Introduce USB MIDI descriptor parser

media/midi/usb_midi_descriptor_parser.cc

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/midi/usb_midi_descriptor_parser.h"
+
+#include "base/logging.h"
+
+namespace media {
+
+namespace {
+
+// The constants below are specified in USB spec, USB audio spec
+// and USB midi spec.
+
+enum DescriptorType {
+  TYPE_DEVICE = 1,
+  TYPE_CONFIGURATION = 2,
+  TYPE_STRING = 3,
+  TYPE_INTERFACE = 4,
+  TYPE_ENDPOINT = 5,
+  TYPE_DEVICE_QUALIFIER = 6,
+  TYPE_OTHER_SPEED_CONFIGURATION = 7,
+  TYPE_INTERFACE_POWER = 8,
+
+  TYPE_CS_INTERFACE = 36,
+  TYPE_CS_ENDPOINT = 37,
+};
+
+enum DescriptorSubType {
+  SUBTYPE_MS_DESCRIPTOR_UNDEFINED = 0,
+  SUBTYPE_MS_HEADER = 1,
+  SUBTYPE_MIDI_IN_JACK = 2,
+  SUBTYPE_MIDI_OUT_JACK = 3,
+  SUBTYPE_ELEMENT = 4,
+};
+
+enum JackType {
+  JACK_TYPE_UNDEFINED = 0,
+  JACK_TYPE_EMBEDDED = 1,
+  JACK_TYPE_EXTERNAL = 2,
+};
+
+const uint8 kAudioInterfaceClass = 1;
+const uint8 kAudioMidiInterfaceSubclass = 3;
+
+class JackMatcher {
+ public:
+  explicit JackMatcher(uint8 id) : id_(id) {}
+
+  bool operator() (const UsbMidiJack& jack) const {
+    return jack.jack_id == id_;
+  }
+
+ private:
+  uint8 id_;
+};
+
+}  // namespace
+
+UsbMidiDescriptorParser::UsbMidiDescriptorParser()
+    : is_parsing_usb_midi_interface_(false),
+      current_endpoint_address_(0),
+      current_cable_number_(0) {}
+
+UsbMidiDescriptorParser::~UsbMidiDescriptorParser() {}
+
+bool UsbMidiDescriptorParser::Parse(UsbMidiDevice* device,
+                                    const uint8* data,
+                                    size_t size,
+                                    std::vector<UsbMidiJack>* jacks) {
+  jacks->clear();
+  bool result = ParseInternal(device, data, size, jacks);
+  if (!result)
+    jacks->clear();
+  Clear();
+  return result;
+}
+
+bool UsbMidiDescriptorParser::ParseInternal(UsbMidiDevice* device,
+                                            const uint8* data,
+                                            size_t size,
+                                            std::vector<UsbMidiJack>* jacks) {
+  const uint8* current = data;
+  while (current < data + size) {
+    uint8 length = current[0];
+    if (length <= 1) {
+      DVLOG(1) << "Descriptor Type is not accessible.";
+      return false;
+    }
+    if (current + length > data + size) {

[DaleCurtis, 2014/01/10 01:55:57]

current + length >= data + size

[yhirano, 2014/01/10 02:30:32]

current_length == data + size means that it is the (valid) last descriptor, so
it's OK.

+      DVLOG(1) << "The header size is incorrect.";
+      return false;
+    }
+    DescriptorType descriptor_type = static_cast<DescriptorType>(current[1]);
+    switch (descriptor_type) {

[DaleCurtis, 2014/01/10 01:55:57]

Instead of checking !is_parsing_usb_midi_interface_ in all the methods, how
about:

const bool is_interface = descriptor_type == TYPE_INTERFACE;
if (is_interface && !ParseInterface(current, length))
  return false;

if (is_interface || !is_parsing_usb_midi_interface_)
  continue;

If you rephrase the while like so, you can avoid duplicating the advance logic:
for (const uint8* current = data; current < data + size; current += current[0])
{}

[yhirano, 2014/01/10 02:30:32]

Thanks, done.

