Start work on error handler

brave/src/main/java/brave/ErrorHandler.java

@@ -0,0 +1,8 @@
+package brave;
+
+public interface ErrorHandler {
+  ErrorHandler NOOP = new NoopErrorHandler();
+
+  void handleError(SpanCustomizer customizer, Throwable throwable);
+
+}

brave/src/main/java/brave/NoopErrorHandler.java

@@ -0,0 +1,10 @@
+package brave;
+
+class NoopErrorHandler implements ErrorHandler {
+  NoopErrorHandler() {
+  }
+
+  @Override
+  public void handleError(SpanCustomizer customizer, Throwable throwable) {
+  }
+}

brave/src/main/java/brave/NoopSpan.java

@@ -51,6 +51,10 @@ static NoopSpan create(TraceContext context) {
     return this;
   }
 
+  @Override public Span error(Throwable throwable) {
+    return this;
+  }
+
   @Override public void finish() {
   }
 

brave/src/main/java/brave/RealSpan.java

@@ -10,9 +10,10 @@
 abstract class RealSpan extends Span {
 
   abstract Recorder recorder();
+  abstract ErrorHandler errorHandler();
 
-  static RealSpan create(TraceContext context, Recorder recorder) {
-    return new AutoValue_RealSpan(context, RealSpanCustomizer.create(context, recorder), recorder);
+  static RealSpan create(TraceContext context, Recorder recorder, ErrorHandler errorHandler) {
+    return new AutoValue_RealSpan(context, RealSpanCustomizer.create(context, recorder), recorder, errorHandler);
   }
 
   @Override public boolean isNoop() {
@@ -54,6 +55,12 @@ static RealSpan create(TraceContext context, Recorder recorder) {
     return this;
   }
 
+  @Override
+  public Span error(Throwable throwable) {
+    errorHandler().handleError(customizer(), throwable);
+    return this;
+  }
+
   @Override public Span remoteEndpoint(Endpoint remoteEndpoint) {
     recorder().remoteEndpoint(context(), remoteEndpoint);
     return this;

brave/src/main/java/brave/Span.java

@@ -89,6 +89,9 @@ public enum Kind {
   /** {@inheritDoc} */
   @Override public abstract Span tag(String key, String value);
 
+  /** Hands errors off to the configured ErrorHandler */
+  public abstract Span error(Throwable throwable);
+
   /**
    * @deprecated use {@link #remoteEndpoint(Endpoint)}, possibly with {@link zipkin.Endpoint#toV2()}
    */

brave/src/main/java/brave/SpanCustomizer.java

@@ -23,6 +23,7 @@
 // Note: this is exposed to users. We cannot add methods to this until Java 8 is required or we do a
 // major version bump
 // BRAVE5: add isNoop to avoid instanceof checks
+// BRAVE5: add error to support error handling
 public interface SpanCustomizer {
   /**
    * Sets the string name for the logical operation this span represents.

brave/src/main/java/brave/Tracer.java

@@ -138,8 +138,9 @@ public Tracer build() {
   final CurrentTraceContext currentTraceContext;
   final boolean traceId128Bit, supportsJoin;
   final AtomicBoolean noop;
+  final ErrorHandler errorHandler;
 
-  Tracer(Tracing.Builder builder, Clock clock, AtomicBoolean noop) {
+  Tracer(Tracing.Builder builder, Clock clock, AtomicBoolean noop, ErrorHandler errorHandler) {
     this.noop = noop;
     this.propagationFactory = builder.propagationFactory;
     this.supportsJoin = builder.supportsJoin && propagationFactory.supportsJoin();
@@ -149,6 +150,7 @@ public Tracer build() {
     this.sampler = builder.sampler;
     this.currentTraceContext = builder.currentTraceContext;
     this.traceId128Bit = builder.traceId128Bit || propagationFactory.requires128BitTraceId();
+    this.errorHandler = errorHandler;
   }
 
   /** @deprecated use {@link Tracing#clock(TraceContext)} */
@@ -302,7 +304,7 @@ public Span toSpan(TraceContext context) {
     if (context == null) throw new NullPointerException("context == null");
     TraceContext decorated = propagationFactory.decorate(context);
     if (!noop.get() && Boolean.TRUE.equals(decorated.sampled())) {
-      return RealSpan.create(decorated, recorder);
+      return RealSpan.create(decorated, recorder, errorHandler);
     }
     return NoopSpan.create(decorated);
   }

brave/src/main/java/brave/Tracing.java

@@ -65,6 +65,8 @@ public final Clock clock(TraceContext context) {
     return tracer().recorder.clock(context);
   }
 
+  abstract public ErrorHandler errorHandler();
+
   // volatile for visibility on get. writes guarded by Tracing.class
   static volatile Tracing current = null;
 
@@ -122,6 +124,7 @@ public static final class Builder {
     boolean traceId128Bit = false;
     boolean supportsJoin = true;
     Propagation.Factory propagationFactory = B3Propagation.FACTORY;
+    ErrorHandler errorHandler = ErrorHandler.NOOP;
 
     /**
      * Controls the name of the service being traced, while still using a default site-local IP.
@@ -274,6 +277,11 @@ public Builder supportsJoin(boolean supportsJoin) {
       return this;
     }
 
+    public Builder errorHandler(ErrorHandler errorHandler) {
+      this.errorHandler = errorHandler;
+      return this;
+    }
+
     public Tracing build() {
       if (clock == null) clock = Platform.get().clock();
       if (endpoint == null) {
@@ -296,10 +304,12 @@ static final class Default extends Tracing {
     final Propagation<String> stringPropagation;
     final CurrentTraceContext currentTraceContext;
     final Clock clock;
+    final ErrorHandler errorHandler;
 
     Default(Builder builder) {
       this.clock = builder.clock;
-      this.tracer = new Tracer(builder, clock, noop);
+      this.errorHandler = builder.errorHandler;
+      this.tracer = new Tracer(builder, clock, noop, errorHandler);
       this.propagationFactory = builder.propagationFactory;
       this.stringPropagation = builder.propagationFactory.create(Propagation.KeyFactory.STRING);
       this.currentTraceContext = builder.currentTraceContext;
@@ -326,6 +336,10 @@ static final class Default extends Tracing {
       return clock;
     }
 
+    @Override public ErrorHandler errorHandler() {
+      return errorHandler;
+    }
+
     private void maybeSetCurrent() {
       if (current != null) return;
       synchronized (Tracing.class) {