tor-browser

MIDIUtils.cpp (5445B)

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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "mozilla/dom/MIDIUtils.h"

#include "mozilla/UniquePtr.h"
#include "mozilla/dom/MIDITypes.h"

// Taken from MIDI IMPLEMENTATION CHART INSTRUCTIONS, MIDI Spec v1.0, Pg. 97
static const uint8_t kCommandByte = 0x80;
static const uint8_t kSysexMessageStart = 0xF0;
static const uint8_t kSystemMessage = 0xF0;
static const uint8_t kSysexMessageEnd = 0xF7;
static const uint8_t kSystemRealtimeMessage = 0xF8;
// Represents the length of all possible command messages.
// Taken from MIDI Spec, Pg. 101v 1.0, Table 2
static const uint8_t kCommandLengths[] = {3, 3, 3, 3, 2, 2, 3};
// Represents the length of all possible system messages. The length of sysex
// messages is variable, so we just put zero since it won't be checked anyways.
// Taken from MIDI Spec v1.0, Pg. 105, Table 5
static const uint8_t kSystemLengths[] = {0, 2, 3, 2, 1, 1, 1, 1};
static const uint8_t kReservedStatuses[] = {0xf4, 0xf5, 0xf9, 0xfd};

namespace mozilla::dom::MIDIUtils {

static bool IsSystemRealtimeMessage(uint8_t aByte) {
 return (aByte & kSystemRealtimeMessage) == kSystemRealtimeMessage;
}

static bool IsCommandByte(uint8_t aByte) {
 return (aByte & kCommandByte) == kCommandByte;
}

static bool IsReservedStatus(uint8_t aByte) {
 for (const auto& msg : kReservedStatuses) {
   if (aByte == msg) {
     return true;
   }
 }

 return false;
}

// Checks validity of MIDIMessage passed to it. Throws debug warnings and
// returns false if message is not valid.
bool IsValidMessage(const MIDIMessage* aMsg) {
 if (aMsg->data().Length() == 0) {
   return false;
 }

 uint8_t cmd = aMsg->data()[0];
 // If first byte isn't a command, something is definitely wrong.
 if (!IsCommandByte(cmd)) {
   NS_WARNING("Constructed a MIDI packet where first byte is not command!");
   return false;
 }

 if (IsReservedStatus(cmd)) {
   NS_WARNING("Using a reserved message");
   return false;
 }

 if (cmd == kSysexMessageStart) {
   // All we can do with sysex is make sure it starts and ends with the
   // correct command bytes and that it does not contain other command bytes.
   if (aMsg->data()[aMsg->data().Length() - 1] != kSysexMessageEnd) {
     NS_WARNING("Last byte of Sysex Message not 0xF7!");
     return false;
   }

   for (size_t i = 1; i < aMsg->data().Length() - 2; i++) {
     if (IsCommandByte(aMsg->data()[i])) {
       return false;
     }
   }

   return true;
 }
 // For system realtime messages, the length should always be 1.
 if (IsSystemRealtimeMessage(cmd)) {
   return aMsg->data().Length() == 1;
 }
 // Otherwise, just use the correct array for testing lengths. We can't tell
 // much about message validity other than that.
 if ((cmd & kSystemMessage) == kSystemMessage) {
   if (cmd - kSystemMessage >=
       static_cast<uint8_t>(std::size(kSystemLengths))) {
     NS_WARNING("System Message Command byte not valid!");
     return false;
   }
   return aMsg->data().Length() == kSystemLengths[cmd - kSystemMessage];
 }
 // For non system commands, we only care about differences in the high nibble
 // of the first byte. Shift this down to give the index of the expected packet
 // length.
 uint8_t cmdIndex = (cmd - kCommandByte) >> 4;
 if (cmdIndex >= std::size(kCommandLengths)) {
   // If our index is bigger than our array length, command byte is unknown;
   NS_WARNING("Unknown MIDI command!");
   return false;
 }
 return aMsg->data().Length() == kCommandLengths[cmdIndex];
}

bool ParseMessages(const nsTArray<uint8_t>& aByteBuffer,
                  const TimeStamp& aTimestamp,
                  nsTArray<MIDIMessage>& aMsgArray) {
 bool inSysexMessage = false;
 UniquePtr<MIDIMessage> currentMsg = nullptr;
 for (const auto& byte : aByteBuffer) {
   if (IsSystemRealtimeMessage(byte)) {
     MIDIMessage rt_msg;
     rt_msg.data().AppendElement(byte);
     rt_msg.timestamp() = aTimestamp;
     if (!IsValidMessage(&rt_msg)) {
       return false;
     }
     aMsgArray.AppendElement(rt_msg);
     continue;
   }

   if (byte == kSysexMessageEnd) {
     if (!inSysexMessage) {
       NS_WARNING(
           "Got sysex message end with no sysex message being processed!");
       return false;
     }
     inSysexMessage = false;
   } else if (IsCommandByte(byte)) {
     if (currentMsg) {
       if (!IsValidMessage(currentMsg.get())) {
         return false;
       }

       aMsgArray.AppendElement(*currentMsg);
     }

     currentMsg = MakeUnique<MIDIMessage>();
     currentMsg->timestamp() = aTimestamp;
   }

   if (!currentMsg) {
     NS_WARNING("No command byte has been encountered yet!");
     return false;
   }

   currentMsg->data().AppendElement(byte);

   if (byte == kSysexMessageStart) {
     inSysexMessage = true;
   }
 }

 if (currentMsg) {
   if (!IsValidMessage(currentMsg.get())) {
     return false;
   }
   aMsgArray.AppendElement(*currentMsg);
 }

 return true;
}

bool IsSysexMessage(const MIDIMessage& aMsg) {
 if (aMsg.data().Length() == 0) {
   return false;
 }
 return aMsg.data()[0] == kSysexMessageStart;
}
}  // namespace mozilla::dom::MIDIUtils