Do not auto-close a GrpcStream. (#58)

Signed-off-by: John Plevyak <jplevyak@gmail.com>

Author: jplevyak

proxy_wasm_api.h

@@ -201,6 +201,7 @@ class GrpcCallHandlerBase {
   RootContext *context() { return context_; }
 
   void cancel();
+  uint32_t token() { return token_; }
 
   virtual void onSuccess(size_t body_size) = 0;
   virtual void onFailure(GrpcStatus status) = 0;
@@ -233,6 +234,7 @@ class GrpcStreamHandlerBase {
   void close(); // NB: callbacks can still occur: reset() to prevent further
                 // callbacks.
   void reset();
+  uint32_t token() { return token_; }
 
   virtual void onReceiveInitialMetadata(uint32_t /* headers */) {}
   virtual void onReceiveTrailingMetadata(uint32_t /* trailers */) {}
@@ -1483,7 +1485,6 @@ inline void RootContext::onGrpcReceive(uint32_t token, size_t body_size) {
     auto it = grpc_streams_.find(token);
     if (it != grpc_streams_.end()) {
       it->second->onReceive(body_size);
-      grpc_streams_.erase(token);
       return;
     }
   }