Vote Graph and GHOST-hunting

.editorconfig

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+root = true
+[*]
+indent_style=tab
+indent_size=tab
+tab_width=4
+end_of_line=lf
+charset=utf-8
+trim_trailing_whitespace=true
+max_line_length=120
+insert_final_newline=true
+
+[*.yml]
+indent_style=space
+indent_size=2
+tab_width=8
+end_of_line=lf

Cargo.toml

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+[package]
+name = "finality-afg"
+version = "0.1.0"
+description = "PBFT-based finality gadget for blockchains"
+authors = ["Parity Technologies <admin@parity.io>"]
+
+[dependencies]

README.md

@@ -1,2 +1,4 @@
 # finality-afg
 finality gadget for blockchains, based on PBFT
+
+Implementation in Rust.

src/lib.rs

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+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of finality-afg.
+
+// finality-afg is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// finality-afg is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with finality-afg. If not, see <http://www.gnu.org/licenses/>.
+
+//! Finality gadget for blockchains.
+//!
+//! https://hackmd.io/svMTltnGQsSR1GCjRKOPbw
+
+mod vote_graph;
+
+use std::fmt;
+
+/// A prevote for a block and its ancestors.
+pub struct Prevote<H> {
+	round: u64,
+	target: H,
+	weight: usize,
+}
+
+/// A precommit for a block and its ancestors.
+pub struct Precommit<H> {
+	round: u64,
+	target: H,
+	weight: usize,
+}
+
+#[derive(Clone, PartialEq, Debug)]
+pub enum Error {
+	BlockNotInSubtree,
+}
+
+impl fmt::Display for Error {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		match *self {
+			Error::BlockNotInSubtree => write!(f, "Block not in subtree of base"),
+		}
+	}
+}
+
+impl ::std::error::Error for Error {
+	fn description(&self) -> &str {
+		match *self {
+			Error::BlockNotInSubtree => "Block not in subtree of base",
+		}
+	}
+}
+
+/// Chain context necessary for implementation of the finality gadget.
+pub trait Chain<H> {
+	/// Get the ancestry of a block up to but not including the base hash.
+	/// Should be in reverse order from `block`'s parent.
+	///
+	/// If the block is not a descendent of `base`, returns an error.
+	fn ancestry(&self, base: H, block: H) -> Result<Vec<H>, Error>;
+}