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.

2 files changed, 106 insertions, 1 deletions

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.