Send agent name from THeaderTransport.java

Summary: One downside of this implementation is that this will be sent with the first response from the Java server as well. But I don't think any clients should care.

Reviewed By: mshneer

Differential Revision: D30954223

fbshipit-source-id: bbdf944ca98c6a159a26ee6e3ece1bc4ec457453

thrift/lib/java/src/main/java/com/facebook/thrift/transport/THeaderTransport.java

@@ -120,9 +120,13 @@ public int getValue() {
   private static final String IDENTITY_HEADER = "identity";
   private static final String ID_VERSION_HEADER = "id_version";
   private static final String ID_VERSION = "1";
+  private static final String CLIENT_METADATA_HEADER = "client_metadata";
+  private static final String CLIENT_METADATA = "{\"agent\":\"THeaderTransport.java\"}";
 
   private String identity;
 
+  private boolean firstRequest = true;
+
   public THeaderTransport(TTransport transport) {
     super(transport);
     writeTransforms = new ArrayList<Transforms>();
@@ -431,6 +435,7 @@ private void readHeaderFormat(int headerSize, byte[] buff) throws TTransportExce
         break;
       }
     }
+    readHeaders.remove(CLIENT_METADATA_HEADER);
     readHeaders.putAll(readPersistentHeaders);
 
     // Read in the data section.
@@ -614,6 +619,11 @@ public void flushImpl(boolean oneway) throws TTransportException {
       transformData.limit(transformData.position());
       transformData.position(0);
 
+      if (firstRequest) {
+        firstRequest = false;
+        writeHeaders.put(CLIENT_METADATA_HEADER, CLIENT_METADATA);
+      }
+
       if (identity != null && identity.length() > 0) {
         writeHeaders.put(ID_VERSION_HEADER, ID_VERSION);
         writeHeaders.put(IDENTITY_HEADER, identity);