# Mapping 9P to REST

### 26 Jul 2007

Now that the PHP bindings to libixp are somewhat usable, I’ve moved on to the JavaScript portion of my project. The first (and easier!) part of it is to map 9P to a RESTful scheme, so traditional web developers can use 9P without having to learn anything new.

The PHP bindings to libixp was an important pre-requisite to achieve this: presenting a REST interface to an existing 9P serve would require a “bridge” at the middle, to convert REST requests to 9P requests and vice-versa with responses. This “bridge” may be present at any location that is mutually accessible by the client wanting RESTful access and the server providing the 9P service. This bridge can be easily coded in PHP using the new libixp bindings.

To those not very familiar with REST, it is simply a way of accessing resources using plain-old HTTP. It’s become quite popular with web developers these days, as a much simpler alternative to SOAP. A lot of web services these days are RESTful, including those offered by Amazon and Yahoo.

From the client’s perspective, accessing a 9P resource boils down to 4 things: reading, creating, modifying and deleting. These operations map neatly onto the GET, PUT, POST and DELETE HTTP requests, respectively. And thus, we have our REST URI scheme. This scheme would be enough if my bridge exposes only a single 9P serve as a REST service. As an example, suppose I start a bridge at http://plan9.kix.in/rest/ that exposes only the tcp!sources.cs.bell-labs.com!564 9P serve, to read the file named lsr I would perform a GET request at http://plan9.kix.in/rest/lsr.

However, the plot thickens when I want to design a bridge that allows access to any 9P service (which is definitely better). Now we need to encode the information represented in Plan 9 as: tcp!sources.cs.bell-labs.com!564 into a HTTP URI. The intuitive thing to do would be something like: [ROOT]/[PROTOCOL]/[9P-URI]/[PORT]/[FILE-PATH].

Hmm. That leads to really long URI’s like http://plan9.kix.in/rest/tcp/sources.cs.bell-labs.com/564/lsr. Besides that, there are several things that need to be worked out. What happens when you do a GET on a file that is actually a directory? What about parameters to GET that you usually pass to a read() function: Suppose you want to read the first 1024 bytes of a file only?