From 1997864ec240ac1c93eadf6aac4e0b84b9938cb8 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Sun, 27 Nov 2016 22:23:12 -0800
Subject: [PATCH] coins: refactor compression.

---
 lib/blockchain/coins.js    |  4 +-
 lib/blockchain/compress.js | 79 ++++++++++++++++++++++----------------
 lib/primitives/coin.js     |  2 +-
 lib/script/script.js       | 16 ++++++--
 4 files changed, 61 insertions(+), 40 deletions(-)

diff --git a/lib/blockchain/coins.js b/lib/blockchain/coins.js
index 591400d1..cce0501c 100644
--- a/lib/blockchain/coins.js
+++ b/lib/blockchain/coins.js
@@ -383,7 +383,7 @@ Coins.parseCoin = function parseCoin(data, hash, index) {
     if (pos === index) {
       if (spent)
         return;
-      decompress.script(br, coin.script);
+      decompress.script(coin.script, br);
       coin.value = br.readVarint();
       return coin;
     }
@@ -505,7 +505,7 @@ CoinEntry.prototype.toCoin = function toCoin(coins, index) {
   // Seek to the coin's offset.
   br.seek(this.offset);
 
-  decompress.script(br, coin.script);
+  decompress.script(coin.script, br);
 
   coin.value = br.readVarint();
 
diff --git a/lib/blockchain/compress.js b/lib/blockchain/compress.js
index 13a61964..32ff8756 100644
--- a/lib/blockchain/compress.js
+++ b/lib/blockchain/compress.js
@@ -20,7 +20,6 @@ var ec = require('../crypto/ec');
  */
 
 function compressScript(script, bw) {
-  var prefix = 0;
   var data;
 
   // Attempt to compress the output scripts.
@@ -28,62 +27,80 @@ function compressScript(script, bw) {
   // they are serialized as minimaldata, as
   // we need to recreate them when we read
   // them.
+
+  // P2PKH -> 1 | key-hash
+  // Saves 5 bytes.
   if (script.isPubkeyhash(true)) {
-    prefix = 1;
     data = script.code[2].data;
-  } else if (script.isScripthash()) {
-    prefix = 2;
-    data = script.code[1].data;
-  } else if (script.isPubkey(true)) {
-    prefix = 3;
-    data = script.code[0].data;
-
-    // Try to compress the key.
-    data = compressKey(data);
-
-    // If we can't compress it,
-    // just store the script.
-    if (!data)
-      prefix = 0;
+    bw.writeU8(1);
+    bw.writeBytes(data);
+    return bw;
   }
 
-  bw.writeU8(prefix);
-
-  if (prefix === 0)
-    bw.writeVarBytes(script.toRaw());
-  else
+  // P2SH -> 2 | script-hash
+  // Saves 3 bytes.
+  if (script.isScripthash()) {
+    data = script.code[1].data;
+    bw.writeU8(2);
     bw.writeBytes(data);
+    return bw;
+  }
+
+  // P2PK -> 3 | compressed-key
+  // Only works if the key is valid.
+  // Saves up to 34 bytes.
+  if (script.isPubkey(true)) {
+    data = script.code[0].data;
+    if (ec.publicKeyVerify(data)) {
+      data = compressKey(data);
+      bw.writeU8(3);
+      bw.writeBytes(data);
+      return bw;
+    }
+  }
+
+  // Raw -> 0 | varlen | script
+  bw.writeU8(0);
+  bw.writeVarBytes(script.toRaw());
+
+  return bw;
 }
 
 /**
  * Decompress a script from buffer reader.
- * @param {BufferReader} br
  * @param {Script} script
+ * @param {BufferReader} br
  */
 
-function decompressScript(br, script) {
-  var key;
+function decompressScript(script, br) {
+  var data;
 
   // Decompress the script.
   switch (br.readU8()) {
     case 0:
-      script.fromRaw(br.readVarBytes());
+      data = br.readVarBytes();
+      script.fromRaw(data);
       break;
     case 1:
-      script.fromPubkeyhash(br.readBytes(20));
+      data = br.readBytes(20, true);
+      script.fromPubkeyhash(data);
       break;
     case 2:
-      script.fromScripthash(br.readBytes(20));
+      data = br.readBytes(20, true);
+      script.fromScripthash(data);
       break;
     case 3:
+      data = br.readBytes(33, true);
       // Decompress the key. If this fails,
       // we have database corruption!
-      key = decompressKey(br.readBytes(33));
-      script.fromPubkey(key);
+      data = decompressKey(data);
+      script.fromPubkey(data);
       break;
     default:
       throw new Error('Bad prefix.');
   }
+
+  return script;
 }
 
 /**
@@ -157,10 +174,6 @@ function decompressValue(value) {
 function compressKey(key) {
   var out;
 
-  // We can't compress it if it's not valid.
-  if (!ec.publicKeyVerify(key))
-    return;
-
   switch (key[0]) {
     case 0x02:
     case 0x03:
diff --git a/lib/primitives/coin.js b/lib/primitives/coin.js
index f4a767c4..a561e5ac 100644
--- a/lib/primitives/coin.js
+++ b/lib/primitives/coin.js
@@ -303,7 +303,7 @@ Coin.prototype.fromCompressed = function fromCompressed(data) {
   this.height = bits >>> 1;
   this.coinbase = (bits & 1) !== 0;
   this.value = br.readVarint();
-  decompress.script(br, this.script);
+  decompress.script(this.script, br);
 
   if (this.height === 0x7fffffff)
     this.height = -1;
diff --git a/lib/script/script.js b/lib/script/script.js
index 07e327a4..266261d8 100644
--- a/lib/script/script.js
+++ b/lib/script/script.js
@@ -1507,10 +1507,18 @@ Script.isCode = function isCode(raw) {
  */
 
 Script.prototype.fromPubkey = function fromPubkey(key) {
-  assert(Buffer.isBuffer(key) && key.length >= 33);
-  this.push(key);
-  this.push(opcodes.OP_CHECKSIG);
-  this.compile();
+  assert(Buffer.isBuffer(key) && key.length >= 33 && key.length <= 65);
+
+  this.raw = new Buffer(1 + key.length + 1);
+  this.raw[0] = key.length;
+  key.copy(this.raw, 1);
+  this.raw[1 + key.length] = opcodes.OP_CHECKSIG;
+
+  key = this.raw.slice(1, 1 + key.length);
+
+  this.code.push(new Opcode(key.length, key));
+  this.code.push(new Opcode(opcodes.OP_CHECKSIG));
+
   return this;
 };