Add method to detect FastCGI environment

Closes #13

README.md

@@ -13,6 +13,7 @@ This module is a drop-in replacement for node's http module (server only). It ca
 
 The implementation is fully compliant with the [FastCGI 1.0 Specification](https://fast-cgi.github.io/spec).
 
+
 Example
 -------
 
@@ -30,6 +31,7 @@ fcgi.createServer(function(req, res) {
 }).listen();
 ```
 
+
 Server constructor
 ------------------
 
@@ -59,6 +61,7 @@ The `createServer` function takes four **optional** parameters:
 
 `valueMap` maps FastCGI value names to keys in the `config` object. For more information read [the next section](#fastcgi-values)
 
+
 FastCGI values
 --------------
 
@@ -79,6 +82,25 @@ fcgi.createServer(function (req, res) { /* ... */ }, {
 
 **WARNING: This `valueMap` thing is complete nonsense and is definitely going to change in the next release.**
 
+
+Listening for connections
+-------------------------
+
+When a FastCGI service is started, the stdin descriptor (fd 0) [is replaced by a bound socket](https://fast-cgi.github.io/spec#accepting-transport-connections). The service application can then start listening on that socket and accept connections.
+
+This is done automatically when you call the `listen` method on the server object without arguments, or with a callback as the only argument.
+
+The `isService` function is provided to check if the current script is being run as a FastCGI service.
+
+```js
+if (fcgi.isService()) {
+    fcgi.createServer(/* ... */).listen();
+} else {
+    console.log("This script must be run as a FastCGI service");
+}
+```
+
+
 Request URL components
 ----------------------
 
@@ -92,6 +114,7 @@ For more information read [section 4.1](https://tools.ietf.org/html/rfc3875#sect
 
 Raw CGI variables can be accessed through the `params` property of the socket object. More information [here](#the-socket-object).
 
+
 Authorizer and filter requests
 ------------------------------
 
@@ -103,6 +126,7 @@ Authorizer requests have no url. Response objects for the authorizer role expose
 
 Filter requests have an additional data stream exposed by the `data` property of [the socket object](#the-socket-object) (`req.socket.data`).
 
+
 The socket object
 -----------------
 
@@ -115,6 +139,7 @@ The socket object exposes three additional properties:
   - `dataStream` implements `stream.Readable`, exposes the FastCGI data stream for the filter role.
   - `errorStream` implements `stream.Writable`, translates writes to stderr FastCGI Records.
 
+
 http module compatibility
 -------------------------
 
@@ -129,6 +154,7 @@ Differences:
   - `req.trailers` will always be empty: CGI scripts never receive trailers
   - `res.writeContinue()` works as expected but should not be used. See first item
 
+
 License
 =======
 

example/cgiFallback.js

@@ -37,8 +37,8 @@ function log(msg) {
 
 var createServer = fcgi.createServer;
 
-// stat fd 0; if it's not a socket switch to plain CGI.
-if (!(fs.fstatSync(0).mode & fs.constants.S_IFSOCK))
+// check if we're running as a FastCGI service; if not, switch to plain CGI.
+if (!fcgi.isService())
     createServer = cgi.createServer;
 
 createServer(function (req, res) {

index.js

@@ -21,7 +21,8 @@
 
 'use strict';
 
-var http = require('http');
+var fs = require('fs'),
+    http = require('http');
 
 var server = require('./lib/server.js'),
     response = require('./lib/response.js');
@@ -48,3 +49,7 @@ exports.AuthorizerResponse = response.AuthorizerResponse;
 exports.createServer = function (responder, authorizer, filter, config) {
     return new server.Server(responder, authorizer, filter, config);
 };
+
+exports.isService = function () {
+    return fs.fstatSync(0).isSocket();
+}