Add highly-experimental 'clone' method

Cloned instances share a common input

Very useful for Stream-based input

Author: lovell

index.js

@@ -760,6 +760,24 @@ Sharp.prototype.metadata = function(callback) {
   }
 };
 
+/*
+  Clone new instance using existing options.
+  Cloned instances share the same input.
+*/
+Sharp.prototype.clone = function() {
+  // Clone existing options
+  var clone = new Sharp();
+  util._extend(clone.options, this.options);
+  clone.streamIn = false;
+  // Pass 'finish' event to clone for Stream-based input
+  this.on('finish', function() {
+    // Clone inherits input data
+    clone.options.bufferIn = this.options.bufferIn;
+    clone.emit('finish');
+  });
+  return clone;
+};
+
 /*
   Get and set cache memory and item limits
 */

src/pipeline.cc

@@ -1222,7 +1222,6 @@ NAN_METHOD(pipeline) {
     baton->bufferInLength = node::Buffer::Length(buffer);
     baton->bufferIn = new char[baton->bufferInLength];
     memcpy(baton->bufferIn, node::Buffer::Data(buffer), baton->bufferInLength);
-    options->Set(NanNew<String>("bufferIn"), NanNull());
   }
   // ICC profile to use when input CMYK image has no embedded profile
   baton->iccProfilePath = *String::Utf8Value(options->Get(NanNew<String>("iccProfilePath"))->ToString());

test/unit/io.js

@@ -106,6 +106,53 @@ describe('Input/output', function() {
     readable.pipe(pipeline).pipe(writable);
   });
 
+  it('Read from Stream and write to multiple Streams', function(done) {
+    var finishEventsExpected = 2;
+    // Output stream 1
+    var output1 = fixtures.path('output.multi-stream.1.jpg');
+    var writable1 = fs.createWriteStream(output1);
+    writable1.on('finish', function() {
+      sharp(output1).toBuffer(function(err, data, info) {
+        if (err) throw err;
+        assert.strictEqual(true, data.length > 0);
+        assert.strictEqual(data.length, info.size);
+        assert.strictEqual('jpeg', info.format);
+        assert.strictEqual(320, info.width);
+        assert.strictEqual(240, info.height);
+        fs.unlinkSync(output1);
+        finishEventsExpected--;
+        if (finishEventsExpected === 0) {
+          done();
+        }
+      });
+    });
+    // Output stream 2
+    var output2 = fixtures.path('output.multi-stream.2.jpg');
+    var writable2 = fs.createWriteStream(output2);
+    writable2.on('finish', function() {
+      sharp(output2).toBuffer(function(err, data, info) {
+        if (err) throw err;
+        assert.strictEqual(true, data.length > 0);
+        assert.strictEqual(data.length, info.size);
+        assert.strictEqual('jpeg', info.format);
+        assert.strictEqual(100, info.width);
+        assert.strictEqual(122, info.height);
+        fs.unlinkSync(output2);
+        finishEventsExpected--;
+        if (finishEventsExpected === 0) {
+          done();
+        }
+      });
+    });
+    // Create parent instance
+    var rotator = sharp().rotate(90);
+    // Cloned instances with differing dimensions
+    rotator.clone().resize(320, 240).pipe(writable1);
+    rotator.clone().resize(100).pipe(writable2);
+    // Go
+    fs.createReadStream(fixtures.inputJpg).pipe(rotator);
+  });
+
   it('Handle Stream to Stream error ', function(done) {
     var pipeline = sharp().resize(320, 240);
     var anErrorWasEmitted = false;