HTTP METHODS IS IDEMPOTENCE AN ILLNESS? Created by Maciej Rząsa 

HTTP REQUEST G E T / u s e r s H T T P / 1 . 1 A c c e p t ­ E n c o d i n g : g z i p ; q = 1 . 0 , d e f l a t e ; q = 0 . 6 , i d e n t i t y ; q = 0 . 3 A c c e p t : * / * U s e r ­ A g e n t : R u b y C o n n e c t i o n : c l o s e H o s t : e x a m p l e . c o m 

HTTP METHOD PROPERTIES safe methods no resource modifications idempotent methods called multiple leaves resource in the same state safe methods are idempotent 

SAFE GET retreive data identified by URL HEAD like GET but without body OPTIONS available communication options, e.g. CORS 

IDEMPOTENT PUT apply a new version of the resource (new or existing) PATCH apply a set of changes to the resource DELETE delete the resource 

UNSAFE AND NON- IDEMPOTENT POST process the body with the resource 

EXAMPLES view a page (and record a page view) change an email of a user make a bank transfer buy a book increment a counter enable/disable option: toggle? 

SUMMARY NEVER change state using GET remember that PUT should be idempotent use idempotent methods where possible (TBC)