Merge rust-bitcoin#515: Add Inventory::network_hash() method

3d524e0 Add Inventory::network_hash() method (Steven Roose)

Pull request description:

  I'm not positive we won't ever had inv items that are not `sha256d::Hash`, though. I would expect them to stay like that, but we never know.

  Would accept that as a reasonable objection against this helper.

ACKs for top commit:
  apoelstra:
    ACK 3d524e0
  tcharding:
    ACK 3d524e0

Tree-SHA512: 97d64b08ff99dbec2d907bdb98aa41ede4a15b988551ad8dd87a10ac5c9750ae4d516bb558c1e4f2171612777355c2baf1ffbe671cb92320a1af64d73bd150dd

Author: apoelstra

bitcoin/src/network/message_blockdata.rs

@@ -42,6 +42,24 @@ pub enum Inventory {
     },
 }
 
+impl Inventory {
+    /// Return the item value represented as a SHA256-d hash.
+    ///
+    /// Returns [None] only for [Inventory::Error].
+    pub fn network_hash(&self) -> Option<[u8; 32]> {
+        match self {
+            Inventory::Error => None,
+            Inventory::Transaction(t) => Some(t.to_byte_array()),
+            Inventory::Block(b) => Some(b.to_byte_array()),
+            Inventory::CompactBlock(b) => Some(b.to_byte_array()),
+            Inventory::WTx(t) => Some(t.to_byte_array()),
+            Inventory::WitnessTransaction(t) => Some(t.to_byte_array()),
+            Inventory::WitnessBlock(b) => Some(b.to_byte_array()),
+            Inventory::Unknown { hash, .. } => Some(*hash),
+        }
+    }
+}
+
 impl Encodable for Inventory {
     #[inline]
     fn consensus_encode<W: io::Write + ?Sized>(&self, w: &mut W) -> Result<usize, io::Error> {