Parse GetBlock messages

zebra-network/src/protocol/codec.rs

@@ -9,7 +9,7 @@ use failure::Error;
 use tokio::codec::{Decoder, Encoder};
 
 use zebra_chain::{
-    block::BlockHeader,
+    block::{BlockHeader, BlockHeaderHash},
     serialization::{ReadZcashExt, WriteZcashExt, ZcashDeserialize, ZcashSerialize},
     transaction::Transaction,
     types::{BlockHeight, Sha256dChecksum},
@@ -417,9 +417,24 @@ impl Codec {
         bail!("unimplemented message type")
     }
 
-    fn read_getblocks<R: Read>(&self, mut _reader: R) -> Result<Message, Error> {
-        trace!("getblocks");
-        bail!("unimplemented message type")
+    fn read_getblocks<R: Read>(&self, mut reader: R) -> Result<Message, Error> {
+        let version = Version(reader.read_u32::<LittleEndian>()?);
+
+        let count = reader.read_compactsize()? as usize;
+        let max_count = self.builder.max_len / 32;
+        let mut block_locator_hashes = Vec::with_capacity(std::cmp::min(count, max_count));
+
+        for _ in 0..count {
+            block_locator_hashes.push(BlockHeaderHash(reader.read_32_bytes()?));
+        }
+
+        let hash_stop = BlockHeaderHash(reader.read_32_bytes()?);
+
+        Ok(Message::GetBlocks {
+            version,
+            block_locator_hashes,
+            hash_stop,
+        })
     }
 
     /// Deserialize a `headers` message.
@@ -458,7 +473,7 @@ impl Codec {
     ) -> Result<Vec<InventoryHash>, Error> {
         let count = reader.read_compactsize()? as usize;
         // Preallocate a buffer, performing a single allocation in the honest
-        // case. Although the size of the recieved data buffer is bounded by the
+        // case. Although the size of the received data buffer is bounded by the
         // codec's max_len field, it's still possible for someone to send a
         // short message with a large count field, so if we naively trust
         // the count field we could be tricked into preallocating a large

zebra-network/src/protocol/message.rs

@@ -4,7 +4,7 @@ use std::net;
 
 use chrono::{DateTime, Utc};
 
-use zebra_chain::block::{Block, BlockHeader};
+use zebra_chain::block::{Block, BlockHeader, BlockHeaderHash};
 use zebra_chain::{transaction::Transaction, types::BlockHeight};
 
 use crate::meta_addr::MetaAddr;
@@ -144,8 +144,36 @@ pub enum Message {
 
     /// A `getblocks` message.
     ///
+    /// Requests the list of blocks starting right after the last
+    /// known hash in `block_locator_hashes`, up to `hash_stop` or 500
+    /// blocks, whichever comes first.
+    ///
+    /// You can send in fewer known hashes down to a minimum of just
+    /// one hash. However, the purpose of the block locator object is
+    /// to detect a wrong branch in the caller's main chain. If the
+    /// peer detects that you are off the main chain, it will send in
+    /// block hashes which are earlier than your last known block. So
+    /// if you just send in your last known hash and it is off the
+    /// main chain, the peer starts over at block #1.
+    ///
     /// [Bitcoin reference](https://en.bitcoin.it/wiki/Protocol_documentation#getblocks)
-    GetBlocks {/* XXX add fields */},
+    // The locator hashes are processed by a node in the order as they
+    // appear in the message. If a block hash is found in the node's
+    // main chain, the list of its children is returned back via the
+    // inv message and the remaining locators are ignored, no matter
+    // if the requested limit was reached, or not.
+    GetBlocks {
+        /// The protocol version.
+        version: Version,
+
+        /// Block locators, from newest back to genesis block.
+        block_locator_hashes: Vec<BlockHeaderHash>,
+
+        /// `BlockHeaderHash` of the last desired block.
+        ///
+        /// Set to zero to get as many blocks as possible (500).
+        hash_stop: BlockHeaderHash,
+    },
 
     /// A `headers` message.
     ///