psbt: make psbt_from_b64 more conventional.

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

bitcoin/psbt.c

@@ -361,11 +361,20 @@ struct wally_tx *psbt_finalize(struct wally_psbt *psbt, bool finalize_in_place)
 	return NULL;
 }
 
-bool psbt_from_b64(const char *b64str, struct wally_psbt **psbt)
+struct wally_psbt *psbt_from_b64(const tal_t *ctx,
+				 const char *b64,
+				 size_t b64len)
 {
-	int wally_err;
-	wally_err = wally_psbt_from_base64(b64str, psbt);
-	return wally_err == WALLY_OK;
+	struct wally_psbt *psbt;
+	char *str = tal_strndup(tmpctx, b64, b64len);
+
+	if (wally_psbt_from_base64(str, &psbt) != WALLY_OK)
+		return NULL;
+
+	/* We promised it would be owned by ctx: libwally uses a dummy owner */
+	tal_steal(ctx, psbt);
+	tal_add_destructor(psbt, psbt_destroy);
+	return psbt;
 }
 
 char *psbt_to_b64(const tal_t *ctx, const struct wally_psbt *psbt)

bitcoin/psbt.h

@@ -74,7 +74,9 @@ bool psbt_input_set_redeemscript(struct wally_psbt *psbt, size_t in,
 struct amount_sat psbt_input_get_amount(struct wally_psbt *psbt,
 					size_t in);
 
-bool psbt_from_b64(const char *b64str, struct wally_psbt **psbt);
+struct wally_psbt *psbt_from_b64(const tal_t *ctx,
+				 const char *b64,
+				 size_t b64len);
 char *psbt_to_b64(const tal_t *ctx, const struct wally_psbt *psbt);
 const u8 *psbt_get_bytes(const tal_t *ctx, const struct wally_psbt *psbt,
 			 size_t *bytes_written);

wallet/walletrpc.c

@@ -1203,11 +1203,8 @@ struct command_result *param_psbt(struct command *cmd,
 				  const jsmntok_t *tok,
 				  struct wally_psbt **psbt)
 {
-	/* Pull out the token into a string, then pass to
-	 * the PSBT parser; PSBT parser can't handle streaming
-	 * atm as it doesn't accept a len value */
-	char *psbt_buff = json_strdup(cmd, buffer, tok);
-	if (psbt_from_b64(psbt_buff, psbt))
+	*psbt = psbt_from_b64(cmd, buffer + tok->start, tok->end - tok->start);
+	if (*psbt)
 		return NULL;
 
 	return command_fail(cmd, JSONRPC2_INVALID_PARAMS,