common/utils: add tal_strdup_or_null helper.

It's not that uncommon to want to pass NULL through, for optional strings.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/coin_mvt.c

@@ -98,11 +98,7 @@ static struct chain_coin_mvt *new_chain_coin_mvt(const tal_t *ctx,
 {
 	struct chain_coin_mvt *mvt = tal(ctx, struct chain_coin_mvt);
 
-	if (account_name)
+	mvt->account_name = tal_strdup_or_null(mvt, account_name);
-		mvt->account_name = tal_strdup(mvt, account_name);
-	else
-		mvt->account_name = NULL;
-
 	mvt->tx_txid = tx_txid;
 	mvt->outpoint = outpoint;
 	mvt->originating_acct = NULL;
@@ -393,11 +389,8 @@ struct coin_mvt *finalize_chain_mvt(const tal_t *ctx,
 	struct coin_mvt *mvt = tal(ctx, struct coin_mvt);
 
 	mvt->account_id = tal_strdup(mvt, chain_mvt->account_name);
-	if (chain_mvt->originating_acct)
+	mvt->originating_acct =
-		mvt->originating_acct =
+		tal_strdup_or_null(mvt, chain_mvt->originating_acct);
-			tal_strdup(mvt, chain_mvt->originating_acct);
-	else
-		mvt->originating_acct = NULL;
 	mvt->hrp_name = tal_strdup(mvt, hrp_name);
 	mvt->type = CHAIN_MVT;
 

common/configvar.c

@@ -13,10 +13,7 @@ struct configvar *configvar_new(const tal_t *ctx,
 				const char *configline)
 {
 	struct configvar *cv = tal(ctx, struct configvar);
-	if (file)
+	cv->file = tal_strdup_or_null(cv, file);
-		cv->file = tal_strdup(cv, file);
-	else
-		cv->file = NULL;
 	cv->src = src;
 	cv->linenum = linenum;
 	cv->configline = tal_strdup(cv, configline);

common/utils.c

@@ -148,6 +148,16 @@ char *utf8_str(const tal_t *ctx, const u8 *buf TAKES, size_t buflen)
 	return ret;
 }
 
+char *tal_strdup_or_null(const tal_t *ctx, const char *str)
+{
+	if (!str) {
+		/* You might have taken NULL; that's legal!  Release now. */
+		taken(str);
+		return NULL;
+	}
+	return tal_strdup(ctx, str);
+}
+
 int tmpdir_mkstemp(const tal_t *ctx, const char *template TAKES, char **created)
 {
 	char *tmpdir = getenv("TMPDIR");

common/utils.h

@@ -88,6 +88,9 @@ bool utf8_check(const void *buf, size_t buflen);
 /* Check it's UTF-8, return copy (or same if TAKES), or NULL if not valid. */
 char *utf8_str(const tal_t *ctx, const u8 *buf TAKES, size_t buflen);
 
+/* Strdup, or pass through NULL */
+char *tal_strdup_or_null(const tal_t *ctx, const char *str);
+
 /* Use the POSIX C locale. */
 void setup_locale(void);
 

lightningd/chaintopology.c

@@ -186,8 +186,7 @@ static void rebroadcast_txs(struct chain_topology *topo)
 
 		tal_arr_expand(&txs->txs, fmt_bitcoin_tx(txs->txs, otx->tx));
 		tal_arr_expand(&txs->allowhighfees, otx->allowhighfees);
-		tal_arr_expand(&txs->cmd_id,
+		tal_arr_expand(&txs->cmd_id, tal_strdup_or_null(txs, otx->cmd_id));
-			       otx->cmd_id ? tal_strdup(txs, otx->cmd_id) : NULL);
 	}
 	tal_free(cleanup_ctx);
 
@@ -277,10 +276,7 @@ void broadcast_tx_(struct chain_topology *topo,
 	otx->cbarg = cbarg;
 	if (taken(otx->cbarg))
 		tal_steal(otx, otx->cbarg);
-	if (cmd_id)
+	otx->cmd_id = tal_strdup_or_null(otx, cmd_id);
-		otx->cmd_id = tal_strdup(otx, cmd_id);
-	else
-		otx->cmd_id = NULL;
 
 	/* Note that if the minimum block is N, we broadcast it when
 	 * we have block N-1! */

lightningd/plugin_hook.c

@@ -262,10 +262,7 @@ bool plugin_hook_call_(struct lightningd *ld, const struct plugin_hook *hook,
 		ph_req->cb_arg = tal_steal(ph_req, cb_arg);
 		ph_req->db = ld->wallet->db;
 		ph_req->ld = ld;
-		if (cmd_id)
+		ph_req->cmd_id = tal_strdup_or_null(ph_req, cmd_id);
-			ph_req->cmd_id = tal_strdup(ph_req, cmd_id);
-		else
-			ph_req->cmd_id = NULL;
 
 		list_head_init(&ph_req->call_chain);
 		for (size_t i=0; i<tal_count(hook->hooks); i++) {

plugins/bkpr/incomestmt.c

@@ -47,12 +47,7 @@ static struct income_event *chain_to_income(const tal_t *ctx,
 	inc->currency = tal_strdup(inc, ev->currency);
 	inc->timestamp = ev->timestamp;
 	inc->outpoint = tal_dup(inc, struct bitcoin_outpoint, &ev->outpoint);
-
+	inc->desc = tal_strdup_or_null(inc, ev->desc);
-	if (ev->desc)
-		inc->desc = tal_strdup(inc, ev->desc);
-	else
-		inc->desc = NULL;
-
 	inc->txid = tal_dup_or_null(inc, struct bitcoin_txid, ev->spending_txid);
 	inc->payment_id = tal_dup_or_null(inc, struct sha256, ev->payment_id);
 
@@ -75,10 +70,7 @@ static struct income_event *channel_to_income(const tal_t *ctx,
 	inc->timestamp = ev->timestamp;
 	inc->outpoint = NULL;
 	inc->txid = NULL;
-	if (ev->desc)
+	inc->desc = tal_strdup_or_null(inc, ev->desc);
-		inc->desc = tal_strdup(inc, ev->desc);
-	else
-		inc->desc = NULL;
 	inc->payment_id = tal_dup_or_null(inc, struct sha256, ev->payment_id);
 
 	return inc;