xapi-stdext-std: remove most functions, optimize escaping functions

[psafont]

The Listext module has a lot of baggage that can be replace with Stdlib, Astring. And what cannot be replaced, it can be made better, especially the escaping.

There are quite a few changes, so it's better to review commit-by-commit.

I need to do some testing to make sure all changes here are safe and undraft this

[cplaursen]

I'll run some system tests on this and have a proper look throughout the day.

[lindig]

Has String.replaced been benchmarked?

[psafont]

Yes, from the message of the commit that introduces it (1174f3a):

If a plain match function cannot be produced and a list needs to be used,
users can convert it to a Char.Map and do the match with a find_opt.
This approach ends up being ~60-70% faster than using plain lists.

The benchmark comparing the new approach with the old one:

  String size 100:
    Optimized: 236.556 μs
    Reference: 1861.600 μs
    Improvement: 87.3% faster

  String size 500:
    Optimized: 1099.030 μs
    Reference: 9665.405 μs
    Improvement: 88.6% faster

  String size 1000:
    Optimized: 2198.777 μs
    Reference: 19115.019 μs
    Improvement: 88.5% faster

It can also be easily run with dune exec ocaml/libs/xapi-stdext/lib/xapi-stdext-std/bench/bench_xstringext.exe

[cplaursen]

So I ran a test suite on the changes and unfortunately a few of the tests failed. Not sure what the best way to share the test results are, but here are some failure excerpts:

XenLivePatchTest:

Expecting RecommendedGuidance is {'RestartToolstack'}, but found RecommendedGuidance is {'RestartToolstack', 'reboot_host_on_xen_livepatch_failure'}
Expecting RecommendedGuidance is set(), but found RecommendedGuidance is {'reboot_host_on_xen_livepatch_failure'}

Networking:

15/12/2025 10:58:17	Host reboot of !genuk-21-05d timed out
15/12/2025 10:58:17	Error running get_console_logs: SSH connection refused (/opt/xenrt/scripts/get_console_logs /tmp/local/scratch/xenrt/guest-console-logs 1765793412 None)
15/12/2025 10:58:17	Retrying CLI command host-get-system-status-capabilities -s 10.71.240.94 -u root -pw '************' uuid=2d825f4f-2967-4126-8327-87ea11742ea6
15/12/2025 10:58:17	Retrying CLI command host-get-system-status-capabilities -s 10.71.240.94 -u root -pw '************' uuid=2d825f4f-2967-4126-8327-87ea11742ea6
15/12/2025 10:58:18	Retrying CLI command host-get-system-status-capabilities -s 10.71.240.94 -u root -pw '************' uuid=2d825f4f-2967-4126-8327-87ea11742ea6
15/12/2025 10:58:18	Exception from host-get-system-status-capabilities: Host genuk-21-05d is not pingable on 10.71.240.94

HAOCx2WE:

15/12/2025 12:14:10	Error running get_console_logs: SSH connection refused (/opt/xenrt/scripts/get_console_logs /tmp/local/scratch/xenrt/guest-console-logs 1765794201 None)
15/12/2025 12:14:12	Exception from host-get-system-status-capabilities: CLI command host-get-system-status-capabilities failed: You attempted an operation which involves a host which could not be contacted.
15/12/2025 12:14:14	Poking Xen from job 4518430 to give us a crashdump on genus-35-071d

Let me know how you'd like to proceed/what info you need from me.

[psafont]

It's difficult to say whether they are related just by looking at those loglines, and I haven't seen the test runs in months to remember well how they could affect the update guidances, or hosts failing to get online.

Thanks for making the builds and running the tests, it's good to know most tests passed! (I guess the ring3BVT+BST)