Add HeadersMessage and parsing support for it. Patch from Roman Mandeleil.

AUTHORS

@@ -10,3 +10,4 @@ Jan Møller <jan.moller@gmail.com>
 Wolfgang Nagele <wolfgang.nagele@gmail.com>
 Jonny Heggheim <hegjon@gmail.com>
 Steve Coughlan <shadders.del@gmail.com>
+Roman Mandeleil <roman.mandeleil@gmail.com>

src/com/google/bitcoin/core/BitcoinSerializer.java

@@ -68,6 +68,8 @@ public class BitcoinSerializer {
         names.put(VersionAck.class, "verack");
         names.put(GetBlocksMessage.class, "getblocks");
         names.put(GetAddrMessage.class, "getaddr");
+        names.put(HeadersMessage.class, "headers");
+
     }
 
     /**
@@ -330,6 +332,8 @@ public class BitcoinSerializer {
             return new Ping();
         } else if (command.equals("verack")) {
             return new VersionAck(params, payloadBytes);
+        } else if (command.equals("headers")) {
+            return new HeadersMessage(params, payloadBytes);
         } else {
             throw new ProtocolException("No support for deserializing message with name " + command);
         }

src/com/google/bitcoin/core/HeadersMessage.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2011 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.bitcoin.core;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A protocol message that contains a repeated series of block headers, sent in response to the "getheaders" command.
+ * This is useful when you want to traverse the chain but know you don't care about the block contents, for example,
+ * because you have a freshly created wallet with no keys.
+ */
+public class HeadersMessage extends Message {
+    private static final Logger log = LoggerFactory.getLogger(HeadersMessage.class);
+
+    // The main client will never send us more than this number of headers.
+    final static int MAX_HEADERS = 2000;
+
+    private List<Block> blockHeaders;
+
+    public HeadersMessage(NetworkParameters params, byte[] payload) throws ProtocolException {
+        super(params, payload, 0);
+    }
+
+    @Override
+    protected void parseLite() throws ProtocolException {
+        if (length == UNKNOWN_LENGTH) {
+            long numHeaders = readVarInt();
+
+            // Each header has 80 bytes and one more byte for transactions number which is 00.
+            length = 81 * (int)numHeaders;
+        }
+    }
+
+    @Override
+    void parse() throws ProtocolException {
+        long numHeaders = readVarInt();
+        if (numHeaders > MAX_HEADERS)
+            throw new ProtocolException("Too many headers: got " + numHeaders + " which is larger than " +
+                                         MAX_HEADERS);
+
+        blockHeaders = new ArrayList<Block>();
+
+        for (int i = 0; i < numHeaders; ++i) {
+            // Read 80 bytes of the header and one more byte for the transaction list, which is always a 00 because the
+            // transaction list is empty.
+            byte[] blockHeader = readBytes(81);
+            if (blockHeader[80] != 00)
+                throw new ProtocolException("Block header does not end with a null byte");
+            Block newBlockHeader = new Block(this.params, blockHeader);
+            blockHeaders.add(newBlockHeader);
+        }
+
+        if (log.isDebugEnabled()) {
+            for (int i = 0; i < numHeaders; ++i) {
+                log.debug(this.blockHeaders.get(i).toString());
+            }
+        }
+    }
+
+
+    public List<Block> getBlockHeaders() {
+        return blockHeaders;
+    }
+}

