Lecture 22: CGI and Electronic Commerce

URL Encoding

When form information is returned to the HTTP server, it is encoded into a format called (using MIME terminology):

application/x-www-form-urlencoded

...or simply "URL-encoded". In this format:

ASCII space characters are (usually) replaced by the "+" character. This is a hangover from an older format, and is not universally used, see next point.
Non-printable characters are given in hexadecimal format, thus: %HH, where the H characters are the two hexadecimal digits of the byte. Sometimes the space character is also sent in this format, as %20.
The fields of a form are encoded as name=value, with each name-value pair separated by the "&" (ampersand) character.
Fields with null values are (normally) not sent, nor are unselected CHECKBOXes and RADIO buttons.