jsonrpc.c

/* Code for JSON_RPC API */
/* eg: { "method" : "dev-echo", "params" : [ "hello", "Arabella!" ], "id" : "1" } */
#include <arpa/inet.h>
#include <ccan/array_size/array_size.h>
#include <ccan/err/err.h>
#include <ccan/io/io.h>
#include <ccan/str/hex/hex.h>
#include <ccan/tal/str/str.h>
#include <common/json.h>
#include <common/memleak.h>
#include <common/version.h>
#include <common/wireaddr.h>
#include <errno.h>
#include <fcntl.h>
#include <lightningd/chaintopology.h>
#include <lightningd/jsonrpc.h>
#include <lightningd/lightningd.h>
#include <lightningd/log.h>
#include <lightningd/options.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/un.h>

struct json_output {
	struct list_node list;
	const char *json;
};

/* jcon and cmd have separate lifetimes: we detach them on either destruction */
static void destroy_jcon(struct json_connection *jcon)
{
	if (jcon->current) {
		log_unusual(jcon->log, "Abandoning current command");
		jcon->current->jcon = NULL;
	}
	/* Make sure this happens last! */
	tal_free(jcon->log);
}

static void destroy_cmd(struct command *cmd)
{
	if (cmd->jcon)
		cmd->jcon->current = NULL;
}

static void json_help(struct command *cmd,
		      const char *buffer, const jsmntok_t *params);

static const struct json_command help_command = {
	"help",
	json_help,
	"List available commands, or give verbose help on one command.",

	.verbose = "help [command]\n"
	"Without [command]:\n"
	"  Outputs an array of objects with 'command' and 'description'\n"
	"With [command]:\n"
	"  Give a single object containing 'verbose', which completely describes\n"
	"  the command inputs and outputs."
};
AUTODATA(json_command, &help_command);

static void json_stop(struct command *cmd,
		      const char *buffer, const jsmntok_t *params)
{
	struct json_result *response = new_json_result(cmd);

	/* This can't have closed yet! */
	cmd->jcon->stop = true;
	json_add_string(response, NULL, "Shutting down");
	command_success(cmd, response);
}

static const struct json_command stop_command = {
	"stop",
	json_stop,
	"Shut down the lightningd process"
};
AUTODATA(json_command, &stop_command);

struct log_info {
	enum log_level level;
	struct json_result *response;
	unsigned int num_skipped;
};

static void add_skipped(struct log_info *info)
{
	if (info->num_skipped) {
		json_object_start(info->response, NULL);
		json_add_string(info->response, "type", "SKIPPED");
		json_add_num(info->response, "num_skipped", info->num_skipped);
		json_object_end(info->response);
		info->num_skipped = 0;
	}
}

static void json_add_time(struct json_result *result, const char *fieldname,
			  struct timespec ts)
{
	char timebuf[100];

	sprintf(timebuf, "%lu.%09u",
		(unsigned long)ts.tv_sec,
		(unsigned)ts.tv_nsec);
	json_add_string(result, fieldname, timebuf);
}

static void log_to_json(unsigned int skipped,
			struct timerel diff,
			enum log_level level,
			const char *prefix,
			const char *log,
			struct log_info *info)
{
	info->num_skipped += skipped;

	if (level < info->level) {
		info->num_skipped++;
		return;
	}

	add_skipped(info);

	json_object_start(info->response, NULL);
	json_add_string(info->response, "type",
			level == LOG_BROKEN ? "BROKEN"
			: level == LOG_UNUSUAL ? "UNUSUAL"
			: level == LOG_INFORM ? "INFO"
			: level == LOG_DBG ? "DEBUG"
			: level == LOG_IO ? "IO"
			: "UNKNOWN");
	json_add_time(info->response, "time", diff.ts);
	json_add_string(info->response, "source", prefix);
	if (level == LOG_IO) {
		assert(tal_count(log) > 0);
		if (log[0])
			json_add_string(info->response, "direction", "IN");
		else
			json_add_string(info->response, "direction", "OUT");

