feat(ftpd): add passive port multiplexing by client IP - #2253
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Expose the PassiveTransferPortMultiplexing setting added in ftpserverlib v0.31.0 (fclairamb/ftpserverlib#623) through a new "passive_port_multiplexing" FTP option. When enabled, clients with different IP addresses can share the same passive port, increasing the number of concurrent passive transfers that can be served with a limited passive port range. Clients behind the same NAT or public IP are treated as a single client for multiplexing purposes. Signed-off-by: Francisco A. Lozano <flozano@gmail.com> Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Extend TestServerGetSettings to assert that the new PassivePortMultiplexing configuration field is propagated to ftpserver.Settings, mirroring the existing PassiveTransferPortRange assertion. Signed-off-by: Francisco A. Lozano <flozano@gmail.com> Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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… a port Add a Linux-only integration test that starts an FTP server with a single-port passive range and PassivePortMultiplexing enabled, then runs several overlapping passive transfers from different loopback source IPs. The transfers are held in-flight at the same time so they genuinely share the one passive port, which is only possible with multiplexing (the test fails by port exhaustion when the flag is off). Each client sends a distinct byte pattern that is read back to verify the server delivered every data connection to the correct session. Signed-off-by: Francisco A. Lozano <flozano@gmail.com> Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Summary
ftpserverlib v0.31.0 added passive port multiplexing by client IP via fclairamb/ftpserverlib#623, exposed as the
Settings.PassiveTransferPortMultiplexingflag. SFTPGo already depends on ftpserverlib v0.32.0 but does not surface the option, so this PR wires it through the FTP configuration.When enabled, FTP clients with different IP addresses can share the same passive port concurrently, instead of requiring one listener per session. This increases the number of simultaneous passive transfers that can be served from a limited passive port range. Clients behind the same NAT / public egress IP are treated as a single client for multiplexing purposes, so the effective limit is based on the observed source IP.
The option is disabled by default, preserving the current behavior.
Changes
internal/ftpd/ftpd.go: newPassivePortMultiplexingfield onConfiguration(passive_port_multiplexing), placed next to the existingpassive_port_rangeoption.internal/ftpd/server.go: map it toftpserver.Settings.PassiveTransferPortMultiplexingwhen building the server settings.internal/config/config.go: register the viper default, alongside the otherftpd.*defaults.sftpgo.json: document the new key in the example configuration.The naming mirrors SFTPGo's existing convention, which drops
Transferfrom the upstream names (PassiveTransferPortRange→passive_port_range), giving the parallelpassive_port_multiplexingkey. The exposure follows the exact same pattern as the sibling boolean flags such asdisable_active_mode.Testing
go build ./...go vet ./internal/ftpd/... ./internal/config/...gofmtclean🤖 Generated with Claude Code