From 521d3d53eda4bfd835a984b4c6cb180b68e02273 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Sun, 24 Apr 2016 19:37:13 +0930
Subject: [PATCH] chaintopology: keep track of the bitcoin block topology.

This allows us to track precise transaction depth ourselves,
particularly in the case of branching.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
 daemon/Makefile        |   2 +
 daemon/chaintopology.c | 429 +++++++++++++++++++++++++++++++++++++++++
 daemon/chaintopology.h |  12 ++
 daemon/lightningd.c    |   4 +
 daemon/lightningd.h    |   3 +
 daemon/timeout.h       |   1 +
 6 files changed, 451 insertions(+)
 create mode 100644 daemon/chaintopology.c
 create mode 100644 daemon/chaintopology.h

diff --git a/daemon/Makefile b/daemon/Makefile
index 1e0554823..dbc62ca90 100644
--- a/daemon/Makefile
+++ b/daemon/Makefile
@@ -15,6 +15,7 @@ DAEMON_LIB_OBJS := $(DAEMON_LIB_SRC:.c=.o)
 
 DAEMON_SRC :=					\
 	daemon/bitcoind.c			\
+	daemon/chaintopology.c			\
 	daemon/controlled_time.c		\
 	daemon/cryptopkt.c			\
 	daemon/dns.c				\
@@ -40,6 +41,7 @@ DAEMON_JSMN_HEADERS := daemon/jsmn/jsmn.h
 
