tx: .maxSize() method

lib/bcoin/tx.js

@@ -70,7 +70,7 @@ TX.prototype.input = function input(i, index) {
 
   var input = {
     out: {
-      tx: i.tx || null,
+      tx: (i.out ? i.out.tx : i.tx) || null,
       hash: hash,
       index: i.out ? i.out.index : i.index,
     },
@@ -180,6 +180,36 @@ TX.prototype.verify = function verify() {
   }, this);
 };
 
+TX.prototype.maxSize = function maxSize() {
+  // Create copy with 0-script inputs
+  var copy = this.clone();
+  copy.inputs.forEach(function(input) {
+    input.script = [];
+  });
+
+  var size = copy.render().length;
+
+  // Add size for signatures and public keys
+  copy.inputs.forEach(function(input) {
+    var s = input.out.tx.outputs[input.out.index].script;
+    if (bcoin.script.isPubkeyhash(s)) {
+      // Signature + len
+      size += 74;
+      // Pub key + len
+      size += 34;
+      return;
+    }
+
+    // Multisig
+    // Empty byte
+    size += 1;
+    // Signature + len
+    size += 74;
+  });
+
+  return size;
+};
+
 TX.prototype.toJSON = function toJSON() {
   // Compact representation
   var ts = new Array(4);

test/wallet-test.js

@@ -67,7 +67,9 @@ describe('Wallet', function() {
       .input(src, 0)
       .out(w.getAddress(), 5460);
 
+    var maxSize = tx.maxSize();
     w.sign(tx);
+    assert(tx.render().length <= maxSize);
     assert(tx.verify());
   });