src/main/java/org/jivesoftware/smack/XMPPConnection.java
void startStreamCompression() throws Exception {
        serverAckdCompression = true;
        // Initialize the reader and writer with the new secured version
        initReaderAndWriter();

        // Set the new writer to use
        packetWriter.setWriter(writer);
        // Send a new opening stream to the server
        packetWriter.openStream();
        // Notify that compression is being used
        synchronized (this) {
            this.notify();
        }
    }
void startStreamCompression() throws Exception {
        serverAckdCompression = true;
        // Initialize the reader and writer with the new secured version
        initReaderAndWriter();

        // Set the new writer to use
        packetWriter.setWriter(writer);
        // Send a new opening stream to the server
        packetWriter.openStream();
        // Notify that compression is being used
        synchronized (this) {
            this.notify();
        }
    }
Start using stream compression since the server has acknowledged stream
compression.

@throws Exception
if there is an exception starting stream compression.