usb_util: Add descriptors

add config descriptors, endpoint descriptors, interface descriptors.

BUG=chromium:831850
TEST=cargo test
CQ-DEPEND=CL:1135783

Change-Id: If74c407f198725bdc6a3096b03d6fe02dcd29ec8
Reviewed-on: https://chromium-review.googlesource.com/1299716
Commit-Ready: Jingkui Wang <jkwang@google.com>
Tested-by: Jingkui Wang <jkwang@google.com>
Reviewed-by: Jingkui Wang <jkwang@google.com>

usb_util/src/config_descriptor.rs

@@ -2,11 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+use super::interface_descriptor::InterfaceDescriptor;
 use bindings;
 use bindings::libusb_config_descriptor;
+use std::ops::Deref;
 
 /// ConfigDescriptor wraps libusb_config_descriptor.
-/// TODO(jkwang) Add utility functions to make ConfigDescriptor actually useful.
 pub struct ConfigDescriptor {
     descriptor: *mut libusb_config_descriptor,
 }
@@ -29,4 +30,37 @@ impl ConfigDescriptor {
         assert!(!descriptor.is_null());
         ConfigDescriptor { descriptor }
     }
+
+    /// Get interface by number and alt setting.
+    pub fn get_interface_descriptor(
+        &self,
+        interface_num: u8,
+        alt_setting: i32,
+    ) -> Option<InterfaceDescriptor> {
+        let config_descriptor = self.deref();
+        if interface_num >= config_descriptor.bNumInterfaces {
+            return None;
+        }
+        // Safe because interface num is checked.
+        let interface = unsafe { &*(config_descriptor.interface.offset(interface_num as isize)) };
+
+        if alt_setting >= interface.num_altsetting {
+            return None;
+        }
+        // Safe because setting num is checked.
+        unsafe {
+            Some(InterfaceDescriptor::new(
+                &*(interface.altsetting.offset(alt_setting as isize)),
+            ))
+        }
+    }
+}
+
+impl Deref for ConfigDescriptor {
+    type Target = libusb_config_descriptor;
+
+    fn deref(&self) -> &libusb_config_descriptor {
+        // Safe because 'self.descriptor' is valid.
+        unsafe { &*(self.descriptor) }
+    }
 }

usb_util/src/endpoint_descriptor.rs

@@ -0,0 +1,56 @@
+// Copyright 2018 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+use super::types::{EndpointDirection, EndpointType};
+use bindings::libusb_endpoint_descriptor;
+use std::ops::Deref;
+
+/// ConfigDescriptor wraps libusb_interface_descriptor.
+pub struct EndpointDescriptor<'a>(&'a libusb_endpoint_descriptor);
+
+const ENDPOINT_DESCRIPTOR_DIRECTION_MASK: u8 = 1 << 7;
+const ENDPOINT_DESCRIPTOR_NUMBER_MASK: u8 = 0xf;
+const ENDPOINT_DESCRIPTOR_ATTRIBUTES_TYPE_MASK: u8 = 0x3;
+
+impl<'a> EndpointDescriptor<'a> {
+    // Create new endpoint descriptor.
+    pub fn new(descriptor: &libusb_endpoint_descriptor) -> EndpointDescriptor {
+        EndpointDescriptor(descriptor)
+    }
+
+    // Get direction of this endpoint.
+    pub fn get_direction(&self) -> EndpointDirection {
+        let direction = self.0.bEndpointAddress & ENDPOINT_DESCRIPTOR_DIRECTION_MASK;
+        if direction > 0 {
+            EndpointDirection::DeviceToHost
+        } else {
+            EndpointDirection::HostToDevice
+        }
+    }
+
+    // Get endpoint number.
+    pub fn get_endpoint_number(&self) -> u8 {
+        self.0.bEndpointAddress & ENDPOINT_DESCRIPTOR_NUMBER_MASK
+    }
+
+    // Get endpoint type.
+    pub fn get_endpoint_type(&self) -> Option<EndpointType> {
+        let ep_type = self.0.bmAttributes & ENDPOINT_DESCRIPTOR_ATTRIBUTES_TYPE_MASK;
+        match ep_type {
+            0 => Some(EndpointType::Control),
+            1 => Some(EndpointType::Isochronous),
+            2 => Some(EndpointType::Bulk),
+            3 => Some(EndpointType::Interrupt),
+            _ => None,
+        }
+    }
+}
+
+impl<'a> Deref for EndpointDescriptor<'a> {
+    type Target = libusb_endpoint_descriptor;
+
+    fn deref(&self) -> &libusb_endpoint_descriptor {
+        self.0
+    }
+}

usb_util/src/interface_descriptor.rs

@@ -0,0 +1,39 @@
+// Copyright 2018 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+use super::endpoint_descriptor::EndpointDescriptor;
+use bindings::libusb_interface_descriptor;
+use std::ops::Deref;
+
+/// ConfigDescriptor wraps libusb_interface_descriptor.
+pub struct InterfaceDescriptor<'a>(&'a libusb_interface_descriptor);
+
+impl<'a> InterfaceDescriptor<'a> {
+    /// Create a new Interface descriptor.
+    pub fn new(descriptor: &'a libusb_interface_descriptor) -> InterfaceDescriptor<'a> {
+        InterfaceDescriptor(descriptor)
+    }
+
+    /// Get endpoint descriptor at index.
+    pub fn endpoint_descriptor(&self, ep_idx: u8) -> Option<EndpointDescriptor> {
+        if ep_idx >= self.0.bNumEndpoints {
+            return None;
+        }
+
+        // Safe because idx is checked.
+        unsafe {
+            Some(EndpointDescriptor::new(
+                &*(self.0.endpoint.offset(ep_idx as isize)),
+            ))
+        }
+    }
+}
+
+impl<'a> Deref for InterfaceDescriptor<'a> {
+    type Target = libusb_interface_descriptor;
+
+    fn deref(&self) -> &libusb_interface_descriptor {
+        self.0
+    }
+}

usb_util/src/lib.rs

@@ -14,6 +14,8 @@ extern crate data_model;
 pub mod error;
 pub mod config_descriptor;
 pub mod device_handle;
+pub mod endpoint_descriptor;
+pub mod interface_descriptor;
 pub mod libusb_context;
 pub mod libusb_device;
 pub mod types;