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Python WSGI introduction

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Ageeleshwar K
Ageeleshwar K

This document provides an overview of the Web Server Gateway Interface (WSGI) specification and its components. WSGI defines the interface between web servers and web applications to allow them to evolve independently. It outlines the operations and responses expected between servers and applications. WSGI allows for easy integration of middleware components into applications and servers. Common Python web servers, frameworks, and middleware examples are also described to demonstrate how WSGI enables components to work together.

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A Portion Of WSGI With Akilesh
What ? Why ? And How ? • A specification for an interface between a web server and web application • Allows servers, frameworks, applications to evolve independent of each other • Allows easy intergration of middlewares into existing applications and servers • Outlines the Operations and Responses a server expects from an application and vice versa
Components of a web service Client Internet Web Server Middleware Application Application1 Application2
Webservers ● Pythonic – Gunicorn – Tornado – Twisted – Zope ● Non Pythonic – Apache – Just too many of them
Web Application ● Frameworks – Allow quicker application development cycle – Abstract all mundane jobs and allows user to concentrate on logic/business – Often use several tools like ● Templating engine – For generating page layout from datastructure ● PasteDeploy – For loading and chaining multiple web applications ● Routers – For routing a http request to a correct application ● Applications themselves may be chained to implement a complex logic ● Some of the middleware may be third party applications
Examples ● Frameworks – Django – Flask ● Theming – Bootstrap ● Templating engine – Jinja – Mako ● Middleware – Ldap authentication using django ● Some of these may perform all other the above jobs. But the user has the power to mix and match, thanks to wsgi.
Play by the rules ● Application has to be a callable. Anything with a __call__ method with do. Methods, Classes, Objects all are welcome. ● Application should handle any number of calls. Server invokes application once for every http request. ● Application returns and Iterable that yields bytestrings. ● Server iterates over the Iterable and sends the data without buffering.
More rules ● Application accepts two objects, name not a contraint – environ – A dictionary of request , os and wsgi params – start_response – A callable that ● accepts two params – Status – HTTP Status String object – Headers -- HTTP Response headers List of tuples of header-value – exec_info (optional) – typically the result of 'sys.exc_info()' ● And returns one – Write – A callable that inturn accepts one argument ● Body – A bytestring to be sent to the client – Write – Sends the bytestring to the client – This is for legacy application only. New applications must not use this interface
More rules ● Application must call start_response with appropriate arguments before returning ● Server stores the Status and Headers, but will wait untill Applications returns an Iterable and the Iterable has yielded its first bytestring ● If Application sends an 'Content-Length' header to start_response, Server should not send any more data to than specified by the length ● If Application sends exec_info optional argument server should erase the
Server receives request Server extract request headers And populates 'environ' Server calls Application(environ, start_response) Application executes Logic Application calls start_respons(status, headers) start_response saves status and headers Appliation returns body Server returns status, headers and body Server validates status, headers and body
Middlewares ● Plays both server and application game ● Secretly slips between server, application and other middlewares ● Absolutely Transparent ● Used to integrate apps built using different frameworks, third party modules, routing, load balancing, anything else you wish for
Getting Dirty from wsgiref.simple_server import make_server def my_application(environ, start_response): response_headers = [('Content-Type', 'text/html'), ('Akilesh', 'Cool head')] status_code = '200 OK' writer = start_response(status_code, response_headers) # ignore the writer # it exists only for legacy applications ret = {'request method': environ['REQUEST_METHOD'], 'path': environ['PATH_INFO'], 'query string': environ['QUERY_STRING']} return str(ret) httpd = make_server('localhost', 9090, my_application) httpd.serve_forever()
Thank you akilesh1597@gmail.com Come back for more...

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Python WSGI introduction

  • 2. What ? Why ? And How ? • A specification for an interface between a web server and web application • Allows servers, frameworks, applications to evolve independent of each other • Allows easy intergration of middlewares into existing applications and servers • Outlines the Operations and Responses a server expects from an application and vice versa
  • 3. Components of a web service Client Internet Web Server Middleware Application Application1 Application2
  • 4. Webservers ● Pythonic – Gunicorn – Tornado – Twisted – Zope ● Non Pythonic – Apache – Just too many of them
  • 5. Web Application ● Frameworks – Allow quicker application development cycle – Abstract all mundane jobs and allows user to concentrate on logic/business – Often use several tools like ● Templating engine – For generating page layout from datastructure ● PasteDeploy – For loading and chaining multiple web applications ● Routers – For routing a http request to a correct application ● Applications themselves may be chained to implement a complex logic ● Some of the middleware may be third party applications
  • 6. Examples ● Frameworks – Django – Flask ● Theming – Bootstrap ● Templating engine – Jinja – Mako ● Middleware – Ldap authentication using django ● Some of these may perform all other the above jobs. But the user has the power to mix and match, thanks to wsgi.
  • 7. Play by the rules ● Application has to be a callable. Anything with a __call__ method with do. Methods, Classes, Objects all are welcome. ● Application should handle any number of calls. Server invokes application once for every http request. ● Application returns and Iterable that yields bytestrings. ● Server iterates over the Iterable and sends the data without buffering.
  • 8. More rules ● Application accepts two objects, name not a contraint – environ – A dictionary of request , os and wsgi params – start_response – A callable that ● accepts two params – Status – HTTP Status String object – Headers -- HTTP Response headers List of tuples of header-value – exec_info (optional) – typically the result of 'sys.exc_info()' ● And returns one – Write – A callable that inturn accepts one argument ● Body – A bytestring to be sent to the client – Write – Sends the bytestring to the client – This is for legacy application only. New applications must not use this interface
  • 9. More rules ● Application must call start_response with appropriate arguments before returning ● Server stores the Status and Headers, but will wait untill Applications returns an Iterable and the Iterable has yielded its first bytestring ● If Application sends an 'Content-Length' header to start_response, Server should not send any more data to than specified by the length ● If Application sends exec_info optional argument server should erase the
  • 10. Server receives request Server extract request headers And populates 'environ' Server calls Application(environ, start_response) Application executes Logic Application calls start_respons(status, headers) start_response saves status and headers Appliation returns body Server returns status, headers and body Server validates status, headers and body
  • 11. Middlewares ● Plays both server and application game ● Secretly slips between server, application and other middlewares ● Absolutely Transparent ● Used to integrate apps built using different frameworks, third party modules, routing, load balancing, anything else you wish for
  • 12. Getting Dirty from wsgiref.simple_server import make_server def my_application(environ, start_response): response_headers = [('Content-Type', 'text/html'), ('Akilesh', 'Cool head')] status_code = '200 OK' writer = start_response(status_code, response_headers) # ignore the writer # it exists only for legacy applications ret = {'request method': environ['REQUEST_METHOD'], 'path': environ['PATH_INFO'], 'query string': environ['QUERY_STRING']} return str(ret) httpd = make_server('localhost', 9090, my_application) httpd.serve_forever()