Fossil

*/
static int fileedit_ajax_boostrap(int requirePost){
  login_check_credentials();
  if( !g.perm.Write ){
    fileedit_ajax_error(403,"Write permissions required.");
    return 0;
  }else if(0==cgi_csrf_safe(requirePost)){
    fileedit_ajax_error(403,
                        "CSRF violation (make sure sending of HTTP "
                        "Referer headers is enabled for XHR "
                        "connections).");
    return 0;
  }
  return 1;
}
/*
** Returns true if the current user is allowed to edit the given
** filename, as determined by fileedit_is_editable(), else false,

# The fileedit Page

This document describes the limitations of, caveats for, and
disclaimers for the [](/fileedit) page, which provides users with
[checkin privileges](./caps/index.md) basic editing features for files
via the web interface.

# Important Caveats and Disclaimers

Predictably, the ability to edit files in a repository from a web
browser halfway around the world comes with several obligatory caveats
and disclaimers...

## `/fileedit` Does *Nothing* by Default.

In order to "activate" it, a user with [the "setup"
permission](./caps/index.md) must set the
[fileedit-glob](/help?cmd=fileedit-glob) repository setting to a
comma- or newline-delimited list of globs representing a whitelist of
files which may be edited online. Any user with commit access may then
edit files matching one of those globs. Certain pages within the UI
get an "edit" link added to them when the current user's permissions
and the whitelist both permit editing of that file.

## CSRF & HTTP Referrer Headers

In order to protect against [Cross-site Request Forgery (CSRF)][csrf]
attacks, Fossil UI features which write to the database require that
the browser send the so-called [HTTP `Referer` header][referer]
(noting that the misspelling of "referrer" is a historical accident
which has long-since been standardized!). Modern browsers, by default,
include such information automatically for *interactive* actions which
lead to a request, e.g. clicking on a link back to the same
server. However, `/fileedit` uses asynchronous ["XHR"][xhr]
connections, which browsers *may* treat differently than strictly
interactive elements.

- **Firefox**: configuration option `network.http.sendRefererHeader`
  specifies whether the `Referer` header is sent. It must have a value
  of 2 (which is the default) for XHR requests to get the `Referer`
  header. Purely interactive Fossil features, in which users directly
  activate links or forms, work with a level of 1 or higher.
- **Chrome**: apparently requires an add-on in order to change this
  policy, so Chrome without such an add-on will not suppress this
  header.
- **Safari**: ???
- **Other browsers**: ???

If `/filepage` shows an error message saying "CSRF violation," the
problem is that the browser is not sending a `Referer` header to XHR
connections. Fossil does not offer a way to disable its CSRF
protections.

[referer]: https://en.wikipedia.org/wiki/HTTP_referer
[csrf]: https://en.wikipedia.org/wiki/Cross-site_request_forgery
[xhr]: https://en.wikipedia.org/wiki/XMLHttpRequest

## `/fileedit` **Works by Creating Commits**

Thus any edits made via that page become a normal part of the
repository's blockchain.

## `/fileedit` is *Intended* for use with Embedded Docs

... and similar text files, and is most certainly
**not intended for editing code**.

Editing files with unusual syntax requirements, e.g. hard tabs in
makefiles, may break them. *You Have Been Warned.*

Similarly, though every effort is made to retain the end-of-line
style used by being-edited files, the round-trip through an HTML
textarea element may change the EOLs. The Commit section of the page
offers three different options for how to treat newlines when saving
changes. **Files with mixed EOL styles** *will be normalized to a single
EOL style* when modified using `/fileedit`. When "inheriting" the EOL
style from a previous version which has mixed styles, the first EOL
style detected in the previous version of the file is used.

## `/fileedit` **is Not a Replacement for a Checkout**

A full-featured checkout allows far more possibilities than this basic
online editor permits, and the feature scope of `/fileedit` is
intentionally kept small, implementing only the bare necessities
needed for performing basic edits online. It *is not, and will never
be, a replacement for a checkout.*

- The ability to edit/manipulate files which are in a local
checkout. (If you have a checkout, use your local editor, not
`/fileedit`.)
- Editing of non-text files, e.g. images. Use a checkout and your
preferred graphics editor.
- Support for syncing/pulling/pushing of a repository before and/or
after edits. Those features cannot be *reliably* provided via a web
interface for several reasons.



Similarly, some *potential* features have significant downsides,
abuses, and/or implementation hurdles which make the decision of
whether or not to implement them subject to notable contributor
debate. e.g. the ability to add new files or remove/rename older
files.


## `/fileedit` **Stores Only Limited Local Edits While Working**

When changes are made to a given checkin/file combination,
`/fileedit` will, if possible, store them in [`window.localStorage`
or `window.sessionStorage`][html5storage], if available, but...

- Which storage is used is unspecified and may differ across
  environments.
- If neither of those is available, the storage is transient and
  will not survive a page reload. In this case, the UI issues a clear
  warning in the editor tab.
- It stores only the most recent checkin/file combinations which have
  been modified (exactly how many may differ - the number will be
  noted somewhere in the UI). Note that changing the "executable bit"
  is counted as a modification, but the checkin *comment* is *not*
  and is reset after a commit.
- If its internal limit on the number of modified files is exceeded,
  it silently discards the oldest edits to keep the list at its limit.

Edits are saved whenever the editor component fires its "change"
event, which essentially means as soon as it loses input focus. Thus
to force the browser to save any pending changes, simply click
somwhere on the page outside of the editor.

Exactly how long `localStorage` will survive, and how much it or
`sessionStorage` can hold, is environment-dependent. `sessionStorage`
will survive until the current browser tab is closed, but it survives
across reloads of the same tab.

If `/filepage` determines that no peristent storage is available a
warning is displayed on the editor page.

[html5storage]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Storage_API

## The Power is Yours, but...

> "With great power comes great responsibility."

**Use this feature judiciously, *if at all*.**

Now, with those warnings and caveats out of the way...

such events...

## Integrating Syntax Highlighting

Assuming a repository has integrated a 3rd-party syntax highlighting
solution, it can probably (depending on its API) be told how to
highlight `/fileedit`'s wiki/markdown-format previews. Here are
instructions for doing so with [highlightjs](https://highlightjs.org/):

At the very bottom of the [site skin's footer](customskin.md), add a
script tag similar to the following:

```javascript
<script nonce="$<nonce>">
if(window.fossil && fossil.page && fossil.page.name==='fileedit'){