refactor the state_sync to handle the long fork (#1902)

* split horizon into two explicit values for cut through and txhashset request

* let node which has 2-7 days of history be able to handle forks larger than 2 days

* add test simulate_long_fork

* add pause/resume feature on p2p for tests

* refactor the state_sync

* ignore the test case simulate_long_fork for normal Travis-CI

* refactor function check_txhashset_needed to be shared with body_sync

* fix: state TxHashsetDone should allow header sync

core/src/consensus.rs

@@ -92,6 +92,14 @@ pub const MAX_SECONDARY_SCALING: u64 = 8 << 11;
 /// easier to reason about.
 pub const CUT_THROUGH_HORIZON: u32 = WEEK_HEIGHT as u32;
 
+/// Default number of blocks in the past to determine the height where we request
+/// a txhashset (and full blocks from). Needs to be long enough to not overlap with
+/// a long reorg.
+/// Rational behind the value is the longest bitcoin fork was about 30 blocks, so 5h.
+/// We add an order of magnitude to be safe and round to 2x24h of blocks to make it
+/// easier to reason about.
+pub const STATE_SYNC_THRESHOLD: u32 = 2 * DAY_HEIGHT as u32;
+
 /// Weight of an input when counted against the max block weight capacity
 pub const BLOCK_INPUT_WEIGHT: usize = 1;
 

core/src/global.rs

@@ -20,7 +20,7 @@ use consensus::HeaderInfo;
 use consensus::{
 	graph_weight, BASE_EDGE_BITS, BLOCK_TIME_SEC, COINBASE_MATURITY, CUT_THROUGH_HORIZON,
 	DAY_HEIGHT, DIFFICULTY_ADJUST_WINDOW, INITIAL_DIFFICULTY, PROOFSIZE, SECOND_POW_EDGE_BITS,
-	UNIT_DIFFICULTY
+	STATE_SYNC_THRESHOLD, UNIT_DIFFICULTY,
 };
 use pow::{self, CuckatooContext, EdgeType, PoWContext};
 /// An enum collecting sets of parameters used throughout the
@@ -51,7 +51,10 @@ pub const AUTOMATED_TESTING_COINBASE_MATURITY: u64 = 3;
 pub const USER_TESTING_COINBASE_MATURITY: u64 = 3;
 
 /// Testing cut through horizon in blocks
-pub const TESTING_CUT_THROUGH_HORIZON: u32 = 20;
+pub const TESTING_CUT_THROUGH_HORIZON: u32 = 70;
+
+/// Testing state sync threshold in blocks
+pub const TESTING_STATE_SYNC_THRESHOLD: u32 = 20;
 
 /// Testing initial graph weight
 pub const TESTING_INITIAL_GRAPH_WEIGHT: u32 = 1;
@@ -237,6 +240,16 @@ pub fn cut_through_horizon() -> u32 {
 	}
 }
 
+/// Threshold at which we can request a txhashset (and full blocks from)
+pub fn state_sync_threshold() -> u32 {
+	let param_ref = CHAIN_TYPE.read();
+	match *param_ref {
+		ChainTypes::AutomatedTesting => TESTING_STATE_SYNC_THRESHOLD,
+		ChainTypes::UserTesting => TESTING_STATE_SYNC_THRESHOLD,
+		_ => STATE_SYNC_THRESHOLD,
+	}
+}
+
 /// Are we in automated testing mode?
 pub fn is_automated_testing_mode() -> bool {
 	let param_ref = CHAIN_TYPE.read();