Successfully read the mlocatedb header.

This commit shows how to read the mlocatedb header,
with a test to assert that the read is correct.

.gitignore

@@ -0,0 +1,2 @@
+/target
+Cargo.lock

Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "mlocate-rs"
+version = "0.1.0"
+authors = ["Elf M. Sternberg <elf.sternberg@gmail.com>"]
+edition = "2018"
+license = "MPL-2.0+"
+description = "Rust implementation of the Linux mlocate client, with library."
+repository = "https://github.com/elfsternberg/mlocate-rs"
+readme = "./README.md"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+globset = "0.4.8"
+regex = "1.5.4"
+clap = "2.33.3"
+structview = "1.1.0"

src/lib.rs

@@ -0,0 +1,42 @@
+extern crate structview;
+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],
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::fs::File;
+    use std::io::{BufRead, BufReader};
+
+    #[test]
+    fn can_read_header() -> Result<(), String> {
+        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()),
+            },
+            Err(_) => Err("The header could not be read".to_owned()),
+        }
+    }
+}