WSAPI
Lua Web Server API

## Installation

To install WSAPI you need to have LuaRocks. Just install the `wsapi` package. If you want FastCGI support you need to have the FastCGI dev kit installed, and use the `wsapi-fcgi` LuaRocks package. If you want Xavante support installed use the `wsapi-xavante` LuaRocks package.

The WSAPI rock copies samples, docs and support files to its path inside your local Rocks repository.

There is an all-in-one installer script that installs Lua, LuaRocks, and `wsapi-xavante` in a single step. Download the tarball, unpack it, then run the provided `wsapi-install` script in its path. Run `wsapi-install --help` for installation options.

### About web servers

To run WSAPI applications you will also need a web server such as Xavante, Apache, Lighttpd, or IIS (available only for Windows). Xavante is a webserver written in pure Lua. To use the Xavante connector, install the "wsapi-xavante" rock (it is already installed if you used the `wsapi-install` script).

## A Simple WSAPI Application

WSAPI applications are Lua functions that take an environment and return the status code, response headers and an output iterator. A very simple application is the following:

    function hello(wsapi_env)
      local headers = { ["Content-type"] = "text/html" }

      local function hello_text()
        coroutine.yield("<html><body>")
        coroutine.yield("<p>Hello Wsapi!</p>")
        coroutine.yield("<p>PATH_INFO: " .. wsapi_env.PATH_INFO .. "</p>")
        coroutine.yield("<p>SCRIPT_NAME: " .. wsapi_env.SCRIPT_NAME .. "</p>")
        coroutine.yield("</body></html>")
      end

      return 200, headers, coroutine.wrap(hello_text)
    end

If you have some experience with web development the example code above should be self-explanatory.

Applications usually are not implemented as naked functions, though, but packaged inside Lua modules with a `run` function that is the entry point for WSAPI. This `run` function is then passed to your server's WSAPI connector. The generic application launchers provided with WSAPI respect this pattern.

This is how the above example would look packaged this way (for example, in a hello.lua file):

    #!/usr/bin/env wsapi.cgi

    module(..., package.seeall)

    function run(wsapi_env)
      local headers = { ["Content-type"] = "text/html" }

      local function hello_text()
        coroutine.yield("<html><body>")
        coroutine.yield("<p>Hello Wsapi!</p>")
        coroutine.yield("<p>PATH_INFO: " .. wsapi_env.PATH_INFO .. "</p>")
        coroutine.yield("<p>SCRIPT_NAME: " .. wsapi_env.SCRIPT_NAME .. "</p>")
        coroutine.yield("</body></html>")
      end

      return 200, headers, coroutine.wrap(hello_text)
    end

The first line tells the UNIX-based web servers such as Apache to run WSAPI's generic CGI launcher when executing this file as a CGI script.

## Running the application

This step depends on your server and the connector you want to use.

### Xavante

If you installed the `wsapi-xavante` package you already have a Xavante launcher with WSAPI support. Just run the `wsapi` script in the path you want as your document root, and point your browser either to the `hello.lua` or `hello.ws` script (both extensions are treated as WSAPI applications). See `wsapi --help` for the launcher's configuration options.

### UNIX-like (Apache, Lighty, etc.) CGI/FastCGI

You can run hello.lua directly as a CGI script, through the generic CGI launcher wsapi. Just give execute permission hello.lua and put it in a URL-accessible path with execute permission. You should then see something like this when accessing the corresponding hello.lua URL:

        Hello Wsapi!
        PATH\_INFO: /
        SCRIPT\_NAME: /cgi-bin/hello.lua

The generic FastCGI launcher wsapi-fcgi can also run the hello.lua file directly. Configuration depends on your web server, but you should tell it to run .lua files as FastCGI scripts with wsapi-fcgi as the wrapper (the configuration is analogous to the necessary for running PHP scripts with FastCGI). As an example, this are the changes in `httpd.conf` for using Apache's *mod_fcgid*:

        AddHandler fcgid-script .lua
        FCGIWrapper /usr/bin/wsapi-fcgi .lua

You can also run hello.lua through a launcher script specially tailored to it. The driver script is very similar for both connectors. For CGI it can be this one (hello.cgi):

    #!/usr/bin/env lua

    require "wsapi.cgi"
    require "hello"
    wsapi.cgi.run(hello.run)

For FastCGI (hello.fcgi):

    #!/usr/bin/env lua

    require "wsapi.fastcgi"
    require "hello"
    wsapi.fastcgi.run(hello.run)

You may need to change lua to the name or your Lua interpreter executable. Now flag the launcher as executable and put it in a URL-accessible path that has execute permissions. You should see something like this when accessing the corresponding URL:

        Hello Wsapi!
        PATH\_INFO: /
        SCRIPT\_NAME: /cgi-bin/hello.cgi

### Windows IIS CGI/FastCGI

The generic launchers on Windows are called wsapi.exe and wsapi-fcgi.exe. You should associate the .lua file extension with one of them on IIS' management console. Then copy hello.lua to some URL-accessible path.

For CGI there is also a launcher.exe that you can rename to hello.exe and it will run the hello.cgi application launcher (not the hello.lua application!). Both should be in the same path, and it should be URL-accessible and have execute permissions on IIS. You should point your browser to hello.exe.

## Writing WSAPI connectors

A WSAPI connector builds the environment from information passed by the web server and calls a WSAPI application, sending the response back to the web server. The first thing a connector needs is a way to specify which application to run, and this is highly connector specific. Most connectors receive the application entry point as a parameter (but WSAPI provides special applications called generic launchers as a convenience).

The environment is a Lua table containing the CGI metavariables (at minimum the RFC3875 ones) plus any server-specific metainformation. It also contains an input field, a stream for the request's data, and an error field, a stream for the server's error log. The input field answers to the read([n]) method, where n is the number of bytes you want to read (or nil if you want the whole input). The error field answers to the write(...) method.

The environment should return the empty string instead of nil for undefined metavariables, and the `PATH\_INFO` variable should return "/" even if the path is empty. Behavior among the connectors should be uniform: `SCRIPT\_NAME` should hold the URI up to the part where you identify which application you are serving, if applicable (again, this is highly connector specific), while `PATH\_INFO` should hold the rest of the URL.

After building the environment the connector calls the application passing the environment to it, and collecting three return values: the HTTP status code, a table with headers, and the output iterator. The connector sends the status and headers right away to the server, as WSAPI does not guarantee any buffering itself. After that it begins calling the iterator and sending output to the server until it returns nil.

The connectors are careful to treat errors gracefully: if they occur before sending the status and headers they return an "Error 500" page instead, if they occur while iterating over the response they append the error message to the response.

## Conveniences for application writers

WSAPI is very low-level and just lets your application pretend that web servers and gateway interfaces are similar, but it does not do any kind of processing/parsing on the request, nor any buffering on the output. Most web applications need these features, so we provide helper libraries to do it.

The first library is wsapi.request. This library encapsulates the environment, parsing the request data (GET and POST) and also handling file uploads and incoming cookies.

The other helper is wsapi.response, which offers a simpler interface (along with buffering) for output instead of the inversion of control of the iterator. It also lets you easily send cookies back to the browser.

Finally there is wsapi.util, which provides URI encoding/decoding and other utility functions.

## WSAPI frameworks

The facilities above make it easier to write applications, but still are very basic. For more advanced web programming there are also frameworks built on top of WSAPI. Examples would be Orbit, which adds niceties as dispatch based on pattern matching over the PATH_INFO, easy serving of static content, easy access to databases, and easy page caching, and SAPI, included in the WSAPI package as the wsapi.sapi application, for running CGILua scripts and Lua pages.

## Testing WSAPI applications

WSAPI comes with a mock connector that can be used for testing. It provides methods to send requests to your application and format responses. Functionality such as assertions and validations is left entirely to the testing framework you choose to use. Here's a simple example of how to use the mock connector:

    local connector = require "wsapi.mock"

    function hello(wsapi_env)
      local headers = { ["Content-type"] = "text/html" }
      local function hello_text()
        coroutine.yield("hello world!")
      end
      return 200, headers, coroutine.wrap(hello_text)
    end

    local app = connector.make_handler(hello)

    do
      local response, request = app:get("/", {hello = "world"})
      assert(response.code                    == 200)
      assert(request.request_method           == "GET")
      assert(request.query_string             == "?hello=world")
      assert(response.headers["Content-type"] == "text/html")
      assert(response.body                    == "hello world!")
    end

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