Remove TraceContext, as has already been done in the specification.

Remove TraceContextSource, as methods from it now belong in Tracer.
Remove Tracer.joinTrace(..) as Span.startChild(..) already does this.

ref:
 - opentracing/opentracing.io#42
 - #7

opentracing/src/main/java/opentracing/Span.java

@@ -22,11 +22,6 @@
  */
 public interface Span {
 
-  /**
-   * Suitable for serializing over the wire, etc.
-   */
-  TraceContext traceContext();
-
   /**
    * Denotes the beginning of a subordinate unit of work.
    *
@@ -64,6 +59,8 @@ public interface Span {
   // numbers kindof suck.. we've no idea if this is a float, how many bits, etc.
   Span setTag(String key, Number value);
 
+  Span setTraceAttribute(String key, String value);
+
   /**
    * {@code message} is a format string and can refer to fields in the payload by path, like so:
    *

opentracing/src/main/java/opentracing/TraceContextCodec.java → opentracing/src/main/java/opentracing/SpanPropagator.java

@@ -16,24 +16,25 @@
 import java.util.Map;
 
 /**
- * Encodes or Decodes a {@linkplain TraceContext trace context} in binary or text formats.
+ * Encodes or Decodes a {@linkplain Span span} in binary or text formats.
  *
- * <p>The toXXX methods are expected to serialize trace contexts into a pair of values representing
- * separately the trace context / span identity, and the trace attributes. This is done specifically
- * for binary protocols that may represent tracing identity in a dedicated fixed-length slot in the
+ * <p>The toXXX methods are expected to serialize spans into a pair of values representing
+ * separately the span / span identity, and the trace attributes.
+ *
+ * This is done specifically for binary protocols that may represent tracing identity in a dedicated fixed-length slot in the
  * binary message format, so that it can be inspected efficiently by the middleware / routing layers
  * without parsing the whole message.
  */
-public interface TraceContextCodec {
+public interface SpanPropagator {
 
   /**
    * Implementation-specific format of a span's identity along with any trace attributes.
    *
    * @param <E> encoding, for example {@code byte[]} for binary, or {@code Map<String, String>} for
    * text.
    */
-  // Can instead explicitly create BinaryEncodedTraceContext, TextEncodedTraceContext, just.. cluttery
-  interface EncodedTraceContext<E> {
+  // Can instead explicitly create BinaryEncodedSpan, TextEncodedSpan, just.. cluttery
+  interface EncodedSpan<E> {
     /** Encoded span identifier. */
     E spanIdentity();
 
@@ -42,30 +43,30 @@ interface EncodedTraceContext<E> {
   }
 
   /**
-   * Encodes the trace context into a binary representation of the span's identity and trace
+   * Encodes the span into a binary representation of the span's identity and trace
    * attributes.
    */
-  EncodedTraceContext<byte[]> toBinary(TraceContext tc);
+  EncodedSpan<byte[]> toBinary(Span tc);
 
   /**
-   * Decodes a trace context from a binary representation of the span's identity and trace
+   * Decodes a span from a binary representation of the span's identity and trace
    * attributes.
    *
    * @throws IllegalArgumentException if the encoded data is malformed.
    */
-  TraceContext fromBinary(EncodedTraceContext<byte[]> encoded);
+  Span fromBinary(EncodedSpan<byte[]> encoded);
 
   /**
-   * Encodes the trace context into a text representation of the span's identity and trace
+   * Encodes the span into a text representation of the span's identity and trace
    * attributes.
    */
-  EncodedTraceContext<Map<String, String>> toText(TraceContext tc);
+  EncodedSpan<Map<String, String>> toText(Span tc);
 
   /**
-   * Decodes a trace context from a text representation of the span's identity and trace
+   * Decodes a span from a text representation of the span's identity and trace
    * attributes.
    *
    * @throws IllegalArgumentException if the encoded data is malformed.
    */
-  TraceContext fromText(EncodedTraceContext<Map<String, String>> encoded);
+  Span fromText(EncodedSpan<Map<String, String>> encoded);
 }

opentracing/src/main/java/opentracing/Tracer.java

@@ -33,22 +33,5 @@ public interface Tracer {
    */
   Span startTrace(String operationName);
 
-  /**
-   * Like {@link #startTrace(String)}, but the returned span is made a child of {@code parent}.
-   */
-  Span joinTrace(String operationName, TraceContext parent);
-
-  /**
-   * StartSpanWithContext returns a span with the given {@code operationName} and an association
-   * with {@code context} (rather than creating a fresh root context like {@link
-   * #startTrace(String)} or a fresh child context like {@link #joinTrace(String, TraceContext)}).
-   *
-   * <p>Note that the following calls are equivalent
-   * <pre>{@code
-   * Span feed = tracer.startSpanWithContext("GetFeed", traceContextSource.newRoot());
-   * ...
-   * Span feed = tracer.startTrace("GetFeed");
-   * }</pre>
-   */
-  Span startSpanWithContext(String operationName, TraceContext context);
+  SpanPropagator getSpanPropagator();
 }