Use async.parallel for cleaner flow control in colorTransaction

lib/protocol/ColoringEngine.js

@@ -133,37 +133,52 @@ ColoringEngine.prototype.colorTransaction = function (transaction, cb) {
       if (markerOutputPayload) {
         // Extract the marker output (asset quantity and metadata) information
         markerOutput = MarkerOutput.prototype.deserializePayload(markerOutputPayload);
-        // If valid marker output information was extracted, do not process further outputs
+        // If valid marker output information was extracted, we have all the
+        // information necessary to compute the colored outputs for this tx
         if (markerOutput) {
           foundMarkerOutput = true;
 
-          // Fetch the colored outputs for the previous transaction
+          // Build a recursive backtracking function for each of this
+          // transactions inputs. Looking at the colored outputs from
+          // transactions linked to this transaction's inputs will allow
+          // us to dertermine which assets flow into the current transaction.
+          var prevouts = [];
           transaction.inputs().forEach(function (i, idx) {
-            // 'i' is a 2 element array [(Buffer) outHash, (int) outIndex]
-            var outHash = buffertools.reverse(i[0]).toString('hex');
-            coloringEngine.getOutput(outHash, idx, function (err, inTx) {
-              if (err) return cb(err);
-
-              // Add this transaction to the list of inputs
-              inputs[idx] = (inTx);
-
-              // If all inputs have been processed, compute asset ids
-              if (inputs.length == transaction.ins.length) {
-                outputsWithAssetIds = ColoringEngine.prototype._computeAssetIds(
-                  inputs,
-                  outIdx,
-                  transaction.outs,
-                  markerOutput.assetQuantities);
-
-                // If valid asset ids were computed, return them
-                if (outputsWithAssetIds) {
-                  return cb(null, outputsWithAssetIds);
-                } else {
-                  return cb(null, makeUncoloredResponse(transaction));
-                }
-              }
+
+            prevouts.push(function (fcb) {
+              var outHash = buffertools.reverse(i[0]).toString('hex');
+              coloringEngine.getOutput(outHash, idx, fcb);
             });
           }, coloringEngine);
+
+          // Fetch the colored outputs for each previous transaction
+          async.parallel(prevouts, function (err, inTxs){
+            if (err) return cb(err);
+
+            // Store results of all recursive backtracking
+            inputs = inTxs;
+
+            // Ensure all inputs were processed
+            if (inputs.length !== transaction.ins.length) {
+              return ("Error processing inputs: expected "
+                + transaction.ins.length + " results, got " + inputs.length);
+            }
+
+            // Compute the asset ids of the colored outputs
+            outputsWithAssetIds = ColoringEngine.prototype._computeAssetIds(
+              inputs,
+              outIdx,
+              transaction.outs,
+              markerOutput.assetQuantities);
+
+            if (outputsWithAssetIds) {
+              // If successful, return the colored outputs
+              return cb(null, outputsWithAssetIds);
+            } else {
+              // Otherwise, the transaction should be considered uncolored
+              return cb(null, makeUncoloredResponse(transaction));
+            }
+          });
         }
       }
     }