FOSSIL_NONCE environment variable.

<h3>3.1 Input Content</h3>

If the HTTP request includes content (for example if this is a POST request)
then the CONTENT_LENGTH value will be positive and the data for the content
will be readable on standard input.


<h2>4.0 CGI Outputs</h2>

CGI programs construct a reply by writing to standard output.  The first
few lines of output are parameters intended for the web server that invoked
the CGI.  These are followed by a blank line and then the content.

then Fossil will adds its own header and footer to the HTML.  The
page title contained in the added header will be extracted from the
"data-title" attribute.

Except for the three cases noted above, Fossil makes no changes or
additions to the CGI-generated content.  Fossil just passes the verbatim
content back up the stack towards the requester.

<h3>4.1 <tt>GATEWAY_INTERFACE</tt> and Recursive Calls to fossil</h3>

Like many CGI-aware applications, if fossil sees the environment
variable <tt>GATEWAY_INTERFACE</tt> when it starts up, it assumes it
is running in a CGI environment and behaves differently than when it
is run in a non-CGI interactive session. If you intend to run fossil
itself from within an extension CGI script, e.g. to run a query
against the repository or simply fetch the fossil binary version, make
sure to <em>unset</em> the <tt>GATEWAY_INTERFACE</tt> environment
variable before doing so, otherwise the invocation will behave as if
it's being run in CGI mode.

<h2>5.0 Filename Restrictions</h2>

For security reasons, Fossil places restrictions on the names of files
in the extroot directory that can participate in the extension CGI
mechanism: