lightningd: add force-feerates option.

Useful for regtest and testnet.  Sure, you shouldn't use this on mainnet,
but I haven't restricted it because our users are usually pretty clever.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Fixes: #1806
Changelog-Added: config: `force_feerates` option to allow overriding feerate estimates (mainly for regtest).

doc/lightning-listconfigs.7

@@ -148,6 +148,8 @@ On success, an object is returned, containing:
 .IP \[bu]
 \fBlog-timestamps\fR (boolean, optional): \fBlog-timestamps\fR field from config or cmdline, or default
 .IP \[bu]
+\fBforce-feerates\fR (string, optional): \fBforce-feerates\fR field from config or cmdline, if any
+.IP \[bu]
 \fBsubdaemon\fR (string, optional): \fBsubdaemon\fR fields from config or cmdline if any (can be more than one)
 .IP \[bu]
 \fBtor-service-password\fR (string, optional): \fBtor-service-password\fR field from config or cmdline, if any
@@ -268,4 +270,4 @@ Vincenzo Palazzo \fI<vincenzo.palazzo@protonmail.com\fR> wrote the initial versi
 
 Main web site: \fIhttps://github.com/ElementsProject/lightning\fR
 
-\" SHA256STAMP:f813a777c6e074907980797dafd798a48633469a59e1ac526e2581e2b1a14c83
+\" SHA256STAMP:4591f6c754162b2dcdf82a36d584a48795752d39a986bc1d39c49e0cdbea440f

doc/lightning-listconfigs.7.md

@@ -84,6 +84,7 @@ On success, an object is returned, containing:
 - **log-prefix** (string, optional): `log-prefix` field from config or cmdline, or default
 - **log-file** (string, optional): `log-file` field from config or cmdline, or default
 - **log-timestamps** (boolean, optional): `log-timestamps` field from config or cmdline, or default
+- **force-feerates** (string, optional): `force-feerates` field from config or cmdline, if any
 - **subdaemon** (string, optional): `subdaemon` fields from config or cmdline if any (can be more than one)
 - **tor-service-password** (string, optional): `tor-service-password` field from config or cmdline, if any
 [comment]: # (GENERATE-FROM-SCHEMA-END)
@@ -203,4 +204,4 @@ RESOURCES
 ---------
 
 Main web site: <https://github.com/ElementsProject/lightning>
-[comment]: # ( SHA256STAMP:3c3f2cd354ef5b33ad34febd29b04b1861c62d545c6a5b9181eb2b2b3880258f)
+[comment]: # ( SHA256STAMP:ad98179a7b6254a936d4fde179918b6a975e186adcbc396917a0c2ed2888519e)

doc/lightningd-config.5

@@ -316,6 +316,21 @@ How long to wait before sending commitment messages to the peer: in
 theory increasing this would reduce load, but your node would have to be
 extremely busy node for you to even notice\.
 
+
+ \fBforce-feerates\fR==\fIVALUES\fR
+Networks like regtest and testnet have unreliable fee estimates: we
+usually treat them as the minumum (253 sats/kw) if we can't get them\.
+This allows override of one or more of our standard feerates (see
+\fBlightning-feerates\fR(7))\.  Up to 5 values, separated by '/' can be
+provided: if fewer are provided, then the final value is used for the
+remainder\.  The values are in per-kw (roughly 1/4 of bitcoind's per-kb
+values), an in order are "opening", "mutual_close",
+"unilateral_close", "delayed_to_us", "htlc_resolution", and "penalty"\.
+
+
+You would usually put this option in the per-chain config file, to avoid
+setting it on Bitcoin mainnet!  e\.g\. \fB~rusty/.lightning/regtest/config\fR\.
+
 .SH Lightning channel and HTLC options
 
  \fBlarge-channels\fR
@@ -635,4 +650,4 @@ Main web site: \fIhttps://github.com/ElementsProject/lightning\fR
 Note: the modules in the ccan/ directory have their own licenses, but
 the rest of the code is covered by the BSD-style MIT license\.
 
-\" SHA256STAMP:40c9f5e9e4ee5257e25a1fc196d2c85c3bc5b21d3f390a4e7fafa031c4e7ad5e
+\" SHA256STAMP:d456e1acd004f9528d8772231afdecff1aaa01d80161c833483f6f078f4c7d70

doc/lightningd-config.5.md

@@ -257,6 +257,19 @@ How long to wait before sending commitment messages to the peer: in
 theory increasing this would reduce load, but your node would have to be
 extremely busy node for you to even notice.
 
