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androidftpbouncycastlefilezillaapache-commons-net

Android FTPS Upload Issue: '425 Unable to build data connection: TLS session of data connection not resumed'

In my android App, I'm trying to connect and upload files to my FTPS server (using port 21), which is essentially FTP with TLS. The server is a FileZilla Server that works perfectly fine with the FileZilla client. I'm using the following library for the FTPS client:

gradle implementation 'commons-net:commons-net:3.11.1' // FTP

However, I am facing the following error when I try to list directories or list names after connecting and logging in:

425 Unable to build data connection: TLS session of data connection not resumed.

From my research, I found that the Apache Commons Net library does not support TLS connection resumption, which is necessary to reuse the same TLS session for secure file transfers.

I came across this StackOverflow thread: How to connect to FTPS server with data connection using same TLS session? and have already tried implementing solutions mentioned there, but they did not work for me.

I have tried several solutions, including:

  1. https://eng.wealthfront.com/2016/06/10/connecting-to-an-ftps-server-with-ssl-session-reuse-in-java-7-and-8/

Facing the error(No field sessionsByHostAndPort in class Lcom/android/org/conscrypt/ClientSessionContext; (declaration of 'com.android.org.conscrypt.ClientSessionContext' appears in /apex/com.android.conscrypt/javalib/conscrypt.jar))

  1. Using BouncyCastle for TLS:

gradle implementation 'org.bouncycastle:bctls-jdk18on:1.78.1'

However, this did not resolve the issue.

  1. Overriding the _prepareDataSocket_ method of FTPSClient, but this also did not work as intended.

Given that my FTPS client is creating a new TLS session for each file transfer while the server expects the same secure session as the control connection to be reused, I am looking for guidance on how to maintain the same TLS session for data connections or any other solutions that could help resolve this issue.

Solution

  • For everyone facing the same issue, I finally found a solution after spending 2-3 days searching through Stack Overflow, reading blogs, etc. I got help from ferpalos's answer on Stack Overflow. However, I also had to add the RestrictionBypass dependency, as suggested by TomInCode. Now, the connection issue is resolved. However, I'm still unsure if it's entirely safe to use RestrictionBypass.