Hi Christoph
There is such option in my app (heartbeats from server to client) but I’m
curious why connection becomes stale if I don’t send any heartbeats.
On 29/01/16 16:04, "Christoph Nenning" <christoph.nenn...@lex-com.net>
wrote:
>> I have a problem with my java application related to HTTP communication.
>>
>> Application description:
>>
>> 1. Client – server. Server is running in servlet container. We
>> use Tomcat.
>>
>> Client use java HTTP library to communicate with the server.
>>
>> 2. When client establish connection to the server it sends GET
>> request (keepalive) and server creates AsyncContext for the client
>> with 10 days timeout.
>>
>> 3. After connection established server periodically sends data
>> to the client using AsyncContext and on the client side there is
>> special thread which reads and processes the data.
>>
>> Client reading thread example:
>>
>> private class GetRunnable implements Runnable {
>>
>> private final HttpURLConnection httpConn;
>> private final MyConnection myConn;
>>
>> public GetRunnable(final MyConnection myConn) throws
>> IOException, AppException {
>> this.myConn = myConn;
>> final String jSession = myConn.getJSession();
>> httpConn = openHttpUrlConnection(false,
>> httpPostTimeout, jSession);
>> httpConn.connect();
>> final int respCode = httpConn.getResponseCode();
>> if (respCode != HttpURLConnection.HTTP_OK) {
>> String info = "Incorrect response from server,
>> responseCode:" + respCode + ", message:" +
>httpConn.getResponseMessage();
>> log.error(info);
>> throw new AppException(info);
>> } else {
>> log.trace("GET connected");
>> }
>> }
>>
>> @Override
>> public void run() {
>> try (final BufferedReader reader = new BufferedReader
>> (new InputStreamReader(httpConn.getInputStream(), "UTF-8")) ) {
>> log.info("doGet STARTED");
>> final Thread t = Thread.currentThread();
>> while (!t.isInterrupted()) {
>> log.trace("before readline");
>> final String line = reader.readLine();
>> log.trace("after readline: [" + line + "]");
>>
>> //INFO: DATA PROCESSING HERE
>> }
>> } catch (IOException e) {
>> log.error("Error while doGet");
>> } catch (Throwable e) {
>> log.debug("doGet STOPED...");
>> log.error("Error while read input msg, do logoff",
>e);
>> logoff();
>> throw e;
>> }
>> log.debug("doGet STOPED...");
>> myCallback.onGetClose(myConn, connInfo);
>> }
>> }
>>
>> Server side code to push data looks like this:
>>
>> protected int sendMsgs(final MyConnection myConn, final String info) {
>>
>> int res;
>> try {
>> final AsyncContext lAc = _ac;
>> final ServletRequest req = lAc.getRequest();
>> if (!req.isAsyncStarted()) {
>> log.debug("AsyncStarted=false on begin, uid:" +
>> uid + ", sid:" + sid);
>> return -1;
>> }
>>
>> final ServletResponse res = lAc.getResponse();
>> ServletOutputStream os = null;
>> final String text = getData(myConn);
>>
>> if (os == null)
>> os = res.getOutputStream();
>>
>> write2stream(os, text, 0x4000);
>> os.println();
>>
>> if (os != null)
>> os.flush();
>> } catch(IOException ex) {
>> log.error("Notify failed");
>> } catch (InterruptedException e) {
>> log.error("Notify failed");
>> Thread.currentThread().interrupt();
>> } catch (Throwable e) {
>> log.error("Notify failed");
>> logoff(true);
>> }
>>
>> return res;
>> }
>>
>> public static void write2stream(final OutputStream outputStream,
>> final String text, int bufferSize) throws IOException {
>> final CharsetEncoder encoder = getHttpEncodingCharset
>> ().newEncoder();
>>
>> final int fullLen = text.length();
>> final int byteBufferSize = Math.min(bufferSize, fullLen);
>>
>> final int en = (int)(byteBufferSize * (double)
>> encoder.maxBytesPerChar());
>> final byte[] byteArray = new byte[en];
>>
>> final ByteBuffer byteBuffer = ByteBuffer.wrap(byteArray);
>> final CharBuffer charBuffer = CharBuffer.wrap(text);
>> for(int pos=0, len=byteBufferSize;
>> pos < fullLen;
>> pos=len, len=Math.min(pos+byteBufferSize,
>> fullLen)) {
>>
>> try {
>> final CharBuffer window = charBuffer.subSequence(pos,
>len);
>>
>> CoderResult res = encoder.encode(window,
>> byteBuffer, true);
>>
>> if (!res.isUnderflow())
>> res.throwException();
>>
>> res = encoder.flush(byteBuffer);
>>
>> if (!res.isUnderflow())
>> res.throwException();
>>
>> } catch (final CharacterCodingException x) {
>> throw new Error(x);
>> }
>>
>> outputStream.write(byteArray, 0, byteBuffer.position());
>>
>> byteBuffer.clear();
>> encoder.reset();
>> }
>> }
>>
>> Usually this code works fine but it there is no data from server to
>> client for 1 day and after 24 hours (can be 16 or 12) data appears,
>> server cannot send data to the client.
