libremail: file: Add try_touch() function

The try_touch() function is responsible for attempting to create new
files while optionally filling it with initial data

Signed-off-by: Chloe M. <chloe@mirocom.org>

libremail/common/file_subr.c

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2026, Chloe Moffett
+ * Provided under the BSD-3 clause
+ */
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+#include "libremail/file.h"
+
+int
+try_mkdir(const char *path, mode_t mode)
+{
+    if (path == NULL) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    if (access(path, F_OK) != 0) {
+        return mkdir(path, mode);
+    }
+
+    return 0;
+}
+
+int
+try_touch(const char *path, mode_t mode, void *buf, size_t len)
+{
+    ssize_t retlen;
+    int fd;
+
+    if (path == NULL) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    fd = open(path, O_RDONLY | O_CREAT, mode);
+    if (fd < 0) {
+        perror("open");
+        return -1;
+    }
+
+    /* Write the initial contents if we can */
+    if (buf != NULL) {
+        retlen = write(fd, buf, len);
+        if (retlen <= 0) {
+            close(fd);
+            perror("write");
+            return -1;
+        }
+    }
+
+    close(fd);
+    return 0;
+}