Add initial support for b3-propagation headers. (#889)

* Add initial support for b3-propagation headers.

* Update tests and throw exception when missing span_id or trace_id.

* Cleanup and add more tests.

* Update comments. Update tests.

8 files changed, 410 insertions, 8 deletions

diff --git a/api/src/main/java/io/opencensus/trace/SpanId.java b/api/src/main/java/io/opencensus/trace/SpanId.java
index 446a228e..a986d013 100644
--- a/api/src/main/java/io/opencensus/trace/SpanId.java
+++ b/api/src/main/java/io/opencensus/trace/SpanId.java
@@ -84,6 +84,22 @@ public final class SpanId implements Comparable<SpanId> {
   }
 
   /**
+   * Returns a {@code SpanId} built from a lowercase base16 representation.
+   *
+   * @param src the lowercase base16 representation.
+   * @return a {@code SpanId} built from a lowercase base16 representation.
+   * @throws NullPointerException if {@code src} is null.
+   * @throws IllegalArgumentException if {@code src.length} is not {@code 2 * SpanId.SIZE} OR if the
+   *     {@code str} has invalid characters.
+   */
+  public static SpanId fromLowerBase16(String src) {
+    checkArgument(
+        src.length() == 2 * SIZE, "Invalid size: expected %s, got %s", 2 * SIZE, src.length());
+    byte[] bytes = BaseEncoding.base16().lowerCase().decode(src);
+    return new SpanId(bytes);
+  }
+
+  /**
    * Generates a new random {@code SpanId}.
    *
    * @param random The random number generator.
@@ -136,6 +152,15 @@ public final class SpanId implements Comparable<SpanId> {
     return !Arrays.equals(bytes, INVALID.bytes);
   }
 
+  /**
+   * Returns the lowercase base16 encoding of this {@code SpanId}.
+   *
+   * @return the lowercase base16 encoding of this {@code SpanId}.
+   */
+  public String toLowerBase16() {
+    return BaseEncoding.base16().lowerCase().encode(bytes);
+  }
+
   @Override
   public boolean equals(Object obj) {
     if (obj == this) {
diff --git a/api/src/main/java/io/opencensus/trace/TraceId.java b/api/src/main/java/io/opencensus/trace/TraceId.java
index 6badf6e5..44b80a66 100644
--- a/api/src/main/java/io/opencensus/trace/TraceId.java
+++ b/api/src/main/java/io/opencensus/trace/TraceId.java
@@ -85,6 +85,22 @@ public final class TraceId implements Comparable<TraceId> {
   }
 
   /**
+   * Returns a {@code TraceId} built from a lowercase base16 representation.
+   *
+   * @param src the lowercase base16 representation.
+   * @return a {@code TraceId} built from a lowercase base16 representation.
+   * @throws NullPointerException if {@code src} is null.
+   * @throws IllegalArgumentException if {@code src.length} is not {@code 2 * TraceId.SIZE} OR if
+   *     the {@code str} has invalid characters.
+   */
+  public static TraceId fromLowerBase16(String src) {
+    checkArgument(
+        src.length() == 2 * SIZE, "Invalid size: expected %s, got %s", 2 * SIZE, src.length());
+    byte[] bytes = BaseEncoding.base16().lowerCase().decode(src);
+    return new TraceId(bytes);
+  }
+
+  /**
    * Generates a new random {@code TraceId}.
    *
    * @param random the random number generator.
@@ -138,6 +154,15 @@ public final class TraceId implements Comparable<TraceId> {
   }
 