		json_add_hex(info->response, "data", log+1, tal_count(log)-1);
	} else
		json_add_string(info->response, "log", log);

	json_object_end(info->response);
}

static void json_getlog(struct command *cmd,
			const char *buffer, const jsmntok_t *params)
{
	struct log_info info;
	struct log_book *lr = cmd->ld->log_book;
	jsmntok_t *level;

	if (!json_get_params(cmd, buffer, params, "?level", &level, NULL)) {
		return;
	}

	info.num_skipped = 0;

	if (!level)
		info.level = LOG_INFORM;
	else if (json_tok_streq(buffer, level, "io"))
		info.level = LOG_IO;
	else if (json_tok_streq(buffer, level, "debug"))
		info.level = LOG_DBG;
	else if (json_tok_streq(buffer, level, "info"))
		info.level = LOG_INFORM;
	else if (json_tok_streq(buffer, level, "unusual"))
		info.level = LOG_UNUSUAL;
	else {
		command_fail(cmd, "Invalid level param");
		return;
	}

	info.response = new_json_result(cmd);
	json_object_start(info.response, NULL);
	if (deprecated_apis)
		json_add_time(info.response, "creation_time", log_init_time(lr)->ts);
	json_add_time(info.response, "created_at", log_init_time(lr)->ts);
	json_add_num(info.response, "bytes_used", (unsigned int)log_used(lr));
	json_add_num(info.response, "bytes_max", (unsigned int)log_max_mem(lr));
	json_array_start(info.response, "log");
	log_each_line(lr, log_to_json, &info);
	json_array_end(info.response);
	json_object_end(info.response);
	command_success(cmd, info.response);
}

static const struct json_command getlog_command = {
	"getlog",
	json_getlog,
	"Show logs, with optional log {level} (info|unusual|debug|io)"
};
AUTODATA(json_command, &getlog_command);

#if DEVELOPER
static void json_rhash(struct command *cmd,
		       const char *buffer, const jsmntok_t *params)
{
	struct json_result *response = new_json_result(cmd);
	jsmntok_t *secrettok;
	struct sha256 secret;

	if (!json_get_params(cmd, buffer, params,
			     "secret", &secrettok,
			     NULL)) {
		return;
	}

	if (!hex_decode(buffer + secrettok->start,
			secrettok->end - secrettok->start,
			&secret, sizeof(secret))) {
		command_fail(cmd, "'%.*s' is not a valid 32-byte hex value",
			     (int)(secrettok->end - secrettok->start),
			     buffer + secrettok->start);
		return;
	}

	/* Hash in place. */
	sha256(&secret, &secret, sizeof(secret));
	json_object_start(response, NULL);
	json_add_hex(response, "rhash", &secret, sizeof(secret));
	json_object_end(response);
	command_success(cmd, response);
}

static const struct json_command dev_rhash_command = {
	"dev-rhash",
	json_rhash,
	"Show SHA256 of {secret}"
};
AUTODATA(json_command, &dev_rhash_command);

static void json_crash(struct command *cmd,
		       const char *buffer, const jsmntok_t *params)
{
	fatal("Crash at user request");
}

static const struct json_command dev_crash_command = {
	"dev-crash",
	json_crash,
	"Crash lightningd by calling fatal()"
};
AUTODATA(json_command, &dev_crash_command);
#endif /* DEVELOPER */

static void json_getinfo(struct command *cmd,
			 const char *buffer, const jsmntok_t *params)
{
	struct json_result *response = new_json_result(cmd);

