feat: Add duplex streams (#48)

.gitignore

@@ -1,6 +1,7 @@
 node_modules/
 test/out/
 test/write.png
+test/duplex.jpg
 .nyc_output/
 *.swo
 *.swp

README.md

@@ -16,6 +16,7 @@ $ npm install simple-thumbnail --save
 ## Usage
 
 ```js
+const fs = require('fs')
 const genThumbnail = require('simple-thumbnail')
 
 // promise
@@ -41,6 +42,11 @@ app.get('/some/endpoint', (req, res) => {
     .then(() => console.log('done!'))
     .catch(err => console.error(err))
 })
+
+// duplex streams
+fs.createReadStream('path/to/image')
+  .pipe(genThumbnail(null, null, '250x?'))
+  .pipe(fs.createWriteStream('output/file/path.jpg'))
 ```
 
 ## Getting FFmpeg
@@ -66,13 +72,13 @@ download()
 
 #### genThumbnail(input, output, size, [config])
 
-Returns of a `Promise` which resolves on thumbnail creation.
+Returns of a `Promise` which resolves on thumbnail creation, or a `stream.Duplex` (see below).
 
 #### input
 
-Type: `String | stream.Readable`
+Type: `String | stream.Readable | Null`
 
-The URL, file path, or read-stream of an image or video.
+The URL, file path, or read-stream of an image or video. If both the input and output are null, then `genThumbnail` will return a `stream.Duplex`.
 
 #### output
 

index.js

@@ -1,6 +1,7 @@
 'use strict'
 
 const { spawn } = require('child_process')
+const { Duplex } = require('stream')
 
 /**
  * Parse a size string (eg. '240x?')
@@ -124,6 +125,42 @@ function ffmpegStreamExecute (path, args, rstream) {
   return Promise.resolve(ffmpeg.stdout)
 }
 
+class DuplexFfmpeg extends Duplex {
+  constructor (ffmpeg) {
+    super()
+    this.ffmpeg = ffmpeg
+  }
+
+  _read (size) {
+    this.ffmpeg.stdout.on('data', data => {
+      this.push(data)
+    })
+  }
+
+  _write (...args) {
+    this.ffmpeg.on('close', () => {
+      this.end()
+    })
+    this.ffmpeg.stdin._write(...args)
+  }
+
+  _final () {}
+}
+
+/**
+ * Return a duplex stream
+ * @func    ffmpegDuplexExecute
+ * @param   {String}          path      The path of the ffmpeg binary
+ * @param   {Array<string>}   args      An array of arguments for ffmpeg
+ *                                      the standard input of ffmpeg
+ * @returns {stream.Duplex}  A duplex stream :)
+ */
+function ffmpegDuplexExecute (path, args) {
+  const ffmpeg = spawn(path, args, { shell: true })
+
+  return new DuplexFfmpeg(ffmpeg)
+}
+
 /**
  * Generates a thumbnail from the first frame of a video file
  * @func    genThumbnail
@@ -133,7 +170,7 @@ function ffmpegStreamExecute (path, args, rstream) {
  * @param   {Object}  [config={}]  A configuration object
  * @param   {String}  [config.path='ffmpeg']    Path of the ffmpeg binary
  * @param   {String}  [config.seek='00:00:00']  Time to seek for videos
- * @returns {Promise}                           Resolves on completion, or rejects on error
+ * @returns {Promise|stream.Duplex}             Resolves on completion, or rejects on error
  */
 function genThumbnail (input, output, size, config = {}) {
   const ffmpegPath = config.path || process.env.FFMPEG_PATH || 'ffmpeg'
@@ -149,6 +186,10 @@ function genThumbnail (input, output, size, config = {}) {
     seek
   )
 
+  if (input === null && output === null) {
+    console.log(args)
+    return ffmpegDuplexExecute(ffmpegPath, args)
+  }
   if (output === null) {
     return ffmpegStreamExecute(ffmpegPath, args, rstream)
   }