lightning/lightningd/chaintopology.c

#include "bitcoin/block.h"
#include "bitcoin/feerate.h"
#include "bitcoin/script.h"
#include "bitcoin/tx.h"
#include "bitcoind.h"
#include "chaintopology.h"
#include "jsonrpc.h"
#include "lightningd.h"
#include "log.h"
#include "watch.h"
#include <ccan/array_size/array_size.h>
#include <ccan/asort/asort.h>
#include <ccan/build_assert/build_assert.h>
#include <ccan/io/io.h>
#include <ccan/tal/str/str.h>
#include <common/json_command.h>
#include <common/jsonrpc_errors.h>
#include <common/memleak.h>
#include <common/param.h>
#include <common/timeout.h>
#include <common/utils.h>
#include <inttypes.h>
#include <lightningd/channel_control.h>
#include <lightningd/gossip_control.h>
#include <lightningd/io_loop_with_timers.h>

/* Mutual recursion via timer. */
static void try_extend_tip(struct chain_topology *topo);

/* get_init_blockhash sets topo->root, start_fee_estimate clears
 * feerate_uninitialized (even if unsuccessful) */
static void maybe_completed_init(struct chain_topology *topo)
{
	if (topo->feerate_uninitialized)
		return;
	if (!topo->root)
		return;
	io_break(topo);
}

static void next_topology_timer(struct chain_topology *topo)
{
	/* This takes care of its own lifetime. */
	notleak(new_reltimer(topo->timers, topo,
			     time_from_sec(topo->poll_seconds),
			     try_extend_tip, topo));
}

static bool we_broadcast(const struct chain_topology *topo,
			 const struct bitcoin_txid *txid)
{
	const struct outgoing_tx *otx;

	list_for_each(&topo->outgoing_txs, otx, list) {
		if (bitcoin_txid_eq(&otx->txid, txid))
			return true;
	}
	return false;
}

static void filter_block_txs(struct chain_topology *topo, struct block *b)
{
	size_t i;
	struct amount_sat owned;

	/* Now we see if any of those txs are interesting. */
	for (i = 0; i < tal_count(b->full_txs); i++) {
		const struct bitcoin_tx *tx = b->full_txs[i];
		struct bitcoin_txid txid;
		size_t j;

		/* Tell them if it spends a txo we care about. */
		for (j = 0; j < tx->wtx->num_inputs; j++) {
			struct txwatch_output out;
			struct txowatch *txo;
			bitcoin_tx_input_get_txid(tx, j, &out.txid);
			out.index = tx->wtx->inputs[j].index;

			txo = txowatch_hash_get(&topo->txowatches, &out);
			if (txo) {
				wallet_transaction_add(topo->ld->wallet,
						       tx, b->height, i);
				txowatch_fire(txo, tx, j, b);
			}
		}

		owned = AMOUNT_SAT(0);
		if (txfilter_match(topo->bitcoind->ld->owned_txfilter, tx)) {
			wallet_extract_owned_outputs(topo->bitcoind->ld->wallet,
						     tx, &b->height,
						     &owned);
		}

		/* We did spends first, in case that tells us to watch tx. */
		bitcoin_txid(tx, &txid);
		if (watching_txid(topo, &txid) || we_broadcast(topo, &txid) ||
		    !amount_sat_eq(owned, AMOUNT_SAT(0))) {
			wallet_transaction_add(topo->ld->wallet,
					       tx, b->height, i);
		}
	}
	b->full_txs = tal_free(b->full_txs);
}

size_t get_tx_depth(const struct chain_topology *topo,
		    const struct bitcoin_txid *txid)
{
	u32 blockheight = wallet_transaction_height(topo->ld->wallet, txid);

	if (blockheight == 0)
		return 0;
	return topo->tip->height - blockheight + 1;
}

struct txs_to_broadcast {
	/* We just sent txs[cursor] */
	size_t cursor;
	/* These are hex encoded already, for bitcoind_sendrawtx */
	const char **txs;

