refactor(dpi/ssdp): case-fold header name without allocating#290
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The ST/NT header lookup converted each header line into a fresh
lowercased `String` (`line.to_lowercase()`) just to compare the
3-byte prefix "st:" / "nt:". For an SSDP message with N header
lines this allocates N times per packet, and only the prefix actually
needs case-insensitive comparison.
Replace the `to_lowercase` allocation with
`line.get(..3).is_some_and(|p| p.eq_ignore_ascii_case("st:") ||
p.eq_ignore_ascii_case("nt:"))`. The value extraction via
`line.get(3..)` is unchanged.
Add `test_ssdp_mixed_case_st_and_nt_headers` exercising all four
case mixes (`ST`/`St`/`sT`/`st` and the same for `NT`) to
lock the case-insensitivity invariant per HTTP/1.1 §3.2 field-name
rules — a future refactor that drops the case fold will fail this
test rather than silently regress.
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@0xghost42 thanks a lot, this lgtm! |
This was referenced May 20, 2026
domcyrus
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May 21, 2026
The header loop in `analyze_http` lowercased every header line via `to_lowercase()` only to compare the result against the two ASCII literals "host" and "user-agent". That allocates a fresh `String` per header line per packet, on the DPI hot path. HTTP/1.1 §3.2 makes field-names case-insensitive, so compare in place with `str::eq_ignore_ascii_case` — no allocation, behavior preserved. Add `test_http_mixed_case_host_and_user_agent_headers` covering four case mixes per header name so a future refactor that drops the case-insensitive compare fails this test instead of silently regressing — same shape as the regression tests added in #290 (SSDP) and #278 (NetBIOS). Refs #300
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Summary
The ST/NT header lookup in
analyze_ssdpconverted each header line into a fresh lowercasedStringjust to compare the 3-byte prefix\"st:\"/\"nt:\". For an SSDP packet with N header lines this allocates N times per packet, and only the prefix actually needs case-insensitive comparison.Replace the per-line
to_lowercase()allocation withline.get(..3).is_some_and(|p| p.eq_ignore_ascii_case(\"st:\") || p.eq_ignore_ascii_case(\"nt:\")). The value extraction vialine.get(3..)is unchanged, since both\"st:\"and\"nt:\"are exactly 3 ASCII bytes.Behavior is unchanged: the field-name check is still case-insensitive (HTTP/1.1 §3.2), and the value is still trimmed and required to be non-empty.
Why a regression test
The existing tests only exercise upper-case
ST:/NT:, so dropping the case-fold would not have failed any test. The newtest_ssdp_mixed_case_st_and_nt_headersexercises all four case mixes per field name (ST,St,sT,standNT,Nt,nT,nt) so a future refactor that drops the case fold will fail this test instead of silently regressing — same shape as the regression test added in #278 fordecode_netbios_name.Verification
cargo test --lib: 360 passed, 0 failed (8 innetwork::dpi::ssdp, incl. the new test).cargo clippy --all-targets -- -D warnings: clean.cargo fmt --check: clean.Notes
Real SSDP traffic from UPnP devices commonly uses mixed-case header names — the Microsoft Windows SSDP stack and the Linux miniupnpd implementation both differ from each other in capitalisation, and HTTP §3.2 explicitly makes the field-name case-insensitive.