   /**
+   * Returns the lowercase base16 encoding of this {@code TraceId}.
+   *
+   * @return the lowercase base16 encoding of this {@code TraceId}.
+   */
+  public String toLowerBase16() {
+    return BaseEncoding.base16().lowerCase().encode(bytes);
+  }
+
+  /**
    * Returns the lower 8 bytes of the trace-id as a long value, assuming little-endian order. This
    * is used in ProbabilitySampler.
    *
diff --git a/api/src/test/java/io/opencensus/trace/SpanIdTest.java b/api/src/test/java/io/opencensus/trace/SpanIdTest.java
index 36226da5..4a5bc2ae 100644
--- a/api/src/test/java/io/opencensus/trace/SpanIdTest.java
+++ b/api/src/test/java/io/opencensus/trace/SpanIdTest.java
@@ -28,7 +28,7 @@ import org.junit.runners.JUnit4;
 @RunWith(JUnit4.class)
 public class SpanIdTest {
   private static final byte[] firstBytes = new byte[] {0, 0, 0, 0, 0, 0, 0, 'a'};
-  private static final byte[] secondBytes = new byte[] {(byte) 0xFF, 0, 0, 0, 0, 0, 0, 0};
+  private static final byte[] secondBytes = new byte[] {(byte) 0xFF, 0, 0, 0, 0, 0, 0, 'A'};
   private static final SpanId first = SpanId.fromBytes(firstBytes);
   private static final SpanId second = SpanId.fromBytes(secondBytes);
 
@@ -45,6 +45,20 @@ public class SpanIdTest {
   }
 
   @Test
+  public void fromLowerBase16() {
+    assertThat(SpanId.fromLowerBase16("0000000000000000")).isEqualTo(SpanId.INVALID);
+    assertThat(SpanId.fromLowerBase16("0000000000000061")).isEqualTo(first);
+    assertThat(SpanId.fromLowerBase16("ff00000000000041")).isEqualTo(second);
+  }
+
+  @Test
+  public void toLowerBase16() {
+    assertThat(SpanId.INVALID.toLowerBase16()).isEqualTo("0000000000000000");
+    assertThat(first.toLowerBase16()).isEqualTo("0000000000000061");
+    assertThat(second.toLowerBase16()).isEqualTo("ff00000000000041");
+  }
+
+  @Test
   public void getBytes() {
     assertThat(first.getBytes()).isEqualTo(firstBytes);
     assertThat(second.getBytes()).isEqualTo(secondBytes);
@@ -71,6 +85,6 @@ public class SpanIdTest {
   public void traceId_ToString() {
     assertThat(SpanId.INVALID.toString()).contains("0000000000000000");
     assertThat(first.toString()).contains("0000000000000061");
-    assertThat(second.toString()).contains("ff00000000000000");
+    assertThat(second.toString()).contains("ff00000000000041");
   }
 }
diff --git a/api/src/test/java/io/opencensus/trace/TraceIdTest.java b/api/src/test/java/io/opencensus/trace/TraceIdTest.java
index 8c1a1004..c8b5dc8f 100644
--- a/api/src/test/java/io/opencensus/trace/TraceIdTest.java
+++ b/api/src/test/java/io/opencensus/trace/TraceIdTest.java
@@ -30,7 +30,7 @@ public class TraceIdTest {
   private static final byte[] firstBytes =
       new byte[] {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 'a'};
   private static final byte[] secondBytes =
-      new byte[] {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 'A'};
+      new byte[] {(byte) 0xFF, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 'A'};
   private static final TraceId first = TraceId.fromBytes(firstBytes);
   private static final TraceId second = TraceId.fromBytes(secondBytes);
 
