Oddµ: A minimal wiki

This program runs a wiki. It serves all the Markdown files (ending in .md) into web pages and allows you to edit them. If your files don't provide their own title (# title), the file name (without .md) is used for the title. Subdirectories are created as necessary.

This is a minimal wiki. There is no version history. It's well suited as a secondary medium: collaboration and conversation happens elsewhere, in chat, on social media. The wiki serves as the text repository that results from these discussions.

The wiki lists no recent changes. The expectation is that the people that care were involved in the discussions beforehand.

The wiki also produces no feed. The assumption is that announcements are made on social media: blogs, news aggregators, discussion forums, the fediverse, but humans. There is no need for bots.

As you'll see below, the idea is that the webserver handles as many tasks as possible. It logs requests, does rate limiting, handles encryption, gets the certificates, and so on. The web server acts as a reverse proxy and the wiki ends up being a content management system with almost no structure – or endless malleability, depending on your point of view.

And last but not least: µ is the letter mu, so Oddµ is usually written Oddmu. 🙃

Markdown

This wiki uses a Markdown library to generate the web pages from Markdown. There are two extensions Oddmu adds to the library: local links and hashtags.

Local links use double square brackets [[like this]]. If you need to change the link text, you need to use regular Markdown. Don't forget to percent-encode the link target. Example: [here](like%20this).

Hashtags link to searches for the hashtag. Hashtags are separate from titles because there is no space after the hash. Use the underscore to use hashtags consisting of multiple words.

# Title

Text

#Tag #Another_Tag

The Markdown processor comes with a few extensions, some of which are enable by default:

• emphasis markers inside words are ignored
• tables are supported
• fenced code blocks are supported
• autolinking of "naked" URLs are supported
• strikethrough using two tildes is supported (~~like this~~)
• it is strict about prefix heading rules
• you can specify an id for headings ({#id})
• trailing backslashes turn into line breaks
• definition lists are supported
• MathJax is supported (but needs a separte setup)

A table with footers and a columnspan:

Name    | Age
--------|------
Bob     ||
Alice   | 23
========|======
Total   | 23

A definition list:

Cat
: Fluffy animal everyone likes

Internet
: Vector of transmission for pictures of cats

Templates

The template files are the HTML files in the working directory: add.html, edit.html, search.html, upload.html and view.html. Feel free to change the templates and restart the server. The first change you should make is to replace the email address in view.html. 😄

See Structuring the web with HTML to learn more about HTML.

Modifying the styles in the templates would be another good start to get a feel for it. See Learn to style HTML using CSS to learn more about style sheets.

The templates can refer to the following properties of a page:

{{.Title}} is the page title. If the page doesn't provide its own title, the page name is used.

{{.Name}} is the page name, escaped for use in URLs. More specifically, it is URI escaped except for the slashes. The page name doesn't include the .md extension.

{{.Html}} is the rendered Markdown, as HTML.

{{printf "%s" .Body}} is the Markdown, as a string (the data itself is a byte array and that's why we need to call printf).

For the search.html template only:

{{.Results}} indicates if there were any search results.

{{.Items}} is an array of pages, each containing a search result. A search result is a page (with the properties seen above). Thus, to refer to them, you need to use a {{range .Items}} … {{end}} construct.

For search results, {{.Html}} is the rendered Markdown of a page summary, as HTML.

{{.Score}} is a numerical score for search results.

The upload.html template cannot refer to anything.

When calling the save action, the page name is take from the URL and the page content is taken from the body form parameter. To illustrate, here's how to edit a page using curl:

curl --form body="Did you bring a towel?" \
  http://localhost:8080/save/welcome

The wiki uses the standard html/template library to do this. There's more information on writing templates in the documentation for the text/template library.

Non-English hyphenation

Automatic hyphenation by the browser requires two things: The style sheet must indicate hyphen: auto for an HTML element such as body, and that element must have a lang set (usually a two letter language code such as de for German). This happens in the template files, such as view.html and search.html.

Oddmu uses the lingua library to detect languages. If you know that you're only going to use a small number of languages – or just a single language! – you can set the environment variable ODDMU_LANGUAGES to a comma-separated list of ISO 639-1 codes, e.g. "en" or "en,de,fr,pt".

Building

go build

Test

The working directory is where pages are saved and where templates are loaded from. You need a copy of the template files in this directory. Here's how to start it in the source directory:

go run .

The program serves the local directory as a wiki on port 8080. Point your browser to http://localhost:8080/ to get started. This is equivalent to http://localhost:8080/view/index – the first page you'll create, most likely.

If you ran it in the source directory, try http://localhost:8080/view/README – this serves the README file you're currently reading.

You can change the port by setting the ODDMU_PORT environment variable.

Deploying it using systemd

As root, on your server:

adduser --system --home /home/oddmu oddmu

Copy all the files into /home/oddmu to your server: oddmu, oddmu.service, and all the template files ending in .html.

Edit the oddmu.service file. These are the three lines you most likely have to take care of:

ExecStart=/home/oddmu/oddmu
WorkingDirectory=/home/oddmu
Environment="ODDMU_PORT=8080"
Environment="ODDMU_LANGUAGES=en,de"

Install the service file and enable it:

ln -s /home/oddmu/oddmu.service /etc/systemd/system/
systemctl enable --now oddmu

Check the log:

journalctl --unit oddmu

Follow the log:

journalctl --follow --unit oddmu

Edit the first page using lynx:

lynx http://localhost:8080/view/index

Web server setup

HTTPS is not part of the wiki. You probably want to configure this in your webserver. I guess you could use stunnel, too. If you're using Apache, you might have set up a site like I did, below. In my case, that'd be /etc/apache2/sites-enabled/500-transjovian.conf:

MDomain transjovian.org
MDCertificateAgreement accepted

<VirtualHost *:80>
    ServerName transjovian.org
    RewriteEngine on
    RewriteRule ^/(.*) https://%{HTTP_HOST}/$1 [redirect]
</VirtualHost>
<VirtualHost *:443>
    ServerAdmin alex@alexschroeder.ch
    ServerName transjovian.org
    SSLEngine on
    ProxyPassMatch ^/(search|(view|edit|save|add|append|upload|drop)/(.*))?$ http://localhost:8080/$1
</VirtualHost>

First, it manages the domain, getting the necessary certificates. It redirects regular HTTP traffic from port 80 to port 443. It turns on the SSL engine for port 443. It proxies the requests for the wiki to port 8080.

