Add: fs option & tests. Closes pillarjs#160

	* Add: new option to specify which file system to use to serve files by default.
	* Add: exported erros for basic file system interface check
	* Add: basic tests via global injection

HISTORY.md

@@ -1,6 +1,6 @@
 unreleased
 ==========
-
+  * Add `fs` option
   * deps: depd@~2.0.0
     - Replace internal `eval` usage with `Function` constructor
     - Use instance methods on `process` to check for listeners

README.md

@@ -119,6 +119,15 @@ Serve files relative to `path`.
 Byte offset at which the stream starts, defaults to 0. The start is inclusive,
 meaning `start: 2` will include the 3rd byte in the stream.
 
+##### fs
+
+**Default**: [require('fs')](https://nodejs.org/api/fs.html)
+
+File system to serve files by default. 
+```js
+  send(req, path, { fs: mockedFileSystem })
+```
+
 #### Events
 
 The `SendStream` is an event emitter and will emit the following events:

index.js

@@ -20,7 +20,6 @@ var encodeUrl = require('encodeurl')
 var escapeHtml = require('escape-html')
 var etag = require('etag')
 var fresh = require('fresh')
-var fs = require('fs')
 var mime = require('mime')
 var ms = require('ms')
 var onFinished = require('on-finished')
@@ -84,6 +83,10 @@ function send (req, path, options) {
   return new SendStream(req, path, options)
 }
 
+var errors = {}
+errors.INVALID_OPTION_FS_STAT = new TypeError('Invalid option: Incompatible file system interface: fs.stat() method is expected')
+errors.INVALID_OPTION_FS_CRTSTRM = new TypeError('Invalid option: Incompatible file system interface: fs.createReadStream() method is expected')
+send.errors = errors
 /**
  * Initialize a `SendStream` with the given `path`.
  *
@@ -102,6 +105,18 @@ function SendStream (req, path, options) {
   this.path = path
   this.req = req
 
+  // Dynamically import `fs` if not it is not provided by config
+  this.fs = opts.fs || require('fs')
+
+  // Checking if provided "fs" is compatible
+  if (typeof this.fs.stat !== 'function') {
+    throw errors.INVALID_OPTION_FS_STAT
+  }
+
+  if (typeof this.fs.createReadStream !== 'function') {
+    throw errors.INVALID_OPTION_FS_CRTSTRM
+  }
+
   this._acceptRanges = opts.acceptRanges !== undefined
     ? Boolean(opts.acceptRanges)
     : true
@@ -718,7 +733,7 @@ SendStream.prototype.sendFile = function sendFile (path) {
   var self = this
 
   debug('stat "%s"', path)
-  fs.stat(path, function onstat (err, stat) {
+  this.fs.stat(path, function onstat (err, stat) {
     if (err && err.code === 'ENOENT' && !extname(path) && path[path.length - 1] !== sep) {
       // not found, check extensions
       return next(err)
@@ -739,7 +754,7 @@ SendStream.prototype.sendFile = function sendFile (path) {
     var p = path + '.' + self._extensions[i++]
 
     debug('stat "%s"', p)
-    fs.stat(p, function (err, stat) {
+    self.fs.stat(p, function (err, stat) {
       if (err) return next(err)
       if (stat.isDirectory()) return next()
       self.emit('file', p, stat)
@@ -767,7 +782,7 @@ SendStream.prototype.sendIndex = function sendIndex (path) {
     var p = join(path, self._index[i])
 
     debug('stat "%s"', p)
-    fs.stat(p, function (err, stat) {
+    self.fs.stat(p, function (err, stat) {
       if (err) return next(err)
       if (stat.isDirectory()) return next()
       self.emit('file', p, stat)
@@ -793,7 +808,7 @@ SendStream.prototype.stream = function stream (path, options) {
   var res = this.res
 
   // pipe
-  var stream = fs.createReadStream(path, options)
+  var stream = this.fs.createReadStream(path, options)
   this.emit('stream', stream)
   stream.pipe(res)
 

test/send.js

@@ -1418,6 +1418,37 @@ describe('send(file, options)', function () {
       })
     })
   })
+
+  describe('fs', function () {
+    var FS_STAT = send.errors.INVALID_OPTION_FS_STAT
+    var CRTSTRM = send.errors.INVALID_OPTION_FS_CRTSTRM
+    it('must provide fs.stat()', function (done) {
+      try {
+        send(void 0, '', { fs: { createReadStream: function () {} } })
+      } catch (err) {
+        if (err === FS_STAT) {
+          done()
+        } else {
+          done(new Error('Must throw INVALID_OPTION_FS_STAT'))
+        }
+        return
+      }
+      done()
+    })
+    it('must implement fs.createReadStream()', function (done) {
+      try {
+        send(void 0, '', { fs: { stat: function () {} } })
+      } catch (err) {
+        if (err === CRTSTRM) {
+          done()
+        } else {
+          done(new Error('Must throw INVALID_OPTION_FS_CRTSTRM'))
+        }
+        return
+      }
+      done()
+    })
+  })
 })
 
 describe('send.mime', function () {