<title>How The Fossil Download Page Works</title>
<h1 align="center">How The Download Page Works</h1>

<h2>1.0 Overview</h2>

The [/uv/download.html|Download] page for the Fossil self-hosting
repository is implemented using [./unvers.wiki|unversioned files].
The "download.html" screen itself, and the various build products
are all stored as unversioned content.  The download.html page
uses XMLHttpRequest() to retrieve the [/help?cmd=/juvlist|/juvlist] webpage
for a list of all unversioned files.  Javascript in the
[/uv/download.js?mimetype=text/plain|download.js] file (which is
sourced by "download.html") then figures out which unversioned files are
build products and paints appropriate icons on the displayed
download page.

When a new version is generated, the developers use the
[/help?cmd=uv|fossil uv edit] command to make minor changes
to the "[/uv/download.js?mimetype=text/plain|download.js]"
file so that it knows about the
new version number.  Then the developers run
the [/help?cmd=uv|fossil uv add] command for each
build product.  Finally, the
[/help?cmd=uv|fossil uv sync] command is run to push all
the content up to servers.  All
[./selfhost.wiki|three self-hosting repositories] for Fossil
are updated automatically.

<h2>2.0 Details</h2>

The current text of the "download.html" and "download.js" files can
be seen at:

   *   [/uv/download.html?mimetype=text/plain]
   *   [/uv/download.js?mimetype=text/plain]

Notice how the hyperlinks above use the "mimetype=text/plain"
query parameter in order to display the file as plain text
instead of the usual HTML or Javascript.

The default mimetype for "download.html" is
text/html.  But because the entire page is enclosed within

    <b>&lt;div class='fossil-doc' data-title='Download Page'&gt;...&lt;/div&gt;</b>

Fossil knows to add its standard header and footer information to the
document, making it look just like any other page.  See
"[./embeddeddoc.wiki|embedded documentation]" for further details on
how &lt;div class='fossil-doc'&gt; this works.

With each new release, the "releases" variable in the javascript on
the [/uv/download.js?mimetype=text/plain|download.js] page is
edited (using "[/help?cmd=uv|fossil uv edit download.js]") to add
details of the release.

When the JavaScript in the "download.js" file runs, it requests
a listing of all unversioned content using the /juvlist URL.
([/juvlist|sample /juvlist output]).  The content of the download page is
constructed by matching unversioned files against regular expressions
in the "releases" variable.

Build products need to be constructed on different machines.  The precompiled
binary for Linux is compiled on Linux, the precompiled binary for Windows
is compiled on Windows10, and so forth.  After a new release is tagged,
the release manager goes around to each of the target platforms, checks
out the release and compiles it, then runs
[/help?cmd=uv|fossil uv add] for the build product followed by
[/help?cmd=uv|fossil uv sync] to push the new build product to the
[./selfhost.wiki|various servers].  This process is repeated for
each build product.

When older builds are retired from the download page, the
[/uv/download.js?mimetype=text/plain|download.js] page is again
edited to remove the corresponding entry from the "release" variable
and the edit is synced using
[/help?cmd=uv|fossil uv sync].  This causes the build products to
disappear from the download page immediately.  But those build products
are still taking up space in the unversioned content table of the
server repository.  To purge the obsolete build products, one or
more [/help?cmd=uv|fossil uv rm] commands are run, followed by
another [/help?cmd=uv|fossil uv sync].  It is important to purge
obsolete build products since they take up a lot of space.
At [/repo-tabsize] you can see that the unversioned table takes up
a substantial fraction of the repository.

<h2>3.0 Security</h2>

Only users with the [/setup_ulist_notes|"y" permission] are allowed
to push unversioned content up to the servers.  Having the ability
to push check-ins (the [/setup_ulist_notes|"i" permission]) is not
sufficient.

On the Fossil project there are 67 people (as of 2017-03-24) who have
check-in privileges.  But only 3 core developers
can push unversioned content and thus
change the build products on the download page.  Minimizing the number
of people who can change the build products helps to ensure that
rogue binaries do not slip onto the download page unnoticed.
