Compare timestamps with 100ns resolution instead of 1ns

SMB only supports 100ns, so we may have missed corruption in
the following case:

1) Files are stored on ext4, cshatag runs and tags all files
2) Files are moved to SMB
3) Some file content gets corrupted during the move
4) cshatag considers these as "outdated" instead of "corrupt"

100ns should be good enough for everything, and avoids this
problem.

#21

check.go

@@ -33,6 +33,18 @@ func (ts *fileTimestamp) prettyPrint() string {
 	return fmt.Sprintf("%010d.%09d", ts.s, ts.ns)
 }
 
+// equal100ns compares ts and ts2 with 100ns resolution.
+// Why 100ns? That's what SMB supports.
+func (ts *fileTimestamp) equal100ns(ts2 *fileTimestamp) bool {
+	if ts.s != ts2.s {
+		return false
+	}
+	if ts.ns/100 != ts2.ns/100 {
+		return false
+	}
+	return true
+}
+
 type fileAttr struct {
 	ts     fileTimestamp
 	sha256 []byte
@@ -144,7 +156,7 @@ func checkFile(fn string) {
 		return
 	}
 
-	if stored.ts == actual.ts {
+	if stored.ts.equal100ns(&actual.ts) {
 		if bytes.Equal(stored.sha256, actual.sha256) {
 			if !args.q {
 				fmt.Printf("<ok> %s\n", fn)

tests/run_tests.sh

@@ -204,4 +204,21 @@ diff -u 11.expected 11.out
 ../cshatag -remove foo.txt > 11.out2
 diff -u 11.expected 11.out2
 
+echo '*** Testing 100ns resolution ***'
+# https://github.com/rfjakob/cshatag/issues/21
+rm -rf foo.txt
+# Datestring generated using "date --rfc-3339=ns"
+touch --date="2023-04-16 20:56:16.585798497+02:00" foo.txt
+../cshatag foo.txt > /dev/null
+echo asd > foo.txt
+touch --date="2023-04-16 20:56:16.585798400+02:00" foo.txt
+set +e
+../cshatag foo.txt &> /dev/null
+RES=$?
+set -e
+if [[ $RES -ne 5 ]]; then
+	echo "returned $RES, should have returned error code 5"
+	exit 1
+fi
+
 echo "*** ALL TESTS PASSED ***"