QFormDataPartBuilder: delay encoding of the part's name to build() time

This is a prerequisite for making QFormDataBuilder::part() return an
existing part instead of creating new parts with the same name
(idempotence), which was pointed out in API review.

Task-number: QTBUG-125985
Change-Id: I642e56cc7cb3562304573930a01aa1aafa817f36
Reviewed-by: Mate Barany <mate.barany@qt.io>
(cherry picked from commit 9503e2c92c2d3b8f5bb9c86274d2430eb0a57880)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/network/access/qformdatabuilder.cpp

@@ -30,24 +30,6 @@ QT_BEGIN_NAMESPACE
     \sa QHttpPart, QHttpMultiPart, QFormDataBuilder
 */
 
-static QByteArray nameToByteArray(QStringView view)
-{
-    return view.toUtf8();
-}
-
-static QByteArray nameToByteArray(QLatin1StringView view)
-{
-    if (!QtPrivate::isAscii(view))
-        return view.toString().toUtf8(); // ### optimize
-
-    return QByteArray::fromRawData(view.data(), view.size());
-}
-
-static QByteArray nameToByteArray(QUtf8StringView view)
-{
-    return QByteArray::fromRawData(view.data(), view.size());
-}
-
 static void escapeNameAndAppend(QByteArray &dst, QByteArrayView src)
 {
     for (auto c : src) {
@@ -57,20 +39,32 @@ static void escapeNameAndAppend(QByteArray &dst, QByteArrayView src)
     }
 }
 
+static void escapeNameAndAppend(QByteArray &dst, QStringView src)
+{
+    qsizetype last = 0;
+
+    // equivalent to for (auto chunk : qTokenize(src, any_of("\\\""))), if there was such a thing
+    for (qsizetype i = 0, end = src.size(); i != end; ++i) {
+        const auto c = src[i];
+        if (c == u'"' || c == u'\\') {
+            const auto chunk = src.sliced(last, i - last);
+            dst += QUtf8::convertFromUnicode(chunk); // ### optimize
+            dst += '\\';
+            last = i;
+        }
+    }
+    dst += QUtf8::convertFromUnicode(src.sliced(last));
+}
+
 /*!
     Constructs a QFormDataPartBuilder object and sets \a name as the name
     parameter of the form-data.
 */
 QFormDataPartBuilder::QFormDataPartBuilder(QAnyStringView name, PrivateConstructor /*unused*/)
+    : m_name{name.toString()}
 {
     static_assert(std::is_nothrow_move_constructible_v<decltype(m_body)>);
     static_assert(std::is_nothrow_move_assignable_v<decltype(m_body)>);
-
-    const auto enc = name.visit([](auto name) { return nameToByteArray(name); });
-
-    m_headerValue += "form-data; name=\"";
-    escapeNameAndAppend(m_headerValue, enc);
-    m_headerValue += "\"";
 }
 
 /*!
@@ -210,19 +204,25 @@ QHttpPart QFormDataPartBuilder::build()
 {
     QHttpPart httpPart;
 
+    QByteArray headerValue;
+
+    headerValue += "form-data; name=\"";
+    escapeNameAndAppend(headerValue, m_name);
+    headerValue += "\"";
+
     if (!m_originalBodyName.isNull()) {
         const bool utf8 = !QtPrivate::isAscii(m_originalBodyName);
         const auto enc = utf8 ? m_originalBodyName.toUtf8() : m_originalBodyName.toLatin1();
-        m_headerValue += "; filename=\"";
+        headerValue += "; filename=\"";
-        escapeNameAndAppend(m_headerValue, enc);
+        escapeNameAndAppend(headerValue, enc);
-        m_headerValue += "\"";
+        headerValue += "\"";
         if (utf8) {
             // For 'filename*' production see
             // https://datatracker.ietf.org/doc/html/rfc5987#section-3.2.1
             // For providing both filename and filename* parameters see
             // https://datatracker.ietf.org/doc/html/rfc6266#section-4.3 and
             // https://datatracker.ietf.org/doc/html/rfc8187#section-4.2
-            m_headerValue += "; filename*=UTF-8''" + enc.toPercentEncoding();
+            headerValue += "; filename*=UTF-8''" + enc.toPercentEncoding();
         }
     }
 
@@ -244,7 +244,7 @@ QHttpPart QFormDataPartBuilder::build()
     if (!m_mimeType.isEmpty())
         httpPart.setHeader(QNetworkRequest::ContentTypeHeader, m_mimeType);
 
-    httpPart.setHeader(QNetworkRequest::ContentDispositionHeader, m_headerValue);
+    httpPart.setHeader(QNetworkRequest::ContentDispositionHeader, std::move(headerValue));
 
     if (auto d = std::get_if<QIODevice*>(&m_body))
         httpPart.setBodyDevice(*d);

src/network/access/qformdatabuilder.h

@@ -34,7 +34,7 @@ public:
     Q_NETWORK_EXPORT explicit QFormDataPartBuilder(QAnyStringView name, PrivateConstructor);
 
     QFormDataPartBuilder(QFormDataPartBuilder &&other) noexcept
-        : m_headerValue(std::move(other.m_headerValue)),
+        : m_name(std::move(other.m_name)),
           m_originalBodyName(std::move(other.m_originalBodyName)),
           m_httpHeaders(std::move(other.m_httpHeaders)),
           m_body(std::move(other.m_body)),
@@ -46,7 +46,7 @@ public:
     QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QFormDataPartBuilder)
     void swap(QFormDataPartBuilder &other) noexcept
     {
-        m_headerValue.swap(other.m_headerValue);
+        m_name.swap(other.m_name);
         m_originalBodyName.swap(other.m_originalBodyName);
         m_httpHeaders.swap(other.m_httpHeaders);
         m_body.swap(other.m_body);
@@ -75,7 +75,7 @@ private:
                                                          QAnyStringView mimeType);
     QHttpPart build();
 
-    QByteArray m_headerValue;
+    QString m_name;
     QByteArray m_mimeType;
     QString m_originalBodyName;
     QHttpHeaders m_httpHeaders;