	/* Command to complete when we're done, if and only if dev-broadcast triggered */
	struct command *cmd;
};

/* We just sent the last entry in txs[].  Shrink and send the next last. */
static void broadcast_remainder(struct bitcoind *bitcoind,
				int exitstatus, const char *msg,
				struct txs_to_broadcast *txs)
{
	/* These are expected. */
	if (strstr(msg, "txn-mempool-conflict")
	    || strstr(msg, "transaction already in block chain"))
		log_debug(bitcoind->log,
			  "Expected error broadcasting tx %s: %s",
			  txs->txs[txs->cursor], msg);
	else if (exitstatus)
		log_unusual(bitcoind->log, "Broadcasting tx %s: %i %s",
			    txs->txs[txs->cursor], exitstatus, msg);

	txs->cursor++;
	if (txs->cursor == tal_count(txs->txs)) {
		if (txs->cmd)
			was_pending(command_success(txs->cmd,
						    null_response(txs->cmd)));
		tal_free(txs);
		return;
	}

	/* Broadcast next one. */
	bitcoind_sendrawtx(bitcoind, txs->txs[txs->cursor],
			   broadcast_remainder, txs);
}

/* FIXME: This is dumb.  We can group txs and avoid bothering bitcoind
 * if any one tx is in the main chain. */
static void rebroadcast_txs(struct chain_topology *topo, struct command *cmd)
{
	/* Copy txs now (peers may go away, and they own txs). */
	struct txs_to_broadcast *txs;
	struct outgoing_tx *otx;

	txs = tal(topo, struct txs_to_broadcast);
	txs->cmd = cmd;

	/* Put any txs we want to broadcast in ->txs. */
	txs->txs = tal_arr(txs, const char *, 0);
	list_for_each(&topo->outgoing_txs, otx, list) {
		if (wallet_transaction_height(topo->ld->wallet, &otx->txid))
			continue;

		tal_arr_expand(&txs->txs, tal_strdup(txs, otx->hextx));
	}

	/* Let this do the dirty work. */
	txs->cursor = (size_t)-1;
	broadcast_remainder(topo->bitcoind, 0, "", txs);
}

static void destroy_outgoing_tx(struct outgoing_tx *otx)
{
	list_del(&otx->list);
}

static void clear_otx_channel(struct channel *channel, struct outgoing_tx *otx)
{
	if (otx->channel != channel)
		fatal("channel %p, otx %p has channel %p", channel, otx, otx->channel);
	otx->channel = NULL;
}

static void broadcast_done(struct bitcoind *bitcoind,
			   int exitstatus, const char *msg,
			   struct outgoing_tx *otx)
{
	/* Channel gone?  Stop. */
	if (!otx->channel) {
		tal_free(otx);
		return;
	}

	/* No longer needs to be disconnected if channel dies. */
	tal_del_destructor2(otx->channel, clear_otx_channel, otx);

	if (otx->failed_or_success) {
		otx->failed_or_success(otx->channel, exitstatus, msg);
		tal_free(otx);
	} else {
		/* For continual rebroadcasting, until channel freed. */
		tal_steal(otx->channel, otx);
		list_add_tail(&bitcoind->ld->topology->outgoing_txs, &otx->list);
		tal_add_destructor(otx, destroy_outgoing_tx);
	}
}

void broadcast_tx(struct chain_topology *topo,
		  struct channel *channel, const struct bitcoin_tx *tx,
		  void (*failed_or_success)(struct channel *channel,
				 int exitstatus, const char *err))
{
	/* Channel might vanish: topo owns it to start with. */
	struct outgoing_tx *otx = tal(topo, struct outgoing_tx);
	const u8 *rawtx = linearize_tx(otx, tx);

