Ensure chain state is at threshold security level before looking for updates.

ethcore/src/client/client.rs

@@ -1377,7 +1377,7 @@ impl BlockChainClient for Client {
 		self.registrar.lock().as_ref()
 			.and_then(|r| r.get_address(&(name.as_bytes().sha3()), "A").ok())
 			.and_then(|a| if a.is_zero() { None } else { Some(a) })
-	} 
+	}
 }
 
 impl MiningBlockChainClient for Client {

ethcore/src/types/blockchain_info.rs

@@ -18,6 +18,7 @@
 
 use util::{U256, H256};
 use header::BlockNumber;
+use types::security_level::SecurityLevel;
 
 /// Information about the blockchain gathered together.
 #[derive(Clone, Debug, Binary)]
@@ -41,3 +42,15 @@ pub struct BlockChainInfo {
 	/// Number of the first block on the best sequence.
 	pub first_block_number: Option<BlockNumber>,
 }
+
+impl BlockChainInfo {
+	/// Determine the security model for the current state.
+	pub fn security_level(&self) -> SecurityLevel {
+		// TODO: Detect SecurityLevel::FullState : https://github.com/ethcore/parity/issues/3834
+		if self.ancient_block_number.is_none() || self.first_block_number.is_none() {
+			SecurityLevel::FullProofOfWork
+		} else {
+			SecurityLevel::PartialProofOfWork(self.best_block_number - self.first_block_number.expect("Guard condition means this is not none"))
+		}
+	}
+}

ethcore/src/types/security_level.rs

@@ -16,13 +16,25 @@
 
 //! Indication of how secure the chain is.
 
+use header::BlockNumber;
+
 /// Indication of how secure the chain is.
 #[derive(Debug, PartialEq, Copy, Clone, Hash, Eq, Binary)]
 pub enum SecurityLevel {
-	/// Chain was synced through manually evaluating all transactions from genesis.
-	Full,
-	/// All blocks are known to have a valid PoW from genesis.
-	Continuous,
-	/// Some headers (the argument) are known to have a valid PoW from genesis.
-	Light(u64),
+	/// All blocks from genesis to chain head are known to have valid state transitions and PoW.
+	FullState,
+	/// All blocks from genesis to chain head are known to have a valid PoW.
+	FullProofOfWork,
+	/// Some recent headers (the argument) are known to have a valid PoW.
+	PartialProofOfWork(BlockNumber),
 }
+
+impl SecurityLevel {
+	/// `true` for `FullPoW`/`FullState`.
+	pub fn is_full(&self) -> bool {
+		match *self {
+			SecurityLevel::FullState | SecurityLevel::FullProofOfWork => true,
+			_ => false,
+		} 
+	}
+}