@@ -53,6 +53,21 @@ public class TraceIdTest {
   }
 
   @Test
+  public void fromLowerBase16() {
+    assertThat(TraceId.fromLowerBase16("00000000000000000000000000000000"))
+        .isEqualTo(TraceId.INVALID);
+    assertThat(TraceId.fromLowerBase16("00000000000000000000000000000061")).isEqualTo(first);
+    assertThat(TraceId.fromLowerBase16("ff000000000000000000000000000041")).isEqualTo(second);
+  }
+
+  @Test
+  public void toLowerBase16() {
+    assertThat(TraceId.INVALID.toLowerBase16()).isEqualTo("00000000000000000000000000000000");
+    assertThat(first.toLowerBase16()).isEqualTo("00000000000000000000000000000061");
+    assertThat(second.toLowerBase16()).isEqualTo("ff000000000000000000000000000041");
+  }
+
+  @Test
   public void traceId_CompareTo() {
     assertThat(first.compareTo(second)).isGreaterThan(0);
     assertThat(second.compareTo(first)).isLessThan(0);
@@ -73,6 +88,6 @@ public class TraceIdTest {
   public void traceId_ToString() {
     assertThat(TraceId.INVALID.toString()).contains("00000000000000000000000000000000");
     assertThat(first.toString()).contains("00000000000000000000000000000061");
-    assertThat(second.toString()).contains("00000000000000000000000000000041");
+    assertThat(second.toString()).contains("ff000000000000000000000000000041");
   }
 }
diff --git a/api/src/test/java/io/opencensus/trace/TracerTest.java b/api/src/test/java/io/opencensus/trace/TracerTest.java
index 7c65742e..8f0ac64f 100644
--- a/api/src/test/java/io/opencensus/trace/TracerTest.java
+++ b/api/src/test/java/io/opencensus/trace/TracerTest.java
@@ -23,9 +23,7 @@ import static org.mockito.Mockito.when;
 import io.grpc.Context;
 import io.opencensus.common.Scope;
 import org.junit.Before;
-import org.junit.Rule;
 import org.junit.Test;
-import org.junit.rules.ExpectedException;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
 import org.mockito.Mock;
@@ -38,7 +36,6 @@ import org.mockito.MockitoAnnotations;
 public class TracerTest {
   private static final Tracer noopTracer = Tracer.getNoopTracer();
   private static final String SPAN_NAME = "MySpanName";
-  @Rule public ExpectedException thrown = ExpectedException.none();
   @Mock private Tracer tracer;
   @Mock private SpanBuilder spanBuilder;
   @Mock private Span span;
diff --git a/impl_core/src/main/java/io/opencensus/implcore/trace/propagation/B3Format.java b/impl_core/src/main/java/io/opencensus/implcore/trace/propagation/B3Format.java
new file mode 100644
index 00000000..c27234db
--- /dev/null
+++ b/impl_core/src/main/java/io/opencensus/implcore/trace/propagation/B3Format.java
@@ -0,0 +1,105 @@
+/*
+ * Copyright 2017, OpenCensus Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.opencensus.implcore.trace.propagation;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+import com.google.common.annotations.VisibleForTesting;
+import io.opencensus.trace.SpanContext;
+import io.opencensus.trace.SpanId;
+import io.opencensus.trace.TraceId;
+import io.opencensus.trace.TraceOptions;
+import io.opencensus.trace.propagation.SpanContextParseException;
+import io.opencensus.trace.propagation.TextFormat;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Implementation of the B3 propagation protocol. See <a
+ * href=https://github.com/openzipkin/b3-propagation>b3-propagation</a>.