	otx->channel = channel;
	bitcoin_txid(tx, &otx->txid);
	otx->hextx = tal_hex(otx, rawtx);
	otx->failed_or_success = failed_or_success;
	tal_free(rawtx);
	tal_add_destructor2(channel, clear_otx_channel, otx);

	log_add(topo->log, " (tx %s)",
		type_to_string(tmpctx, struct bitcoin_txid, &otx->txid));

	wallet_transaction_add(topo->ld->wallet, tx, 0, 0);
	bitcoind_sendrawtx(topo->bitcoind, otx->hextx, broadcast_done, otx);
}

static enum watch_result closeinfo_txid_confirmed(struct lightningd *ld,
						  struct channel *channel,
						  const struct bitcoin_txid *txid,
						  unsigned int depth)
{
	/* We delete ourselves first time, so should not be reorged out!! */
	assert(depth > 0);
	/* Subtle: depth 1 == current block. */
	wallet_confirm_tx(ld->wallet, txid,
			  get_block_height(ld->topology) + 1 - depth);
	return DELETE_WATCH;
}

/* We need to know if close_info UTXOs (which the wallet doesn't natively know
 * how to spend, so is not in the normal path) get reconfirmed.
 *
 * This can happen on startup (where we manually unwind 100 blocks) or on a
 * reorg.  The db NULLs out the confirmation_height, so we can't easily figure
 * out just the new ones (and removing the ON DELETE SET NULL clause is
 * non-trivial).
 *
 * So every time, we just set a notification for every tx in this class we're
 * not already watching: there are not usually many, nor many reorgs, so the
 * redundancy is OK.
 */
static void watch_for_utxo_reconfirmation(struct chain_topology *topo,
					  struct wallet *wallet)
{
	struct utxo **unconfirmed;

	unconfirmed = wallet_get_unconfirmed_closeinfo_utxos(tmpctx, wallet);
	for (size_t i = 0; i < tal_count(unconfirmed); i++) {
		assert(unconfirmed[i]->close_info != NULL);
		assert(unconfirmed[i]->blockheight == NULL);

		if (find_txwatch(topo, &unconfirmed[i]->txid, NULL))
			continue;

		notleak(watch_txid(topo, topo, NULL, &unconfirmed[i]->txid,
				   closeinfo_txid_confirmed));
	}
}

const char *feerate_name(enum feerate feerate)
{
	switch (feerate) {
	case FEERATE_URGENT: return "urgent";
	case FEERATE_NORMAL: return "normal";
	case FEERATE_SLOW: return "slow";
	}
	abort();
}

struct command_result *param_feerate_estimate(struct command *cmd,
					      u32 **feerate_per_kw,
					      enum feerate feerate)
{
	*feerate_per_kw = tal(cmd, u32);
	**feerate_per_kw = try_get_feerate(cmd->ld->topology, feerate);
	if (!**feerate_per_kw)
		return command_fail(cmd, LIGHTNINGD, "Cannot estimate fees");

	return NULL;
}

/* Mutual recursion via timer. */
static void next_updatefee_timer(struct chain_topology *topo);

static void init_feerate_history(struct chain_topology *topo,
				 enum feerate feerate, u32 val)
{
	for (size_t i = 0; i < FEE_HISTORY_NUM; i++)
		topo->feehistory[feerate][i] = val;
}

static void add_feerate_history(struct chain_topology *topo,
				enum feerate feerate, u32 val)
{
	memmove(&topo->feehistory[feerate][1], &topo->feehistory[feerate][0],
		(FEE_HISTORY_NUM - 1) * sizeof(u32));
	topo->feehistory[feerate][0] = val;
}

