Separation of concerns. We now have a trait for identifying

a database type, and an implementation for mLocate.  That's a
start.

src/database.rs

@@ -0,0 +1,3 @@
+pub trait LocateDb {
+    fn is(magic: &[u8]) -> bool;
+}

src/lib.rs

@@ -1,15 +1,33 @@
-extern crate structview;
-use structview::{u32_be, View};
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-#[derive(Clone, Copy, View)]
-#[repr(C)]
-pub struct MlHeader {
-    magic: [u8; 8], /* '\0', 'm', 'l', 'o', 'c', 'a', 't', 'e' */
-    conf_size: u32_be,
-    version: u8,
-    check_visibility: u8,
-    pad: [u8; 2],
-}
+//! MLocate
+//!
+//! The readme has the full explanation, but the `locate` suite of
+//! tools present in all Linux distributions is used to locate files
+//! on your storage device.  Rather than search the device directly,
+//! `locate` scans a catalog file created during downtime.
+//!
+//! `MLocate` is the most popular implementation of the locate system,
+//! but it has three annoying flaws:
+//!
+//! 1. The archive file isn't very compressed.
+//! 2. The archive file is always an average of 12 hours out of date.
+//! 3. The archive is accessible only through a command line program.
+//!
+//! This program intends to read one of two different formats, the
+//! classic mlocate format, or a new format that exploits a few nifty
+//! tricks to try and make the database file smaller and access
+//! faster.
+
+extern crate structview;
+
+pub mod database;
+pub mod mlocate_db;
+
+use crate::database::LocateDb;
+use crate::mlocate_db::MlHeader;
 
 #[cfg(test)]
 mod tests {
@@ -22,20 +40,10 @@ mod tests {
         let db = File::open("/var/lib/mlocate/mlocate.db").expect("Unable to open file");
         let mut reader = BufReader::new(db);
         match reader.fill_buf() {
-            Ok(buffer) => match MlHeader::view(&buffer[0..32]) {
-                Ok(header) => {
-                    let text = &header.magic[1..8];
-                    assert_eq!(text, *b"mlocate");
-                    assert_eq!(header.version, 0);
-                    let magic = std::str::from_utf8(text).unwrap_or("ERROR");
-                    println!(
-                        "magic: {}\nversion: {}\nconf_size: {}\nvisibility: {}",
-                        magic, header.version, header.conf_size, header.check_visibility
-                    );
-                    Ok(())
-                }
-                Err(_) => Err("The header did not unpack.".to_owned()),
-            },
+            Ok(buffer) => {
+                assert!(MlHeader::is(buffer), "Could not read DB");
+                Ok(())
+            }
             Err(_) => Err("The header could not be read".to_owned()),
         }
     }

src/mlocate_db/mod.rs

@@ -0,0 +1,25 @@
+use crate::database::LocateDb;
+use structview::{u32_be, View};
+
+#[derive(Clone, Copy, View)]
+#[repr(C)]
+pub struct MlHeader {
+    magic: [u8; 8], /* '\0', 'm', 'l', 'o', 'c', 'a', 't', 'e' */
+    conf_size: u32_be,
+    version: u8,
+    check_visibility: u8,
+    pad: [u8; 2],
+}
+
+impl LocateDb for MlHeader {
+    fn is(magic: &[u8]) -> bool {
+        if magic.len() < 32 {
+            false
+        } else {
+            match MlHeader::view(&magic[0..32]) {
+                Ok(header) => header.magic[0..8] == *b"\0mlocate" && header.version == 0,
+                Err(_) => false,
+            }
+        }
+    }
+}