[Tracing] Expose trace serialization as part of tracing interface

src/libplatform/tracing/trace-writer.cc

Index: src/libplatform/tracing/trace-writer.cc
diff --git a/src/libplatform/tracing/trace-writer.cc b/src/libplatform/tracing/trace-writer.cc
index 6d94350cfd9d165a5c632cb8088a928a598afa96..1c2ca3ab7be2ffafd01ec4d3c15806fa2d9d26d2 100644
--- a/src/libplatform/tracing/trace-writer.cc
+++ b/src/libplatform/tracing/trace-writer.cc
@@ -13,114 +13,15 @@ namespace v8 {
 namespace platform {
 namespace tracing {
 
-// Currently we do not support JSON-escaping strings in trace arguments.
-// Thus we perform an IsJSONString() check before writing any string argument.
-// In particular, this means strings cannot have control characters or \.
-V8_INLINE static bool IsJSONString(const char* str) {
-  size_t len = strlen(str);
-  for (size_t i = 0; i < len; ++i) {
-    if (iscntrl(str[i]) || str[i] == '\\') {
-      return false;
-    }
-  }
-  return true;
+JSONTraceWriter::JSONTraceWriter(std::ostream& stream)
+    : trace_serializer_(stream) {
+  trace_serializer_.WritePrefix();
 }
 
-void JSONTraceWriter::AppendArgValue(uint8_t type,
-                                     TraceObject::ArgValue value) {
-  switch (type) {
-    case TRACE_VALUE_TYPE_BOOL:
-      stream_ << (value.as_bool ? "true" : "false");
-      break;
-    case TRACE_VALUE_TYPE_UINT:
-      stream_ << value.as_uint;
-      break;
-    case TRACE_VALUE_TYPE_INT:
-      stream_ << value.as_int;
-      break;
-    case TRACE_VALUE_TYPE_DOUBLE: {
-      std::string real;
-      double val = value.as_double;
-      if (std::isfinite(val)) {
-        std::ostringstream convert_stream;
-        convert_stream << val;
-        real = convert_stream.str();
-        // Ensure that the number has a .0 if there's no decimal or 'e'.  This
-        // makes sure that when we read the JSON back, it's interpreted as a
-        // real rather than an int.
-        if (real.find('.') == std::string::npos &&
-            real.find('e') == std::string::npos &&
-            real.find('E') == std::string::npos) {
-          real += ".0";
-        }
-      } else if (std::isnan(val)) {
-        // The JSON spec doesn't allow NaN and Infinity (since these are
-        // objects in EcmaScript).  Use strings instead.
-        real = "\"NaN\"";
-      } else if (val < 0) {
-        real = "\"-Infinity\"";
-      } else {
-        real = "\"Infinity\"";
-      }
-      stream_ << real;
-      break;
-    }
-    case TRACE_VALUE_TYPE_POINTER:
-      // JSON only supports double and int numbers.
-      // So as not to lose bits from a 64-bit pointer, output as a hex string.
-      stream_ << "\"" << value.as_pointer << "\"";
-      break;
-    case TRACE_VALUE_TYPE_STRING:
-    case TRACE_VALUE_TYPE_COPY_STRING:
-      // Strings are currently not JSON-escaped, so we need to perform a check
-      // to see if they are valid JSON strings.
-      CHECK(value.as_string != nullptr && IsJSONString(value.as_string));
-      stream_ << (value.as_string ? value.as_string : "NULL");
-      break;
-    default:
-      UNREACHABLE();
-      break;
-  }
-}
-
-JSONTraceWriter::JSONTraceWriter(std::ostream& stream) : stream_(stream) {
-  stream_ << "{\"traceEvents\":[";
-}
-
-JSONTraceWriter::~JSONTraceWriter() { stream_ << "]}"; }
+JSONTraceWriter::~JSONTraceWriter() { trace_serializer_.WriteSuffix(); }
 
 void JSONTraceWriter::AppendTraceEvent(TraceObject* trace_event) {
-  if (append_comma_) stream_ << ",";
-  append_comma_ = true;
-  stream_ << "{\"pid\":" << trace_event->pid()
-          << ",\"tid\":" << trace_event->tid()
-          << ",\"ts\":" << trace_event->ts()
-          << ",\"tts\":" << trace_event->tts() << ",\"ph\":\""
-          << trace_event->phase() << "\",\"cat\":\""
-          << TracingController::GetCategoryGroupName(
-                 trace_event->category_enabled_flag())
-          << "\",\"name\":\"" << trace_event->name()
-          << "\",\"dur\":" << trace_event->duration()
-          << ",\"tdur\":" << trace_event->cpu_duration();
-  if (trace_event->flags() & TRACE_EVENT_FLAG_HAS_ID) {
-    if (trace_event->scope() != nullptr) {
-      stream_ << ",\"scope\":\"" << trace_event->scope() << "\"";
-    }
-    // So as not to lose bits from a 64-bit integer, output as a hex string.
-    stream_ << ",\"id\":\"0x" << std::hex << trace_event->id() << "\""
-            << std::dec;
-  }
-  stream_ << ",\"args\":{";
-  const char** arg_names = trace_event->arg_names();
-  const uint8_t* arg_types = trace_event->arg_types();
-  TraceObject::ArgValue* arg_values = trace_event->arg_values();
-  for (int i = 0; i < trace_event->num_args(); ++i) {
-    if (i > 0) stream_ << ",";
-    stream_ << "\"" << arg_names[i] << "\":";
-    AppendArgValue(arg_types[i], arg_values[i]);
-  }
-  stream_ << "}}";
-  // TODO(fmeawad): Add support for Flow Events.
+  trace_serializer_.AppendTraceEvent(trace_event);
 }
 
 void JSONTraceWriter::Flush() {}