 DAEMON_HEADERS :=				\
 	daemon/bitcoind.h			\
+	daemon/chaintopology.h			\
 	daemon/configdir.h			\
 	daemon/controlled_time.h		\
 	daemon/cryptopkt.h			\
diff --git a/daemon/chaintopology.c b/daemon/chaintopology.c
new file mode 100644
index 000000000..9e662e824
--- /dev/null
+++ b/daemon/chaintopology.c
@@ -0,0 +1,429 @@
+#include "bitcoind.h"
+#include "chaintopology.h"
+#include "lightningd.h"
+#include "log.h"
+#include "timeout.h"
+#include "watch.h"
+#include <ccan/ptrint/ptrint.h>
+#include <ccan/structeq/structeq.h>
+
+static struct timeout topology_timeout;
+
+struct tx_in_block {
+	struct list_node list;
+	struct txwatch *w;
+	struct block *block;
+};
+
+struct block {
+	int height;
+
+	/* We can have a single parent */
+	struct sha256_double prevblkid;
+	/* ... but multiple children. */
+	struct block **nexts;
+
+	/* Key for hash table */
+	struct sha256_double blkid;
+	u32 mediantime;
+
+	/* Transactions in this block we care about */
+	struct list_head txs;
+};
+
+/* Hash blocks by sha */
+static const struct sha256_double *keyof_block_map(const struct block *b)
+{
+	return &b->blkid;
+}
+
+static size_t hash_sha(const struct sha256_double *key)
+{
+	size_t ret;
+
+	memcpy(&ret, key, sizeof(ret));
+	return ret;
+}
+
+static bool block_eq(const struct block *b, const struct sha256_double *key)
+{
+	return structeq(&b->blkid, key);
+}
+HTABLE_DEFINE_TYPE(struct block, keyof_block_map, hash_sha, block_eq, block_map);
+
+struct topology {
+	struct block **tips;
+	struct sha256_double *newtips;
+	struct block_map block_map;
+};
+
+static struct block *connect_blocks(struct topology *topo,
+				    const struct sha256_double *blkid)
+{
+	struct block *b = block_map_get(&topo->block_map, blkid);
+	struct block *prev;
+	size_t n;
+
+	/* Hooked in already? */
+	if (b->height != -1)
+		return b;
+
+	prev = connect_blocks(topo, &b->prevblkid);
+	b->height = prev->height + 1;
+	n = tal_count(prev->nexts);
+	tal_resize(&prev->nexts, n+1);
+	prev->nexts[n] = b;
+
+	return b;
+}
+
+/* This is expensive, but reorgs are usually short and txs are few.
+ *
+ * B                TX
+ *  o--------o-------o
+ *   \
+ *    \      TX
+ *     ------o-------o-------o
+ *
+ *
+ * This counts as depth 1, not 2, since the top fork may be extended.
+ *
+ * B            
+ *  o--------o-------o
+ *   \
+ *    \      TX
+ *     ------o-------o-------o
+ *
+ * This TX counts as depth 0 by our algorithm, which treats "not in chain"
+ * as "next in chain".
+ *
+ * B            
+ *  o--------o-------o-------o
+ *   \
+ *    \      TX
+ *     ------o-------o-------o
+ *
+ * This counts as -1.
+ *
+ * We calculate the "height" of a tx (subtraction from best tips gives us the 
+ * the depth).
+ *
+ * 1) The height of a tx in a particular branch is the height of the block it
+ *    appears in, or the max height + 1 (assuming it's pending).
+ * 2) The overall height of a tx is the maximum height on any branch.
+ */
+
+static bool tx_in_block(const struct block *b, const struct txwatch *w)
+{
+	struct tx_in_block *tx;
+
+	list_for_each(&b->txs, tx, list) {
+		if (tx->w == w)
+			return true;
+	}
+	return false;
+}
+
+/* FIXME: Cache this on the tips. */
+static size_t get_tx_branch_height(const struct topology *topo,
+				   const struct block *tip,
+				   const struct txwatch *w,
+				   size_t max)
+{
+	const struct block *b;
+
+	for (b = tip; b; b = block_map_get(&topo->block_map, &b->prevblkid)) {
+		if (tx_in_block(b, w))
+			return b->height;
+		/* Don't bother returning less than max */
+		if (b->height < max)
+			return max;
+	}
+
+	return tip->height + 1;
+}
+
+size_t get_tx_depth(struct lightningd_state *dstate, const struct txwatch *w)
+{
+	const struct topology *topo = dstate->topology;
+	size_t i, max = 0, longest = 0;
+
+	/* Calculate tx height. */
+	for (i = 0; i < tal_count(topo->tips); i++) {
+		size_t h = get_tx_branch_height(topo, topo->tips[i], w, max);
+		if (h > max)
+			max = h;
+
+		/* Grab longest tip while we're here. */
+		if (topo->tips[i]->height > longest)
+			longest = topo->tips[i]->height;
+	}
+
+	return longest + 1 - max;
+}
+
+#if 0
+static void reevaluate_txs_from(struct lightningd_state *dstate,
+				struct block *common,
+				struct block *b)
+{
+	struct topology *topo = dstate->topology;
