Add truncated flag for tail worker events

When set, indicates that the tail worker event was truncated due
to the event buffer being full.

src/workerd/api/trace.c++

@@ -201,7 +201,8 @@ TraceItem::TraceItem(jsg::Lock& js, const Trace& trace)
       scriptTags(getTraceScriptTags(trace)),
       outcome(getTraceOutcome(trace)),
       cpuTime(trace.cpuTime / kj::MILLISECONDS),
-      wallTime(trace.wallTime / kj::MILLISECONDS) {}
+      wallTime(trace.wallTime / kj::MILLISECONDS),
+      truncated(trace.truncated) {}
 
 kj::Maybe<TraceItem::EventInfo> TraceItem::getEvent(jsg::Lock& js) {
   return eventInfo.map([](auto& info) -> TraceItem::EventInfo {
@@ -260,6 +261,8 @@ jsg::Optional<kj::Array<kj::StringPtr>> TraceItem::getScriptTags() {
 
 kj::StringPtr TraceItem::getOutcome() { return outcome; }
 
+bool TraceItem::getTruncated() { return truncated; }
+
 uint TraceItem::getCpuTime() { return cpuTime; }
 
 uint TraceItem::getWallTime() { return wallTime; }

src/workerd/api/trace.h

@@ -102,6 +102,7 @@ class TraceItem final: public jsg::Object {
 
   uint getCpuTime();
   uint getWallTime();
+  bool getTruncated();
 
   JSG_RESOURCE_TYPE(TraceItem) {
     JSG_LAZY_READONLY_INSTANCE_PROPERTY(event, getEvent);
@@ -115,6 +116,7 @@ class TraceItem final: public jsg::Object {
     JSG_LAZY_READONLY_INSTANCE_PROPERTY(dispatchNamespace, getDispatchNamespace);
     JSG_LAZY_READONLY_INSTANCE_PROPERTY(scriptTags, getScriptTags);
     JSG_LAZY_READONLY_INSTANCE_PROPERTY(outcome, getOutcome);
+    JSG_LAZY_READONLY_INSTANCE_PROPERTY(truncated, getTruncated);
   }
 
   void visitForMemoryInfo(jsg::MemoryTracker& tracker) const;
@@ -133,6 +135,7 @@ class TraceItem final: public jsg::Object {
   kj::String outcome;
   uint cpuTime;
   uint wallTime;
+  bool truncated;
 };
 
 // When adding a new TraceItem eventInfo type, it is important not to

src/workerd/io/trace.c++

@@ -272,6 +272,7 @@ void Trace::copyTo(rpc::Trace::Builder builder) {
     }
   }
 
+  builder.setTruncated(truncated);
   builder.setOutcome(outcome);
   builder.setCpuTime(cpuTime / kj::MILLISECONDS);
   builder.setWallTime(wallTime / kj::MILLISECONDS);
@@ -571,6 +572,7 @@ void WorkerTracer::log(kj::Date timestamp, LogLevel logLevel, kj::String message
   size_t newSize = trace->bytesUsed + sizeof(Trace::Log) + message.size();
   if (newSize > MAX_TRACE_BYTES) {
     trace->exceededLogLimit = true;
+    trace->truncated = true;
     // We use a JSON encoded array/string to match other console.log() recordings:
     trace->logs.add(
         timestamp, LogLevel::WARN,
@@ -598,6 +600,7 @@ void WorkerTracer::addException(kj::Date timestamp, kj::String name, kj::String
   }
   if (newSize > MAX_TRACE_BYTES) {
     trace->exceededExceptionLimit = true;
+    trace->truncated = true;
     trace->exceptions.add(
         timestamp, kj::str("Error"),
         kj::str("Trace resource limit exceeded; subsequent exceptions not recorded."),
@@ -621,6 +624,7 @@ void WorkerTracer::addDiagnosticChannelEvent(kj::Date timestamp,
                    message.size();
   if (newSize > MAX_TRACE_BYTES) {
     trace->exceededDiagnosticChannelEventLimit = true;
+    trace->truncated = true;
     trace->diagnosticChannelEvents.add(timestamp, kj::str("workerd.LimitExceeded"),
                                        kj::Array<kj::byte>());
     return;

src/workerd/io/trace.h

@@ -292,6 +292,7 @@ class Trace final : public kj::Refcounted {
   kj::Duration cpuTime;
   kj::Duration wallTime;
 
+  bool truncated = false;
   bool exceededLogLimit = false;
   bool exceededExceptionLimit = false;
   bool exceededDiagnosticChannelEventLimit = false;

src/workerd/io/worker-interface.capnp

@@ -135,6 +135,9 @@ struct Trace @0x8e8d911203762d34 {
     channel @1 :Text;
     message @2 :Data;
   }
+
+  truncated @24 :Bool;
+  # Indicates that the trace was truncated due to reaching the maximum size limit.
 }
 
 struct ScheduledRun @0xd98fc1ae5c8095d0 {