Tracing V2 prototype [NOT FOR REVIEW]

base/trace_event/v2/append_only_proto_message.cc

Index: base/trace_event/v2/append_only_proto_message.cc
diff --git a/base/trace_event/v2/append_only_proto_message.cc b/base/trace_event/v2/append_only_proto_message.cc
new file mode 100644
index 0000000000000000000000000000000000000000..85a0947717c8b9d819e804b112f6820efd1a48ae
--- /dev/null
+++ b/base/trace_event/v2/append_only_proto_message.cc
@@ -0,0 +1,174 @@
+// Copyright 2016 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 "base/trace_event/v2/append_only_proto_message.h"
+
+#include "base/logging.h"
+#include "base/trace_event/v2/proto_utils.h"
+#include "build/build_config.h"
+
+
+// TODO size vs length naming inconsistency.
+// TODO bitmap for mandatory / optional fields
+
+namespace {
+
+enum {
+  PROTO_VARINT = 0,
+  PROTO_FIXED_64BIT = 1,
+  PROTO_LENGTH_LIMITED = 2,
+  PROTO_FIXED_32BIT = 5,
+};
+
+}  // namespace
+
+namespace base {
+namespace trace_event {
+namespace v2 {
+
+// static
+const size_t AppendOnlyProtoMessage::kMaxMessageLength =
+    1ul << (AppendOnlyProtoMessage::kMaxMessageLengthFieldSize * 7);
+
+AppendOnlyProtoMessage::AppendOnlyProtoMessage()
+    : buffer_(nullptr),
+      size_(0),
+      write_size_field_on_finalization_(false),
+      size_already_written_(0),
+      current_nested_message_(nullptr),
+      sealed_(false) {}
+
+AppendOnlyProtoMessage::~AppendOnlyProtoMessage() {}
+
+size_t AppendOnlyProtoMessage::Finalize() {
+  if (sealed_)
+    return size_;
+
+  if (current_nested_message_)
+    EndNestedMessage();
+
+  if (write_size_field_on_finalization_) {
+    // Write the length of the nested message a posteriori, forcing a 32-bit
+    // leading-zero varint. This is a slight bending of the proto encoding,
+    // essentially size = 7 gets encoded as 0x87,0x80,0x80,0x00 instead of 0x07.
+    // The problem here is that we cannot know upfront how big the nested message
+    // was. There is precedent for this (TODO link internal bug).
+    // TODO optimization: upon beginmessage we could get a promise of the max
+    // length of the submessage to avoid wasting 2 bytes if we know upfront that
+    // the message is going to be always < 64k.
+    DCHECK_LT(size_, kMaxMessageLength);
+    uint8_t word[kMaxMessageLengthFieldSize];
+    ProtoUtils::EncodeRedundantVarIntUnsigned(size_ - size_already_written_,
+                                              kMaxMessageLengthFieldSize,
+                                              word);
+    buffer_->WriteReservedBytes(size_field_, word, kMaxMessageLengthFieldSize);
+  }
+
+  // No more changes allowed.
+  sealed_ = true;
+  return size_;
+}
+
+void AppendOnlyProtoMessage::WriteToBuffer(const uint8_t* src, size_t size) {
+  buffer_->WriteBytes(src, size);
+  size_ += size;
+}
+
+void AppendOnlyProtoMessage::AppendVarIntSigned(uint32_t field_id,
+                                                int64_t value) {
+  // TODO ZigZag encoding.
+  AppendVarIntUnsigned(field_id, value);  // HACK, this is not supporting signed.
+}
+
+void AppendOnlyProtoMessage::AppendVarIntUnsigned(uint32_t field_id,
+                                                  uint64_t value) {
+  if (current_nested_message_)
+    EndNestedMessage();
+
+  uint8_t data[32];
+  size_t data_size;
+  data_size = ProtoUtils::EncodeVarIntUnsigned(ProtoUtils::GetVarIntFieldHeader(field_id), data);
+  data_size += ProtoUtils::EncodeVarIntUnsigned(value, &data[data_size]);
+  WriteToBuffer(data, data_size);
+}
+
+void AppendOnlyProtoMessage::AppendFloat(uint32_t field_id, float value) {
+  if (current_nested_message_)
+    EndNestedMessage();
+
+  uint8_t data[32];
+  size_t data_size;
+  data_size = ProtoUtils::EncodeVarIntUnsigned(ProtoUtils::GetFixed32FieldHeader(field_id), data);
+
+#if defined(ARCH_CPU_LITTLE_ENDIAN)
+  memcpy(&data[data_size], &value, sizeof(value));
+#else
+#error big-endian encoding not implemented.
+#endif
+
+  data_size += sizeof(value);
+  WriteToBuffer(data, data_size);
+}
+
+void AppendOnlyProtoMessage::AppendDouble(uint32_t field_id, double value) {
+  if (current_nested_message_)
+    EndNestedMessage();
+
+  uint8_t data[32];
+  size_t data_size;
+  data_size = ProtoUtils::EncodeVarIntUnsigned(ProtoUtils::GetFixed64FieldHeader(field_id), data);
+  memcpy(&data[data_size], &value, sizeof(value));
+  data_size += sizeof(value);
+  WriteToBuffer(data, data_size);
+}
+
+void AppendOnlyProtoMessage::AppendString(uint32_t field_id, const char* str) {
+  if (current_nested_message_)
+    EndNestedMessage();
+
+  const size_t str_length = strlen(str);
+  AppendBytes(field_id, str, str_length);
+}
+
+void AppendOnlyProtoMessage::AppendBytes(uint32_t field_id, const void* value, size_t size) {
+  if (current_nested_message_)
+    EndNestedMessage();
+
+  // Write the proto preamble (field id, type and length of the buffer).
+  uint8_t data[32];
+  size_t data_size;
+  data_size = ProtoUtils::EncodeVarIntUnsigned(ProtoUtils::GetLengthLimitedFieldHeader(field_id), data);
+  data_size += ProtoUtils::EncodeVarIntUnsigned(size, &data[data_size]);
+  WriteToBuffer(data, data_size);
+
+  // Write the actual buffer.
+  WriteToBuffer(reinterpret_cast<const uint8_t*>(value), size);
+}
+
+void AppendOnlyProtoMessage::BeginNestedMessage(
+    uint32_t field_id,
+    AppendOnlyProtoMessage* message) {
+  if (current_nested_message_)
+    EndNestedMessage();
+
+  message->set_buffer_writer(buffer_writer());
+  uint8_t data[32];
+  size_t data_size;
+  data_size = ProtoUtils::EncodeVarIntUnsigned(ProtoUtils::GetLengthLimitedFieldHeader(field_id), data);
+  WriteToBuffer(data, data_size);
+
+  // The length of the nested message cannot be known upfront. So right now
+  // just reserve the bytes to encode the size after the nested message is done.
+  message->set_write_size_field_on_finalization(buffer_->ReserveBytes(kMaxMessageLengthFieldSize));
+  current_nested_message_ = message;
+}
+
+void AppendOnlyProtoMessage::EndNestedMessage() {
+  size_ += current_nested_message_->Finalize();
+  current_nested_message_ = nullptr;
+}
+
+}  // namespace v2
+}  // namespace trace_event
+}  // namespace base