ContextProto.java

// ------------- Context API --------------
// Based on top of grpc.Context
// (We could also use it directly and add the automatic Scope handling).
// Note: Cannot use String directly for the keys, as an imposition done
//       by grpc.Context.
// Questions:
//    - Should we allow some form of extensibility to allow
//      users to provide logic/storage?
public final class Context {
  public static Context current();
  public static Scope setCurrent(Context ctx);
  public static Context getEmptyContext();
  public static <V> Context.Key<V> createKey(String name);

  public <V> Context setValue(Context.Key<V>, V value);
  public V getValue(Context.Key<V> key);
}

// ------------- Propagation API --------------
public interface HttpInjector {
  <C> void inject(Context ctx, C carrier, Setter<C> setter);
}

public interface HttpExtractor {
  <C> Context extract(C carrrier, Getter<C> getter);
}

// ------------- Baggage API --------------
// Questions:
//    - Should we allow values other than String?
public interface BaggageSetter {
  public Context setValue(Context ctx, String key, String value);
  public Context setValue(String key, String value); // Context.current()

  public String getValue(Context ctx, String key);
  public String getValue(String key); // Context.current()

  public void removeValue(Context ctx, String key);
  public void removeValue(String key); // Context.current()

  public void clear(Context ctx);
  public void clear(); // Context.current()

  public HttpInjector getHttpInjector();
  public HttpExtractor getHttpExtractor();
}

// ------------- Observability API --------------
public interface CorrelationSetter {
  public Context setValue(Context ctx, <List>CorrelationLabel labels, HopLimit hopLimit);
  public Context setValue(<List>CorrelationLabel labels, HopLimit hopLimit); // Context.current()

  public HttpInjector getHttpInjector();
  public HttpExtractor getHttpExtractor();
}

public CorrelationLabel {
  public String key();
  public String value();
}