[RFC weston v2] Add safe_strtoint() helper

[Bryce Harrington]

Adds a safe strtol helper function, modeled loosely after Wayland
scanner's strtouint.  This encapsulates the various quirks of strtol
behavior, and streamlines the interface to just handling base-10 numbers
with a simple true/false error indicator and a uint32_t return by
reference.

Signed-off-by: Bryce Harrington <bryce at osg.samsung.com>
---

Thanks everyone for the review comments, I've tried to fold in all the
suggestions.  In particular:

 * Uses "safe_" as prefix.  Still open to alternate name ideas.

 * Instead of leaving errno unchanged, now this propagates strtol's
   errno and sets EINVAL in a couple cases.

 * Range is checked, with ERANGE set if not within limits for int32_t.

I'll be on vacation next week, so leaving this as RFC to collect
feedback one more round; then I'll refactor all the strtol calls to use
this where appropriate and implement test cases.

 shared/string-helpers.h | 76 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 shared/string-helpers.h

diff --git a/shared/string-helpers.h b/shared/string-helpers.h
new file mode 100644
index 0000000..1bc9816
--- /dev/null
+++ b/shared/string-helpers.h
@@ -0,0 +1,76 @@
+/*
+ * Copyright © 2016 Samsung Electronics Co., Ltd
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef WESTON_STRING_HELPERS_H
+#define WESTON_STRING_HELPERS_H
+
+#ifdef	__cplusplus
+extern "C" {
+#endif
+
+#include <stdlib.h>
+#include <errno.h>
+
+/* Convert string to integer
+ *
+ * Parses a base-10 number from the given string.  Checks that the
+ * string is not blank, contains only numerical characters, and is
+ * within the range of -INT_MAX to INT_MAX.  If the validation is
+ * successful the result is stored in *value; otherwise *value is
+ * unchanged and errno is set appropriately.
+ *
+ * \return true if number parsed successfully, false on error
+ */
+static inline bool
+safe_strtoint(const char *str, int32_t *value)
+{
+	long ret;
+	char *end;
+
+	assert(str != NULL);
+
+	errno = 0;
+	ret = strtol(str, &end, 10);
+	if (errno != 0) {
+		return false;
+	} else if (end == str || *end != '\0') {
+		errno = EINVAL;
+		return false;
+	}
+
+	*value = (int32_t)ret;
+	if ((long)*value != ret) {
+		errno = ERANGE;
+		return false;
+	}
+
+	return true;
+}
+
+#ifdef	__cplusplus
+}
+#endif
+
+#endif /* WESTON_STRING_HELPERS_H */
-- 
1.9.1