FnAPI proto changes for ordered list state.

model/fn-execution/src/main/proto/org/apache/beam/model/fn_execution/v1/beam_fn_api.proto

@@ -1021,6 +1021,29 @@ message StateKey {
     bytes map_key = 5;
   }
 
+  // Represents a request for an ordered list of values associated with a
+  // specified user key and window for a PTransform. See
+  // https://s.apache.org/beam-fn-state-api-and-bundle-processing for further
+  // details.
+  //
+  // The response data stream will be a concatenation of all entries of sort key
+  // and V's associated with the specified user key and window.
+  // See https://s.apache.org/beam-fn-api-send-and-receive-data for further
+  // details.
+  message OrderedListUserState {
+    // (Required) The id of the PTransform containing user state.
+    string transform_id = 1;
+    // (Required) The id of the user state.
+    string user_state_id = 2;
+    // (Required) The window encoded in a nested context.
+    bytes window = 3;
+    // (Required) The key of the currently executing element encoded in a
+    // nested context.
+    bytes key = 4;
+    // (Required) The sort range encoded in a nested context.
+    OrderedListRange range = 5;
+  }
+
   // (Required) One of the following state keys must be set.
   oneof type {
     Runner runner = 1;
@@ -1031,6 +1054,7 @@ message StateKey {
     MultimapKeysValuesSideInput multimap_keys_values_side_input = 8;
     MultimapKeysUserState multimap_keys_user_state = 6;
     MultimapUserState multimap_user_state = 7;
+    OrderedListUserState ordered_list_user_state = 9;
   }
 }
 
@@ -1055,6 +1079,8 @@ message StateGetResponse {
   // Represents a part of a logical byte stream. Elements within
   // the logical byte stream are encoded in the nested context and
   // concatenated together.
+  //
+  // See also the note about OrderedListState in StateAppendRequest.
   bytes data = 2;
 }
 
@@ -1063,6 +1089,11 @@ message StateAppendRequest {
   // Represents a part of a logical byte stream. Elements within
   // the logical byte stream are encoded in the nested context and
   // multiple append requests are concatenated together.
+  //
+  // For OrderedListState, elements of should be encoded with the
+  // beam:coder:kv:v1 coder, where the first (key) component must be a
+  // beam:coder:varint:v1 and the second (value) component must be encoded
+  // with a beam:coder:length_prefix:v1 coder.
   bytes data = 1;
 }
 
@@ -1075,6 +1106,12 @@ message StateClearRequest {}
 // A response to clear state.
 message StateClearResponse {}
 
+// A message describes a sort key range [start, end).
+message OrderedListRange {
+  int64 start = 1;
+  int64 end = 2;
+}
+
 /*
  * Logging API
  *