Oxicloud/benches/ROUND28.md

Round 28 — extend the PROPFIND oc:id buffer (ROUND27 §H1) to the REPORT emit loops

A small follow-through: ROUND27 §H1 replaced the per-row oc:id String with one reused oc_buf in the two NextCloud PROPFIND page loops, but the four REPORT emit loops (report_handler) shared the identical per-row-String shape and were explicitly deferred there. This round applies the same validated transformation to them.

The change

report_handler's two REPORT handlers (filter-files favorites REPORT and search REPORT) each emit a file loop and a folder loop, and each row did:

let oc_id = fid.map(|id| format_oc_id(id, file_id_svc));   // one String per row
…
write_{file,folder}_response(&mut xml, …, (fid, oc_id.as_deref()), …)

AFTER hoists one oc_buf per handler (reused across both its loops, beside the same pattern the PROPFIND loops already use) and computes the id into it with format_oc_id_into (added in ROUND27):

let mut oc_buf = String::new();          // once per handler
…
let oc_id: Option<&str> = match fid {
    Some(id) => { format_oc_id_into(&mut oc_buf, id, file_id_svc); Some(oc_buf.as_str()) }
    None => None,
};
write_{file,folder}_response(&mut xml, …, (fid, oc_id), …)

1 String/row → 0 (amortized to one buffer per handler) across all four REPORT loops. The write_*_response functions already take Option<&str>, so their signatures are unchanged and the emitted oc:id bytes are byte-identical.

Benchmark

This is the same transformation validated in ROUND27 §H1 (bench_round27_micro): a per-row format_oc_id String vs one reused buffer via format_oc_id_into, byte-identical output. §H1 measured it on a 500-row page:

arm	ns/op	allocs/op
BEFORE	34 185.3	1 000.00
AFTER	14 484.9	2.00

998 → 0 per-row allocs, 2.16–2.36× wall. ROUND28 applies that proven change to four more instances of the identical pattern (the REPORT loops), so no new benchmark is needed — the §H1 gate is the evidence. REPORT/search is lower-traffic than PROPFIND, so the aggregate impact is smaller, but it removes the last per-row oc:id allocation from the NC emit surface.

Not shipped — carried forward

• format_oc_id_into for the trashbin per-item writer (write_trash_item_response) would need the buffer threaded through its signature (it is a per-item fn, not a loop with a hoisted buffer); low traffic, deferred.
• REPORT per-row href buffer (nc_href allocates per row) — the ROUND20 deferred href-buffer item; wants an nc_href_into + a precomputed encoded-user, a separate alloc pass.
• S3 read zero-copy forward — a genuine framing tradeoff (fewer, larger coalesced frames vs more, smaller zero-copy frames) that cannot be faithfully benchmarked without a real S3/MinIO fixture; not shipped on synthetic evidence.
• Frontend folder-listing cache / /resources ETag — the real bandwidth win needs a backend ETag on the listing feed + conditional 304, plus SWR wiring that respects cursor pagination. A dedicated backend+frontend feature.

Environment / methodology

• Source-only extension of the ROUND27 §H1 change; the benchmark evidence is bench_round27_micro §H1. Verified: cargo fmt --all --check clean, cargo clippy --features bench -- -D warnings clean, cargo test --lib --features bench green.