Add fromBuffer and toBuffer to PrivateKey

lib/privatekey.js

@@ -152,12 +152,8 @@ PrivateKey._transformBuffer = function(buf, network) {
 
   var info = {};
 
-  if (buf.length === 1 + 32 + 1 && buf[1 + 32 + 1 - 1] === 1) {
+  if (buf.length === 32) {
-    info.compressed = true;
+    return PrivateKey._transformBNBuffer(buf, network);
-  } else if (buf.length === 1 + 32) {
-    info.compressed = false;
-  } else {
-    throw new Error('Length of buffer must be 33 (uncompressed) or 34 (compressed)');
   }
 
   info.network = Networks.get(buf[0], 'privatekey');
@@ -173,10 +169,33 @@ PrivateKey._transformBuffer = function(buf, network) {
     throw new TypeError('Private key network mismatch');
   }
 
+  if (buf.length === 1 + 32 + 1 && buf[1 + 32 + 1 - 1] === 1) {
+    info.compressed = true;
+  } else if (buf.length === 1 + 32) {
+    info.compressed = false;
+  } else {
+    throw new Error('Length of buffer must be 33 (uncompressed) or 34 (compressed)');
+  }
+
   info.bn = BN.fromBuffer(buf.slice(1, 32 + 1));
 
   return info;
+};
 
+/**
+ * Internal function to transform a BN buffer into a private key
+ *
+ * @param {Buffer} buf
+ * @param {Network|string} [network] - a {@link Network} object, or a string with the network name
+ * @returns {object} an Object with keys: bn, network, and compressed
+ * @private
+ */
+PrivateKey._transformBNBuffer = function(buf, network) {
+  var info = {};
+  info.network = Networks.get(network) || Networks.defaultNetwork;
+  info.bn = BN.fromBuffer(buf);
+  info.compressed = false;
+  return info;
 };
 
 /**
@@ -204,9 +223,20 @@ PrivateKey.fromJSON = function(json) {
   return new PrivateKey(json);
 };
 
+/**
+ * Instantiate a PrivateKey from a Buffer with the DER or WIF representation
+ *
+ * @param {Buffer} arg
+ * @param {Network} network
+ * @return {PrivateKey}
+ */
+PrivateKey.fromBuffer = function(arg, network) {
+  return new PrivateKey(arg, network);
+};
 
 /**
  * Internal function to transform a JSON string on plain object into a private key
+ * return this.
  *
  * @param {String} json - A JSON string or plain object
  * @returns {Object} An object with keys: bn, network and compressed

test/privatekey.js

@@ -268,11 +268,18 @@ describe('PrivateKey', function() {
 
   });
 
-  describe('#toBuffer', function() {
+  describe('buffer serialization', function() {
-    it('should output known buffer', function() {
+    it('returns an expected value when creating a PrivateKey from a buffer', function() {
       var privkey = new PrivateKey(BN.fromBuffer(buf), 'livenet');
       privkey.toString().should.equal(buf.toString('hex'));
     });
+
+    it('roundtrips correctly when using toBuffer/fromBuffer', function() {
+      var privkey = new PrivateKey(BN.fromBuffer(buf));
+      var toBuffer = new PrivateKey(privkey.toBuffer());
+      var fromBuffer = PrivateKey.fromBuffer(toBuffer.toBuffer());
+      fromBuffer.toString().should.equal(privkey.toString());
+    });
   });
 
   describe('#toBigNumber', function() {