dom/midi/MIDIUtils.cpp

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim:set ts=2 sw=2 sts=2 et cindent: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #include "mozilla/dom/MIDITypes.h"
   8 #include "mozilla/dom/MIDIUtils.h"
   9 #include "mozilla/UniquePtr.h"
  10
  11 // Taken from MIDI IMPLEMENTATION CHART INSTRUCTIONS, MIDI Spec v1.0, Pg. 97
  12 static const uint8_t kCommandByte = 0x80;
  13 static const uint8_t kSysexMessageStart = 0xF0;
  14 static const uint8_t kSystemMessage = 0xF0;
  15 static const uint8_t kSysexMessageEnd = 0xF7;
  16 static const uint8_t kSystemRealtimeMessage = 0xF8;
  17 // Represents the length of all possible command messages.
  18 // Taken from MIDI Spec, Pg. 101v 1.0, Table 2
  19 static const uint8_t kCommandLengths[] = {3, 3, 3, 3, 2, 2, 3};
  20 // Represents the length of all possible system messages. The length of sysex
  21 // messages is variable, so we just put zero since it won't be checked anyways.
  22 // Taken from MIDI Spec v1.0, Pg. 105, Table 5
  23 static const uint8_t kSystemLengths[] = {0, 2, 3, 2, 1, 1, 1, 1};
  24 static const uint8_t kReservedStatuses[] = {0xf4, 0xf5, 0xf9, 0xfd};
  25
  26 namespace mozilla::dom::MIDIUtils {
  27
  28 static bool IsSystemRealtimeMessage(uint8_t aByte) {
  29   return (aByte & kSystemRealtimeMessage) == kSystemRealtimeMessage;
  30 }
  31
  32 static bool IsCommandByte(uint8_t aByte) {
  33   return (aByte & kCommandByte) == kCommandByte;
  34 }
  35
  36 static bool IsReservedStatus(uint8_t aByte) {
  37   for (const auto& msg : kReservedStatuses) {
  38     if (aByte == msg) {
  39       return true;
  40     }
  41   }
  42
  43   return false;
  44 }
  45
  46 // Checks validity of MIDIMessage passed to it. Throws debug warnings and
  47 // returns false if message is not valid.
  48 bool IsValidMessage(const MIDIMessage* aMsg) {
  49   if (aMsg->data().Length() == 0) {
  50     return false;
  51   }
  52
  53   uint8_t cmd = aMsg->data()[0];
  54   // If first byte isn't a command, something is definitely wrong.
  55   if (!IsCommandByte(cmd)) {
  56     NS_WARNING("Constructed a MIDI packet where first byte is not command!");
  57     return false;
  58   }
  59
  60   if (IsReservedStatus(cmd)) {
  61     NS_WARNING("Using a reserved message");
  62     return false;
  63   }
  64
  65   if (cmd == kSysexMessageStart) {
  66     // All we can do with sysex is make sure it starts and ends with the
  67     // correct command bytes and that it does not contain other command bytes.
  68     if (aMsg->data()[aMsg->data().Length() - 1] != kSysexMessageEnd) {
  69       NS_WARNING("Last byte of Sysex Message not 0xF7!");
  70       return false;
  71     }
  72
  73     for (size_t i = 1; i < aMsg->data().Length() - 2; i++) {
  74       if (IsCommandByte(aMsg->data()[i])) {
  75         return false;
  76       }
  77     }
  78
  79     return true;
  80   }
  81   // For system realtime messages, the length should always be 1.
  82   if (IsSystemRealtimeMessage(cmd)) {
  83     return aMsg->data().Length() == 1;
  84   }
  85   // Otherwise, just use the correct array for testing lengths. We can't tell
  86   // much about message validity other than that.
  87   if ((cmd & kSystemMessage) == kSystemMessage) {
  88     if (cmd - kSystemMessage >=
  89         static_cast<uint8_t>(std::size(kSystemLengths))) {
  90       NS_WARNING("System Message Command byte not valid!");
  91       return false;
  92     }
  93     return aMsg->data().Length() == kSystemLengths[cmd - kSystemMessage];
  94   }
  95   // For non system commands, we only care about differences in the high nibble
  96   // of the first byte. Shift this down to give the index of the expected packet
  97   // length.
  98   uint8_t cmdIndex = (cmd - kCommandByte) >> 4;
  99   if (cmdIndex >= std::size(kCommandLengths)) {
 100     // If our index is bigger than our array length, command byte is unknown;
 101     NS_WARNING("Unknown MIDI command!");
 102     return false;
 103   }
 104   return aMsg->data().Length() == kCommandLengths[cmdIndex];
 105 }
 106
 107 bool ParseMessages(const nsTArray<uint8_t>& aByteBuffer,
 108                    const TimeStamp& aTimestamp,
 109                    nsTArray<MIDIMessage>& aMsgArray) {
 110   bool inSysexMessage = false;
 111   UniquePtr<MIDIMessage> currentMsg = nullptr;
 112   for (const auto& byte : aByteBuffer) {
 113     if (IsSystemRealtimeMessage(byte)) {
 114       MIDIMessage rt_msg;
 115       rt_msg.data().AppendElement(byte);
 116       rt_msg.timestamp() = aTimestamp;
 117       if (!IsValidMessage(&rt_msg)) {
 118         return false;
 119       }
 120       aMsgArray.AppendElement(rt_msg);
 121       continue;
 122     }
 123
 124     if (byte == kSysexMessageEnd) {
 125       if (!inSysexMessage) {
 126         NS_WARNING(
 127             "Got sysex message end with no sysex message being processed!");
 128         return false;
 129       }
 130       inSysexMessage = false;
 131     } else if (IsCommandByte(byte)) {
 132       if (currentMsg) {
 133         if (!IsValidMessage(currentMsg.get())) {
 134           return false;
 135         }
 136
 137         aMsgArray.AppendElement(*currentMsg);
 138       }
 139
 140       currentMsg = MakeUnique<MIDIMessage>();
 141       currentMsg->timestamp() = aTimestamp;
 142     }
 143
 144     if (!currentMsg) {
 145       NS_WARNING("No command byte has been encountered yet!");
 146       return false;
 147     }
 148
 149     currentMsg->data().AppendElement(byte);
 150
 151     if (byte == kSysexMessageStart) {
 152       inSysexMessage = true;
 153     }
 154   }
 155
 156   if (currentMsg) {
 157     if (!IsValidMessage(currentMsg.get())) {
 158       return false;
 159     }
 160     aMsgArray.AppendElement(*currentMsg);
 161   }
 162
 163   return true;
 164 }
 165
 166 bool IsSysexMessage(const MIDIMessage& aMsg) {
 167   if (aMsg.data().Length() == 0) {
 168     return false;
 169   }
 170   return aMsg.data()[0] == kSysexMessageStart;
 171 }
 172 }  // namespace mozilla::dom::MIDIUtils