	json_object_start(response, NULL);
	json_add_pubkey(response, "id", &cmd->ld->id);
	if (cmd->ld->portnum) {
		json_add_num(response, "port", cmd->ld->portnum);
		json_array_start(response, "address");
		for (size_t i = 0; i < tal_count(cmd->ld->wireaddrs); i++)
			json_add_address(response, NULL, cmd->ld->wireaddrs+i);
		json_array_end(response);
	}
	json_add_string(response, "version", version());
	json_add_num(response, "blockheight", get_block_height(cmd->ld->topology));
	json_add_string(response, "network", get_chainparams(cmd->ld)->network_name);
	json_object_end(response);
	command_success(cmd, response);
}

static const struct json_command getinfo_command = {
	"getinfo",
	json_getinfo,
	"Show information about this node"
};
AUTODATA(json_command, &getinfo_command);

static size_t num_cmdlist;

static struct json_command **get_cmdlist(void)
{
	static struct json_command **cmdlist;
	if (!cmdlist)
		cmdlist = autodata_get(json_command, &num_cmdlist);

	return cmdlist;
}

static void json_help(struct command *cmd,
		      const char *buffer, const jsmntok_t *params)
{
	unsigned int i;
	struct json_result *response = new_json_result(cmd);
	struct json_command **cmdlist = get_cmdlist();
	jsmntok_t *cmdtok;

	if (!json_get_params(cmd, buffer, params, "?command", &cmdtok, NULL)) {
		return;
	}

	json_object_start(response, NULL);
	if (cmdtok) {
		for (i = 0; i < num_cmdlist; i++) {
			if (json_tok_streq(buffer, cmdtok, cmdlist[i]->name)) {
				if (!cmdlist[i]->verbose)
					json_add_string(response,
							"verbose",
							"HELP! Please contribute"
							" a description for this"
							" command!");
				else
					json_add_string_escape(response,
							       "verbose",
							       cmdlist[i]->verbose);
				goto done;
			}
		}
		command_fail(cmd, "Unknown command '%.*s'",
			     cmdtok->end - cmdtok->start,
			     buffer + cmdtok->start);
		return;
	}

	json_array_start(response, "help");
	for (i = 0; i < num_cmdlist; i++) {
		json_add_object(response,
				"command", JSMN_STRING,
				cmdlist[i]->name,
				"description", JSMN_STRING,
				cmdlist[i]->description,
				NULL);
	}
	json_array_end(response);

done:
	json_object_end(response);
	command_success(cmd, response);
}

static const struct json_command *find_cmd(const char *buffer,
					   const jsmntok_t *tok)
{
	unsigned int i;
	struct json_command **cmdlist = get_cmdlist();

	/* cmdlist[i]->name can be NULL in test code. */
	for (i = 0; i < num_cmdlist; i++)
		if (cmdlist[i]->name
		    && json_tok_streq(buffer, tok, cmdlist[i]->name))
			return cmdlist[i];
	return NULL;
}

static void connection_result(struct json_connection *jcon,
			      const char *id,
			      const char *res,
			      const char *err,
			      int code,
			      const struct json_result *data)
{
	struct json_output *out = tal(jcon, struct json_output);
	const tal_t *tmpctx;
	const char* data_str;

	if (err == NULL)
		out->json = tal_fmt(out,
				    "{ \"jsonrpc\": \"2.0\", "
				    "\"result\" : %s,"
				    " \"id\" : %s }\n",
				    res, id);
	else {
		tmpctx = tal_tmpctx(out);
		if (data)
			data_str = tal_fmt(tmpctx,
					   ", \"data\" : %s",
					   json_result_string(data));
		else
			data_str = "";

		out->json = tal_fmt(out,
				    "{ \"jsonrpc\": \"2.0\", "
				    " \"error\" : "
				      "{ \"code\" : %d,"
				      " \"message\" : %s%s },"
				    " \"id\" : %s }\n",
				    code, err, data_str,
				    id);
		tal_free(tmpctx);
	}

