Details
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Task
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Resolution: Unresolved
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P3: Somewhat important
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All
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8
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Foundation PM Staging
Description
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.