Thus, this is what happens:

• The user tells the browser to visit transjovian.org
• The browser sends a request for http://transjovian.org (on port 80)
• Apache redirects this to https://transjovian.org/ by default (now on port 443)
• This is proxied to http://transjovian.org:8080/ (no encryption, on port 8080)

Restart the server, gracefully:

apachectl graceful

To serve both HTTP and HTTPS, don't redirect from the first virtual host to the second – instead just proxy to the wiki like you did for the second virtual host: use a copy of the ProxyPassMatch directive instead of RewriteEngine on and RewriteRule.

Access

Access control is not part of the wiki. By default, the wiki is editable by all. This is most likely not what you want unless you're running it stand-alone, unconnected to the Internet.

You probably want to configure this in your webserver. If you're using Apache, you might have set up a site like the following.

Create a new password file called .htpasswd and add the user "alex":

cd /home/oddmu
htpasswd -c .htpasswd alex

To add more users, don't use the -c option or you will overwrite it!

To add another user:

htpasswd .htpasswd berta

To delete remove a user:

htpasswd -D .htpasswd berta

Modify your site configuration and protect the /edit/, /save/, /add/, /append/, /upload/ and /drop/ URLs with a password by adding the following to your <VirtualHost *:443> section:

<LocationMatch "^/(edit|save|add|append|upload|drop)/">
  AuthType Basic
  AuthName "Password Required"
  AuthUserFile /home/oddmu/.htpasswd
  Require valid-user
</LocationMatch>

Serve static files

If you want to serve static files as well, add a document root to your webserver configuration. Using Apache, for example:

DocumentRoot /home/oddmu/static
<Directory /home/oddmu/static>
    Require all granted
</Directory>

Create this directory, making sure to give it a permission that your webserver can read (world readable file, world readable and executable directory). Populate it with files.

Make sure that none of the static files look like the wiki paths /view/, /edit/, /save/, /add/, /append/, /upload/, /drop/ or /search. For example, create a file called robots.txt containing the following, tellin all robots that they're not welcome.

User-agent: *
Disallow: /

You site now serves /robots.txt without interfering with the wiki, and without needing a wiki page.

Wikipedia has more information.

Different logins for different access rights

What if you have a site with various subdirectories and each subdirectory is for a different group of friends? You can set this up using your webserver. One way to do this is to require specific usernames (which must have a password in the password file mentioned above.

This requires a valid login by the user "alex" or "berta":

<LocationMatch "^/(edit|save|add|append|upload|drop)/intetebi/">
  Require user alex berta
</LocationMatch>

Private wikis

Based on the above, you can prevent people from reading the wiki, too. The LocationMatch must cover the /view/ URLs. In order to protect everything, use a Location directive that matches everything:

<Location />
  AuthType Basic
  AuthName "Password Required"
  AuthUserFile /home/oddmu/.htpasswd
  Require valid-user
</Location>

Virtual hosting

Virtual hosting in this context means that the program serves two different sites for two different domains from the same machine. Oddmu doesn't support that, but your webserver does. Therefore, start an Oddmu instance for every domain name, each listening on a different port. Then set up your web server such that ever domain acts as a reverse proxy to a different Oddmu instance.

Understanding search

The index indexes trigrams. Each group of three characters is a trigram. A document with content "This is a test" is turned to lower case and indexed under the trigrams "thi", "his", "is ", "s i", " is", "is ", "s a", " a ", "a t", " te", "tes", "est".

Each query is split into words and then processed the same way. A query with the words "this test" is turned to lower case and produces the trigrams "thi", "his", "tes", "est". This means that the word order is not considered when searching for documents.

This also means that there is no stemming. Searching for "testing" won't find "This is a test" because there are no matches for the trigrams "sti", "tin", "ing".

These trigrams are looked up in the index, resulting in the list of documents. Each document found is then scored. Each of the following increases the score by one point:

• the entire phrase matches
• a word matches
• a word matches at the beginning of a word
• a word matches at the end of a word
• a word matches as a whole word

A document with content "This is a test" when searched with the phrase "this test" therefore gets a score of 8: the entire phrase does not match but each word gets four points.

Trigrams are sometimes strange: In a text containing the words "main" and "rail", a search for "mail" returns a match because the trigrams "mai" and "ail" are found. In this situation, the result has a score of 0.

Limitations

Page titles are filenames with .md appended. If your filesystem cannot handle it, it can't be a page name.

The pages are indexed as the server starts and the index is kept in memory. If you have a ton of pages, this surely wastes a lot of memory.

Files may not end with a tilde (~) – these are backup files.

You cannot edit uploaded files. If you upload a file called hello.txt and attempt to edit it by using /edit/hello.txt you will create a page with the name hello.txt.md instead.

You cannot delete uploaded files via the web.

Bugs

If you spot any, contact me.

References

Writing Web Applications provided the initial code for this wiki.

For the proxy stuff, see Apache: mod_proxy.

For the usernames and password stuff, see Apache: Authentication and Authorization.