	/* Queue for writing, and wake writer (and maybe reader). */
	list_add_tail(&jcon->output, &out->list);
	io_wake(jcon);
}

struct json_result *null_response(const tal_t *ctx)
{
	struct json_result *response;

	response = new_json_result(ctx);
	json_object_start(response, NULL);
	json_object_end(response);
	return response;
}

void json_add_pubkey(struct json_result *response,
		     const char *fieldname,
		     const struct pubkey *key)
{
	u8 der[PUBKEY_DER_LEN];

	pubkey_to_der(der, key);
	json_add_hex(response, fieldname, der, sizeof(der));
}

void json_add_txid(struct json_result *result, const char *fieldname,
		   const struct bitcoin_txid *txid)
{
	char hex[hex_str_size(sizeof(*txid))];

	bitcoin_txid_to_hex(txid, hex, sizeof(hex));
	json_add_string(result, fieldname, hex);
}

bool json_tok_pubkey(const char *buffer, const jsmntok_t *tok,
		     struct pubkey *pubkey)
{
	return pubkey_from_hexstr(buffer + tok->start,
				  tok->end - tok->start, pubkey);
}

void json_add_short_channel_id(struct json_result *response,
			       const char *fieldname,
			       const struct short_channel_id *id)
{
	json_add_string(response, fieldname,
			type_to_string(response, struct short_channel_id, id));
}

bool json_tok_short_channel_id(const char *buffer, const jsmntok_t *tok,
			       struct short_channel_id *scid)
{
	return short_channel_id_from_str(buffer + tok->start,
					 tok->end - tok->start,
					 scid);
}

void json_add_address(struct json_result *response, const char *fieldname,
		      const struct wireaddr *addr)
{
	/* No need to print padding */
	if (addr->type == ADDR_TYPE_PADDING)
		return;

	json_object_start(response, fieldname);
	char *addrstr = tal_arr(response, char, INET6_ADDRSTRLEN);
	if (addr->type == ADDR_TYPE_IPV4) {
		inet_ntop(AF_INET, addr->addr, addrstr, INET_ADDRSTRLEN);
		json_add_string(response, "type", "ipv4");
		json_add_string(response, "address", addrstr);
		json_add_num(response, "port", addr->port);
	} else if (addr->type == ADDR_TYPE_IPV6) {
		inet_ntop(AF_INET6, addr->addr, addrstr, INET6_ADDRSTRLEN);
		json_add_string(response, "type", "ipv6");
		json_add_string(response, "address", addrstr);
		json_add_num(response, "port", addr->port);
	}
	json_object_end(response);
}

#define JSONRPC2_INVALID_REQUEST	-32600
#define JSONRPC2_METHOD_NOT_FOUND	-32601
#define JSONRPC2_INVALID_PARAMS		-32602

void command_success(struct command *cmd, struct json_result *result)
{
	struct json_connection *jcon = cmd->jcon;

	if (!jcon) {
		log_unusual(cmd->ld->log,
			    "Command returned result after jcon close");
		tal_free(cmd);
		return;
	}
	assert(jcon->current == cmd);
	connection_result(jcon, cmd->id, json_result_string(result),
			  NULL, 0, NULL);
	log_debug(jcon->log, "Success");
	jcon->current = tal_free(cmd);
}

static void command_fail_v(struct command *cmd,
			   int code,
			   const struct json_result *data,
			   const char *fmt, va_list ap)
{
	char *quote, *error;
	struct json_connection *jcon = cmd->jcon;

	if (!jcon) {
		log_unusual(cmd->ld->log,
			    "Command failed after jcon close");
		tal_free(cmd);
		return;
	}

	error = tal_vfmt(cmd, fmt, ap);

	log_debug(jcon->log, "Failing: %s", error);

	/* Remove " */
	while ((quote = strchr(error, '"')) != NULL)
		*quote = '\'';

