Add --skip-pkts and --skip-to-secs to allow skipping packets when replaying

[Exchizz]

Standards checklist:

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• I have read the contribution guide and followed all the instructions.
• The code follows the code style guide detailed in the wiki.
• The code is mine or it's from somewhere with an MIT-compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable and I have tested it myself, to the best of my abilities.
• If the code introduces new aliases, I provide a valid use case for all plugin users down below.

Changes:

• Add --skip-pkts x as parameter to tcpreplay. It adds support for skipping the first X packets in a pcap file
• Add --skip-to-secs Y as parameter to tcpreplay. It adds support for skipping until Y seconds into the pcap file. The seconds is absolute since since the unix epoch

Other comments:

We needed this in a project where we used a series of pcap files for storing sound and video recordings. If a user wanted to start a replay from a certain date and time we would know which pcap file to replay (based on the filename of the pcap file) and by using --skip-to-seconds we could jump to the date and time in the pcap file.

[fklassen]

A couple changes required before I could accept this.

Also reviewing the use case for this. Why is this needed?

[fklassen]

This change must be also implemented in send_dual_packets()

[fklassen]

This also must be copied to This change must be also implemented in send_dual_packets()`

[Exchizz]

We are using tcpreplay to replay video streams. We save video streams in chunks of 1 min. By being able to skip into pcap files we can easily jump back and forth in our recordings :)

Do you want me to make a new pull request with the changes added to send_dial_packets()? (I'm not very experienced with github)

[fklassen]

We are using tcpreplay to replay video streams. We save video streams in chunks of 1 min. By being able to skip into pcap files we can easily jump back and forth in our recordings :)

Do you want me to make a new pull request with the changes added to send_dial_packets()? (I'm not very experienced with github)

Sorry for the delay. Just commit changes directly into this branch and push up.

I'll try to get this into 4.4.0 if I see changes in the next few days. I plan a release by the end of January.

[Exchizz]

Sorry for the late reply. Would you still like to merge this PR if I rebase and verify it still works ?

[fklassen]

I would not guarantee that I can get it in to 4.5, but a rebase and test cases would help. Please rebase and target from this branch I created for you https://github.com/appneta/tcpreplay/tree/PR_478_skip_feature_rebase_4.5.0.

Also, new PRs will contain this checklist. Please apply it to the PR. https://github.com/appneta/tcpreplay/blob/PR_478_skip_feature_rebase_4.5.0/.github/PULL_REQUEST_TEMPLATE.md

[Exchizz]

Let me know what you think :)

[fklassen]

Did some testing in staging branch and decided to push to next release. This introduces new bugs:

1. doesn't work when 2 interfaces are being replayed
2. will skip into all supplied PCAP files

Most likely the skip logic has to happen in the calling functions. Also, documentation needs improvement.