Add the get_sd_card_usage function to the Storage struct

This patch adds support for the NK_get_SD_usage_data function.  It
returns a range of the SD card that has not been accessed during this
power cycle.

4 files changed, 51 insertions, 3 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b477c3b..cebe8cb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ SPDX-License-Identifier: CC0-1.0
   - Add the `connect_path` function to the `Manager` struct.
 - Add the `get_status` function to the `Device` trait.
 - Rename `Status::get_status` to `get_storage_status`.
+- Add the `get_sd_card_usage` function to the `Storage` struct.
 
 # v0.4.0 (2020-01-02)
 - Remove the `test-pro` and `test-storage` features.
diff --git a/TODO.md b/TODO.md
index aaa6856..3c095e0 100644
--- a/TODO.md
+++ b/TODO.md
@@ -5,7 +5,6 @@ SPDX-License-Identifier: CC0-1.0
 
 - Add support for the currently unsupported commands:
     - `NK_fill_SD_card_with_random_data`
-    - `NK_get_SD_usage_data`
     - `NK_get_progress_bar_value`
 - Clear passwords from memory.
 - Lock password safe in `PasswordSafe::drop()` (see [nitrokey-storage-firmware
diff --git a/src/device/storage.rs b/src/device/storage.rs
index 08ec4e9..a2c598b 100644
--- a/src/device/storage.rs
+++ b/src/device/storage.rs
@@ -1,7 +1,8 @@
-// Copyright (C) 2019-2019 Robin Krahl <robin.krahl@ireas.org>
+// Copyright (C) 2019-2020 Robin Krahl <robin.krahl@ireas.org>
 // SPDX-License-Identifier: MIT
 
 use std::fmt;
+use std::ops;
 
 use nitrokey_sys;
 
@@ -635,6 +636,45 @@ impl<'a> Storage<'a> {
         })
     }
 
+    /// Returns a range of the SD card that has not been used to during this power cycle.
+    ///
+    /// The Nitrokey Storage tracks read and write access to the SD card during a power cycle.
+    /// This method returns a range of the SD card that has not been accessed during this power
+    /// cycle.  The range is relative to the total size of the SD card, so both values are less
+    /// than or equal to 100.  This can be used as a guideline when creating a hidden volume.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// let mut manager = nitrokey::take()?;
+    /// let storage = manager.connect_storage()?;
+    /// let usage = storage.get_sd_card_usage()?;
+    /// println!("SD card usage: {}..{}", usage.start, usage.end);
+    /// # Ok::<(), nitrokey::Error>(())
+    /// ```
+    pub fn get_sd_card_usage(&self) -> Result<ops::Range<u8>, Error> {
+        let mut usage_data = nitrokey_sys::NK_SD_usage_data {
+            write_level_min: 0,
+            write_level_max: 0,
+        };
+        let result = unsafe { nitrokey_sys::NK_get_SD_usage_data(&mut usage_data) };
+        match get_command_result(result) {
+            Ok(_) => {
+                if usage_data.write_level_min > usage_data.write_level_max
+                    || usage_data.write_level_max > 100
+                {
+                    Err(Error::UnexpectedError)
+                } else {
+                    Ok(ops::Range {
+                        start: usage_data.write_level_min,
+                        end: usage_data.write_level_max,
+                    })
+                }
+            }
+            Err(err) => Err(err),
+        }
+    }
+
     /// Blinks the red and green LED alternatively and infinitely until the device is reconnected.
     pub fn wink(&mut self) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_wink() })
diff --git a/tests/device.rs b/tests/device.rs
index f2a7031..070f3c1 100644
--- a/tests/device.rs
+++ b/tests/device.rs
@@ -1,4 +1,4 @@
-// Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
+// Copyright (C) 2018-2020 Robin Krahl <robin.krahl@ireas.org>
 // SPDX-License-Identifier: MIT
 
 mod util;
@@ -640,6 +640,14 @@ fn clear_new_sd_card_warning(device: Storage) {
 }
 
 #[test_device]
+fn get_sd_card_usage(device: Storage) {
+    let range = unwrap_ok!(device.get_sd_card_usage());
+
+    assert!(range.end >= range.start);
+    assert!(range.end <= 100);
+}
+
+#[test_device]
 fn export_firmware(device: Storage) {
     let mut device = device;
     assert_cmd_err!(