This seems like something that should exist? Wireshark's 'Analyze > Follow > TCP Stream'’s 'Save As…', 'entire stream', 'hex dump' is kind of what I want, but it doesn't have timestamps, and it doesn't have a way to put everything (multiple flows, UDP packets also) in one file. Either I need an easy-to-use Rust library to do that directly from pcap files or some format that represents bytes moving over the flow (like sets of lines with a timestamp, flow id, and pretty hexdump of the bytes) with a tool that produces it from pcap. My library mostly operates at the TCP level (also some UDP), so I need to reconstruct the TCP flows in my tool to feed to my library. Speaking of which: for one of my libraries, I want to make a diagnostic tool that replays an interaction. When I get a bug report with a pcap file I'm happy because I know I'll be able to see exactly what happened. pcap files are like freshly baked chocolate chip cookies. This is awesome because literally every network analysis tool in the universe understands pcap files. I mentioned really briefly that tcpdump lets you save pcap files.

Tcpdump wireshark pcap format