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https://issues.apache.org/jira/browse/NET-412?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sebb resolved NET-412.
----------------------
Resolution: Fixed
Fix Version/s: 3.1
> Apache Commons TFTP implementation subject to Sorcerer's Apprentice Syndrome
> ----------------------------------------------------------------------------
>
> Key: NET-412
> URL: https://issues.apache.org/jira/browse/NET-412
> Project: Commons Net
> Issue Type: Bug
> Components: TFTP
> Affects Versions: 2.2, 3.0
> Environment: Java 6 patch 20
> Reporter: Chuck Wolber
> Priority: Critical
> Fix For: 3.1
>
>
> This is regarding the org.apache.commons.net.tftp.TFTPClient class.
> In the sendFile() method, when a duplicate TFTP ACK is received, the "if
> (lastBlock == block)" section of code fails and control moves to the "else"
> statement. The else block checks to see if the ACK is for the previous DATA
> packet, and if so, sends control back to the _sendPacket label where the DATA
> packet is resent.
> This is in direct violation of Sorcerer's Apprentice Syndrome as defined in
> RFC 1123 section 4.2.3.1:
> "the sender (i.e., the side originating the DATA packets) must never resend
> the current DATA packet on receipt of a duplicate ACK"
> The proper else block would look something like this:
> {noformat}
> {
> continue _receivePacket;
> }
> {noformat}
> This enables the client to ignore the duplicated ACK and listen for ACK+1. If
> ACK+1 never comes in, the listener should timeout and attempt to resend the
> current data packet. As described in NET-410, the TFTP client also does not
> properly handle re-transmits either. It is recommended that this issue and
> NET-410 be implemented in tandem.
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