+ **force-feerates**==*VALUES*
+Networks like regtest and testnet have unreliable fee estimates: we
+usually treat them as the minumum (253 sats/kw) if we can't get them.
+This allows override of one or more of our standard feerates (see
+lightning-feerates(7)).  Up to 5 values, separated by '/' can be
+provided: if fewer are provided, then the final value is used for the
+remainder.  The values are in per-kw (roughly 1/4 of bitcoind's per-kb
+values), an in order are "opening", "mutual_close",
+"unilateral_close", "delayed_to_us", "htlc_resolution", and "penalty".
+
+You would usually put this option in the per-chain config file, to avoid
+setting it on Bitcoin mainnet!  e.g. `~rusty/.lightning/regtest/config`.
+
 ### Lightning channel and HTLC options
 
  **large-channels**

doc/schemas/listconfigs.schema.json

@@ -235,6 +235,10 @@
 	    "type": "boolean",
 	    "description": "`log-timestamps` field from config or cmdline, or default"
 	},
+	"force-feerates": {
+	    "type": "string",
+	    "description": "force-feerate configuration setting, if any"
+	},
 	"subdaemon": {
 	    "type": "string",
 	    "description": "`subdaemon` fields from config or cmdline if any (can be more than one)"

lightningd/bitcoind.c

@@ -187,6 +187,12 @@ static void estimatefees_callback(const char *buf, const jsmntok_t *toks,
 			bitcoin_plugin_error(call->bitcoind, buf, toks,
 					     "estimatefees",
 					     "missing '%s' field", feerate_name(f));
+		/* We still use the bcli plugin for min and max, even with
+		 * force_feerates */
+		if (f < tal_count(call->bitcoind->ld->force_feerates)) {
+			feerates[f] = call->bitcoind->ld->force_feerates[f];
+			continue;
+		}
 
 		/* FIXME: We could trawl recent blocks for median fee... */
 		if (!json_to_u32(buf, feeratetok, &feerates[f])) {

lightningd/chaintopology.h

@@ -22,6 +22,7 @@ struct txwatch;
 
 /* FIXME: move all feerate stuff out to new lightningd/feerate.[ch] files */
 enum feerate {
+	/* DO NOT REORDER: force-feerates uses this order! */
 	FEERATE_OPENING,
 	FEERATE_MUTUAL_CLOSE,
 	FEERATE_UNILATERAL_CLOSE,

lightningd/lightningd.c

@@ -290,6 +290,11 @@ static struct lightningd *new_lightningd(const tal_t *ctx)
 	 * each invoice we generate has a different set of channels.  */
 	ld->rr_counter = 0;
 
+	/*~ Because fee estimates on testnet and regtest are unreliable,
+	 * we allow overriding them with --force-feerates, in which
+	 * case this is a pointer to an enum feerate-indexed array of values */
+	ld->force_feerates = NULL;
+
 	return ld;
 }
 

lightningd/lightningd.h

@@ -199,6 +199,10 @@ struct lightningd {
 	/* RPC response to send once we've shut down. */
 	const char *stop_response;
 
+	/* Used these feerates instead of whatever bcli returns (up to
+	 * FEERATE_PENALTY). */
+	u32 *force_feerates;
+
 #if DEVELOPER
 	/* If we want to debug a subdaemon/plugin. */
 	const char *dev_debug_subprocess;

lightningd/options.c

@@ -131,6 +131,51 @@ static char *opt_set_mode(const char *arg, mode_t *m)
 	return NULL;
 }
 