+ */
+final class B3Format extends TextFormat {
+  @VisibleForTesting static final String X_B3_TRACE_ID = "X─B3─TraceId";
+  @VisibleForTesting static final String X_B3_SPAN_ID = "X─B3─SpanId";
+  @VisibleForTesting static final String X_B3_PARENT_SPAN_ID = "X─B3─ParentSpanId";
+  @VisibleForTesting static final String X_B3_SAMPLED = "X─B3─Sampled";
+  @VisibleForTesting static final String X_B3_FLAGS = "X-B3-Flags";
+  private static final List<String> FIELDS =
+      Collections.unmodifiableList(
+          Arrays.asList(
+              X_B3_TRACE_ID, X_B3_SPAN_ID, X_B3_PARENT_SPAN_ID, X_B3_SAMPLED, X_B3_FLAGS));
+
+  // Used as the upper TraceId.SIZE hex characters of the traceID. B3-propagation used to send
+  // TraceId.SIZE hex characters (8-bytes traceId) in the past.
+  private static final String UPPER_TRACE_ID = "0000000000000000";
+  // Sampled value via the X_B3_SAMPLED header.
+  private static final String SAMPLED_VALUE = "1";
+  // "Debug" sampled value.
+  private static final String FLAGS_VALUE = "1";
+
+  @Override
+  public List<String> fields() {
+    return FIELDS;
+  }
+
+  @Override
+  public <C> void inject(SpanContext spanContext, C carrier, Setter<C> setter) {
+    checkNotNull(spanContext, "spanContext");
+    checkNotNull(setter, "setter");
+    checkNotNull(carrier, "carrier");
+    setter.put(carrier, X_B3_TRACE_ID, spanContext.getTraceId().toLowerBase16());
+    setter.put(carrier, X_B3_SPAN_ID, spanContext.getSpanId().toLowerBase16());
+    if (spanContext.getTraceOptions().isSampled()) {
+      setter.put(carrier, X_B3_SAMPLED, SAMPLED_VALUE);
+    }
+  }
+
+  @Override
+  public <C> SpanContext extract(C carrier, Getter<C> getter) throws SpanContextParseException {
+    checkNotNull(carrier, "carrier");
+    checkNotNull(getter, "getter");
+    try {
+      TraceId traceId;
+      String traceIdStr = getter.get(carrier, X_B3_TRACE_ID);
+      if (traceIdStr != null) {
+        if (traceIdStr.length() == TraceId.SIZE) {
+          // This is an 8-byte traceID.
+          traceIdStr = UPPER_TRACE_ID + traceIdStr;
+        }
+        traceId = TraceId.fromLowerBase16(traceIdStr);
+      } else {
+        throw new SpanContextParseException("Missing X_B3_TRACE_ID.");
+      }
+      SpanId spanId;
+      String spanIdStr = getter.get(carrier, X_B3_SPAN_ID);
+      if (spanIdStr != null) {
+        spanId = SpanId.fromLowerBase16(spanIdStr);
+      } else {
+        throw new SpanContextParseException("Missing X_B3_SPAN_ID.");
+      }
+      TraceOptions traceOptions = TraceOptions.DEFAULT;
+      if (SAMPLED_VALUE.equals(getter.get(carrier, X_B3_SAMPLED))
+          || FLAGS_VALUE.equals(getter.get(carrier, X_B3_FLAGS))) {
+        traceOptions = TraceOptions.builder().setIsSampled(true).build();
+      }
+      return SpanContext.create(traceId, spanId, traceOptions);
+    } catch (IllegalArgumentException e) {
+      throw new SpanContextParseException("Invalid input.", e);
+    }
+  }
+}
diff --git a/impl_core/src/main/java/io/opencensus/implcore/trace/propagation/BinaryFormatImpl.java b/impl_core/src/main/java/io/opencensus/implcore/trace/propagation/BinaryFormatImpl.java
index 6075c80b..8a4377d3 100644
--- a/impl_core/src/main/java/io/opencensus/implcore/trace/propagation/BinaryFormatImpl.java
