fetch gas price corpus from network when needed

ethcore/light/src/client/header_chain.rs

@@ -241,6 +241,14 @@ impl HeaderChain {
 		self.block_header(BlockId::Latest).expect("Header for best block always stored; qed")
 	}
 
+	/// Get an iterator over a block and its ancestry.
+	pub fn ancestry_iter(&self, start: BlockId) -> AncestryIter {
+		AncestryIter {
+			next: self.block_header(start),
+			chain: self,
+		}
+	}
+
 	/// Get the nth CHT root, if it's been computed.
 	///
 	/// CHT root 0 is from block `1..2048`.
@@ -295,6 +303,25 @@ impl HeapSizeOf for HeaderChain {
 	}
 }
 
+/// Iterator over a block's ancestry.
+pub struct AncestryIter<'a> {
+	next: Option<encoded::Header>,
+	chain: &'a HeaderChain,
+}
+
+impl<'a> Iterator for AncestryIter<'a> {
+	type Item = encoded::Header;
+
+	fn next(&mut self) -> Option<encoded::Header> {
+		let next = self.next.take();
+		if let Some(p_hash) = next.as_ref().map(|hdr| hdr.parent_hash()) {
+			self.next = self.chain.block_header(BlockId::Hash(p_hash));
+		}
+
+		next
+	}
+}
+
 #[cfg(test)]
 mod tests {
 	use super::HeaderChain;

ethcore/light/src/client/mod.rs

@@ -33,7 +33,7 @@ use io::IoChannel;
 
 use util::{Bytes, H256, Mutex, RwLock};
 
-use self::header_chain::HeaderChain;
+use self::header_chain::{AncestryIter, HeaderChain};
 
 pub use self::service::Service;
 
@@ -62,6 +62,9 @@ pub trait LightChainClient: Send + Sync {
 	/// Get the best block header.
 	fn best_block_header(&self) -> encoded::Header;
 
+	/// Get an iterator over a block and its ancestry.
+	fn ancestry_iter<'a>(&'a self, start: BlockId) -> Box<Iterator<Item=encoded::Header> + 'a>;
+
 	/// Get the signing network ID.
 	fn signing_network_id(&self) -> Option<u64>;
 
@@ -167,6 +170,11 @@ impl Client {
 		self.chain.best_header()
 	}
 
+	/// Get an iterator over a block and its ancestry.
+	pub fn ancestry_iter(&self, start: BlockId) -> AncestryIter {
+		self.chain.ancestry_iter(start)
+	}
+
 	/// Get the signing network id.
 	pub fn signing_network_id(&self) -> Option<u64> {
 		self.engine.signing_network_id(&self.latest_env_info())
@@ -269,6 +277,10 @@ impl LightChainClient for Client {
 		Client::best_block_header(self)
 	}
 
+	fn ancestry_iter<'a>(&'a self, start: BlockId) -> Box<Iterator<Item=encoded::Header> + 'a> {
+		Box::new(Client::ancestry_iter(self, start))
+	}
+
 	fn signing_network_id(&self) -> Option<u64> {
 		Client::signing_network_id(self)
 	}