	/* Now surround in quotes. */
	quote = tal_fmt(cmd, "\"%s\"", error);

	assert(jcon->current == cmd);
	connection_result(jcon, cmd->id, NULL, quote, code, data);
	jcon->current = tal_free(cmd);
}
void command_fail(struct command *cmd, const char *fmt, ...)
{
	va_list ap;
	va_start(ap, fmt);
	command_fail_v(cmd, -1, NULL, fmt, ap);
	va_end(ap);
}
void command_fail_detailed(struct command *cmd,
			   int code, const struct json_result *data,
			   const char *fmt, ...)
{
	va_list ap;
	va_start(ap, fmt);
	command_fail_v(cmd, code, data, fmt, ap);
	va_end(ap);
}

void command_still_pending(struct command *cmd)
{
	notleak_with_children(cmd);
	notleak(cmd->jcon);
	cmd->pending = true;
}

static void json_command_malformed(struct json_connection *jcon,
				   const char *id,
				   const char *error)
{
	return connection_result(jcon, id, NULL, error,
				 JSONRPC2_INVALID_REQUEST,
				 NULL);
}

static void parse_request(struct json_connection *jcon, const jsmntok_t tok[])
{
	const jsmntok_t *method, *id, *params;
	const struct json_command *cmd;

	assert(!jcon->current);
	if (tok[0].type != JSMN_OBJECT) {
		json_command_malformed(jcon, "null",
				       "Expected {} for json command");
		return;
	}

	method = json_get_member(jcon->buffer, tok, "method");
	params = json_get_member(jcon->buffer, tok, "params");
	id = json_get_member(jcon->buffer, tok, "id");

	if (!id) {
		json_command_malformed(jcon, "null", "No id");
		return;
	}
	if (id->type != JSMN_STRING && id->type != JSMN_PRIMITIVE) {
		json_command_malformed(jcon, "null",
				       "Expected string/primitive for id");
		return;
	}

	/* This is a convenient tal parent for duration of command
	 * (which may outlive the conn!). */
	jcon->current = tal(jcon->ld, struct command);
	jcon->current->jcon = jcon;
	jcon->current->ld = jcon->ld;
	jcon->current->pending = false;
	jcon->current->id = tal_strndup(jcon->current,
					json_tok_contents(jcon->buffer, id),
					json_tok_len(id));
	tal_add_destructor(jcon->current, destroy_cmd);

	if (!method || !params) {
		command_fail_detailed(jcon->current,
				      JSONRPC2_INVALID_REQUEST, NULL,
				      method ? "No params" : "No method");
		return;
	}

	if (method->type != JSMN_STRING) {
		command_fail_detailed(jcon->current,
				      JSONRPC2_INVALID_REQUEST, NULL,
				      "Expected string for method");
		return;
	}

	cmd = find_cmd(jcon->buffer, method);
	if (!cmd) {
		command_fail_detailed(jcon->current,
				      JSONRPC2_METHOD_NOT_FOUND, NULL,
				      "Unknown command '%.*s'",
				      (int)(method->end - method->start),
				      jcon->buffer + method->start);
		return;
	}
	if (cmd->deprecated && !deprecated_apis) {
		command_fail_detailed(jcon->current,
				      JSONRPC2_METHOD_NOT_FOUND, NULL,
				      "Command '%.*s' is deprecated",
				      (int)(method->end - method->start),
				      jcon->buffer + method->start);
		return;
	}

	db_begin_transaction(jcon->ld->wallet->db);
	cmd->dispatch(jcon->current, jcon->buffer, params);
	db_commit_transaction(jcon->ld->wallet->db);

