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>

3 files changed, 48 insertions, 0 deletions

diff --git a/lib/Makemodule.am b/lib/Makemodule.am
index 5a8ffaa..f49ff91 100644
--- a/lib/Makemodule.am
+++ b/lib/Makemodule.am
@@ -45,6 +45,7 @@ libutil_a_SOURCES += lib/util/print_version.c lib/util/mkdir_p.c
 libutil_a_SOURCES += lib/util/str_table.c include/str_table.h
 libutil_a_SOURCES += lib/util/dirstack.c lib/util/padd_file.c
 libutil_a_SOURCES += lib/util/read_data_at.c lib/util/crc32.c
+libutil_a_SOURCES += lib/util/source_date_epoch.c
 
 if WITH_GZIP
 libcompress_a_SOURCES += lib/comp/gzip.c
diff --git a/lib/fstree/fstree.c b/lib/fstree/fstree.c
index 3c240e7..6955c17 100644
--- a/lib/fstree/fstree.c
+++ b/lib/fstree/fstree.c
@@ -7,6 +7,7 @@
 #include "config.h"
 
 #include "fstree.h"
+#include "util.h"
 
 #include <string.h>
 #include <stdlib.h>
@@ -110,6 +111,7 @@ int fstree_init(fstree_t *fs, size_t block_size, char *defaults)
 	memset(fs, 0, sizeof(*fs));
 	fs->defaults.st_mode = S_IFDIR | 0755;
 	fs->defaults.st_blksize = block_size;
+	fs->defaults.st_mtime = get_source_date_epoch();
 	fs->block_size = block_size;
 
 	if (defaults != NULL && process_defaults(&fs->defaults, defaults) != 0)
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;
+}