+      case TYPE_INTERFACE:
+        if (!ParseInterface(current, length))
+          return false;
+        break;
+      case TYPE_CS_INTERFACE:
+        // We are assuming that the corresponding INTERFACE precedes
+        // the CS_INTERFACE descriptor, as specified.
+        if (!ParseCSInterface(device, current, length))
+          return false;
+        break;
+      case TYPE_ENDPOINT:
+        // We are assuming that endpoints are contained in an interface.
+        if (!ParseEndpoint(current, length))
+          return false;
+        break;
+      case TYPE_CS_ENDPOINT:
+        // We are assuming that the corresponding ENDPOINT precedes
+        // the CS_ENDPOINT descriptor, as specified.
+        if (!ParseCSEndpoint(current, length, jacks))
+          return false;
+        break;
+      default:
+        // Ignore uninteresting types.
+        break;
+    }
+    current += length;
+  }
+  return true;
+}
+
+bool UsbMidiDescriptorParser::ParseInterface(const uint8* data, size_t size) {
+  if (size != 9) {
+    DVLOG(1) << "INTERFACE header size is incorrect.";
+    return false;
+  }
+  incomplete_jacks_.clear();
+
+  uint8 interface_class = data[5];
+  uint8 interface_subclass = data[6];
+
+  // All descriptors of endpoints contained in this interface
+  // precede the next INTERFACE descriptor.
+  is_parsing_usb_midi_interface_ =
+      interface_class == kAudioInterfaceClass &&
+      interface_subclass == kAudioMidiInterfaceSubclass;
+  return true;
+}
+
+bool UsbMidiDescriptorParser::ParseCSInterface(UsbMidiDevice* device,
+                                               const uint8* data,
+                                               size_t size) {
+  if (!is_parsing_usb_midi_interface_)
+    return true;
+
+  // Descriptor Type and Descriptor Subtype should be accessible.
+  if (size < 3) {
+    DVLOG(1) << "CS_INTERFACE header size is incorrect.";
+    return false;
+  }
+
+  DescriptorSubType subtype = static_cast<DescriptorSubType>(data[2]);
+
+  switch (subtype) {

[DaleCurtis, 2014/01/10 01:55:57]

Replace the switch with an early return if !IN_JACK && !OUT_JACK return true? 
Allows you to deindent this whole section a few tabs.

[yhirano, 2014/01/10 02:30:32]

Done.

+    case SUBTYPE_MIDI_IN_JACK:
+    case SUBTYPE_MIDI_OUT_JACK: {
+      if (size < 6) {
+        DVLOG(1) << "CS_INTERFACE (MIDI JACK) header size is incorrect.";
+        return false;
+      }
+      uint8 jack_type = data[3];
+      uint8 id = data[4];
+      if (jack_type == JACK_TYPE_EMBEDDED) {
+        // We can't determine the associated endpoint now.
+        incomplete_jacks_.push_back(UsbMidiJack(device, id, 0, 0));
+      }
+      break;
+    }
+    default:
+      break;
+  }
+  return true;
+}
+
+bool UsbMidiDescriptorParser::ParseEndpoint(const uint8* data, size_t size) {
+  if (!is_parsing_usb_midi_interface_)
+    return true;
+
+  if (size < 4) {
+    DVLOG(1) << "ENDPOINT header size is incorrect.";
+    return false;
+  }
+  current_endpoint_address_ = data[2];
+  current_cable_number_ = 0;
+  return true;
+}
+
+bool UsbMidiDescriptorParser::ParseCSEndpoint(const uint8* data,
+                                              size_t size,
+                                              std::vector<UsbMidiJack>* jacks) {
+  const size_t kSizeForEmptyJacks = 4;
+  if (!is_parsing_usb_midi_interface_)
+    return true;
+  // CS_ENDPOINT must be of size 4 + n where n is the number of associated
+  // jacks.
+  if (size < kSizeForEmptyJacks) {
+    DVLOG(1) << "CS_ENDPOINT header size is incorrect.";
+    return false;
+  }
+  uint8 num_jacks = data[3];
+  if (size != kSizeForEmptyJacks + num_jacks) {
+    DVLOG(1) << "CS_ENDPOINT header size is incorrect.";
+    return false;
+  }
+
+  for (size_t i = 0; i < num_jacks; ++i) {
+    uint8 jack = data[kSizeForEmptyJacks + i];
+    std::vector<UsbMidiJack>::iterator it =
+        std::find_if(incomplete_jacks_.begin(),
+                     incomplete_jacks_.end(),
+                     JackMatcher(jack));
+    if (it == incomplete_jacks_.end()) {
+      DVLOG(1) << "A non-existing MIDI jack is associated.";
+      return false;
+    }
+    if (current_cable_number_ > 0xf) {
+      DVLOG(1) << "Cable number should range from 0x0 to 0xf.";
+      return false;
+    }
+    // CS_ENDPOINT follows ENDPOINT and hence we can use the following
+    // member variables.
+    it->cable_number = current_cable_number_++;
+    it->endpoint_address = current_endpoint_address_;
+    jacks->push_back(*it);
+    incomplete_jacks_.erase(it);
+  }
+  return true;
+}
+
+void UsbMidiDescriptorParser::Clear() {
+  is_parsing_usb_midi_interface_ = false;
+  current_endpoint_address_ = 0;
+  current_cable_number_ = 0;
+  incomplete_jacks_.clear();
+}
+
+}  // namespace media