From 4152d9fc0cca9cb129994e3bd8967c7613e306af Mon Sep 17 00:00:00 2001
From: Austin Abell <austinabell8@gmail.com>
Date: Thu, 23 Jan 2020 09:29:54 -0500
Subject: [PATCH] Build block header from pre pow data and proof (#3178)

* Implement validation and generation of block header by proof and pre pow

* Optimize

* handle missed ser result errors and test invalid pre_pow

* switch to specific error mapping

* clean import
---
 core/src/core/block.rs | 23 ++++++++++++++++++++++-
 core/tests/block.rs    | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/core/src/core/block.rs b/core/src/core/block.rs
index c24df1a2b..bc15624eb 100644
--- a/core/src/core/block.rs
+++ b/core/src/core/block.rs
@@ -25,7 +25,10 @@ use crate::core::{
 };
 use crate::global;
 use crate::pow::{verify_size, Difficulty, Proof, ProofOfWork};
-use crate::ser::{self, FixedLength, PMMRable, Readable, Reader, Writeable, Writer};
+use crate::ser::{
+	self, deserialize_default, serialize_default, FixedLength, PMMRable, Readable, Reader,
+	Writeable, Writer,
+};
 use chrono::naive::{MAX_DATE, MIN_DATE};
 use chrono::prelude::{DateTime, NaiveDateTime, Utc};
 use chrono::Duration;
@@ -34,6 +37,7 @@ use std::collections::HashSet;
 use std::fmt;
 use std::iter::FromIterator;
 use std::sync::Arc;
+use util::from_hex;
 use util::RwLock;
 use util::{secp, static_secp_instance};
 
@@ -350,6 +354,23 @@ impl BlockHeader {
 		header_buf
 	}
 
+	/// Constructs a header given pre_pow string, nonce, and proof
+	pub fn from_pre_pow_and_proof(
+		pre_pow: String,
+		nonce: u64,
+		proof: Proof,
+	) -> Result<Self, Error> {
+		// Convert hex pre pow string
+		let mut header_bytes = from_hex(pre_pow)
+			.map_err(|e| Error::Serialization(ser::Error::HexError(e.to_string())))?;
+		// Serialize and append serialized nonce and proof
+		serialize_default(&mut header_bytes, &nonce)?;
+		serialize_default(&mut header_bytes, &proof)?;
+
+		// Deserialize header from constructed bytes
+		Ok(deserialize_default(&mut &header_bytes[..])?)
+	}
+
 	/// Total difficulty accumulated by the proof of work on this header
 	pub fn total_difficulty(&self) -> Difficulty {
 		self.pow.total_difficulty
diff --git a/core/tests/block.rs b/core/tests/block.rs
index 69a03fe0a..7b42da707 100644
--- a/core/tests/block.rs
+++ b/core/tests/block.rs
@@ -26,6 +26,7 @@ use crate::core::core::{
 };
 use crate::core::libtx::build::{self, input, output};
 use crate::core::libtx::ProofBuilder;
+use crate::core::pow::Proof;
 use crate::core::{global, ser};
 use chrono::Duration;
 use grin_core as core;
@@ -569,3 +570,36 @@ fn wrong_amount_range_proof() {
 		_ => panic!("Bad range proof should be invalid"),
 	}
 }
+
+#[test]
+fn validate_header_proof() {
+	let keychain = ExtKeychain::from_random_seed(false).unwrap();
+	let builder = ProofBuilder::new(&keychain);
+	let prev = BlockHeader::default();
+	let key_id = ExtKeychain::derive_key_id(1, 1, 0, 0, 0);
+	let b = new_block(vec![], &keychain, &builder, &prev, &key_id);
+
+	let mut header_buf = vec![];
+	{
+		let mut writer = ser::BinWriter::default(&mut header_buf);
+		b.header.write_pre_pow(&mut writer).unwrap();
+		b.header.pow.write_pre_pow(&mut writer).unwrap();
+	}
+	let pre_pow = util::to_hex(header_buf);
+
+	let reconstructed = BlockHeader::from_pre_pow_and_proof(
+		pre_pow,
+		b.header.pow.nonce,
+		b.header.pow.proof.clone(),
+	)
+	.unwrap();
+	assert_eq!(reconstructed, b.header);
+
+	// assert invalid pre_pow returns error
+	assert!(BlockHeader::from_pre_pow_and_proof(
+		"0xaf1678".to_string(),
+		b.header.pow.nonce,
+		b.header.pow.proof.clone(),
+	)
+	.is_err());
+}