Merge pull request #190 from ydb-platform/fix_start_partition_session…

…_settings_builder

Fix StartPartitionSessionSettings.Builder methods return value, add comments

topic/src/main/java/tech/ydb/topic/settings/StartPartitionSessionSettings.java

@@ -28,12 +28,34 @@ public static class Builder {
         private Long readOffset;
         private Long commitOffset;
 
-        public void setReadOffset(Long readOffset) {
+        /**
+         * Reads in this partition session will start from offset no less than readOffset.
+         * If readOffset is set, server will check if that readOffset is not less than the actual committed offset.
+         * If the check fails then server will send an error message (status != SUCCESS) and close the stream.
+         * If readOffset is not set or is null (which is default), no check will be made.
+         *
+         * InitRequest.max_lag and InitRequest.read_from could lead to skip of more messages.
+         * Server will return data starting from offset that is maximum of actual committed offset, read_offset (if set)
+         * and offsets calculated from InitRequest.max_lag and InitRequest.read_from.
+         *
+         * @param readOffset Offset to read from. Default: null
+         * @return Builder
+         */
+        public Builder setReadOffset(Long readOffset) {
             this.readOffset = readOffset;
+            return this;
         }
 
-        public void setCommitOffset(Long commitOffset) {
+        /**
+         * Make server know that all messages with offsets less than commitOffset were fully processed by client.
+         * Server will commit this position if it is not already done.
+         *
+         * @param commitOffset Commit offset, following the offset of last processed (committed) message. Default: null
+         * @return Builder
+         */
+        public Builder setCommitOffset(Long commitOffset) {
             this.commitOffset = commitOffset;
+            return this;
         }
 
         public StartPartitionSessionSettings build() {