How to Maintain TLS Session Reuse for Data Connections in FTPS with Apache Commons Net?

How to Maintain TLS Session for Data Connection in FTPS with Apache Commons Net

Problem:

Connecting to an FTPS server that requires data connection to use the same TLS session as the control connection using Apache Commons Net.

Solution:

Requirement:

The server must support TLS session reuse for data connections.

Apache Commons Net Overriding:

Override the _prepareDataSocket_ method in a custom FTPSClient implementation to manage session reuse, similar to what Cyberduck does in its FTPClient.java.

JDK Compatibility:

In Java 8u161 and later, session reuse may not work by default. To enable it:

System.setProperty("jdk.tls.useExtendedMasterSecret", "false");

Alternative Implementation:

An alternative implementation can be found in the following Apache Commons Net JIRA issue: https://issues.apache.org/jira/browse/NET-408.

Android-Specific Considerations:

For Android, bypass SDK restrictions to access reflection fields for session management: https://issues.apache.org/jira/browse/NET-776.

Post-Java 8u161 Changes:

In newer versions of Java, sessionsByHostAndPort should be used instead of sessionHostPortCache.

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