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Osgood Application File

Thomas Hunter II edited this page Jul 18, 2019 · 2 revisions

An Osgood Application file has access to a global object called app. By setting various properties on this object, we're able to configure the behavior of our application.

App Configuration

app.interface: This is the name of the interface we'll listen on. It defaults to 0.0.0.0, which means all interfaces. You can also set it to 127.0.0.1, which means only requests from the local machine will work. You can also set it to the IP address of a hardware interface on your machine.

app.port: This is the port which Osgood will listen on. By default, it listens on 8080.

app.interface = '127.0.0.1';
app.port = 8080;
app.host = 'localhost';

Routing

After the application basics have been configured, we can go ahead and configure the different routes used in our application. This can be done by calling methods on the app objects. Each of these methods have the same signature:

  • app.get(routePattern, workerFilename, policyFunction)
  • app.post(...)
  • app.put(...)
  • app.patch(...)
  • app.delete(...)
  • app.head(...)
  • app.options(...)
  • app.trace(...)
  • app.connect(...)

Route Pattern

The route pattern is essentially a glob with the added ability to extract URL parameters. It is specifically matched against the path of the requested URL. Here's a quick explanation of how it works:

  • An asterisk (*) refers to any character that isn't a forward slash
  • A colon (:) followed by [a-zA-Z0-9_] is similar to an asterisk but is captured for context.params.paramName
  • A double asterisk (**) refers to any character including a forward slash

Worker Filename

This is the path to the file to be loaded for handling requests.

Policy Function

Policy Functions are used for configuring the security policies used by Osgood Workers. They're configured by calling methods available on the policy argument. The only policies currently available in Osgood are available on the policy.outboundHttp object.

The following example will only match requests for GET http://localhost:8000/users:

app.get('/users', 'foo.js', policy => {
  policy.outboundHttp.allowGet('http://localhost:5984/users/_all_docs');
});

Routing Examples

The following example will match requests for GET http://localhost:8000/users/admin but will not match requests for either GET http://localhost:8000/users/admin/xyz or POST http://localhost:8000/users/admin:

app.get('/users/:id', 'view.js', policy => {
  policy.outboundHttp.allowGet('http://localhost:5984/users/*');
});

API Security Policies

Osgood applies the Principle of Least Privilege on a per-worker basis. This means that by default a worker isn't allowed to talk to third party services. By writing policies the developer is able to whitelist ahead of time which outbound services can be communicated with, and how they may be communicated with.

These policies are based on our existing Intrinsic for Node.js HTTP Policies, which have proved to be a simple and effective approach for securing servers.

A policy function looks like this:

(policy) => {
  policy.outboundHttp.allowGet('http://api.local:123/users/*');
  policy.outboundHttp.allowPost('http://api.local:123/widgets/**');
}

Policies are configured by using the policy.outboundHttp object. This object has several methods correlating to popular HTTP methods, each with the same signature:

  • allowGet(urlPattern)
  • allowPost(...)
  • allowPut(...)
  • allowPatch(...)
  • allowDelete(...)
  • allowHead(...)
  • allowOptions(...)
  • allowTrace(...)
  • allowConnect(...)

The urlPattern argument is similar in syntax to the incoming HTTP request pattern, except that there are no parameter capturing.

  • An asterisk (*) refers to any character that isn't a forward slash
  • A double asterisk (**) refers to any character including a forward slash

Port numbers should only be supplied if the URL is using using a port which doesn't match the protocol, for example http: with 80 or https: with 443.

Static Routes

Static routes can be configured using the app.static() method.

app.static(routePrefix, path);

Unlike the other routes which accept complex patterns, the routePrefix argument here only works as a prefix. For example with a value of /assets, any request falling under http://localhost:3000/assets will trigger the static route.

The path argument is a path to a directory to serve content from. With a value set to public, and a routePrefix set to /assets, a request for http://localhost:3000/assets/styles/main.css will translate to ./public/styles/main.css.

The Content-Type header is inferred solely based on the file extension. For example, the file style.css will result in text/css, whereas a file without an extension such as foobar will fallback to application/octet-stream.

Caveats:

  • The path argument must point to a directory, not a file
  • There is no concept of an index file
    • Any request directly to a directory without a filename (i.e. /assets) will fail
    • We may allow this to be configurable in the future, e.g., setting to index.html
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