Make a backup of the crontab file on deletion

src/crontab.c

@@ -464,7 +464,11 @@ static void list_cmd(void) {
 }
 
 static void delete_cmd(void) {
-	char n[MAX_FNAME] = "";
+	char n[MAX_FNAME] = "", BackupFilename[MAX_FNAME];
+	int t;
+	FILE *CrontabFile;
+	FILE *BackupFile;
+
 	if (PromptOnDelete == 1) {
 		printf("crontab: really delete %s's crontab? ", User);
 		fflush(stdout);
@@ -479,13 +483,53 @@ static void delete_cmd(void) {
 		fprintf(stderr, "path too long\n");
 		exit(ERROR_EXIT);
 	}
-	if (unlink(n) != 0) {
-		if (errno == ENOENT)
-			fprintf(stderr, "no crontab for %s\n", User);
-		else
+	if (!glue_strings(BackupFilename, sizeof Filename, tmp_path(),
+			"crontab.XXXXXX", '/')) {
+		fprintf(stderr, "path too long\n");
+		exit(ERROR_EXIT);
+	}
+
+	if (!(CrontabFile = fopen(n, "r"))) {
+		if (errno != ENOENT) {
 			perror(n);
+			exit(ERROR_EXIT);
+		}
+		fprintf(stderr, "no crontab for %s\n", User);
+		exit(ERROR_EXIT);
+	}
+
+	if (swap_uids() == -1) {
+		perror("swapping uids");
 		exit(ERROR_EXIT);
 	}
+	if (-1 == (t = mkstemp(BackupFilename))) {
+		perror(BackupFilename);
+		exit(ERROR_EXIT);
+	}
+	if (swap_uids_back() < OK) {
+		perror("swapping uids back");
+		exit(ERROR_EXIT);
+	}
+
+	if (!(BackupFile = fdopen(t, "r+"))) {
+		perror("fdopen");
+		exit(ERROR_EXIT);
+	}
+
+	int ch = '\0';
+	if (EOF != ch)
+		while (EOF != (ch = get_char(CrontabFile)))
+			putc(ch, BackupFile);
+
+	fclose(CrontabFile);
+	fclose(BackupFile);
+
+	if (unlink(n) != 0) {
+		perror(n);
+		exit(ERROR_EXIT);
+	}
+	fprintf(stderr, "Deleted crontab for user %s.\nBackup is saved at %s\n", User, BackupFilename);
+
 	poke_daemon();
 }