From 7897ec88f426773cea38ce8c21091a05718a09e7 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Thu, 14 Dec 2023 15:31:38 +0100
Subject: [PATCH] QHttpHeaders: add value(name, fall-back)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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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>
---
 src/network/access/qhttpheaders.cpp           | 23 +++++++++++++++++++
 src/network/access/qhttpheaders.h             |  3 +++
 .../access/qhttpheaders/tst_qhttpheaders.cpp  |  4 +++-
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/network/access/qhttpheaders.cpp b/src/network/access/qhttpheaders.cpp
index de2f7e148a4..683eab21d4d 100644
--- a/src/network/access/qhttpheaders.cpp
+++ b/src/network/access/qhttpheaders.cpp
@@ -974,6 +974,29 @@ void QHttpHeaders::removeAt(qsizetype i)
     d->headers.removeAt(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 636f535c88a..98b4ad62d1a 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;
 
diff --git a/tests/auto/network/access/qhttpheaders/tst_qhttpheaders.cpp b/tests/auto/network/access/qhttpheaders/tst_qhttpheaders.cpp
index 8e6c77e3dd8..a88506fbfed 100644
--- a/tests/auto/network/access/qhttpheaders/tst_qhttpheaders.cpp
+++ b/tests/auto/network/access/qhttpheaders/tst_qhttpheaders.cpp
@@ -168,9 +168,10 @@ void tst_QHttpHeaders::accessors()
     QVERIFY(h1.has(QHttpHeaders::WellKnownHeader::Accept));
     QVERIFY(h1.has("accept"));
 
-    // values()
+    // values()/value()
 #define EXISTS_NOT(H, N) do {                       \
         QVERIFY(!H.has(N));                         \
+        QCOMPARE(H.value(N, "ENOENT"), "ENOENT");   \
         const auto values = H.values(N);            \
         QVERIFY(values.isEmpty());                  \
         QVERIFY(H.combinedValue(N).isNull());       \
@@ -180,6 +181,7 @@ void tst_QHttpHeaders::accessors()
         const std::array expected = { __VA_ARGS__ };                \
         static_assert(std::tuple_size_v<decltype(expected)> == X);  \
         QVERIFY(H.has(N));                                          \
+        QCOMPARE(H.value(N, "ENOENT"), expected.front());           \
         const auto values = H.values(N);                            \
         QCOMPARE(values.size(), X);                                 \
         QCOMPARE(values.front(), expected.front());                 \