+++ b/impl_core/src/main/java/io/opencensus/implcore/trace/propagation/BinaryFormatImpl.java
@@ -59,7 +59,7 @@ import io.opencensus.trace.propagation.SpanContextParseException;
  *       </ul>
  * </ul>
  */
-public final class BinaryFormatImpl extends BinaryFormat {
+final class BinaryFormatImpl extends BinaryFormat {
   private static final byte VERSION_ID = 0;
   private static final int VERSION_ID_OFFSET = 0;
   // The version_id/field_id size in bytes.
diff --git a/impl_core/src/test/java/io/opencensus/implcore/trace/propagation/B3FormatTest.java b/impl_core/src/test/java/io/opencensus/implcore/trace/propagation/B3FormatTest.java
new file mode 100644
index 00000000..45514d06
--- /dev/null
+++ b/impl_core/src/test/java/io/opencensus/implcore/trace/propagation/B3FormatTest.java
@@ -0,0 +1,221 @@
+/*
+ * Copyright 2017, OpenCensus Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.opencensus.implcore.trace.propagation;
+
+import static com.google.common.truth.Truth.assertThat;
+import static io.opencensus.implcore.trace.propagation.B3Format.X_B3_FLAGS;
+import static io.opencensus.implcore.trace.propagation.B3Format.X_B3_PARENT_SPAN_ID;
+import static io.opencensus.implcore.trace.propagation.B3Format.X_B3_SAMPLED;
+import static io.opencensus.implcore.trace.propagation.B3Format.X_B3_SPAN_ID;
+import static io.opencensus.implcore.trace.propagation.B3Format.X_B3_TRACE_ID;
+
+import io.opencensus.trace.SpanContext;
+import io.opencensus.trace.SpanId;
+import io.opencensus.trace.TraceId;
+import io.opencensus.trace.TraceOptions;
+import io.opencensus.trace.propagation.SpanContextParseException;
+import io.opencensus.trace.propagation.TextFormat.Getter;
+import io.opencensus.trace.propagation.TextFormat.Setter;
+import java.util.HashMap;
+import java.util.Map;
+import javax.annotation.Nullable;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Unit tests for {@link B3Format}. */
+@RunWith(JUnit4.class)
+public class B3FormatTest {
+  private static final String TRACE_ID_BASE16 = "ff000000000000000000000000000041";
+  private static final TraceId TRACE_ID = TraceId.fromLowerBase16(TRACE_ID_BASE16);
+  private static final String TRACE_ID_BASE16_EIGHT_BYTES = "0000000000000041";
+  private static final TraceId TRACE_ID_EIGHT_BYTES =
+      TraceId.fromLowerBase16("0000000000000000" + TRACE_ID_BASE16_EIGHT_BYTES);
+  private static final String SPAN_ID_BASE16 = "ff00000000000041";
+  private static final SpanId SPAN_ID = SpanId.fromLowerBase16(SPAN_ID_BASE16);
+  private static final byte[] TRACE_OPTIONS_BYTES = new byte[] {1};
+  private static final TraceOptions TRACE_OPTIONS = TraceOptions.fromBytes(TRACE_OPTIONS_BYTES);
+  private final B3Format b3Format = new B3Format();
+  @Rule public ExpectedException thrown = ExpectedException.none();
+  private final Setter<Map<String, String>> setter =
+      new Setter<Map<String, String>>() {
+        @Override
+        public void put(Map<String, String> carrier, String key, String value) {
+          carrier.put(key, value);
+        }
+      };
+  private final Getter<Map<String, String>> getter =
+      new Getter<Map<String, String>>() {
+        @Nullable
+        @Override
+        public String get(Map<String, String> carrier, String key) {
+          return carrier.get(key);
+        }
+      };
+
+  @Test