+static char *opt_force_feerates(const char *arg, struct lightningd *ld)
+{
+	char **vals = tal_strsplit(tmpctx, arg, "/", STR_EMPTY_OK);
+	size_t n;
+
+	/* vals has NULL at end, enum feerate is 0 based */
+	if (tal_count(vals) - 1 > FEERATE_PENALTY + 1)
+		return "Too many values";
+
+	if (!ld->force_feerates)
+		ld->force_feerates = tal_arr(ld, u32, FEERATE_PENALTY + 1);
+
+	n = 0;
+	for (size_t i = 0; i < tal_count(ld->force_feerates); i++) {
+		char *err = opt_set_u32(vals[n], &ld->force_feerates[i]);
+		if (err)
+			return err;
+		fprintf(stderr, "Set feerate %zu based on val %zu\n", i, n);
+		if (vals[n+1])
+			n++;
+	}
+	return NULL;
+}
+
+static char *fmt_force_feerates(const tal_t *ctx, const u32 *force_feerates)
+{
+	char *ret;
+	size_t last;
+
+	if (!force_feerates)
+		return NULL;
+
+	ret = tal_fmt(ctx, "%i", force_feerates[0]);
+	last = 0;
+	for (size_t i = 1; i < tal_count(force_feerates); i++) {
+		if (force_feerates[i] == force_feerates[i-1])
+			continue;
+		/* Different?  Catchup! */
+		for (size_t j = last + 1; j <= i; j++)
+			tal_append_fmt(&ret, "/%i", force_feerates[j]);
+		last = i;
+	}
+	return ret;
+}
+
 #if EXPERIMENTAL_FEATURES
 static char *opt_set_accept_extra_tlv_types(const char *arg,
 					     struct lightningd *ld)
@@ -1003,6 +1048,10 @@ static void register_opts(struct lightningd *ld)
 			 "Set the file mode (permissions) for the "
 			 "JSON-RPC socket");
 
+	opt_register_arg("--force-feerates",
+			 opt_force_feerates, NULL, ld,
+			 "Set testnet/regtest feerates in sats perkw, opening/mutual_close/unlateral_close/delayed_to_us/htlc_resolution/penalty: if fewer specified, last number applies to remainder");
+
 	opt_register_arg("--subdaemon", opt_subdaemon, NULL,
 			 ld, "Arg specified as SUBDAEMON:PATH. "
 			 "Specifies an alternate subdaemon binary. "
@@ -1423,6 +1472,8 @@ static void add_config(struct lightningd *ld,
 			json_add_opt_log_levels(response, ld->log);
 		} else if (opt->cb_arg == (void *)opt_disable_plugin) {
 			json_add_opt_disable_plugins(response, ld->plugins);
+		} else if (opt->cb_arg == (void *)opt_force_feerates) {
+			answer = fmt_force_feerates(name0, ld->force_feerates);
 		} else if (opt->cb_arg == (void *)opt_important_plugin) {
 			/* Do nothing, this is already handled by
 			 * opt_add_plugin.  */

tests/test_misc.py

@@ -2561,3 +2561,48 @@ def test_getlog(node_factory):
     # This should not
     logs = l1.rpc.getlog(level='io')['log']
     assert [l for l in logs if l['type'] == 'SKIPPED'] == []
+
+
+def test_force_feerates(node_factory):
+    l1 = node_factory.get_node(options={'force-feerates': 1111})
+    assert l1.rpc.listconfigs()['force-feerates'] == '1111'
+
+    assert l1.rpc.feerates('perkw')['perkw'] == {
+        "opening": 1111,
+        "mutual_close": 1111,
+        "unilateral_close": 1111,
+        "delayed_to_us": 1111,
+        "htlc_resolution": 1111,
+        "penalty": 1111,
+        "min_acceptable": 1875,
+        "max_acceptable": 150000}
+
+    l1.stop()
+    l1.daemon.opts['force-feerates'] = '1111/2222'
+    l1.start()
+
+    assert l1.rpc.listconfigs()['force-feerates'] == '1111/2222'
+    assert l1.rpc.feerates('perkw')['perkw'] == {
+        "opening": 1111,
+        "mutual_close": 2222,
+        "unilateral_close": 2222,
+        "delayed_to_us": 2222,
+        "htlc_resolution": 2222,
+        "penalty": 2222,
+        "min_acceptable": 1875,
+        "max_acceptable": 150000}
+
+    l1.stop()
+    l1.daemon.opts['force-feerates'] = '1111/2222/3333/4444/5555/6666'
+    l1.start()
+
+    assert l1.rpc.listconfigs()['force-feerates'] == '1111/2222/3333/4444/5555/6666'
+    assert l1.rpc.feerates('perkw')['perkw'] == {
+        "opening": 1111,
+        "mutual_close": 2222,
+        "unilateral_close": 3333,
+        "delayed_to_us": 4444,
+        "htlc_resolution": 5555,
+        "penalty": 6666,
+        "min_acceptable": 1875,
+        "max_acceptable": 150000}