From 852233e4ac1b3109e2b73f876edaba68052f0c2f Mon Sep 17 00:00:00 2001
From: Gav Wood <i@gavwood.com>
Date: Sat, 28 Nov 2015 03:08:57 +0100
Subject: [PATCH] HashDB and initial OverlayDB

---
 src/hashdb.rs   |  6 +++---
 src/lib.rs      |  1 +
 src/memorydb.rs | 24 ++++++++++++++++++++----
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/src/hashdb.rs b/src/hashdb.rs
index d023fe70d..48f5182bc 100644
--- a/src/hashdb.rs
+++ b/src/hashdb.rs
@@ -14,10 +14,10 @@ pub trait HashDB {
 	///   let mut m = MemoryDB::new();
 	///   let hello_bytes = "Hello world!".as_bytes();
 	///   let hash = m.insert(hello_bytes);
-	///   assert_eq!(m.lookup(&hash).unwrap(), &hello_bytes);
+	///   assert_eq!(m.lookup(&hash).unwrap(), hello_bytes);
 	/// }
 	/// ```
-	fn lookup(&self, key: &H256) -> Option<&Bytes>;
+	fn lookup(&self, key: &H256) -> Option<Bytes>;
 
 	/// Check for the existance of a hash-key.
 	///
@@ -75,7 +75,7 @@ pub trait HashDB {
 	///   m.insert(d);	// OK - now it's "empty" again.
 	///   assert!(!m.exists(key));
 	///   m.insert(d);	// OK - now we've
-	///   assert_eq!(m.lookup(key).unwrap(), &d);
+	///   assert_eq!(m.lookup(key).unwrap(), d);
 	/// }
 	/// ```
 	fn kill(&mut self, key: &H256);
diff --git a/src/lib.rs b/src/lib.rs
index f7f446ddc..cb03d00b7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -16,6 +16,7 @@ pub mod db;
 pub mod sha3;
 pub mod hashdb;
 pub mod memorydb;
+pub mod overlaydb;
 pub mod bloom;
 
 //pub mod network;
diff --git a/src/memorydb.rs b/src/memorydb.rs
index 55fdc12da..2f54b4524 100644
--- a/src/memorydb.rs
+++ b/src/memorydb.rs
@@ -25,7 +25,7 @@ use std::collections::HashMap;
 ///
 ///   let k = m.insert(d);
 ///   assert!(m.exists(&k));
-///   assert_eq!(m.lookup(&k).unwrap(), &d);
+///   assert_eq!(m.lookup(&k).unwrap(), d);
 ///
 ///   m.insert(d);
 ///   assert!(m.exists(&k));
@@ -38,7 +38,7 @@ use std::collections::HashMap;
 ///
 ///   m.insert(d);
 ///   assert!(m.exists(&k));
-///   assert_eq!(m.lookup(&k).unwrap(), &d);
+///   assert_eq!(m.lookup(&k).unwrap(), d);
 ///
 ///   m.kill(&k);
 ///   assert!(!m.exists(&k));
@@ -84,12 +84,27 @@ impl MemoryDB {
 			.collect();
 		for empty in empties { self.data.remove(&empty); }
 	}
+
+	/// Grab the number of references a particular `key` has. Returns None if the key
+	/// doesn't exist.
+	fn refs(&self, key: &H256) -> Option<i32> {
+		self.data.get(key).map(|&(_, rc)| rc)
+	}
+
+	/// Grab the value associated with a particular `key`. Returns None if the key
+	/// doesn't exist.
+	///
+	/// Even when Some is returned, this is only guaranteed to return something useful
+	/// when `refs(key) > 0`.
+	fn value(&self, key: &H256) -> Option<&Bytes> {
+		self.data.get(key).map(|&(ref d, _)| d)
+	}
 }
 
 impl HashDB for MemoryDB {
-	fn lookup(&self, key: &H256) -> Option<&Bytes> {
+	fn lookup(&self, key: &H256) -> Option<Bytes> {
 		match self.data.get(key) {
-			Some(&(ref d, rc)) if rc > 0 => Some(d),
+			Some(&(ref d, rc)) if rc > 0 => Some(d.clone()),
 			_ => None
 		}
 	}
@@ -116,6 +131,7 @@ impl HashDB for MemoryDB {
 		}
 		key
 	}
+
 	fn kill(&mut self, key: &H256) {
 		if match self.data.get_mut(key) {
 			Some(&mut (_, ref mut x)) => { *x -= 1; false }