Parse messages

zebra-network/src/protocol/codec.rs

@@ -445,7 +445,7 @@ impl Codec {
     fn read_headers<R: Read>(&self, mut reader: R) -> Result<Message, 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
@@ -462,9 +462,25 @@ impl Codec {
         Ok(Message::Headers(headers))
     }
 
-    fn read_getheaders<R: Read>(&self, mut _reader: R) -> Result<Message, Error> {
-        trace!("getheaders");
-        bail!("unimplemented message type")
+    // XXX This and `read_getblocks` are pretty similar, abstract away?
+    fn read_getheaders<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::GetHeaders {
+            version,
+            block_locator_hashes,
+            hash_stop,
+        })
     }
 
     fn _read_generic_inventory_hash_vector<R: Read>(

zebra-network/src/protocol/message.rs

@@ -188,8 +188,31 @@ pub enum Message {
 
     /// A `getheaders` message.
     ///
+    /// Requests a series of block headers starting right after the
+    /// last known hash in `block_locator_hashes`, up to `hash_stop`
+    /// or 2000 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#getheaders)
-    GetHeaders {/* XXX add fields */},
+    GetHeaders {
+        /// The protocol version.
+        version: Version,
+
+        /// Block locators, from newest back to genesis block.
+        block_locator_hashes: Vec<BlockHeaderHash>,
+
+        /// `BlockHeaderHash` of the last desired block header.
+        ///
+        /// Set to zero to get as many block headers as possible (2000).
+        hash_stop: BlockHeaderHash,
+    },
 
     /// An `inv` message.
     ///