class expects a filename and a dictionary and set the content to a string. It will look for a file with the specified filename under the folder self.config["TEMPLATE_FOLDER"] (if not specified in the config file it will default to a folder named “templates” under the directory from which the python script is run). It will then loop the dictionary’s keys as the strings to be replaced, and the corresponding values as the replacements. Finally, it will set the content property to the resulting string.

This is an extremely simple and inefficient template’s handling: there are many better libraries out there (e.g. Jinja2, Pystache) if you want a better template handling: at the end of the day you have to set the self.content variable to the string that will be served over HTTP (to serve a default text/html content-type).

Please note that UTF-8 will be served by default and currently other character-set support is not planned.

TODO

  • document how basic auth can be configured
  • support for Python 3k
  • handle config file parse error
  • parametric routes
  • sanitize path in url request
  • handle file upload
  • safely handle non UTF-8 chars in POST request

Project details


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