	/* If they didn't complete it, they must call command_still_pending */
	if (jcon->current)
		assert(jcon->current->pending);
}

bool json_get_params(struct command *cmd,
		     const char *buffer, const jsmntok_t param[], ...)
{
	va_list ap;
	const char **names;
	size_t num_names;
	 /* Uninitialized warnings on p and end */
	const jsmntok_t **tokptr, *p = NULL, *end = NULL;

	if (param->type == JSMN_ARRAY) {
		if (param->size == 0)
			p = NULL;
		else
			p = param + 1;
		end = json_next(param);
	} else if (param->type != JSMN_OBJECT) {
		command_fail_detailed(cmd, JSONRPC2_INVALID_PARAMS, NULL,
				      "Expected array or object for params");
		return false;
	}

	num_names = 0;
	names = tal_arr(cmd, const char *, num_names + 1);
	va_start(ap, param);
	while ((names[num_names] = va_arg(ap, const char *)) != NULL) {
		tokptr = va_arg(ap, const jsmntok_t **);
		bool compulsory = true;
		if (names[num_names][0] == '?') {
			names[num_names]++;
			compulsory = false;
		}
		if (param->type == JSMN_ARRAY) {
			*tokptr = p;
			if (p) {
				p = json_next(p);
				if (p == end)
					p = NULL;
			}
		} else {
			*tokptr = json_get_member(buffer, param,
						  names[num_names]);
		}
		/* Convert 'null' to NULL */
		if (*tokptr
		    && (*tokptr)->type == JSMN_PRIMITIVE
		    && buffer[(*tokptr)->start] == 'n') {
			*tokptr = NULL;
		}
		if (compulsory && !*tokptr) {
			va_end(ap);
			command_fail_detailed(cmd, JSONRPC2_INVALID_PARAMS, NULL,
					      "Missing '%s' parameter",
					      names[num_names]);
			return false;
		}
		num_names++;
		tal_resize(&names, num_names + 1);
	}

	va_end(ap);

	/* Now make sure there aren't any params which aren't valid */
	if (param->type == JSMN_ARRAY) {
		if (param->size > num_names) {
			tal_free(names);
			command_fail_detailed(cmd, JSONRPC2_INVALID_PARAMS, NULL,
					      "Too many parameters:"
					      " got %u, expected %zu",
					      param->size, num_names);
			return false;
		}
	} else {
		const jsmntok_t *t;

		end = json_next(param);

		/* Find each parameter among the valid names */
		for (t = param + 1; t < end; t = json_next(t+1)) {
			bool found = false;
			for (size_t i = 0; i < num_names; i++) {
				if (json_tok_streq(buffer, t, names[i]))
					found = true;
			}
			if (!found) {
				tal_free(names);
				command_fail_detailed(cmd,
						      JSONRPC2_INVALID_PARAMS,
						      NULL,
						      "Unknown parameter '%.*s'",
						      t->end - t->start,
						      buffer + t->start);
				return false;
			}
		}
	}

	tal_free(names);
	return true;
}

static struct io_plan *write_json(struct io_conn *conn,
				  struct json_connection *jcon)
{
	struct json_output *out;

	out = list_pop(&jcon->output, struct json_output, list);
	if (!out) {
		if (jcon->stop) {
			log_unusual(jcon->log, "JSON-RPC shutdown");
			/* Return us to toplevel lightningd.c */
			io_break(jcon->ld);
			return io_close(conn);
		}

		/* Reader can go again now. */
		io_wake(jcon);
		return io_out_wait(conn, jcon, write_json, jcon);
	}

	jcon->outbuf = tal_steal(jcon, out->json);
	tal_free(out);

	log_io(jcon->log, false, jcon->outbuf, strlen(jcon->outbuf));
	return io_write(conn,
			jcon->outbuf, strlen(jcon->outbuf), write_json, jcon);
}

static struct io_plan *read_json(struct io_conn *conn,
				 struct json_connection *jcon)
{
	jsmntok_t *toks;
	bool valid;

	log_io(jcon->log, true, jcon->buffer + jcon->used, jcon->len_read);

	/* Resize larger if we're full. */
	jcon->used += jcon->len_read;
	if (jcon->used == tal_count(jcon->buffer))
		tal_resize(&jcon->buffer, jcon->used * 2);

again:
	toks = json_parse_input(jcon->buffer, jcon->used, &valid);
	if (!toks) {
		if (!valid) {
			log_unusual(jcon->ld->log,
				    "Invalid token in json input: '%.*s'",
				    (int)jcon->used, jcon->buffer);
			return io_close(conn);
		}
		/* We need more. */
		goto read_more;
	}

