new state api state_getKeys to expose storage keys (#1380)

substrate/core/state-machine/src/backend.rs

@@ -86,6 +86,9 @@ pub trait Backend<H: Hasher> {
 	/// Get all key/value pairs into a Vec.
 	fn pairs(&self) -> Vec<(Vec<u8>, Vec<u8>)>;
 
+	/// Get all keys with given prefix
+	fn keys(&self, prefix: &Vec<u8>) -> Vec<Vec<u8>>;
+
 	/// Try convert into trie backend.
 	fn try_into_trie_backend(self) -> Option<TrieBackend<Self::TrieBackendStorage, H>>;
 }
@@ -283,6 +286,10 @@ impl<H: Hasher> Backend<H> for InMemory<H> where H::Out: HeapSizeOf {
 		self.inner.get(&None).into_iter().flat_map(|map| map.iter().map(|(k, v)| (k.clone(), v.clone()))).collect()
 	}
 
+	fn keys(&self, prefix: &Vec<u8>) -> Vec<Vec<u8>> {
+		self.inner.get(&None).into_iter().flat_map(|map| map.keys().filter(|k| k.starts_with(prefix)).cloned()).collect()
+	}
+
 	fn try_into_trie_backend(self) -> Option<TrieBackend<Self::TrieBackendStorage, H>> {
 		let mut mdb = MemoryDB::default();	// TODO: should be more correct and use ::new()
 		let mut root = None;

substrate/core/state-machine/src/proving_backend.rs

@@ -146,6 +146,10 @@ impl<'a, S, H> Backend<H> for ProvingBackend<'a, S, H>
 		self.backend.pairs()
 	}
 
+	fn keys(&self, prefix: &Vec<u8>) -> Vec<Vec<u8>> {
+		self.backend.keys(prefix)
+	}
+
 	fn storage_root<I>(&self, delta: I) -> (H::Out, MemoryDB<H>)
 		where I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>
 	{

substrate/core/state-machine/src/trie_backend.rs

@@ -105,6 +105,26 @@ impl<S: TrieBackendStorage<H>, H: Hasher> Backend<H> for TrieBackend<S, H> where
 		}
 	}
 
+	fn keys(&self, prefix: &Vec<u8>) -> Vec<Vec<u8>> {
+		let mut read_overlay = MemoryDB::default();	// TODO: use new for correctness
+		let eph = Ephemeral::new(self.essence.backend_storage(), &mut read_overlay);
+
+		let collect_all = || -> Result<_, Box<TrieError<H::Out>>> {
+			let trie = TrieDB::<H>::new(&eph, self.essence.root())?;
+			let mut v = Vec::new();
+			for x in trie.iter()? {
+				let (key, _) = x?;
+				if key.starts_with(prefix) {
+					v.push(key.to_vec());
+				}
+			}
+
+			Ok(v)
+		};
+
+		collect_all().map_err(|e| debug!(target: "trie", "Error extracting trie keys: {}", e)).unwrap_or_default()
+	}
+
 	fn storage_root<I>(&self, delta: I) -> (H::Out, MemoryDB<H>)
 		where I: IntoIterator<Item=(Vec<u8>, Option<Vec<u8>>)>
 	{