Server Features

For many tests, writing one or more static HTML files is sufficient. However there are a large class of tests for which this approach is insufficient, including:

  • Tests that require cross-domain access

  • Tests that depend on setting specific headers or status codes

  • Tests that need to inspect the browser-sent request

  • Tests that require state to be stored on the server

  • Tests that require precise timing of the response.

To make writing such tests possible, we are using a number of server-side components designed to make it easy to manipulate the precise details of the response:

  • wptserve, a custom Python HTTP server

  • pywebsocket, an existing websockets server

wptserve is a Python-based web server. By default it serves static files in the test suite. For more sophisticated requirements, several mechanisms are available to take control of the response. These are outlined below.

Tests Involving Multiple Origins

Our test servers are guaranteed to be accessible through two domains and five subdomains under each. The ‘main’ domain is unnamed; the other is called ‘alt’. These subdomains are: www, www1, www2, 天気の良い日, and élève; there is also nonexistent which is guaranteed not to resolve. In addition, the HTTP server listens on two ports, and the WebSockets server on one. These subdomains and ports must be used for cross-origin tests.

Tests must not hardcode the hostname of the server that they expect to be running on or the port numbers, as these are not guaranteed by the test environment. Instead they can get this information in one of two ways:

  • From script, using the location API.

  • By using a textual substitution feature of the server.

In order for the latter to work, a file must either have a name of the form {name}.sub.{ext} e.g. example-test.sub.html or be referenced through a URL containing pipe=sub in the query string e.g. example-test.html?pipe=sub. The substitution syntax uses {{ }} to delimit items for substitution. For example to substitute in the main host name, one would write: {{host}}.

To get full domains, including subdomains, there is the hosts dictionary, where the first dimension is the name of the domain, and the second the subdomain. For example, {{hosts[][www]}} would give the www subdomain under the main (unnamed) domain, and {{hosts[alt][élève]}} would give the élève subdomain under the alt domain.

For mostly historic reasons, the subdomains of the main domain are also available under the domains dictionary; this is identical to hosts[].

Ports are also available on a per-protocol basis. For example, {{ports[ws][0]}} is replaced with the first (and only) WebSockets port, while {{ports[http][1]}} is replaced with the second HTTP port.

The request URL itself can be used as part of the substitution using the location dictionary, which has entries matching the window.location API. For example, {{location[host]}} is replaced by hostname:port for the current request, matching

Tests Requiring Special Headers

For tests requiring that a certain HTTP header is set to some static value, a file with the same path as the test file except for an an additional .headers suffix may be created. For example for /example/test.html, the headers file would be /example/test.html.headers. This file consists of lines of the form

header-name: header-value

For example

Content-Type: text/html; charset=big5

To apply the same headers to all files in a directory use a __dir__.headers file. This will only apply to the immediate directory and not subdirectories.

Headers files may be used in combination with substitutions by naming the file e.g. test.html.sub.headers.

Tests Requiring Full Control Over The HTTP Response

For full control over the request and response, the server provides the ability to write .asis files; these are served as literal HTTP responses. In other words, they are sent byte-for-byte to the server without adding an HTTP status line, headers, or anything else. This makes them suitable for testing situations where the precise bytes on the wire are static, and control over the timing is unnecessary, but the response does not conform to HTTP requirements.

The server also provides the ability to write Python “handlers”–Python scripts that have access to request data and can manipulate the content and timing of the response. Responses are also influenced by the pipe query string parameter.

Tests Requiring HTTP/2.0

To make a test run over an HTTP/2.0 connection, use .h2. in the filename. By default the HTTP/2.0 server can be accessed using port 9000. At the moment accessing tests that use .h2. over ports that do not use an HTTP/2.0 server also succeeds, so beware of that when creating them.

The HTTP/2.0 server supports handlers that work per-frame; these, along with the API are documented in Writing H2 Tests.

Tests Requiring WebTransport over HTTP/3

We do not support loading a test over WebTransport over HTTP/3 yet, but a test can establish a WebTransport session to the test server.

The WebTransport over HTTP/3 server is not yet enabled by default, so WebTransport tests will fail unless --enable-webtransport is specified to ./wpt run.

Test Features specified as query params

Alternatively to specifying Test Features in the test filename, they can be specified by setting the wpt_flags in the test variant. For example, the following variant will be loaded over HTTPS:

<meta name="variant" content="?wpt_flags=https">

https, h2 and www features are supported by wpt_flags.

Multiple features can be specified by having multiple wpt_flags. For example, the following variant will be loaded over HTTPS and run on the www subdomain.

<meta name="variant" content="wpt_flags=www&wpt_flags=https">