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/inc/libremail/common.h

@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2026, Chloe Moffett
+ * Provided under the BSD-3 clause
+ */
+
+#ifndef LIBREMAIL_COMMON_H
+#define LIBREMAIL_COMMON_H 1
+
+/* Length of SHA256 hash in bytes */
+#define SHA256_N_BYTES 32
+
+#endif  /* !LIBREMAIL_COMMON_H */

libremail/inc/libremail/file.h

@@ -18,4 +18,16 @@
  */
 int try_mkdir(const char *path, mode_t mode);
 
+/*
+ * Attempt to create a new file if it doesn't exist
+ *
+ * @path: Path to file to create
+ * @mode: Desired mode to assign
+ * @buf:  Buffer of initial data (NULLable)
+ * @len:  Length of initial data
+ *
+ * Returns zero on success
+ */
+int try_touch(const char *path, mode_t mode, void *buf, size_t len);
+
 #endif  /* !LIBREMAIL_FILE_H */