Web MIDI: move MIDI message validating logic into message_util.{cc|h}

media/midi/message_util.cc

Index: media/midi/message_util.cc
diff --git a/media/midi/message_util.cc b/media/midi/message_util.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7d58ac3888eff8f0a3d7649d1c86098d5e7c6606
--- /dev/null
+++ b/media/midi/message_util.cc
@@ -0,0 +1,103 @@
+// 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/message_util.h"
+
+#include "base/logging.h"
+#include "base/metrics/histogram_macros.h"
+
+namespace midi {
+
+size_t GetMessageLength(uint8_t status_byte) {
+  if (status_byte < 0x80)
+    return 0;
+  if (0x80 <= status_byte && status_byte <= 0xbf)
+    return 3;
+  if (0xc0 <= status_byte && status_byte <= 0xdf)
+    return 2;
+  if (0xe0 <= status_byte && status_byte <= 0xef)
+    return 3;
+
+  switch (status_byte) {
+    case 0xf0:
+      return 0;
+    case 0xf1:
+      return 2;
+    case 0xf2:
+      return 3;
+    case 0xf3:
+      return 2;
+    case 0xf4:  // Reserved
+    case 0xf5:  // Reserved
+      return 0;
+    case 0xf6:
+      return 1;
+    case 0xf7:
+      return 0;
+    case 0xf8:
+    case 0xf9:
+    case 0xfa:
+    case 0xfb:
+    case 0xfc:
+    case 0xfd:
+    case 0xfe:
+    case 0xff:
+      return 1;
+    default:
+      NOTREACHED();
+      return 0;
+  }
+}
+
+bool IsDataByte(uint8_t data) {
+  return (data & 0x80) == 0;
+}
+
+bool IsSystemRealTimeMessage(uint8_t data) {
+  return 0xf8 <= data;
+}
+
+bool IsSystemMessage(uint8_t data) {
+  return 0xf0 <= data;
+}
+
+bool IsValidWebMIDIData(const std::vector<uint8_t>& data) {
+  bool in_sysex = false;
+  size_t sysex_start_offset = 0;
+  size_t waiting_data_length = 0;
+  for (size_t i = 0; i < data.size(); ++i) {
+    const uint8_t current = data[i];
+    if (IsSystemRealTimeMessage(current))
+      continue;  // Real time message can be placed at any point.
+    if (waiting_data_length > 0) {
+      if (!IsDataByte(current))
+        return false;  // Error: |current| should have been data byte.
+      --waiting_data_length;
+      continue;  // Found data byte as expected.
+    }
+    if (in_sysex) {
+      if (data[i] == kEndOfSysExByte) {
+        in_sysex = false;
+        UMA_HISTOGRAM_COUNTS("Media.Midi.SysExMessageSizeUpTo1MB",
+                             static_cast<base::HistogramBase::Sample>(
+                                 i - sysex_start_offset + 1));
+      } else if (!IsDataByte(current)) {
+        return false;  // Error: |current| should have been data byte.
+      }
+      continue;  // Found data byte as expected.
+    }
+    if (current == kSysExByte) {
+      in_sysex = true;
+      sysex_start_offset = i;
+      continue;  // Found SysEX
+    }
+    waiting_data_length = GetMessageLength(current);
+    if (waiting_data_length == 0)
+      return false;  // Error: |current| should have been a valid status byte.
+    --waiting_data_length;  // Found status byte
+  }
+  return waiting_data_length == 0 && !in_sysex;
+}
+
+}  // namespace midi