+	size_t i;
+	struct tx_in_block *tx;
+
+	/* Careful!  Callbacks could cause arbitrary txs to be deleted. */
+again:
+	b->tx_deleted = false;
+
+	list_for_each(&b->txs, tx, list) {
+		size_t dist = get_tx_distance(common, tx->w);
+		int depth;
+
+		/* Worst case, distance is one past tips. */
+		depth = topo->tips[0]->height - (b->height + dist);
+		assert(depth >= -1);
+
+#if 0 /* When we replace notifications */
+		if (tx->w->depth != depth) {
+			tx->w->depth = depth;
+			tx->w->cb(tx->w->peer, depth, tx->w->cbdata);
+			if (b->tx_deleted)
+				goto again;
+		}
+#endif
+	}
+
+	for (i = 0; i < tal_count(b->nexts); i++)
+		reevaluate_txs_from(dstate, common, b->nexts[i]);
+}
+
+static struct block *find_common(struct topology *topo,
+				 struct block *a, struct block *b)
+{
+	/* Special case for first time, when we have no previous tips */
+	if (!a)
+		return b;
+	    
+	/* Get to same height to start. */ 
+	while (a->height > b->height)
+		a = block_map_get(&topo->block_map, &a->prevblkid);
+	while (b->height > a->height)
+		b = block_map_get(&topo->block_map, &b->prevblkid);
+
+	while (a != b) {
+		a = block_map_get(&topo->block_map, &a->prevblkid);
+		b = block_map_get(&topo->block_map, &b->prevblkid);
+	}
+	return a;
+}
+#endif
+
+static void topology_changed(struct lightningd_state *dstate)
+{
+	struct topology *topo = dstate->topology;
+	size_t i;
+
+#if 0
+	struct block *common = NULL;
+
+	/* topo->tips is NULL for very first time. */
+	if (topo->tips) {
+		for (i = 0; i < tal_count(topo->tips); i++)
+			common = find_common(topo, common, topo->tips[i]);
+	}
+#endif
+
+	tal_free(topo->tips);
+	topo->tips = tal_arr(topo, struct block *, tal_count(topo->newtips));
+	for (i = 0; i < tal_count(topo->newtips); i++)
+		topo->tips[i] = connect_blocks(topo, &topo->newtips[i]);
+
+	/* FIXME: Tell watch code to re-evaluate all txs. */
+}
+
+static void remove_tx(struct tx_in_block *t)
+{
+	list_del_from(&t->block->txs, &t->list);
+}
+
+static void add_tx_to_block(struct block *b, struct txwatch *w)
+{
+	/* We attach this to watch, so removed when that is */
+	struct tx_in_block *t = tal(w, struct tx_in_block);
+
+	t->block = b;
+	t->w = w;
+	list_add_tail(&b->txs, &t->list);
+	tal_add_destructor(t, remove_tx);
+}
+
+static struct block *add_block(struct lightningd_state *dstate,
+			       struct sha256_double *blkid,
+			       struct sha256_double *prevblock,
+			       struct sha256_double *txids,
+			       u32 mediantime)
+{
+	size_t i;
+	struct topology *topo = dstate->topology;
+	struct block *b = tal(topo, struct block);
+
+	assert(!block_map_get(&topo->block_map, blkid));
+
+	/* We fill these out in topology_changed */
+	b->height = -1;
+	b->nexts = tal_arr(b, struct block *, 0);
+
+	b->mediantime = mediantime;
+	b->blkid = *blkid;
+	b->prevblkid = *prevblock;
+
+	/* See if any of those txids are interesting. */
+	list_head_init(&b->txs);
+	for (i = 1; i < tal_count(txids); i++) {
+		struct txwatch *w;
+
+		w = txwatch_hash_get(&dstate->txwatches, &txids[i]);
+		if (w)
+			add_tx_to_block(b, w);
+	}
+
+	block_map_add(&topo->block_map, b);
+	return b;
+}
+
+static void gather_blocks(struct lightningd_state *dstate,
+			  struct sha256_double *blkid,
+			  struct sha256_double *prevblock,
+			  struct sha256_double *txids,
+			  u32 mediantime,
+			  ptrint_t *p)
+{
+	struct topology *topo = dstate->topology;
+	ptrdiff_t i;
+
+	add_block(dstate, blkid, prevblock, txids, mediantime);
+
+	/* Recurse if we need prev. */
+	if (!block_map_get(&topo->block_map, prevblock)) {
+		bitcoind_getblock(dstate, prevblock, gather_blocks, p);
+		return;
+	}
+
+	/* Recurse if more tips to map. */
+	for (i = ptr2int(p) + 1; i < tal_count(topo->newtips); i++) {
+		if (!block_map_get(&topo->block_map, &topo->newtips[i])) {
+			bitcoind_getblock(dstate, &topo->newtips[i],
+					  gather_blocks, int2ptr(i));
+			return;
+		}
+	}
+
+	/* All done. */
+	topology_changed(dstate);
+
+	refresh_timeout(dstate, &topology_timeout);
+}
+
+static bool tips_changed(struct sha256_double *blockids, struct block **tips)
+{
+	size_t i;
+
+	/* First time */
+	if (!tips)
+		return true;
+
+	if (tal_count(blockids) != tal_count(tips))
+		return true;
+
+	for (i = 0; i < tal_count(tips); i++)
+		if (!structeq(&blockids[i], &tips[i]->blkid))
