[GitHub] massakam opened a new pull request #943: Start receiving messages after WebSocket session established

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massakam opened a new pull request #943: Start receiving messages after WebSocket session established
URL: https://github.com/apache/incubator-pulsar/pull/943
 
 
   ### Motivation
   
   In rare cases, WebSocket client that start consuming can not receive any messages from WebSocket Proxy even though messages still in the backlog.
   As a result of the investigation, I found that NullPointerException occurred at either of the following lines:
   
   * https://github.com/apache/incubator-pulsar/blob/bcc74044288932acc9e83b04001bf1ced17d7780/pulsar-websocket/src/main/java/org/apache/pulsar/websocket/ConsumerHandler.java#L118
   * https://github.com/apache/incubator-pulsar/blob/bcc74044288932acc9e83b04001bf1ced17d7780/pulsar-websocket/src/main/java/org/apache/pulsar/websocket/ConsumerHandler.java#L136
   
   It seems that `getSession()` returns null because WebSocket session establishment has not been completed.
   
   ### Modifications
   
   Move the first call of `receiveMessage()` from the constructor to `onWebSocketConnect()` in ConsumerHandler.
   
   ### Result
   
   ConsumerHandler starts receiving messages after WebSocket session established.
   Therefore, we can avoid NullPointerException.

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