Implement support for SOURCE_DATE_EPOCH environment variable

reproducible-builds.org suggests the use of an environment variable
as a source for time stamps:

https://reproducible-builds.org/specs/source-date-epoch/

This commit adds support for setting the default mtime from the variable,
if it is set and only defaulting to 0 if not. The timestamp given by the
command line switch takes precedence.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 45 insertions, 0 deletions

diff --git a/lib/util/source_date_epoch.c b/lib/util/source_date_epoch.c
new file mode 100644
index 0000000..1397e52
--- /dev/null
+++ b/lib/util/source_date_epoch.c
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * source_date_epoch.h
+ *
+ * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
+ */
+#include "config.h"
+#include "util.h"
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <ctype.h>
+
+uint32_t get_source_date_epoch(void)
+{
+	const char *str, *ptr;
+	uint32_t x, tval = 0;
+
+	str = getenv("SOURCE_DATE_EPOCH");
+
+	if (str == NULL || *str == '\0')
+		return 0;
+
+	for (ptr = str; *ptr != '\0'; ++ptr) {
+		if (!isdigit(*ptr))
+			goto fail_nan;
+
+		x = (*ptr) - '0';
+
+		if (tval > (UINT32_MAX - x) / 10)
+			goto fail_ov;
+
+		tval = tval * 10 + x;
+	}
+
+	return tval;
+fail_ov:
+	fprintf(stderr, "WARNING: SOURCE_DATE_EPOCH=%s does not fit into "
+		"32 bit integer\n", str);
+	return 0;
+fail_nan:
+	fprintf(stderr, "WARNING: SOURCE_DATE_EPOCH=%s is not a positive "
+		"number\n", str);
+	return 0;
+}