+			return true;
+	return false;
+}
+	
+static void check_chaintips(struct lightningd_state *dstate,
+			    struct sha256_double *blockids,
+			    void *arg)
+{
+	size_t i;
+	struct topology *topo = dstate->topology;
+
+	/* We assume chaintip ordering: if we're wrong, it's just slow */
+	if (!tips_changed(blockids, topo->tips))
+		goto out;
+
+	/* Start iterating on first unknown tip. */
+	topo->newtips = tal_steal(topo, blockids);
+	for (i = 0; i < tal_count(topo->newtips); i++) {
+		if (block_map_get(&topo->block_map, &topo->newtips[i]))
+			continue;
+		bitcoind_getblock(dstate, &topo->newtips[i], gather_blocks,
+				  int2ptr(i));
+		return;
+	}
+
+	log_unusual(dstate->base_log, "Chaintips changed but all blocks known?");
+	topology_changed(dstate);
+
+out:
+	refresh_timeout(dstate, &topology_timeout);
+}
+
+static void start_poll_chaintips(struct lightningd_state *dstate)
+{
+	if (!list_empty(&dstate->bitcoin_req)) {
+		log_unusual(dstate->base_log,
+			    "Delaying start poll: commands in progress");
+		refresh_timeout(dstate, &topology_timeout);
+	} else
+		bitcoind_get_chaintips(dstate, check_chaintips, NULL);
+}
+
+static void init_topo(struct lightningd_state *dstate,
+		      struct sha256_double *blkid,
+		      struct sha256_double *prevblock,
+		      struct sha256_double *txids,
+		      u32 mediantime,
+		      ptrint_t *p)
+{
+	struct block *b;
+
+	b = add_block(dstate, blkid, prevblock, txids, mediantime);
+	b->height = ptr2int(p);
+
+	/* Now grab chaintips immediately. */
+	bitcoind_get_chaintips(dstate, check_chaintips, NULL);
+}
+
+static void get_init_block(struct lightningd_state *dstate,
+			   const struct sha256_double *blkid,
+			   ptrint_t *blknum)
+{
+	bitcoind_getblock(dstate, blkid, init_topo, blknum);
+}
+
+static void get_init_blockhash(struct lightningd_state *dstate, u32 blockcount,
+			       void *unused)
+{
+	u32 start;
+
+	if (blockcount < 100)
+		start = 0;
+	else
+		start = blockcount - 100;
+
+	/* Start topology from 100 blocks back. */
+	bitcoind_getblockhash(dstate, start, get_init_block, int2ptr(start));
+}
+
+void setup_topology(struct lightningd_state *dstate)
+{
+	dstate->topology = tal(dstate, struct topology);
+	dstate->topology->tips = NULL;
+	dstate->topology->newtips = NULL;
+	block_map_init(&dstate->topology->block_map);
+
+	init_timeout(&topology_timeout, dstate->config.poll_seconds,
+		     start_poll_chaintips, dstate);
+	bitcoind_getblockcount(dstate, get_init_blockhash, NULL);
+}
diff --git a/daemon/chaintopology.h b/daemon/chaintopology.h
new file mode 100644
index 000000000..f99ce7769
--- /dev/null
+++ b/daemon/chaintopology.h
@@ -0,0 +1,12 @@
+#ifndef LIGHTNING_DAEMON_CHAINTOPOLOGY_H
+#define LIGHTNING_DAEMON_CHAINTOPOLOGY_H
+#include "config.h"
+#include <stddef.h>
+
+struct lightningd_state;
+struct txwatch;
+
+size_t get_tx_depth(struct lightningd_state *dstate, const struct txwatch *w);
+void setup_topology(struct lightningd_state *dstate);
+
+#endif /* LIGHTNING_DAEMON_CRYPTOPKT_H */
diff --git a/daemon/lightningd.c b/daemon/lightningd.c
index b7629f95b..1448fb50e 100644
--- a/daemon/lightningd.c
+++ b/daemon/lightningd.c
@@ -1,4 +1,5 @@
 #include "bitcoind.h"
+#include "chaintopology.h"
 #include "configdir.h"
 #include "controlled_time.h"
 #include "jsonrpc.h"
@@ -276,6 +277,9 @@ int main(int argc, char *argv[])
 	/* Create timer to do watches. */
 	setup_watch_timer(dstate);
 
+	/* Initialize block topology. */
+	setup_topology(dstate);
+
 	/* Make sure we use the artificially-controlled time for timers */
 	io_time_override(controlled_time);
 	
diff --git a/daemon/lightningd.h b/daemon/lightningd.h
index 9ea995a9f..c3bc201bf 100644
--- a/daemon/lightningd.h
+++ b/daemon/lightningd.h
@@ -62,6 +62,9 @@ struct lightningd_state {
 	/* Any pending timers. */
 	struct timers timers;
 
+	/* Cached block topology. */
+	struct topology *topology;
+	
 	/* Our peers. */
 	struct list_head peers;
 
diff --git a/daemon/timeout.h b/daemon/timeout.h
index 90ffee45f..12c0cdcd9 100644
--- a/daemon/timeout.h
+++ b/daemon/timeout.h
@@ -2,6 +2,7 @@
 #define LIGHTNING_DAEMON_TIMEOUT_H
 #include "config.h"
 
+#include <ccan/tal/tal.h>
 #include <ccan/time/time.h>
 #include <ccan/timer/timer.h>
 #include <ccan/typesafe_cb/typesafe_cb.h>