Add Tracestate into SpanContext. (#1359)

* Add Tracestate into SpanContext.

* Remove empty constructor from Tracestate.Builder

* Add info in the changelog.

3 files changed, 53 insertions, 15 deletions

diff --git a/api/src/main/java/io/opencensus/trace/SpanContext.java b/api/src/main/java/io/opencensus/trace/SpanContext.java
index 66a6bfbc..49ed751b 100644
--- a/api/src/main/java/io/opencensus/trace/SpanContext.java
+++ b/api/src/main/java/io/opencensus/trace/SpanContext.java
@@ -30,9 +30,11 @@ import javax.annotation.concurrent.Immutable;
  */
 @Immutable
 public final class SpanContext {
+  private static final Tracestate TRACESTATE_DEFAULT = Tracestate.builder().build();
   private final TraceId traceId;
   private final SpanId spanId;
   private final TraceOptions traceOptions;
+  private final Tracestate tracestate;
 
   /**
    * The invalid {@code SpanContext}.
@@ -40,7 +42,7 @@ public final class SpanContext {
    * @since 0.5
    */
   public static final SpanContext INVALID =
-      new SpanContext(TraceId.INVALID, SpanId.INVALID, TraceOptions.DEFAULT);
+      new SpanContext(TraceId.INVALID, SpanId.INVALID, TraceOptions.DEFAULT, TRACESTATE_DEFAULT);
 
   /**
    * Creates a new {@code SpanContext} with the given identifiers and options.
@@ -49,10 +51,26 @@ public final class SpanContext {
    * @param spanId the span identifier of the span context.
    * @param traceOptions the trace options for the span context.
    * @return a new {@code SpanContext} with the given identifiers and options.
-   * @since 0.5
+   * @deprecated use {@link #create(TraceId, SpanId, TraceOptions, Tracestate)}.
    */
+  @Deprecated
   public static SpanContext create(TraceId traceId, SpanId spanId, TraceOptions traceOptions) {
-    return new SpanContext(traceId, spanId, traceOptions);
+    return create(traceId, spanId, traceOptions, TRACESTATE_DEFAULT);
+  }
+
+  /**
+   * Creates a new {@code SpanContext} with the given identifiers and options.
+   *
+   * @param traceId the trace identifier of the span context.
+   * @param spanId the span identifier of the span context.
+   * @param traceOptions the trace options for the span context.
+   * @param tracestate the trace state for the span context.
+   * @return a new {@code SpanContext} with the given identifiers and options.
+   * @since 0.16
+   */
+  public static SpanContext create(
+      TraceId traceId, SpanId spanId, TraceOptions traceOptions, Tracestate tracestate) {
+    return new SpanContext(traceId, spanId, traceOptions, tracestate);
   }
 
   /**
@@ -76,9 +94,9 @@ public final class SpanContext {
   }
 
   /**
-   * Returns the trace options associated with this {@code SpanContext}.
+   * Returns the {@code TraceOptions} associated with this {@code SpanContext}.
    *
-   * @return the trace options associated with this {@code SpanContext}.
+   * @return the {@code TraceOptions} associated with this {@code SpanContext}.
    * @since 0.5
    */
   public TraceOptions getTraceOptions() {
@@ -86,6 +104,16 @@ public final class SpanContext {
   }
 
   /**
+   * Returns the {@code Tracestate} associated with this {@code SpanContext}.
+   *
+   * @return the {@code Tracestate} associated with this {@code SpanContext}.
+   * @since 0.5
+   */
+  public Tracestate getTracestate() {
+    return tracestate;
+  }
+
+  /**
    * Returns true if this {@code SpanContext} is valid.
    *
    * @return true if this {@code SpanContext} is valid.
@@ -127,9 +155,11 @@ public final class SpanContext {
         + "}";
   }
 
