Use drop() instead of disconnect()

Previously, the user had to explicitly call diconnect() to terminate the
connection to the Nitrokey.  Now NK_logout() is called automatically
once the device is out of scope as UnauthenticatedDevice implements
Drop.  AdminAuthenticatedDevice and UserAuthenticatedDevice do not have
to implement Drop, as it will be called recursively.

3 files changed, 8 insertions, 26 deletions

diff --git a/TODO.md b/TODO.md
index b9efdbd..b2fa21e 100644
--- a/TODO.md
+++ b/TODO.md
@@ -36,10 +36,10 @@
   - `NK_list_devices_by_cpuID`
   - `NK_connect_with_ID`
 - Fix timing issues with the `totp` and `totp_pin` test cases.
-- Consider implementing `Drop` instead of the method `disconnect`.
 - Find an example for `set_time`, also adapt `get_totp_code`.
 - Improve log level documentation.
 - Clear passwords from memory.
 - Find a nicer syntax for the `write_config` test.
 - Fix segmentation faults when freeing string literals with old Nitrokey
   versions (fixed in libnitrokey commit 7a8550d).
+- Prevent construction of internal types.
diff --git a/src/lib.rs b/src/lib.rs
index 817ee0a..1548950 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -329,30 +329,6 @@ static TEMPORARY_PASSWORD_LENGTH: usize = 25;
 /// [`get_hotp_code`]: #method.get_hotp_code
 /// [`get_totp_code`]: #method.get_totp_code
 pub trait Device {
-    /// Closes the connection to this device.  This method consumes the device.
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::CommandError;
-    ///
-    /// # fn try_main() -> Result<(), CommandError> {
-    /// let device = nitrokey::connect()?;
-    /// // perform tasks ...
-    /// device.disconnect();
-    /// #     Ok(())
-    /// # }
-    /// ```
-    fn disconnect(self)
-    where
-        Self: std::marker::Sized,
-    {
-        unsafe {
-            nitrokey_sys::NK_logout();
-        }
-    }
-
     /// Sets the time on the Nitrokey.  This command may set the time to
     /// arbitrary values.  `time` is the number of seconds since January 1st,
     /// 1970 (Unix timestamp).
@@ -1110,6 +1086,12 @@ impl UnauthenticatedDevice {
     }
 }
 
+impl Drop for UnauthenticatedDevice {
+    fn drop(&mut self) {
+        unsafe { nitrokey_sys::NK_logout(); }
+    }
+}
+
 impl Device for UnauthenticatedDevice {}
 
 impl UserAuthenticatedDevice {
diff --git a/src/tests/pro.rs b/src/tests/pro.rs
index 732c248..feadcbc 100644
--- a/src/tests/pro.rs
+++ b/src/tests/pro.rs
@@ -48,7 +48,7 @@ fn connect() {
 #[cfg_attr(not(feature = "test-pro"), ignore)]
 fn disconnect() {
     set_debug(false);
-    ::connect().unwrap().disconnect();
+    ::connect().unwrap();
     unsafe {
         let ptr = ::nitrokey_sys::NK_device_serial_number();
         assert!(!ptr.is_null());