1 files changed, 157 insertions, 0 deletions
diff --git a/testing/web-platform/tests/tools/wptserve/docs/pipes.rst b/testing/web-platform/tests/tools/wptserve/docs/pipes.rst
new file mode 100644
index 000000000..c606140d4
--- /dev/null
+++ b/testing/web-platform/tests/tools/wptserve/docs/pipes.rst
@@ -0,0 +1,157 @@
+Pipes
+======
+
+Pipes are functions that may be used when serving files to alter parts
+of the response. These are invoked by adding a pipe= query parameter
+taking a | separated list of pipe functions and parameters. The pipe
+functions are applied to the response from left to right. For example::
+
+  GET /sample.txt?pipe=slice(1,200)|status(404).
+
+This would serve bytes 1 to 199, inclusive, of foo.txt with the HTTP status
+code 404.
+
+There are several built-in pipe functions, and it is possible to add
+more using the `@pipe` decorator on a function, if required.
+
+.. note::
+   Because of the way pipes compose, using some pipe functions prevents the
+   content-length of the response from being known in advance. In these cases
+   the server will close the connection to indicate the end of the response,
+   preventing the use of HTTP 1.1 keepalive.
+
+Built-In Pipes
+--------------
+
+sub
+~~~
+
+Used to substitute variables from the server environment, or from the
+request into the response.
+
+Substitutions are marked in a file using a block delimited by `{{`
+and `}}`. Inside the block the following variables are available:
+
+  `{{host}}`
+    The host name of the server excluding any subdomain part.
+
+  `{{domains[]}}`
+    The domain name of a particular subdomain
+      e.g. `{{domains[www]}}` for the `www` subdomain.
+
+  `{{ports[][]}}`
+    The port number of servers, by protocol
+      e.g. `{{ports[http][0]}}` for the first (and, depending on setup,
+      possibly only) http server
+
+  `{{headers[]}}`
+    The HTTP headers in the request
+      e.g. `{{headers[X-Test]}}` for a hypothetical `X-Test` header.
+
+  `{{GET[]}}`
+    The query parameters for the request
+      e.g. `{{GET[id]}}` for an id parameter sent with the request.
+
+So, for example, to write a javascript file called `xhr.js` that
+depends on the host name of the server, without hardcoding, one might
+write::
+
+    var server_url = http://{{host}}:{{ports[http][0]}}/path/to/resource;
+    //Create the actual XHR and so on
+
+The file would then be included as:
+
+    <script src="xhr.js?pipe=sub"></script>
+
+This pipe can also be enabled by using a filename `*.sub.ext`, e.g. the file above could be called `xhr.sub.js`.
+
+status
+~~~~~~
+
+Used to set the HTTP status of the response, for example::
+
+    example.js?pipe=status(410)
+
+headers
+~~~~~~~
+
+Used to add or replace http headers in the response. Takes two or
+three arguments; the header name, the header value and whether to
+append the header rather than replace an existing header (default:
+False). So, for example, a request for::
+
+    example.html?pipe=header(Content-Type,text/plain)
+
+causes example.html to be returned with a text/plain content type
+whereas::
+
+    example.html?pipe=header(Content-Type,text/plain,True)
+
+Will cause example.html to be returned with both text/html and
+text/plain content-type headers.
+
+slice
+~~~~~
+
+Used to send only part of a response body. Takes the start and,
+optionally, end bytes as arguments, although either can be null to
+indicate the start or end of the file, respectively. So for example::
+
+    example.txt?pipe=slice(10,20)
+
+Would result in a response with a body containing 10 bytes of
+example.txt including byte 10 but excluding byte 20.
+
+::
+
+    example.txt?pipe=slice(10)
+
+Would cause all bytes from byte 10 of example.txt to be sent, but::
+
+    example.txt?pipe=slice(null,20)
+
+Would send the first 20 bytes of example.txt.
+
+trickle
+~~~~~~~
+
+.. note::
+   Using this function will force a connection close.
+
+Used to send the body of a response in chunks with delays. Takes a
+single argument that is a microsyntax consisting of colon-separated
+commands. There are three types of commands:
+
+* Bare numbers represent a number of bytes to send
+
+* Numbers prefixed `d` indicate a delay in seconds
+
+* Numbers prefixed `r` must only appear at the end of the command, and
+  indicate that the preceding N items must be repeated until there is
+  no more content to send. The number of items to repeat must be even.
+
+In the absence of a repetition command, the entire remainder of the content is
+sent at once when the command list is exhausted. So for example::
+
+    example.txt?pipe=trickle(d1)
+
+causes a 1s delay before sending the entirety of example.txt.
+
+::
+
+    example.txt?pipe=trickle(100:d1)
+
+causes 100 bytes of example.txt to be sent, followed by a 1s delay,
+and then the remainder of the file to be sent. On the other hand::
+
+    example.txt?pipe=trickle(100:d1:r2)
+
+Will cause the file to be sent in 100 byte chunks separated by a 1s
+delay until the whole content has been sent.
+
+
+:mod:`Interface <pipes>`
+------------------------
+
+.. automodule:: wptserve.pipes
+   :members: