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    Bug 
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    Resolution: Unresolved
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    Blocker 
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    None
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    Jenkins Version: 2.204.1
 mattermost-plugin: 3.0.0
 Mattermost Version: 5.6.2
 
After updating to versin 3.0.0 of the mattermost-plugin, notifications are not posted to the Mattermost server 5.6.2 anymore. After a downgrade to version 2.7.1 notifications are posted again.
Unfortunately there is no up-to-date changelog for this new major release to help narrow this down.
The following exception can be found in the log:
2019-12-30 08:48:06.321+0000 [id=285]   WARNING j.p.m.StandardMattermostService#publish: Error posting to Mattermost
java.net.SocketTimeoutException: Read timed out
        at java.net.SocketInputStream.socketRead0(Native Method)
        at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
        at java.net.SocketInputStream.read(SocketInputStream.java:171)
        at java.net.SocketInputStream.read(SocketInputStream.java:141)
        at org.apache.http.impl.io.SessionInputBufferImpl.streamRead(SessionInputBufferImpl.java:137)
        at org.apache.http.impl.io.SessionInputBufferImpl.fillBuffer(SessionInputBufferImpl.java:153)
        at org.apache.http.impl.io.SessionInputBufferImpl.readLine(SessionInputBufferImpl.java:280)
        at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:138)
        at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:56)
        at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:259)
        at org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:163)
        at org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:157)
        at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:273)
        at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:125)
        at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:272)
        at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:186)
        at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
        at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
        at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
        at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:118)
        at jenkins.plugins.mattermost.StandardMattermostService.publish(StandardMattermostService.java:174)
        at jenkins.plugins.mattermost.workflow.MattermostSendStep$MattermostSendStepExecution.run(MattermostSendStep.java:192)
        at jenkins.plugins.mattermost.workflow.MattermostSendStep$MattermostSendStepExecution.run(MattermostSendStep.java:129)
        at org.jenkinsci.plugins.workflow.steps.SynchronousNonBlockingStepExecution.lambda$start$0(SynchronousNonBlockingStepExecution.java:47)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)