From f2964e06fb38e5d588f74ff62d89a9a9d3925596 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Wed, 22 Feb 2017 20:27:19 -0800
Subject: [PATCH] minerblock: ensure constant coinbase size.

---
 lib/mining/miner.js      |  1 +
 lib/mining/minerblock.js | 99 +++++++++++++++++++++++++++++++---------
 2 files changed, 79 insertions(+), 21 deletions(-)

diff --git a/lib/mining/miner.js b/lib/mining/miner.js
index 16f74ebf..3ca66453 100644
--- a/lib/mining/miner.js
+++ b/lib/mining/miner.js
@@ -550,6 +550,7 @@ MinerOptions.prototype.fromOptions = function fromOptions(options) {
     if (typeof flags === 'string')
       flags = new Buffer(flags, 'utf8');
     assert(Buffer.isBuffer(flags));
+    assert(flags.length <= 20, 'Coinbase flags > 20 bytes.');
     this.coinbaseFlags = flags;
   }
 
diff --git a/lib/mining/minerblock.js b/lib/mining/minerblock.js
index 762099b8..c65431ff 100644
--- a/lib/mining/minerblock.js
+++ b/lib/mining/minerblock.js
@@ -116,9 +116,12 @@ MinerBlock.prototype.getRate = function() {
 
 MinerBlock.prototype._init = function _init() {
   var scale = consensus.WITNESS_SCALE_FACTOR;
+  var hash = encoding.ZERO_HASH;
   var block = this.block;
   var cb = this.coinbase;
-  var input, output, nonce;
+  var input, output, commit, padding;
+
+  assert(this.coinbaseFlags.length <= 20);
 
   // Setup our block.
   block.version = this.version;
@@ -136,7 +139,7 @@ MinerBlock.prototype._init = function _init() {
 
   // Let the world know this little
   // miner succeeded.
-  input.script.set(1, this.coinbaseFlags);
+  input.script.set(1, encoding.ZERO_HASH160);
 
   // Smaller nonce for good measure.
   input.script.set(2, util.nonce().slice(0, 4));
@@ -147,42 +150,97 @@ MinerBlock.prototype._init = function _init() {
 
   input.script.compile();
 
+  // Set up the witness nonce.
+  if (this.witness) {
+    input.witness.set(0, block.createWitnessNonce());
+    input.witness.compile();
+  }
+
   cb.inputs.push(input);
 
   // Reward output.
   output = new Output();
-  output.script.fromAddress(this.address);
+  output.script.fromPubkeyhash(encoding.ZERO_HASH160);
 
   cb.outputs.push(output);
 
-  // If we're using segwit, we need to
-  // set up the nonce and commitment.
+  // If we're using segwit, we
+  // need to set up the commitment.
   if (this.witness) {
-    // Our witness nonce is the hash256
-    // of the previous block hash.
-    nonce = block.createWitnessNonce();
-
-    // Set up the witness nonce.
-    input.witness.set(0, nonce);
-    input.witness.compile();
-
     // Commitment output.
-    cb.outputs.push(new Output());
+    commit = new Output();
+    commit.script.fromCommitment(hash);
+    cb.outputs.push(commit);
   }
 
   block.txs.push(cb);
 
-  // Update commitments.
-  this.refresh();
-
   // Initialize weight.
-  this.weight = this.block.getWeight();
+  this.weight = block.getWeight();
 
   // 4 extra bytes for varint tx count.
   this.weight += 4 * scale;
 
+  // Padding for the CB height (constant size).
+  padding = 5 - input.script.code[0].getSize();
+  assert(padding >= 0);
+
+  this.weight += padding * scale;
+
+  // Reserved size.
+  // Without segwit:
+  //   Block weight = 840
+  //   Block stripped size = 210
+  //   Block size = 210
+  //   CB weight = 500
+  //   CB stripped size = 125
+  //   CB size = 125
+  //   Sigops cost = 4
+  // With segwit:
+  //   Block weight = 1064
+  //   Block stripped size = 257
+  //   Block size = 293
+  //   CB weight = 724
+  //   CB stripped size = 172
+  //   CB size = 208
+  //   Sigops cost = 4
+  if (!this.witness) {
+    assert.equal(this.weight, 840);
+    assert.equal(block.getBaseSize() + 4 + padding, 210);
+    assert.equal(block.getSize() + 4 + padding, 210);
+    assert.equal(cb.getWeight() + padding * scale, 500);
+    assert.equal(cb.getBaseSize() + padding, 125);
+    assert.equal(cb.getSize() + padding, 125);
+  } else {
+    assert.equal(this.weight, 1064);
+    assert.equal(block.getBaseSize() + 4 + padding, 257);
+    assert.equal(block.getSize() + 4 + padding, 293);
+    assert.equal(cb.getWeight() + padding * scale, 724);
+    assert.equal(cb.getBaseSize() + padding, 172);
+    assert.equal(cb.getSize() + padding, 208);
+  }
+
   // Initialize sigops weight.
-  this.sigops = cb.getSigopsCost(null, this.flags);
+  this.sigops = 4;
+
+  // Setup coinbase flags (variable size).
+  input.script.set(1, this.coinbaseFlags);
+  input.script.compile();
+
+  // Setup output script (variable size).
+  output.script.clear();
+  output.script.fromAddress(this.address);
+
+  // Update commitments.
+  this.refresh();
+
+  // Ensure the variable size
+  // stuff didn't break anything.
+  assert(block.getWeight() <= this.weight,
+    'Coinbase exceeds reserved size!');
+
+  assert(cb.getSigopsCost(null, this.flags) <= this.sigops,
+    'Coinbase exceeds reserved sigops');
 };
 
 /**
@@ -208,7 +266,6 @@ MinerBlock.prototype.refresh = function refresh() {
 
 MinerBlock.prototype.updateCommitment = function updateCommitment() {
   var output = this.coinbase.outputs[1];
-  var flags = this.coinbaseFlags;
   var hash;
 
   // Recalculate witness merkle root.
@@ -216,7 +273,7 @@ MinerBlock.prototype.updateCommitment = function updateCommitment() {
 
   // Update commitment.
   output.script.clear();
-  output.script.fromCommitment(hash, flags);
+  output.script.fromCommitment(hash);
 };
 
 /**