	/* Empty buffer? (eg. just whitespace). */
	if (tal_count(toks) == 1) {
		jcon->used = 0;
		goto read_more;
	}

	parse_request(jcon, toks);

	/* Remove first {}. */
	memmove(jcon->buffer, jcon->buffer + toks[0].end,
		tal_count(jcon->buffer) - toks[0].end);
	jcon->used -= toks[0].end;
	tal_free(toks);

	/* Need to wait for command to finish? */
	if (jcon->current) {
		jcon->len_read = 0;
		return io_wait(conn, jcon, read_json, jcon);
	}

	/* See if we can parse the rest. */
	goto again;

read_more:
	tal_free(toks);
	return io_read_partial(conn, jcon->buffer + jcon->used,
			       tal_count(jcon->buffer) - jcon->used,
			       &jcon->len_read, read_json, jcon);
}

static struct io_plan *jcon_connected(struct io_conn *conn,
				      struct lightningd *ld)
{
	struct json_connection *jcon;

	jcon = tal(conn, struct json_connection);
	jcon->ld = ld;
	jcon->used = 0;
	jcon->buffer = tal_arr(jcon, char, 64);
	jcon->stop = false;
	jcon->current = NULL;
	/* We want to log on destruction, so we free this in destructor. */
	jcon->log = new_log(ld->log_book, ld->log_book, "%sjcon fd %i:",
			    log_prefix(ld->log), io_conn_fd(conn));
	list_head_init(&jcon->output);

	tal_add_destructor(jcon, destroy_jcon);

	return io_duplex(conn,
			 io_read_partial(conn, jcon->buffer,
					 tal_count(jcon->buffer),
					 &jcon->len_read, read_json, jcon),
			 write_json(conn, jcon));
}

static struct io_plan *incoming_jcon_connected(struct io_conn *conn,
					       struct lightningd *ld)
{
	log_debug(ld->log, "Connected json input");

	/* Lifetime of JSON conn is limited to fd connect time. */
	return jcon_connected(notleak(conn), ld);
}

void setup_jsonrpc(struct lightningd *ld, const char *rpc_filename)
{
	struct sockaddr_un addr;
	int fd, old_umask;

	if (streq(rpc_filename, ""))
		return;

	if (streq(rpc_filename, "/dev/tty")) {
		fd = open(rpc_filename, O_RDWR);
		if (fd == -1)
			err(1, "Opening %s", rpc_filename);
		/* Technically this is a leak, but there's only one */
		notleak(io_new_conn(ld, fd, jcon_connected, ld));
		return;
	}

	fd = socket(AF_UNIX, SOCK_STREAM, 0);
	if (fd < 0) {
		errx(1, "domain socket creation failed");
	}
	if (strlen(rpc_filename) + 1 > sizeof(addr.sun_path))
		errx(1, "rpc filename '%s' too long", rpc_filename);
	strcpy(addr.sun_path, rpc_filename);
	addr.sun_family = AF_UNIX;

	/* Of course, this is racy! */
	if (connect(fd, (struct sockaddr *)&addr, sizeof(addr)) == 0)
		errx(1, "rpc filename '%s' in use", rpc_filename);
	unlink(rpc_filename);

	/* This file is only rw by us! */
	old_umask = umask(0177);
	if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)))
		err(1, "Binding rpc socket to '%s'", rpc_filename);
	umask(old_umask);

	if (listen(fd, 1) != 0)
		err(1, "Listening on '%s'", rpc_filename);

	log_debug(ld->log, "Listening on '%s'", rpc_filename);
	/* Technically this is a leak, but there's only one */
	notleak(io_new_listener(ld, fd, incoming_jcon_connected, ld));
}