mtx: allow passing of preferred inputs to coin selector.

lib/primitives/mtx.js

@@ -1592,10 +1592,13 @@ class CoinSelector {
     this.maxFee = -1;
     this.round = false;
     this.changeAddress = null;
+    this.inputs = new Map();
 
     // Needed for size estimation.
     this.estimate = null;
 
+    this.injectInputs();
+
     if (options)
       this.fromOptions(options);
   }
@@ -1687,9 +1690,35 @@ class CoinSelector {
       this.estimate = options.estimate;
     }
 
+    if (options.inputs) {
+      assert(Array.isArray(options.inputs));
+      for (let i = 0; i < options.inputs.length; i++) {
+        const prevout = options.inputs[i];
+        assert(prevout && typeof prevout === 'object');
+        const {hash, index} = prevout;
+        assert(typeof hash === 'string');
+        assert(typeof index === 'number');
+        this.inputs.set(Outpoint.toKey(hash, index), i);
+      }
+    }
+
     return this;
   }
 
+  /**
+   * Attempt to inject existing inputs.
+   * @private
+   */
+
+  injectInputs() {
+    if (this.tx.inputs.length > 0) {
+      for (let i = 0; i < this.tx.inputs.length; i++) {
+        const {prevout} = this.tx.inputs[i];
+        this.inputs.set(prevout.toKey(), i);
+      }
+    }
+  }
+
   /**
    * Initialize the selector with coins to select from.
    * @param {Coin[]} coins
@@ -1749,6 +1778,9 @@ class CoinSelector {
    */
 
   isSpendable(coin) {
+    if (this.tx.view.hasEntry(coin))
+      return false;
+
     if (this.height === -1)
       return true;
 
@@ -1799,6 +1831,33 @@ class CoinSelector {
    */
 
   fund() {
+    // Ensure all preferred inputs first.
+    if (this.inputs.size > 0) {
+      const coins = [];
+
+      for (let i = 0; i < this.inputs.size; i++)
+        coins.push(null);
+
+      for (const coin of this.coins) {
+        const {hash, index} = coin;
+        const key = Outpoint.toKey(hash, index);
+        const i = this.inputs.get(key);
+
+        if (i != null) {
+          coins[i] = coin;
+          this.inputs.delete(key);
+        }
+      }
+
+      if (this.inputs.size > 0)
+        throw new Error('Could not resolve preferred inputs.');
+
+      for (const coin of coins) {
+        this.tx.addCoin(coin);
+        this.chosen.push(coin);
+      }
+    }
+
     while (this.index < this.coins.length) {
       const coin = this.coins[this.index++];