QHttpHeaders: add value(name, fall-back)

The vast majority of header fields appear only once, but there was no
efficient way to get that value: values() returns as a
QList<QByteArray> (allocating) while combinedValue() returns a
QByteArray constructed from values().join() (also allocating).

It follows that the QHttpHeaders API is incomplete (lacks an efficient
basis of operations in EoP terms).

Add a value() function that returns either the value or a
user-provided fall-back as a QByteArrayView. Unlike values() and
combinedValue(), this function can be noexcept, greatly improving
codegen for callers.

Found in API review.

Pick-to: 6.7
Task-number: QTBUG-107042
Change-Id: I2da20815fd46fdd7f150c224f41eee53abed313e
Reviewed-by: Juha Vuolle <juha.vuolle@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

2 files changed, 26 insertions, 0 deletions

diff --git a/src/network/access/qhttpheaders.cpp b/src/network/access/qhttpheaders.cpp
index de2f7e148a..683eab21d4 100644
--- a/src/network/access/qhttpheaders.cpp
+++ b/src/network/access/qhttpheaders.cpp
@@ -975,6 +975,29 @@ void QHttpHeaders::removeAt(qsizetype i)
 }
 
 /*!
+    Returns the value of the (first) header \a name, or \a defaultValue if it
+    doesn't exist.
+
+    \sa value(QHttpHeaders::WellKnownHeader, QByteArrayView)
+*/
+QByteArrayView QHttpHeaders::value(QAnyStringView name, QByteArrayView defaultValue) const noexcept
+{
+    for (const auto &h : std::as_const(d->headers)) {
+        if (headerNameIs(h, name))
+            return h.value;
+    }
+    return defaultValue;
+}
+
+/*!
+    \overload value(QAnyStringView, QByteArrayView)
+*/
+QByteArrayView QHttpHeaders::value(WellKnownHeader name, QByteArrayView defaultValue) const noexcept
+{
+    return value(headerNames[qToUnderlying(name)], defaultValue);
+}
+
+/*!
     Returns the values of header \a name in a list. Returns an empty
     list if header with \a name doesn't exist.
 
diff --git a/src/network/access/qhttpheaders.h b/src/network/access/qhttpheaders.h
index 636f535c88..98b4ad62d1 100644
--- a/src/network/access/qhttpheaders.h
+++ b/src/network/access/qhttpheaders.h
@@ -237,6 +237,9 @@ public:
     Q_NETWORK_EXPORT void removeAll(WellKnownHeader name);
     Q_NETWORK_EXPORT void removeAt(qsizetype i);
 
+    Q_NETWORK_EXPORT QByteArrayView value(QAnyStringView name, QByteArrayView defaultValue = {}) const noexcept;
+    Q_NETWORK_EXPORT QByteArrayView value(WellKnownHeader name, QByteArrayView defaultValue = {}) const noexcept;
+
     Q_NETWORK_EXPORT QList<QByteArray> values(QAnyStringView name) const;
     Q_NETWORK_EXPORT QList<QByteArray> values(WellKnownHeader name) const;