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
  25 namespace mozilla::dom::MIDIUtils {
  26
  27 // Checks validity of MIDIMessage passed to it. Throws debug warnings and
  28 // returns false if message is not valid.
  29 bool IsValidMessage(const MIDIMessage* aMsg) {
  30   if (NS_WARN_IF(!aMsg)) {
  31     return false;
  32   }
  33   // Assert on parser problems
  34   MOZ_ASSERT(aMsg->data().Length() > 0,
  35              "Created a MIDI Message of Length 0. This should never happen!");
  36   uint8_t cmd = aMsg->data()[0];
  37   // If first byte isn't a command, something is definitely wrong.
  38   MOZ_ASSERT((cmd & kCommandByte) == kCommandByte,
  39              "Constructed a MIDI packet where first byte is not command!");
  40   if (cmd == kSysexMessageStart) {
  41     // All we can do with sysex is make sure it starts and  ends with the
  42     // correct command bytes.
  43     if (aMsg->data()[aMsg->data().Length() - 1] != kSysexMessageEnd) {
  44       NS_WARNING("Last byte of Sysex Message not 0xF7!");
  45       return false;
  46     }
  47     return true;
  48   }
  49   // For system realtime messages, the length should always be 1.
  50   if ((cmd & kSystemRealtimeMessage) == kSystemRealtimeMessage) {
  51     return aMsg->data().Length() == 1;
  52   }
  53   // Otherwise, just use the correct array for testing lengths. We can't tell
  54   // much about message validity other than that.
  55   if ((cmd & kSystemMessage) == kSystemMessage) {
  56     if (cmd - kSystemMessage >=
  57         static_cast<uint8_t>(ArrayLength(kSystemLengths))) {
  58       NS_WARNING("System Message Command byte not valid!");
  59       return false;
  60     }
  61     return aMsg->data().Length() == kSystemLengths[cmd - kSystemMessage];
  62   }
  63   // For non system commands, we only care about differences in the high nibble
  64   // of the first byte. Shift this down to give the index of the expected packet
  65   // length.
  66   uint8_t cmdIndex = (cmd - kCommandByte) >> 4;
  67   if (cmdIndex >= ArrayLength(kCommandLengths)) {
  68     // If our index is bigger than our array length, command byte is unknown;
  69     NS_WARNING("Unknown MIDI command!");
  70     return false;
  71   }
  72   return aMsg->data().Length() == kCommandLengths[cmdIndex];
  73 }
  74
  75 uint32_t ParseMessages(const nsTArray<uint8_t>& aByteBuffer,
  76                        const TimeStamp& aTimestamp,
  77                        nsTArray<MIDIMessage>& aMsgArray) {
  78   uint32_t bytesRead = 0;
  79   bool inSysexMessage = false;
  80   UniquePtr<MIDIMessage> currentMsg;
  81   for (auto& byte : aByteBuffer) {
  82     bytesRead++;
  83     if ((byte & kSystemRealtimeMessage) == kSystemRealtimeMessage) {
  84       MIDIMessage rt_msg;
  85       rt_msg.data().AppendElement(byte);
  86       rt_msg.timestamp() = aTimestamp;
  87       aMsgArray.AppendElement(rt_msg);
  88       continue;
  89     }
  90     if (byte == kSysexMessageEnd) {
  91       if (!inSysexMessage) {
  92         MOZ_ASSERT(inSysexMessage);
  93         NS_WARNING(
  94             "Got sysex message end with no sysex message being processed!");
  95       }
  96       inSysexMessage = false;
  97     } else if (byte & kCommandByte) {
  98       if (currentMsg && IsValidMessage(currentMsg.get())) {
  99         aMsgArray.AppendElement(*currentMsg);
 100       }
 101       currentMsg = MakeUnique<MIDIMessage>();
 102       currentMsg->timestamp() = aTimestamp;
 103     }
 104     currentMsg->data().AppendElement(byte);
 105     if (byte == kSysexMessageStart) {
 106       inSysexMessage = true;
 107     }
 108   }
 109   if (currentMsg && IsValidMessage(currentMsg.get())) {
 110     aMsgArray.AppendElement(*currentMsg);
 111   }
 112   return bytesRead;
 113 }
 114
 115 bool IsSysexMessage(const MIDIMessage& aMsg) {
 116   if (aMsg.data().Length() == 0) {
 117     return false;
 118   }
 119   if (aMsg.data()[0] == kSysexMessageStart) {
 120     return true;
 121   }
 122   return false;
 123 }
 124 }  // namespace mozilla::dom::MIDIUtils