From 8da7bc93315cb0c32ad868f17808468b81fa76ec Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B8rn=20Forsman?= <bjorn.forsman@gmail.com>
Date: Wed, 5 Dec 2018 19:52:51 +0100
Subject: [PATCH] Honor the SOURCE_DATE_EPOCH variable
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Implement the SOURCE_DATE_EPOCH specification[1] for reproducible
builds. If SOURCE_DATE_EPOCH is set, use it as timestamp instead of the
current time.

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

Signed-off-by: Bjørn Forsman <bjorn.forsman@gmail.com>
---
 src/boot.c     | 23 +++++++++++++++++++++--
 src/common.c   | 18 ++++++++++++++++--
 src/mkfs.fat.c | 19 ++++++++++++++++---
 3 files changed, 53 insertions(+), 7 deletions(-)

--- a/src/boot.c
+++ b/src/boot.c
@@ -33,6 +33,8 @@
 #include <stdlib.h>
 #include <sys/types.h>
 #include <time.h>
+#include <errno.h>
+#include <ctype.h>
 
 #include "common.h"
 #include "fsck.fat.h"
@@ -672,6 +674,7 @@ void write_volume_label(DOS_FS * fs, cha
 {
     time_t now;
     struct tm *mtime;
+    char *source_date_epoch = NULL;
     off_t offset;
     int created;
     DIR_ENT de;
@@ -687,8 +690,24 @@ void write_volume_label(DOS_FS * fs, cha
     if (de.name[0] == 0xe5)
 	de.name[0] = 0x05;
 
-    now = time(NULL);
-    mtime = (now != (time_t)-1) ? localtime(&now) : NULL;
+    source_date_epoch = getenv("SOURCE_DATE_EPOCH");
+    if (source_date_epoch) {
+        char *tmp = NULL;
+        long long conversion = 0;
+        errno = 0;
+        conversion = strtoll(source_date_epoch, &tmp, 10);
+        now = conversion;
+        if (!isdigit((unsigned char)*source_date_epoch) || *tmp != '\0'
+                || errno != 0 || (long long)now != conversion) {
+            die("SOURCE_DATE_EPOCH is too big or contains non-digits: \"%s\"",
+                source_date_epoch);
+        }
+        mtime = gmtime(&now);
+    } else {
+        now = time(NULL);
+        mtime = (now != (time_t)-1) ? localtime(&now) : NULL;
+    }
+
     if (mtime && mtime->tm_year >= 80 && mtime->tm_year <= 207) {
 	de.time = htole16((unsigned short)((mtime->tm_sec >> 1) +
 					   (mtime->tm_min << 5) +
--- a/src/common.c
+++ b/src/common.c
@@ -30,6 +30,7 @@
 #include <string.h>
 #include <stdarg.h>
 #include <errno.h>
+#include <ctype.h>
 #include <wctype.h>
 #include <termios.h>
 #include <sys/time.h>
@@ -298,8 +299,21 @@ void check_atari(void)
 uint32_t generate_volume_id(void)
 {
     struct timeval now;
+    char *source_date_epoch = NULL;
 
-    if (gettimeofday(&now, NULL) != 0 || now.tv_sec == (time_t)-1 || now.tv_sec < 0) {
+    source_date_epoch = getenv("SOURCE_DATE_EPOCH");
+    if (source_date_epoch) {
+        char *tmp = NULL;
+        long long conversion = 0;
+        errno = 0;
+        conversion = strtoll(source_date_epoch, &tmp, 10);
+        if (!isdigit((unsigned char)*source_date_epoch) || *tmp != '\0'
+                || errno != 0) {
+            die("SOURCE_DATE_EPOCH is too big or contains non-digits: \"%s\"",
+                source_date_epoch);
+        }
+        return (uint32_t)conversion;
+    } else if (gettimeofday(&now, NULL) != 0 || now.tv_sec == (time_t)-1 || now.tv_sec < 0) {
         srand(getpid());
         /* rand() returns int from [0,RAND_MAX], therefore only 31 bits */
         return (((uint32_t)(rand() & 0xFFFF)) << 16) | ((uint32_t)(rand() & 0xFFFF));
--- a/src/mkfs.fat.c
+++ b/src/mkfs.fat.c
@@ -1074,7 +1074,7 @@ static void setup_tables(void)
         }
 
         /* If is not available then generate random 32 bit disk signature */
-        if (invariant)
+        if (invariant || getenv("SOURCE_DATE_EPOCH"))
             disk_sig = volume_id;
         else if (!disk_sig)
             disk_sig = generate_volume_id();
@@ -1287,7 +1287,7 @@ static void setup_tables(void)
 	    de->name[0] = 0x05;
 	de->attr = ATTR_VOLUME;
 	if (create_time != (time_t)-1) {
-	    if (!invariant)
+	    if (!invariant && !getenv("SOURCE_DATE_EPOCH"))
 		ctime = localtime(&create_time);
 	    else
 		ctime = gmtime(&create_time);
@@ -1477,6 +1477,7 @@ int main(int argc, char **argv)
     int blocks_specified = 0;
     struct timeval create_timeval;
     long long conversion;
+    char *source_date_epoch = NULL;
 
     enum {OPT_HELP=1000, OPT_INVARIANT, OPT_MBR, OPT_VARIANT, OPT_CODEPAGE, OPT_OFFSET};
     const struct option long_options[] = {
@@ -1497,8 +1498,20 @@ int main(int argc, char **argv)
 	    program_name = p + 1;
     }
 
-    if (gettimeofday(&create_timeval, NULL) == 0 && create_timeval.tv_sec != (time_t)-1)
+    source_date_epoch = getenv("SOURCE_DATE_EPOCH");
+    if (source_date_epoch) {
+        errno = 0;
+        conversion = strtoll(source_date_epoch, &tmp, 10);
+        create_time = conversion;
+        if (!isdigit((unsigned char)*source_date_epoch) || *tmp != '\0'
+                || errno != 0 || (long long)create_time != conversion) {
+            die("SOURCE_DATE_EPOCH is too big or contains non-digits: \"%s\"",
+                source_date_epoch);
+        }
+    } else if (gettimeofday(&create_timeval, NULL) == 0 && create_timeval.tv_sec != (time_t)-1) {
         create_time = create_timeval.tv_sec;
+    }
+
     volume_id = generate_volume_id();
     check_atari();