/* We sanitize feerates if necessary to put them in descending order. */
static void update_feerates(struct bitcoind *bitcoind,
			    const u32 *satoshi_per_kw,
			    struct chain_topology *topo)
{
	u32 old_feerates[NUM_FEERATES];
	bool changed = false;
	/* Smoothing factor alpha for simple exponential smoothing. The goal is to
	 * have the feerate account for 90 percent of the values polled in the last
	 * 2 minutes. The following will do that in a polling interval
	 * independent manner. */
	double alpha = 1 - pow(0.1,(double)topo->poll_seconds / 120);

	for (size_t i = 0; i < NUM_FEERATES; i++) {
		u32 feerate = satoshi_per_kw[i];

		/* Takes into account override_fee_rate */
		old_feerates[i] = try_get_feerate(topo, i);

		/* If estimatefee failed, don't do anything. */
		if (!feerate)
			continue;

		/* Initial smoothed feerate is the polled feerate */
		if (!old_feerates[i]) {
			old_feerates[i] = feerate;
			init_feerate_history(topo, i, feerate);

			log_debug(topo->log,
					  "Smoothed feerate estimate for %s initialized to polled estimate %u",
					  feerate_name(i), feerate);
		} else
			add_feerate_history(topo, i, feerate);

		/* Smooth the feerate to avoid spikes. */
		u32 feerate_smooth = feerate * alpha + old_feerates[i] * (1 - alpha);
		/* But to avoid updating forever, only apply smoothing when its
		 * effect is more then 10 percent */
		if (abs((int)feerate - (int)feerate_smooth) > (0.1 * feerate)) {
			feerate = feerate_smooth;
			log_debug(topo->log,
					  "... polled feerate estimate for %s (%u) smoothed to %u (alpha=%.2f)",
					  feerate_name(i), satoshi_per_kw[i],
					  feerate, alpha);
		}

		if (feerate < feerate_floor()) {
			feerate = feerate_floor();
			log_debug(topo->log,
					  "... feerate estimate for %s hit floor %u",
					  feerate_name(i), feerate);
		}

		if (feerate != topo->feerate[i]) {
			log_debug(topo->log, "Feerate estimate for %s set to %u (was %u)",
				  feerate_name(i),
				  feerate, topo->feerate[i]);
		}
		topo->feerate[i] = feerate;
	}

	if (topo->feerate_uninitialized) {
		/* This doesn't mean we *have* a fee estimate, but it does
		 * mean we tried. */
		topo->feerate_uninitialized = false;
		maybe_completed_init(topo);
	}

	/* Make sure (known) fee rates are in order. */
	for (size_t i = 0; i < NUM_FEERATES; i++) {
		if (!topo->feerate[i])
			continue;
		for (size_t j = 0; j < i; j++) {
			if (!topo->feerate[j])
				continue;
			if (topo->feerate[j] < topo->feerate[i]) {
				log_unusual(topo->log,
					  "Feerate estimate for %s (%u) above %s (%u)",
					  feerate_name(i), topo->feerate[i],
					  feerate_name(j), topo->feerate[j]);
				topo->feerate[j] = topo->feerate[i];
			}
		}
		if (try_get_feerate(topo, i) != old_feerates[i])
			changed = true;
	}

	if (changed)
		notify_feerate_change(bitcoind->ld);

	next_updatefee_timer(topo);
}

static void start_fee_estimate(struct chain_topology *topo)
{
	/* FEERATE_IMMEDIATE, FEERATE_NORMAL, FEERATE_SLOW */
	const char *estmodes[] = { "CONSERVATIVE", "ECONOMICAL", "ECONOMICAL" };
	const u32 blocks[] = { 2, 4, 100 };

	BUILD_ASSERT(ARRAY_SIZE(blocks) == NUM_FEERATES);

