Apache Commons TFTP implementation subject to Sorcerer's Apprentice Syndrome
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Key: NET-412
URL: https://issues.apache.org/jira/browse/NET-412
Project: Commons Net
Issue Type: Bug
Components: TFTP
Affects Versions: 3.0, 2.2
Environment: Java 6 patch 20
Reporter: Chuck Wolber
Priority: Critical
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:
{
continue _receivePacket;
}
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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