+  public void serialize_SampledContext() {
+    Map<String, String> carrier = new HashMap<String, String>();
+    b3Format.inject(SpanContext.create(TRACE_ID, SPAN_ID, TRACE_OPTIONS), carrier, setter);
+    assertThat(carrier)
+        .containsExactly(
+            X_B3_TRACE_ID, TRACE_ID_BASE16, X_B3_SPAN_ID, SPAN_ID_BASE16, X_B3_SAMPLED, "1");
+  }
+
+  @Test
+  public void serialize_NotSampledContext() {
+    Map<String, String> carrier = new HashMap<String, String>();
+    b3Format.inject(SpanContext.create(TRACE_ID, SPAN_ID, TraceOptions.DEFAULT), carrier, setter);
+    assertThat(carrier)
+        .containsExactly(X_B3_TRACE_ID, TRACE_ID_BASE16, X_B3_SPAN_ID, SPAN_ID_BASE16);
+  }
+
+  @Test
+  public void parseMissingSampledAndMissingFlag() throws SpanContextParseException {
+    Map<String, String> headersNotSampled = new HashMap<String, String>();
+    headersNotSampled.put(X_B3_TRACE_ID, TRACE_ID_BASE16);
+    headersNotSampled.put(X_B3_SPAN_ID, SPAN_ID_BASE16);
+    SpanContext spanContext = SpanContext.create(TRACE_ID, SPAN_ID, TraceOptions.DEFAULT);
+    assertThat(b3Format.extract(headersNotSampled, getter)).isEqualTo(spanContext);
+  }
+
+  @Test
+  public void parseSampled() throws SpanContextParseException {
+    Map<String, String> headersSampled = new HashMap<String, String>();
+    headersSampled.put(X_B3_TRACE_ID, TRACE_ID_BASE16);
+    headersSampled.put(X_B3_SPAN_ID, SPAN_ID_BASE16);
+    headersSampled.put(X_B3_SAMPLED, "1");
+    assertThat(b3Format.extract(headersSampled, getter))
+        .isEqualTo(SpanContext.create(TRACE_ID, SPAN_ID, TRACE_OPTIONS));
+  }
+
+  @Test
+  public void parseZeroSampled() throws SpanContextParseException {
+    Map<String, String> headersNotSampled = new HashMap<String, String>();
+    headersNotSampled.put(X_B3_TRACE_ID, TRACE_ID_BASE16);
+    headersNotSampled.put(X_B3_SPAN_ID, SPAN_ID_BASE16);
+    headersNotSampled.put(X_B3_SAMPLED, "0");
+    assertThat(b3Format.extract(headersNotSampled, getter))
+        .isEqualTo(SpanContext.create(TRACE_ID, SPAN_ID, TraceOptions.DEFAULT));
+  }
+
+  @Test
+  public void parseFlag() throws SpanContextParseException {
+    Map<String, String> headersFlagSampled = new HashMap<String, String>();
+    headersFlagSampled.put(X_B3_TRACE_ID, TRACE_ID_BASE16);
+    headersFlagSampled.put(X_B3_SPAN_ID, SPAN_ID_BASE16);
+    headersFlagSampled.put(X_B3_FLAGS, "1");
+    assertThat(b3Format.extract(headersFlagSampled, getter))
+        .isEqualTo(SpanContext.create(TRACE_ID, SPAN_ID, TRACE_OPTIONS));
+  }
+
+  @Test
+  public void parseZeroFlag() throws SpanContextParseException {
+    Map<String, String> headersFlagNotSampled = new HashMap<String, String>();
+    headersFlagNotSampled.put(X_B3_TRACE_ID, TRACE_ID_BASE16);
+    headersFlagNotSampled.put(X_B3_SPAN_ID, SPAN_ID_BASE16);
+    headersFlagNotSampled.put(X_B3_FLAGS, "0");
+    assertThat(b3Format.extract(headersFlagNotSampled, getter))
+        .isEqualTo(SpanContext.create(TRACE_ID, SPAN_ID, TraceOptions.DEFAULT));
+  }
+
+  @Test
+  public void parseEightBytesTraceId() throws SpanContextParseException {
+    Map<String, String> headersEightBytes = new HashMap<String, String>();
+    headersEightBytes.put(X_B3_TRACE_ID, TRACE_ID_BASE16_EIGHT_BYTES);
+    headersEightBytes.put(X_B3_SPAN_ID, SPAN_ID_BASE16);
