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Task
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Resolution: Unresolved
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P3: Somewhat important
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8
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Foundation PM Staging
This issue stems from this review comment.
User may use the string (QAnyStringView) function overloads, and internally QHttpHeaders checks if the provided string can be mapped to a WellKnownHeader enum.
Currently the code first normalizes the value, and then attempts to map that value to WellKnownHeader. The mapping-attempt could be done before value normalization => we don't unnecessarily normalize the value and allocate memory for it.
However implementing this optimisation is not trivial. The straightforward approach:
struct HeaderName
{
// ...
explicit HeaderName(QAnyStringView name)
{
if (auto h = HeaderName::toWellKnownHeader(name)) // [A] pass directly as QASV
data = *h;
else
data = normalizedName(name);
}
// Returns an enum corresponding with the 'name' if possible. Uses binary search (O(logN)).
static std::optional<QHttpHeaders::WellKnownHeader> toWellKnownHeader(QAnyStringView name) noexcept
{
auto indexesBegin = std::cbegin(orderedHeaderNameIndexes);
auto indexesEnd = std::cend(orderedHeaderNameIndexes);
auto result = std::lower_bound(indexesBegin, indexesEnd, name, ByIndirectHeaderName{});
// [B] modify to case insensitive comparison
if (result != indexesEnd
&& QAnyStringView::compare(name, headerNames.viewAt(*result), Qt::CaseInsensitive) == 0) {
return static_cast<QHttpHeaders::WellKnownHeader>(*result);
}
return std::nullopt;
}
// ...
};
struct ByIndirectHeaderName
{
// [C] QASV operator() overload:
constexpr bool operator()(quint8 lhs, QAnyStringView rhs) const noexcept
{
return QAnyStringView::compare(headerNames.viewAt(lhs), rhs, Qt::CaseInsensitive) < 0;
}
};
works, but according to tst_bench_qhttpheaders, the performance actually decreases because we do case-insensitive comparisons. So some additional mechanism would be needed.