>> In the log there is no error. It is written that everything flushed
>> but client still waiting for data in “final String line =
>reader.readLine();”
>> When 2nd portion of data is sent by the server, then during flush I
>> see the following error
>>
>> 2016-01-26 00:00:00,051|INFO |GWNotify-2/50 |ClientAbort
>> 2016-01-26 00:00:00,051|TRACE|GWNotify-2/50 |
>> ClientAbortException:java.io.IOException: APR error: -32
>> org.apache.catalina.connector.ClientAbortException:
>> java.io.IOException: APR error: -32
>> at org.apache.catalina.connector.OutputBuffer.doFlush
>> (OutputBuffer.java:353) ~[catalina.jar:8.0.30]
>> at org.apache.catalina.connector.OutputBuffer.flush
>> (OutputBuffer.java:317) ~[catalina.jar:8.0.30]
>> at
>> org.apache.catalina.connector.CoyoteOutputStream.flush
>> (CoyoteOutputStream.java:110) ~[catalina.jar:8.0.30]
>>
>> Caused by: java.io.IOException: APR error: -32
>> at
>> org.apache.coyote.http11.InternalAprOutputBuffer.writeToSocket
>> (InternalAprOutputBuffer.java:291) ~[tomcat-coyote.jar:8.0.30]
>> at
>> org.apache.coyote.http11.InternalAprOutputBuffer.writeToSocket
>> (InternalAprOutputBuffer.java:244) ~[tomcat-coyote.jar:8.0.30]
>> at
>> org.apache.coyote.http11.InternalAprOutputBuffer.flushBuffer
>> (InternalAprOutputBuffer.java:213) ~[tomcat-coyote.jar:8.0.30]
>> at
>> org.apache.coyote.http11.AbstractOutputBuffer.flush
>> (AbstractOutputBuffer.java:305) ~[tomcat-coyote.jar:8.0.30]
>> at
>> org.apache.coyote.http11.AbstractHttp11Processor.action
>> (AbstractHttp11Processor.java:765) ~[tomcat-coyote.jar:8.0.30]
>> at org.apache.coyote.Response.action(Response.java:
>> 177) ~[tomcat-coyote.jar:8.0.30]
>> at org.apache.catalina.connector.OutputBuffer.doFlush
>> (OutputBuffer.java:349) ~[catalina.jar:8.0.30]
>> ... 6 more
>>
>> Finally after I stop server I see that GetRunnable client thread is
>> still alive and waiting data from the server in “final String line =
>> reader.readLine();”!!!
>
>
>Hi,
>
>I would send some keep-alive data (e.g. current timestamp) maybe once per
>day or once every 5 hours. The client can just dismiss that data. This
>might help in some situations but there is no 100% guarantee that it
>works
>always.
>
>
>Regards,
>Christoph
>
>
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