tests/com/google/bitcoin/core/BitcoinSerializerTest.java

@@ -200,4 +200,83 @@ public class BitcoinSerializerTest {
         
     }
 
+
+    /**
+     * Get 1 header of the block number 1 (the first one is 0) in the chain
+     */
+    @Test
+    public void testHeaders1() throws Exception {
+
+        BitcoinSerializer bs = new BitcoinSerializer(NetworkParameters.prodNet(), true,
+                null);
+
+        ByteArrayInputStream bais = new ByteArrayInputStream(Hex.decode("f9beb4d9686561" +
+                "646572730000000000520000005d4fab8101010000006fe28c0ab6f1b372c1a6a246ae6" +
+                "3f74f931e8365e15a089c68d6190000000000982051fd1e4ba744bbbe680e1fee14677b" +
+                "a1a3c3540bf7b1cdb606e857233e0e61bc6649ffff001d01e3629900"));
+
+        HeadersMessage hm = (HeadersMessage) bs.deserialize(bais);
+
+        // The first block after the genesis
+        // http://blockexplorer.com/b/1
+        Block block = hm.getBlockHeaders().get(0);
+        String hash = block.getHashAsString();
+        assertEquals(hash, "00000000839a8e6886ab5951d76f411475428afc90947ee320161bbf18eb6048");
+
+        assertEquals(block.transactions.size(), 0);
+
+        assertEquals(Utils.bytesToHexString(block.getMerkleRoot().getBytes()),
+                "0e3e2357e806b6cdb1f70b54c3a3a17b6714ee1f0e68bebb44a74b1efd512098");
+    }
+
+
+    @Test
+    /**
+     * Get 6 headers of blocks 1-6 in the chain
+     */
+    public void testHeaders2() throws Exception {
+        BitcoinSerializer bs = new BitcoinSerializer(NetworkParameters.prodNet(), true,
+                null);
+
+        ByteArrayInputStream bais = new ByteArrayInputStream(Hex.decode("f9beb4d96865616465" +
+                "72730000000000e701000085acd4ea06010000006fe28c0ab6f1b372c1a6a246ae63f74f931e" +
+                "8365e15a089c68d6190000000000982051fd1e4ba744bbbe680e1fee14677ba1a3c3540bf7b1c" +
+                "db606e857233e0e61bc6649ffff001d01e3629900010000004860eb18bf1b1620e37e9490fc8a" +
+                "427514416fd75159ab86688e9a8300000000d5fdcc541e25de1c7a5addedf24858b8bb665c9f36" +
+                "ef744ee42c316022c90f9bb0bc6649ffff001d08d2bd610001000000bddd99ccfda39da1b108ce1" +
+                "a5d70038d0a967bacb68b6b63065f626a0000000044f672226090d85db9a9f2fbfe5f0f9609b387" +
+                "af7be5b7fbb7a1767c831c9e995dbe6649ffff001d05e0ed6d00010000004944469562ae1c2c74" +
+                "d9a535e00b6f3e40ffbad4f2fda3895501b582000000007a06ea98cd40ba2e3288262b28638cec" +
+                "5337c1456aaf5eedc8e9e5a20f062bdf8cc16649ffff001d2bfee0a9000100000085144a84488e" +
+                "a88d221c8bd6c059da090e88f8a2c99690ee55dbba4e00000000e11c48fecdd9e72510ca84f023" +
+                "370c9a38bf91ac5cae88019bee94d24528526344c36649ffff001d1d03e4770001000000fc33f5" +
+                "96f822a0a1951ffdbf2a897b095636ad871707bf5d3162729b00000000379dfb96a5ea8c81700ea4" +
+                "ac6b97ae9a9312b2d4301a29580e924ee6761a2520adc46649ffff001d189c4c9700"));
+
+        HeadersMessage hm = (HeadersMessage) bs.deserialize(bais);
+
+        int nBlocks = hm.getBlockHeaders().size();
+        assertEquals(nBlocks, 6);
+
+        // index 0 block is the number 1 block in the block chain
+        // http://blockexplorer.com/b/1
+        Block zeroBlock = hm.getBlockHeaders().get(0);
+        String zeroBlockHash = zeroBlock.getHashAsString();
+
+        assertEquals("00000000839a8e6886ab5951d76f411475428afc90947ee320161bbf18eb6048",
+                zeroBlockHash);
+        assertEquals(zeroBlock.getNonce(), 2573394689L);
+
+
+        Block thirdBlock = hm.getBlockHeaders().get(3);
+        String thirdBlockHash = thirdBlock.getHashAsString();
+
+        // index 3 block is the number 4 block in the block chain
+        // http://blockexplorer.com/b/4
+        assertEquals("000000004ebadb55ee9096c9a2f8880e09da59c0d68b1c228da88e48844a1485",
+                thirdBlockHash);
+        assertEquals(thirdBlock.getNonce(), 2850094635L);
+    }
+
+
 }