	/* Once per new block head, update fee estimates. */
	bitcoind_estimate_fees(topo->bitcoind, blocks, estmodes, NUM_FEERATES,
			       update_feerates, topo);
}

u32 mutual_close_feerate(struct chain_topology *topo)
{
	return try_get_feerate(topo, FEERATE_NORMAL);
}

u32 opening_feerate(struct chain_topology *topo)
{
	return try_get_feerate(topo, FEERATE_NORMAL);
}

u32 unilateral_feerate(struct chain_topology *topo)
{
	return try_get_feerate(topo, FEERATE_URGENT);
}

u32 feerate_from_style(u32 feerate, enum feerate_style style)
{
	switch (style) {
	case FEERATE_PER_KSIPA:
		return feerate;
	case FEERATE_PER_KBYTE:
		/* Everyone uses satoshi per kbyte, but we use satoshi per ksipa
		 * (don't round down to zero though)! */
		return (feerate + 3) / 4;
	}
	abort();
}

u32 feerate_to_style(u32 feerate_perkw, enum feerate_style style)
{
	switch (style) {
	case FEERATE_PER_KSIPA:
		return feerate_perkw;
	case FEERATE_PER_KBYTE:
		if ((u64)feerate_perkw * 4 > UINT_MAX)
			return UINT_MAX;
		return feerate_perkw * 4;
	}
	abort();
}

static struct command_result *json_feerates(struct command *cmd,
					    const char *buffer,
					    const jsmntok_t *obj UNNEEDED,
					    const jsmntok_t *params)
{
	struct chain_topology *topo = cmd->ld->topology;
	struct json_stream *response;
	u32 feerates[NUM_FEERATES];
	bool missing;
	enum feerate_style *style;

	if (!param(cmd, buffer, params,
		   p_req("style", param_feerate_style, &style),
		   NULL))
		return command_param_failed();

	missing = false;
	for (size_t i = 0; i < ARRAY_SIZE(feerates); i++) {
		feerates[i] = try_get_feerate(topo, i);
		if (!feerates[i])
			missing = true;
	}

	response = json_stream_success(cmd);
	json_object_start(response, NULL);
	json_object_start(response, json_feerate_style_name(*style));
	for (size_t i = 0; i < ARRAY_SIZE(feerates); i++) {
		if (!feerates[i])
			continue;
		json_add_num(response, feerate_name(i),
			     feerate_to_style(feerates[i], *style));
	}
	json_add_u64(response, "min_acceptable",
		     feerate_to_style(feerate_min(cmd->ld, NULL), *style));
	json_add_u64(response, "max_acceptable",
		     feerate_to_style(feerate_max(cmd->ld, NULL), *style));
	json_object_end(response);

	if (missing)
		json_add_string(response, "warning",
				"Some fee estimates unavailable: bitcoind startup?");
	else {
		json_object_start(response, "onchain_fee_estimates");
		/* eg 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 == weight 702 */
		json_add_num(response, "opening_channel_satoshis",
			     opening_feerate(cmd->ld->topology) * 702 / 1000);
		/* eg. 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 == weight 673 */
		json_add_u64(response, "mutual_close_satoshis",
			     mutual_close_feerate(cmd->ld->topology) * 673 / 1000);
		/* eg. 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 == weight 598 */
		json_add_u64(response, "unilateral_close_satoshis",
			     unilateral_feerate(cmd->ld->topology) * 598 / 1000);
		json_object_end(response);
	}

	json_object_end(response);

	return command_success(cmd, response);
}

static const struct json_command feerates_command = {
	"feerates",
	"bitcoin",
	json_feerates,
	"Return feerate estimates, either satoshi-per-kw ({style} perkw) or satoshi-per-kb ({style} perkb)."
};
AUTODATA(json_command, &feerates_command);

static void next_updatefee_timer(struct chain_topology *topo)
{
	/* This takes care of its own lifetime. */
	notleak(new_reltimer(topo->timers, topo,
			     time_from_sec(topo->poll_seconds),
			     start_fee_estimate, topo));
}

/* Once we're run out of new blocks to add, call this. */
static void updates_complete(struct chain_topology *topo)
{
	if (topo->tip != topo->prev_tip) {
		/* Tell lightningd about new block. */
		notify_new_block(topo->bitcoind->ld, topo->tip->height);

