media/midi/midi_message_queue.cc

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "media/midi/midi_message_queue.h"
   6
   7 #include <algorithm>
   8
   9 #include "base/logging.h"
  10 #include "media/midi/midi_message_util.h"
  11
  12 namespace media {
  13 namespace {
  14
  15 const uint8 kSysEx = 0xf0;
  16 const uint8 kEndOfSysEx = 0xf7;
  17
  18 bool IsDataByte(uint8 data) {
  19   return (data & 0x80) == 0;
  20 }
  21
  22 bool IsFirstStatusByte(uint8 data) {
  23   return !IsDataByte(data) && data != kEndOfSysEx;
  24 }
  25
  26 bool IsSystemRealTimeMessage(uint8 data) {
  27   return 0xf8 <= data;
  28 }
  29
  30 }  // namespace
  31
  32 MidiMessageQueue::MidiMessageQueue(bool allow_running_status)
  33     : allow_running_status_(allow_running_status) {}
  34
  35 MidiMessageQueue::~MidiMessageQueue() {}
  36
  37 void MidiMessageQueue::Add(const std::vector<uint8>& data) {
  38   queue_.insert(queue_.end(), data.begin(), data.end());
  39 }
  40
  41 void MidiMessageQueue::Add(const uint8* data, size_t length) {
  42   queue_.insert(queue_.end(), data, data + length);
  43 }
  44
  45 void MidiMessageQueue::Get(std::vector<uint8>* message) {
  46   message->clear();
  47
  48   while (true) {
  49     if (queue_.empty())
  50       return;
  51
  52     const uint8 next = queue_.front();
  53     queue_.pop_front();
  54
  55     // "System Real Time Messages" is a special kind of MIDI messages, which can
  56     // appear at arbitrary byte position of MIDI stream. Here we reorder
  57     // "System Real Time Messages" prior to |next_message_| so that each message
  58     // can be clearly separated as a complete MIDI message.
  59     if (IsSystemRealTimeMessage(next)) {
  60       message->push_back(next);
  61       return;
  62     }
  63
  64     // Here |next_message_[0]| may contain the previous status byte when
  65     // |allow_running_status_| is true. Following condition fixes up
  66     // |next_message_| if running status condition is not fulfilled.
  67     if (!next_message_.empty() &&
  68         ((next_message_[0] == kSysEx && IsFirstStatusByte(next)) ||
  69          (next_message_[0] != kSysEx && !IsDataByte(next)))) {
  70       // An invalid data sequence is found or running status condition is not
  71       // fulfilled.
  72       next_message_.clear();
  73     }
  74
  75     if (next_message_.empty()) {
  76       if (IsFirstStatusByte(next)) {
  77         next_message_.push_back(next);
  78       } else {
  79         // MIDI protocol doesn't provide any error correction mechanism in
  80         // physical layers, and incoming messages can be corrupted, and should
  81         // be corrected here.
  82       }
  83       continue;
  84     }
  85
  86     // Here we can assume |next_message_| starts with a valid status byte.
  87     const uint8 status_byte = next_message_[0];
  88     next_message_.push_back(next);
  89
  90     if (status_byte == kSysEx) {
  91       if (next == kEndOfSysEx) {
  92         std::swap(*message, next_message_);
  93         next_message_.clear();
  94         return;
  95       }
  96       continue;
  97     }
  98
  99     DCHECK(IsDataByte(next));
 100     DCHECK_NE(kSysEx, status_byte);
 101     const size_t target_len = GetMidiMessageLength(status_byte);
 102     if (next_message_.size() < target_len)
 103       continue;
 104     if (next_message_.size() == target_len) {
 105       std::swap(*message, next_message_);
 106       next_message_.clear();
 107       if (allow_running_status_) {
 108         // Speculatively keep the status byte in case of running status. If this
 109         // assumption is not true, |next_message_| will be cleared anyway.
 110         next_message_.push_back(status_byte);
 111       }
 112       return;
 113     }
 114
 115     NOTREACHED();
 116   }
 117 }
 118
 119 }  // namespace media