Fix utf8-decode on CombinedBuffers for nodejs.

Author: oskarhane

lib/internal/utf8.js

@@ -21,12 +21,14 @@
 // with the Buffer API defined in buf.js
 
 import buf from "./buf";
+import {StringDecoder} from 'string_decoder';
 let platformObj = {};
 
+
 try {
   // This will throw an exception is 'buffer' is not available
   require.resolve("buffer");
-
+  let decoder = new StringDecoder('utf8');
   let node = require("buffer");
 
   platformObj = {
@@ -39,7 +41,27 @@ try {
             end = start + length;
         buffer.position = end;
         return buffer._buffer.toString( 'utf8', start, end );
-      } else {
+      } 
+      else if( buffer instanceof buf.CombinedBuffer ) {
+        let remainingBytesToRead = length;
+        // Reduce CombinedBuffers to a decoded string
+        let out = buffer._buffers.reduce(function(last, partBuffer){
+          if(remainingBytesToRead <= 0) {
+            return last;
+          }
+          if(partBuffer.length > remainingBytesToRead) { // When we don't want the whole buffer
+            let lastSlice = partBuffer.readSlice(remainingBytesToRead);
+            partBuffer._updatePos(remainingBytesToRead);
+            remainingBytesToRead = 0;
+            return last + decoder.write(lastSlice._buffer);
+          }
+          remainingBytesToRead -= partBuffer.length;
+          return last + decoder.write(partBuffer._buffer);
+        }, '');
+        out += decoder.end();
+        return out;
+      } 
+      else {
         throw new Error( "Don't know how to decode strings from `" + buffer + "`.");
       }
     }

test/internal/utf8.test.js

@@ -1,5 +1,6 @@
 
 var utf8 = require('../../build/node/internal/utf8');
+var buffers = require('../../build/node/internal/buf');
 
 describe('utf8', function() {
   it('should have a nice clean buffer position after serializing', function() {
@@ -14,6 +15,40 @@ describe('utf8', function() {
     expect( packAndUnpack( "" ) ).toBe( "" );
     expect( packAndUnpack( "åäö123" ) ).toBe( "åäö123"  );
   });
+
+  it('should read/write utf8 from a complete combined buffer', function() {
+    // Given
+    var msg = "asåfqwer";
+    var buf = utf8.encode(msg);
+    var bufa = buf.readSlice(3);
+    var bufb = buf.readSlice(3);
+    var bufc = buf.readSlice(3);
+    var combined = new buffers.CombinedBuffer( [bufa, bufb, bufc] );
+
+    // When
+    var decoded = utf8.decode(combined, combined.length);
+
+    // Then
+    expect(decoded).toBe(msg);
+  });
+
+  it('should read/write utf8 from part of a combined buffer', function() {
+    // Given
+    var msg = "asåfq";
+    var expectMsg = msg.substring(0, msg.length-1);
+    var buf = utf8.encode(msg);
+    var bufa = buf.readSlice(3);
+    var bufb = buf.readSlice(3);
+    var unrelatedData = buffers.alloc(3);
+    var combined = new buffers.CombinedBuffer( [bufa, bufb, unrelatedData] );
+
+    // When 
+    // We read all but the unrelatedData and the last character of bufb
+    var decoded = utf8.decode(combined, combined.length - 1 - unrelatedData.length );
+
+    // Then
+    expect(decoded).toBe(expectMsg);
+  });
 });
 
 function packAndUnpack( str ) {