New option --oiface for outgoing interface

[gsnw-sebast]

With this new option, it should be possible to send a packet on one interface and receive any packet on another. There is no fallback to SO_BINDTODEVICE, for example. The -I option must be used for this.

Unfortunately, it is difficult for me to test this behavior. Therefore, I have only worked with the debugger.

[gemini-code-assist]

Summary of Changes

Hello @gsnw-sebast, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new --oiface command-line option for fping, enabling users to explicitly define the network interface through which outgoing ping packets are sent. This enhancement provides more granular control over network traffic, allowing pings to originate from a specific interface while still permitting the reception of responses from any available interface. The implementation utilizes IP_PKTINFO and IPV6_PKTINFO for robust interface binding.

Highlights

• New --oiface option: Introduced a new command-line option --oiface to specify the outgoing network interface for ping packets.
• Separate send/receive interfaces: This option allows sending packets via a specific interface while still being able to receive responses on any interface, differentiating it from the existing -I (SO_BINDTODEVICE) option.
• IP_PKTINFO implementation: The functionality is implemented using IP_PKTINFO for IPv4 and IPV6_PKTINFO for IPv6, leveraging sendmsg to attach control messages with interface information.
• Test case and documentation: A new test case was added for the --oiface option, and the fping man page was updated to include its description.

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Changelog

• CHANGELOG.md
  • Added an entry for the new --oiface feature.
• ci/test-07-options-i-m.pl
  • Increased the test count and added a new test case for the --oiface option, specifically for Linux.
• doc/fping.pod
  • Documented the newly introduced --oiface command-line option, explaining its purpose.
• src/fping.c
  • Registered the --oiface option in the command-line parser and added logic to handle its argument, calling interface-setting functions.
  • Added a check for IP_PKTINFO availability when --oiface is used.
• src/fping.h
  • Declared new functions socket_set_outgoing_iface_ipv4 and socket_set_outgoing_iface_ipv6.
• src/socket4.c
  • Included net/if.h for interface functions.
  • Added a static variable outgoing_iface_idx_ipv4 to store the outgoing interface index.
  • Implemented socket_set_outgoing_iface_ipv4 to resolve the interface name to an index and set the IP_PKTINFO socket option.
  • Modified socket_sendto_ping_ipv4 to use sendmsg with IP_PKTINFO control messages if an outgoing interface is specified.
• src/socket6.c
  • Included net/if.h for interface functions.
  • Added a static variable outgoing_iface_idx_ipv6 to store the outgoing interface index.
  • Implemented socket_set_outgoing_iface_ipv6 to resolve the interface name to an index and set the IPV6_RECVPKTINFO socket option.
  • Modified socket_sendto_ping_ipv6 to use sendmsg with IPV6_PKTINFO control messages if an outgoing interface is specified.

Activity

• The author, @gsnw-sebast, implemented the --oiface option to allow sending packets on one interface and receiving on another, noting it's distinct from SO_BINDTODEVICE.
• The author mentioned that testing this specific behavior was challenging and primarily relied on debugger analysis.

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[gemini-code-assist]

Code Review

This pull request introduces a new --oiface option to specify the outgoing network interface for ping packets. The implementation correctly uses sendmsg with ancillary data (IP_PKTINFO for IPv4 and IPV6_PKTINFO for IPv6) to achieve this. The changes are well-structured and include documentation and a basic test case. My review includes a couple of suggestions for improvement: one to clarify a comment in the new test and another to make the command-line option parsing more robust to prevent potential issues with future options.

[gemini-code-assist]

Using strstr to check for the option name is not robust. It could lead to incorrect behavior if another long option is added that contains "oiface" as a substring (e.g., --oiface-extra). A more precise check using strncmp would be safer and prevent potential future bugs. This applies to other long option checks in this block as well, but this change should at least be applied for the new option.

            } else if (strncmp(optparse_state.optlongname, "oiface", 6) == 0 && (optparse_state.optlongname[6] == '\0' || optparse_state.optlongname[6] == '=')) {

[coveralls]

coverage: 87.467% (-0.6%) from 88.037%
when pulling 060128c on gsnw:oiface
into b862609 on schweikert:develop.