pjsua: preserve ephemeral TLS and IPv6 ports

[cgsmith]

Description

Closes #5324

When pjsua is configured with --local-port=0, port 0 should be preserved for transports that use automatic port selection.

Currently, pjsua derives IPv6 and TLS transport ports by applying fixed offsets:

• TCP6: TCP port + 10
• TLS: TCP port + 1
• TLS6: TCP port + 10

When the base port is 0, this can result in fixed ports such as 10, 1, or 11 instead of OS-selected ephemeral ports. This may cause startup failures for unprivileged users and makes --local-port=0 behave unexpectedly.

This change applies the offsets only when the configured port is nonzero. Existing behavior for explicitly configured ports is unchanged.

Testing

• Built pjsua successfully on macOS.

[nanangizz]

Thanks, the fix works for the --no-udp case. Tested as an unprivileged user on Linux, with --local-port=0:

Options	master	this PR
--no-udp --use-tls	TLS listener: Permission denied (port 1)	ephemeral ports
--no-udp --ipv6 --use-tls	TCP6 listener: Permission denied (port 10)	ephemeral ports
--ipv6 --use-tls (UDP on)	UDP6 5060, TCP 5060, TCP6 5070, TLS 5071, TLS6 5080	same

With UDP enabled, the UDP6 block still maps port 0 to a fixed 5060 (udp_cfg.port = 5060), which is then copied into tcp_cfg.port, so none of the new checks apply and every port is fixed. A second instance started the same way fails with "address in use". Could you handle it the same way, i.e. if (udp_cfg.port != 0) udp_cfg.port += 10;? The 5060 dates back to a 2010 SIPit change (3f4b8d7), so it doesn't look like intended behaviour for port 0.

[cgsmith]

Thanks, good catch. Pushed bf0352b - the UDP6 block no longer maps port 0 to 5060. It now only adds the +10 offset when the port is nonzero.

Tested on macOS (arm64, OpenSSL, PJ_HAS_IPV6=1), all with --use-tls:

Options	Result
--local-port=0 --ipv6	UDP, UDP6, TCP, TCP6, TLS and TLS6 all on ephemeral ports
--local-port=0 --no-udp	TCP and TLS ephemeral
--local-port=0 --no-udp --ipv6	TCP, TCP6, TLS and TLS6 ephemeral
--local-port=5060 --ipv6	unchanged (UDP 5060, UDP6 5070, TCP 5060, TCP6 5070, TLS 5071, TLS6 5080)

Two instances started with --local-port=0 --ipv6 --use-tls at the same time both come up with no "address in use".

Terminal output

--local-port=0 --ipv6 --use-tls

SIP UDP transport started, published address is 192.168.2.110:56945
SIP UDP IPv6 transport started, published address is [...]:64486
SIP TCP listener ready for incoming connections at 192.168.2.110:64486
SIP TCP listener ready for incoming connections at [...]:64496
SIP TLS listener is ready for incoming connections at 192.168.2.110:64497
SIP TLS listener is ready for incoming connections at [...]:64506

--local-port=0 --no-udp --ipv6 --use-tls

SIP TCP listener ready for incoming connections at 192.168.2.110:52191
SIP TCP listener ready for incoming connections at [...]:52192
SIP TLS listener is ready for incoming connections at 192.168.2.110:52193
SIP TLS listener is ready for incoming connections at [...]:52194