common: validate and properly parse floats

Fixes: #1665.

src/common/meson.build

@@ -10,6 +10,7 @@ labwc_sources += files(
   'mem.c',
   'nodename.c',
   'parse-bool.c',
+  'parse-double.c',
   'scaled_font_buffer.c',
   'scaled_scene_buffer.c',
   'scene-helpers.c',

src/common/parse-double.c

@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <locale.h>
+#include <stdlib.h>
+#include <string.h>
+#include <wlr/util/log.h>
+#include "common/mem.h"
+#include "common/parse-double.h"
+
+struct dec_separator {
+	int index;
+	bool multiple;
+};
+
+struct converted_double {
+	double value;
+	bool valid;
+};
+
+static struct dec_separator
+find_dec_separator(const char *str)
+{
+	struct dec_separator loc = {
+		.index = -1,
+		.multiple = false
+	};
+
+	for (int i = 0; *str; i++, str++) {
+		switch (*str) {
+		case ',':
+		case '.':
+			if (loc.index >= 0) {
+				loc.multiple = true;
+				return loc;
+			} else {
+				loc.index = i;
+			}
+			break;
+		}
+	}
+
+	return loc;
+}
+
+static struct converted_double
+convert_double(const char *str)
+{
+	struct converted_double result = {
+		.value = 0,
+		.valid = true,
+	};
+
+	char *eptr = NULL;
+
+	errno = 0;
+	result.value = strtod(str, &eptr);
+
+	if (errno) {
+		wlr_log(WLR_ERROR, "value '%s' is out of range", str);
+		result.valid = false;
+	}
+
+	if (*eptr) {
+		wlr_log(WLR_ERROR, "value '%s' contains trailing garbage", str);
+		result.valid = false;
+	}
+
+	return result;
+}
+
+bool
+set_double(const char *str, double *val)
+{
+	assert(str);
+	assert(val);
+
+	struct dec_separator dloc = find_dec_separator(str);
+	if (dloc.multiple) {
+		wlr_log(WLR_ERROR,
+			"value '%s' contains multiple decimal markers", str);
+		return false;
+	}
+
+	char *lstr = NULL;
+
+	if (dloc.index >= 0) {
+		lstr = xstrdup(str);
+		struct lconv *lc = localeconv();
+		lstr[dloc.index] = *lc->decimal_point;
+		str = lstr;
+	}
+
+	struct converted_double conv = convert_double(str);
+	if (conv.valid) {
+		*val = conv.value;
+	}
+
+	free(lstr);
+	return conv.valid;
+}