		/* Tell watch code to re-evaluate all txs. */
		watch_topology_changed(topo);

		/* Maybe need to rebroadcast. */
		rebroadcast_txs(topo, NULL);

		/* We've processed these UTXOs */
		db_set_intvar(topo->bitcoind->ld->wallet->db,
			      "last_processed_block", topo->tip->height);

		topo->prev_tip = topo->tip;
	}

	/* Try again soon. */
	next_topology_timer(topo);
}

/**
 * topo_update_spends -- Tell the wallet about all spent outpoints
 */
static void topo_update_spends(struct chain_topology *topo, struct block *b)
{
	const struct short_channel_id *scid;
	for (size_t i = 0; i < tal_count(b->full_txs); i++) {
		const struct bitcoin_tx *tx = b->full_txs[i];
		for (size_t j = 0; j < tx->wtx->num_inputs; j++) {
			const struct wally_tx_input *input = &tx->wtx->inputs[j];
			struct bitcoin_txid txid;
			bitcoin_tx_input_get_txid(tx, j, &txid);

			scid = wallet_outpoint_spend(topo->ld->wallet, tmpctx,
						     b->height, &txid,
						     input->index);
			if (scid) {
				gossipd_notify_spend(topo->bitcoind->ld, scid);
				tal_free(scid);
			}
		}
	}
}

static void topo_add_utxos(struct chain_topology *topo, struct block *b)
{
	for (size_t i = 0; i < tal_count(b->full_txs); i++) {
		const struct bitcoin_tx *tx = b->full_txs[i];
		for (size_t j = 0; j < tx->wtx->num_outputs; j++) {
			const u8 *script = bitcoin_tx_output_get_script(tmpctx, tx, j);
			struct amount_sat amt = bitcoin_tx_output_get_amount(tx, j);

			if (is_p2wsh(script, NULL)) {
				wallet_utxoset_add(topo->ld->wallet, tx, j,
						   b->height, i, script,
						   amt);
			}
		}
	}
}

static void add_tip(struct chain_topology *topo, struct block *b)
{
	/* Attach to tip; b is now the tip. */
	assert(b->height == topo->tip->height + 1);
	b->prev = topo->tip;
	topo->tip->next = b;	/* FIXME this doesn't seem to be used anywhere */
	topo->tip = b;
	wallet_block_add(topo->ld->wallet, b);

	topo_add_utxos(topo, b);
	topo_update_spends(topo, b);

	/* Only keep the transactions we care about. */
	filter_block_txs(topo, b);

	block_map_add(&topo->block_map, b);
	topo->max_blockheight = b->height;
}

static struct block *new_block(struct chain_topology *topo,
			       struct bitcoin_block *blk,
			       unsigned int height)
{
	struct block *b = tal(topo, struct block);

	sha256_double(&b->blkid.shad, &blk->hdr, sizeof(blk->hdr));
	log_debug(topo->log, "Adding block %u: %s",
		  height,
		  type_to_string(tmpctx, struct bitcoin_blkid, &b->blkid));
	assert(!block_map_get(&topo->block_map, &b->blkid));
	b->next = NULL;
	b->prev = NULL;

	b->height = height;

	b->hdr = blk->hdr;

	b->txnums = tal_arr(b, u32, 0);
	b->full_txs = tal_steal(b, blk->tx);

	return b;
}

static void remove_tip(struct chain_topology *topo)
{
	struct block *b = topo->tip;
	struct bitcoin_txid *txs;
	size_t i, n;

	log_debug(topo->log, "Removing stale block %u: %s",
			  topo->tip->height,
			  type_to_string(tmpctx, struct bitcoin_blkid, &b->blkid));

	/* Move tip back one. */
	topo->tip = b->prev;

	if (!topo->tip)
		fatal("Initial block %u (%s) reorganized out!",
		      b->height,
		      type_to_string(tmpctx, struct bitcoin_blkid, &b->blkid));

	txs = wallet_transactions_by_height(b, topo->ld->wallet, b->height);
	n = tal_count(txs);

