Support WebSub and Webmention on a static site
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README.md

lazymention

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tl;dr: Support WebSub and Webmention on a static site

lazymention is a daemon that you run on a server. When you publish to your static IndieWeb site, you ping lazymention, and it will poll your site, parse the microformats2 markup, and send Webmentions and WebSub notifications for content it hasn't seen before.

Webmention functionality is currently done. WebSub is planned for the future.

Installation

$ npm install -g --production lazymention

Limitations

lazymention makes some maintainability tradeoffs that may result in denial-of-service problems if you allow input from sites you don't trust. Specifically:

  • lazymention buffers all HTML pages in memory before parsing microformats2. In the future it may also retrieve multiple HTML pages per job. This may lead to high memory usage.
  • lazymention's handling of microformats2 structures within pages is rather brittle. For example, if you mark an element as both an h-entry and an h-feed, lazymention will probably crash. I will take PRs to fix these problems, especially those caused by nonmalicious markup, but in the meantime your process will be very dead.
  • lazymention does not bother to check if it's sending Webmentions to localhost or loopback addresses. See the Security Considerations section of the Webmention spec.

Please be aware of these constraints before running lazymention in production. The domains option should help with this.

Also, lazymention has no idea how to recurse into subpages of indexes. In the real world, I expect that this will not actually be a real problem.

Running

lazymention will install a command called, fittingly, lazymention. You need to provide, at minimum, a storage location (you can do this on the CLI by passing -s), but not configuring anything else will give you a daemon running on port 8000, which is probably no good.

You can provide configuration options in three ways: CLI flags, environment variables, and JSON configuration files - CLI flags override environment variables and environment variables override JSON configs. The default config file location is /etc/lazymention.json, but you can override this by passing -c <path_to_config.json>. There's a sample file called lazymention.json.sample but be sure to actually look at it; lazymention won't work for you if you don't adjust it a little bit.

If you configure with environment variables, just prefix the configuration values with LAZYMENTION_. CLI flags are just prefixed with --, as you'd expect - just run lazymention --help if this is confusing. You can pass more than one value for --domains (e.g. --domains example.com example.net), as well as passing --domains more than once (e.g. --domains example.com --domains example.net). If you need to specify more than one domain via environment variables, separate them using ,.

You should also set NODE_ENV=production in the environment, regardless of how you're configuring lazymention.

Configuration values

Here's what you can configure:

Name Description Type Default
storage Where to put data. Must be read/writable by the server user. String None
port Port for the HTTP server to bind to. Number 8000
address Address for the HTTP server to bind to. String 0.0.0.0
logger Whether to have the logger write logs. Boolean True
logfile Where to write logs to. String stdout
logLevel Bunyan loglevel for the logger. String info
domains Whitelist of domains to allow in job submissions. Array None

The storage and domains options are required. If you don't want to use a whitelist you can set domains to [], but you're strongly discouraged from doing so because of the security implications. In fact, the reason you have to set this manually is to make sure you know what you're doing.

Using the API

There's exactly one API endpoint, /jobs/submit. To trigger lazymention, POST to this endpoint with a JSON payload in the body. The JSON should contain a url key whose value is the URL to crawl.

If everything goes well, you'll get back 202 Accepted. If something went wrong, you'll get back 400 Bad Request, unless the domain of the URL you provided isn't in the whitelist in which case you'll get 403 Forbidden.

In the future the reponse will contain a URL that lets you check the status of your job, but in the meantime all you get back is a lame 2xx status code.

API clients

There's currently one API client, ping-lazymention. It's nice for gulp tasks.

Have you written another client? Please send a Pull Request updating this section!

Embedding

lazymention has an embedding API, in case you want to reuse its functionality in another Node app. You can access both the overall Express application or just the job submission route.

It is safe to concurrently embed unlimited instances of either in the same process so long as they don't share the same data directory.

Note: your app would have to be AGPL 3.0 or later to comply with the licensing terms, but if this is a big problem I might consider relaxing the requirements so just ping me.

Express application

Available as require('lazymention').makeApp(). You need to pass three arguments. In order:

  1. A configurations object that contains, at minimum, a domain key with the appropriate value
  2. A Bunyan Logger object (or compatible)
  3. A persistence factory function (see below)

Not providing these options as specified will raise AssertionError.

The Express app is configured to parse JSON bodies and to compress response bodies. You can't disable the former because it's required for anything useful to happen and you can't disable the latter because that's a bad idea.

req.log is configured to be a Bunyan child log and req.config is set to the app's config. The API is mounted at /jobs/submit, just like the standalone daemon.

Express Router

Available as require('lazymention').makeRouter(). You need to pass a single argument, a persistence factory function (see below). Not providing this argument will raise AssertionError.

The Router expects certain things:

  1. A req.body with something useful in it (how to populate this is up to you)
  2. A Bunyan Logger (or compatible) available as req.log
  3. A configuration object available as req.config and containing, at minimum, a domains key

Everything else is up to you.

Persistence layer

To work with the embedding API you are required to provide some layer for persistence. You can do whatever you want in this layer; the default implementation reads and writes flat files. You can either reuse the default or implement your own.

You can get to the default implementation with require('lazymention').persistence(<path>). Calling this will return a factory function configured with the filesystem <path> you provided.

If you don't want to use the default implementation, you need to write a factory function. This function will be passed a single parameter, a child of the Bunyan Logger object you passed. Keep in mind that it will be invoked with a different Logger for each request, so connecting out to a database or whatever each and every time this is invoked is probably a terrible idea.

When invoked, your factory function should return an object with two keys, get and set. set must be a function that takes a namespace (string), key (string), an object to set as the value of that key, and a callback with signature (err<Error>). get must be a function that takes a namespace, a lookup key and a callback with signature (err<Error>, data<Object>), data being the object that was set with set.

Values are guaranteed to be JSON-serializable but otherwise there are no restrictions on what they can be.

Author

AJ Jordan alex@strugee.net

License

AGPL 3.0 or later