+    headersEightBytes.put(X_B3_SAMPLED, "1");
+    assertThat(b3Format.extract(headersEightBytes, getter))
+        .isEqualTo(SpanContext.create(TRACE_ID_EIGHT_BYTES, SPAN_ID, TRACE_OPTIONS));
+  }
+
+  @Test
+  public void parseEightBytesTraceId_NotSampledSpanContext() throws SpanContextParseException {
+    Map<String, String> headersEightBytes = new HashMap<String, String>();
+    headersEightBytes.put(X_B3_TRACE_ID, TRACE_ID_BASE16_EIGHT_BYTES);
+    headersEightBytes.put(X_B3_SPAN_ID, SPAN_ID_BASE16);
+    assertThat(b3Format.extract(headersEightBytes, getter))
+        .isEqualTo(SpanContext.create(TRACE_ID_EIGHT_BYTES, SPAN_ID, TraceOptions.DEFAULT));
+  }
+
+  @Test
+  public void parseInvalidTraceId() throws SpanContextParseException {
+    Map<String, String> invalidHeaders = new HashMap<String, String>();
+    invalidHeaders.put(X_B3_TRACE_ID, "abcdefghijklmnop");
+    invalidHeaders.put(X_B3_SPAN_ID, SPAN_ID_BASE16);
+    thrown.expect(SpanContextParseException.class);
+    thrown.expectMessage("Invalid input.");
+    b3Format.extract(invalidHeaders, getter);
+  }
+
+  @Test
+  public void parseInvalidTraceId_Size() throws SpanContextParseException {
+    Map<String, String> invalidHeaders = new HashMap<String, String>();
+    invalidHeaders.put(X_B3_TRACE_ID, "0123456789abcdef00");
+    invalidHeaders.put(X_B3_SPAN_ID, SPAN_ID_BASE16);
+    thrown.expect(SpanContextParseException.class);
+    thrown.expectMessage("Invalid input.");
+    b3Format.extract(invalidHeaders, getter);
+  }
+
+  @Test
+  public void parseMissingTraceId() throws SpanContextParseException {
+    Map<String, String> invalidHeaders = new HashMap<String, String>();
+    invalidHeaders.put(X_B3_SPAN_ID, SPAN_ID_BASE16);
+    thrown.expect(SpanContextParseException.class);
+    thrown.expectMessage("Missing X_B3_TRACE_ID.");
+    b3Format.extract(invalidHeaders, getter);
+  }
+
+  @Test
+  public void parseInvalidSpanId() throws SpanContextParseException {
+    Map<String, String> invalidHeaders = new HashMap<String, String>();
+    invalidHeaders.put(X_B3_TRACE_ID, TRACE_ID_BASE16);
+    invalidHeaders.put(X_B3_SPAN_ID, "abcdefghijklmnop");
+    thrown.expect(SpanContextParseException.class);
+    thrown.expectMessage("Invalid input.");
+    b3Format.extract(invalidHeaders, getter);
+  }
+
+  @Test
+  public void parseInvalidSpanId_Size() throws SpanContextParseException {
+    Map<String, String> invalidHeaders = new HashMap<String, String>();
+    invalidHeaders.put(X_B3_TRACE_ID, TRACE_ID_BASE16);
+    invalidHeaders.put(X_B3_SPAN_ID, "0123456789abcdef00");
+    thrown.expect(SpanContextParseException.class);
+    thrown.expectMessage("Invalid input.");
+    b3Format.extract(invalidHeaders, getter);
+  }
+
+  @Test
+  public void parseMissingSpanId() throws SpanContextParseException {
+    Map<String, String> invalidHeaders = new HashMap<String, String>();
+    invalidHeaders.put(X_B3_TRACE_ID, TRACE_ID_BASE16);
+    thrown.expect(SpanContextParseException.class);
+    thrown.expectMessage("Missing X_B3_SPAN_ID.");
+    b3Format.extract(invalidHeaders, getter);
+  }
+
+  @Test
+  public void fields_list() {
+    assertThat(b3Format.fields())
+        .containsExactly(
+            X_B3_TRACE_ID, X_B3_SPAN_ID, X_B3_PARENT_SPAN_ID, X_B3_SAMPLED, X_B3_FLAGS);
+  }
+}