	/* Notify that txs are kicked out (their height will be set NULL in db) */
	for (i = 0; i < n; i++)
		txwatch_fire(topo, &txs[i], 0);

	wallet_block_remove(topo->ld->wallet, b);
	/* This may have unconfirmed txs: reconfirm as we add blocks. */
	watch_for_utxo_reconfirmation(topo, topo->ld->wallet);
	block_map_del(&topo->block_map, b);
	tal_free(b);
}

static void have_new_block(struct bitcoind *bitcoind UNUSED,
			   struct bitcoin_block *blk,
			   struct chain_topology *topo)
{
	/* Unexpected predecessor?  Free predecessor, refetch it. */
	if (!bitcoin_blkid_eq(&topo->tip->blkid, &blk->hdr.prev_hash))
		remove_tip(topo);
	else
		add_tip(topo, new_block(topo, blk, topo->tip->height + 1));

	/* Try for next one. */
	try_extend_tip(topo);
}

static void get_new_block(struct bitcoind *bitcoind,
			  const struct bitcoin_blkid *blkid,
			  struct chain_topology *topo)
{
	if (!blkid) {
		/* No such block, we're done. */
		updates_complete(topo);
		return;
	}
	bitcoind_getrawblock(bitcoind, blkid, have_new_block, topo);
}

static void try_extend_tip(struct chain_topology *topo)
{
	bitcoind_getblockhash(topo->bitcoind, topo->tip->height + 1,
			      get_new_block, topo);
}

static void init_topo(struct bitcoind *bitcoind UNUSED,
		      struct bitcoin_block *blk,
		      struct chain_topology *topo)
{
	topo->root = new_block(topo, blk, topo->max_blockheight);
	block_map_add(&topo->block_map, topo->root);
	topo->tip = topo->prev_tip = topo->root;

	/* In case we don't get all the way to updates_complete */
	db_set_intvar(topo->bitcoind->ld->wallet->db,
		      "last_processed_block", topo->tip->height);

	maybe_completed_init(topo);
}

static void get_init_block(struct bitcoind *bitcoind,
			   const struct bitcoin_blkid *blkid,
			   struct chain_topology *topo)
{
	bitcoind_getrawblock(bitcoind, blkid, init_topo, topo);
}

static void get_init_blockhash(struct bitcoind *bitcoind, u32 blockcount,
			       struct chain_topology *topo)
{
	/* If bitcoind's current blockheight is below the requested height, just
	 * go back to that height. This might be a new node catching up, or
	 * bitcoind is processing a reorg. */
	if (blockcount < topo->max_blockheight) {
		if (topo->max_blockheight == UINT32_MAX) {
			/* Relative rescan, but we didn't know the blockheight */
			/* Protect against underflow in subtraction.
			 * Possible in regtest mode. */
			if (blockcount < bitcoind->ld->config.rescan)
				topo->max_blockheight = 0;
			else
				topo->max_blockheight = blockcount - bitcoind->ld->config.rescan;
		} else {
			/* Absolute blockheight, but bitcoind's blockheight isn't there yet */
			/* Protect against underflow in subtraction.
			 * Possible in regtest mode. */
			if (blockcount < 1)
				topo->max_blockheight = 0;
			else
				topo->max_blockheight = blockcount - 1;
		}
	}

	/* Rollback to the given blockheight, so we start track
	 * correctly again */
	wallet_blocks_rollback(topo->ld->wallet, topo->max_blockheight);
	/* This may have unconfirmed txs: reconfirm as we add blocks. */
	watch_for_utxo_reconfirmation(topo, topo->ld->wallet);