-  private SpanContext(TraceId traceId, SpanId spanId, TraceOptions traceOptions) {
+  private SpanContext(
+      TraceId traceId, SpanId spanId, TraceOptions traceOptions, Tracestate tracestate) {
     this.traceId = traceId;
     this.spanId = spanId;
     this.traceOptions = traceOptions;
+    this.tracestate = tracestate;
   }
 }
diff --git a/api/src/main/java/io/opencensus/trace/Tracestate.java b/api/src/main/java/io/opencensus/trace/Tracestate.java
index 5535a0ac..f88d3bd3 100644
--- a/api/src/main/java/io/opencensus/trace/Tracestate.java
+++ b/api/src/main/java/io/opencensus/trace/Tracestate.java
@@ -81,7 +81,7 @@ public abstract class Tracestate {
    * @since 0.16
    */
   public static Builder builder() {
-    return new Builder();
+    return new Builder(Builder.EMPTY);
   }
 
   /**
@@ -108,10 +108,6 @@ public abstract class Tracestate {
     // subclass (the auto-value generate class).
     private static final Tracestate EMPTY = create(Collections.<Entry>emptyList());
 
-    private Builder() {
-      this(EMPTY);
-    }
-
     private Builder(Tracestate parent) {
       Utils.checkNotNull(parent, "parent");
       this.parent = parent;
diff --git a/api/src/test/java/io/opencensus/trace/SpanContextTest.java b/api/src/test/java/io/opencensus/trace/SpanContextTest.java
index f5a9954f..54e188c8 100644
--- a/api/src/test/java/io/opencensus/trace/SpanContextTest.java
+++ b/api/src/test/java/io/opencensus/trace/SpanContextTest.java
@@ -32,16 +32,20 @@ public class SpanContextTest {
       new byte[] {0, 0, 0, 0, 0, 0, 0, '0', 0, 0, 0, 0, 0, 0, 0, 0};
   private static final byte[] firstSpanIdBytes = new byte[] {0, 0, 0, 0, 0, 0, 0, 'a'};
   private static final byte[] secondSpanIdBytes = new byte[] {'0', 0, 0, 0, 0, 0, 0, 0};
+  private static final Tracestate firstTracestate = Tracestate.builder().set("foo", "bar").build();
+  private static final Tracestate secondTracestate = Tracestate.builder().set("foo", "baz").build();
   private static final SpanContext first =
       SpanContext.create(
           TraceId.fromBytes(firstTraceIdBytes),
           SpanId.fromBytes(firstSpanIdBytes),
-          TraceOptions.DEFAULT);
+          TraceOptions.DEFAULT,
+          firstTracestate);
   private static final SpanContext second =
       SpanContext.create(
           TraceId.fromBytes(secondTraceIdBytes),
           SpanId.fromBytes(secondSpanIdBytes),
-          TraceOptions.builder().setIsSampled(true).build());
+          TraceOptions.builder().setIsSampled(true).build(),
+          secondTracestate);
 
   @Test
   public void invalidSpanContext() {
@@ -87,6 +91,12 @@ public class SpanContextTest {
   }
 
   @Test
+  public void getTracestate() {
+    assertThat(first.getTracestate()).isEqualTo(firstTracestate);
+    assertThat(second.getTracestate()).isEqualTo(secondTracestate);
+  }
+
+  @Test
   public void spanContext_EqualsAndHashCode() {
     EqualsTester tester = new EqualsTester();
     tester.addEqualityGroup(
@@ -98,13 +108,15 @@ public class SpanContextTest {
         SpanContext.create(
             TraceId.fromBytes(firstTraceIdBytes),
             SpanId.fromBytes(firstSpanIdBytes),
-            TraceOptions.builder().setIsSampled(false).build()));
+            TraceOptions.builder().setIsSampled(false).build(),
+            firstTracestate));
     tester.addEqualityGroup(
         second,
         SpanContext.create(
             TraceId.fromBytes(secondTraceIdBytes),
             SpanId.fromBytes(secondSpanIdBytes),
-            TraceOptions.builder().setIsSampled(true).build()));
+            TraceOptions.builder().setIsSampled(true).build(),
+            secondTracestate));
     tester.testEquals();
   }