	/* Get up to speed with topology. */
	bitcoind_getblockhash(bitcoind, topo->max_blockheight,
			      get_init_block, topo);
}

u32 get_block_height(const struct chain_topology *topo)
{
	return topo->tip->height;
}

u32 try_get_feerate(const struct chain_topology *topo, enum feerate feerate)
{
	return topo->feerate[feerate];
}

u32 feerate_min(struct lightningd *ld, bool *unknown)
{
	u32 min;

	if (unknown)
		*unknown = false;

	/* We can't allow less than feerate_floor, since that won't relay */
	if (ld->config.ignore_fee_limits)
		min = 1;
	else {
		min = try_get_feerate(ld->topology, FEERATE_SLOW);
		if (!min) {
			if (unknown)
				*unknown = true;
		} else {
			const u32 *hist = ld->topology->feehistory[FEERATE_SLOW];

			/* If one of last three was an outlier, use that. */
			for (size_t i = 0; i < FEE_HISTORY_NUM; i++) {
				if (hist[i] < min)
					min = hist[i];
			}
			/* Normally, we use half of slow rate. */
			min /= 2;
		}
	}

	if (min < feerate_floor())
		return feerate_floor();
	return min;
}

/* BOLT #2:
 *
 * Given the variance in fees, and the fact that the transaction may be
 * spent in the future, it's a good idea for the fee payer to keep a good
 * margin (say 5x the expected fee requirement)
 */
u32 feerate_max(struct lightningd *ld, bool *unknown)
{
	u32 feerate;
	const u32 *feehistory = ld->topology->feehistory[FEERATE_URGENT];

	if (unknown)
		*unknown = false;

	if (ld->config.ignore_fee_limits)
		return UINT_MAX;

	/* If we don't know feerate, don't limit other side. */
	feerate = try_get_feerate(ld->topology, FEERATE_URGENT);
	if (!feerate) {
		if (unknown)
			*unknown = true;
		return UINT_MAX;
	}

	/* If one of last three was an outlier, use that. */
	for (size_t i = 0; i < FEE_HISTORY_NUM; i++) {
		if (feehistory[i] > feerate)
			feerate = feehistory[i];
	}
	return feerate * ld->config.max_fee_multiplier;
}

/* On shutdown, channels get deleted last.  That frees from our list, so
 * do it now instead. */
static void destroy_chain_topology(struct chain_topology *topo)
{
	struct outgoing_tx *otx;

	while ((otx = list_pop(&topo->outgoing_txs, struct outgoing_tx, list)))
		tal_free(otx);
}

struct chain_topology *new_topology(struct lightningd *ld, struct log *log)
{
	struct chain_topology *topo = tal(ld, struct chain_topology);

	topo->ld = ld;
	block_map_init(&topo->block_map);
	list_head_init(&topo->outgoing_txs);
	txwatch_hash_init(&topo->txwatches);
	txowatch_hash_init(&topo->txowatches);
	topo->log = log;
	memset(topo->feerate, 0, sizeof(topo->feerate));
	topo->bitcoind = new_bitcoind(topo, ld, log);
	topo->poll_seconds = 30;
	topo->feerate_uninitialized = true;
	topo->root = NULL;
	return topo;
}

void setup_topology(struct chain_topology *topo,
		    struct timers *timers,
		    u32 min_blockheight, u32 max_blockheight)
{
	memset(&topo->feerate, 0, sizeof(topo->feerate));
	topo->timers = timers;

	topo->min_blockheight = min_blockheight;
	topo->max_blockheight = max_blockheight;

	/* Make sure bitcoind is started, and ready */
	wait_for_bitcoind(topo->bitcoind);

	bitcoind_getblockcount(topo->bitcoind, get_init_blockhash, topo);

	tal_add_destructor(topo, destroy_chain_topology);

	start_fee_estimate(topo);

	/* Once it gets initial block, it calls io_break() and we return. */
	io_loop_with_timers(topo->ld);
}

void begin_topology(struct chain_topology *topo)
{
	try_extend_tip(topo);
}