Made it compile and work on Qt4.8, bar some tests.

.gitmodules

@@ -0,0 +1,6 @@
+[submodule "src/qjson-backport"]
+	path = src/qjson-backport
+	url = https://github.com/5in4/qjson-backport.git
+[submodule "src/mimetypes"]
+	path = src/mimetypes
+	url = http://code.qt.io/cgit/playground/mimetypes.git/

CMakeLists.txt

@@ -28,7 +28,25 @@ set(CMAKECONFIG_INSTALL_DIR "${LIB_INSTALL_DIR}/cmake/${PROJECT_NAME}" CACHE STR
 set(DOC_INSTALL_DIR share/doc/${PROJECT_NAME} CACHE STRING "Documentation installation directory relative to the install prefix")
 set(EXAMPLES_INSTALL_DIR "${LIB_INSTALL_DIR}/${PROJECT_NAME}/examples" CACHE STRING "Examples installation directory relative to the install prefix")
 
-find_package(Qt5Network 5.1 REQUIRED)
+find_package(Qt5Network 5.1 QUIET)
+if (NOT Qt5Network_FOUND)
+    message("-- QT minimum version 5.1 not found, trying with minimum version 4.8")
+
+    find_package(Qt4 4.8 QUIET COMPONENTS QtGui QtCore QtNetwork)
+    if (NOT Qt4_FOUND)
+        message("-- QT minimum version 4.8 not found")
+
+        message(FATAL_ERROR "Qt minimum versio 4.8 is required")
+    endif()
+endif()
+
+message("-- Using QT version ${QT_VERSION_MAJOR}.${QT_VERSION_MINOR}.${QT_VERSION_PATCH}")
+
+if (Qt4_FOUND)
+    find_package(Git REQUIRED)
+    message("-- Updating git submodules for QT4 compilation ${Qt4_VERSION}")
+    execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init --recursive)
+endif()
 
 set(CMAKE_INCLUDE_CURRENT_DIR ON)
 set(CMAKE_AUTOMOC ON)

README.md

@@ -13,7 +13,7 @@ QHttpEngine requires a modern C++ compiler supported by the Qt framework. Some e
 - GCC (including MinGW-w64)
 - Clang
 
-CMake 2.8.11+ and Qt 5.1+ are required to build the library.
+CMake 2.8.11+ and Qt 4.8+ are required to build the library. If Qt 5.1+ is not available, then two external projects are used as submodules, which provide missing Qt5 functionalities: qjson-backport and mimetypes.
 
 ### Build Instructions
 

examples/chatserver/CMakeLists.txt

@@ -3,7 +3,11 @@ set(SRC
     main.cpp
 )
 
-qt5_add_resources(QRC resources.qrc)
+if (Qt4_FOUND)
+    QT4_ADD_RESOURCES(QRC resources.qrc)
+else()
+    qt5_add_resources(QRC resources.qrc)
+endif()
 
 add_executable(chatserver ${SRC} ${QRC})
 target_link_libraries(chatserver QHttpEngine)

examples/chatserver/main.cpp

@@ -20,8 +20,13 @@
  * IN THE SOFTWARE.
  */
 
+#include <QtGlobal>
+
+#if QT_VERSION >= 0x050000   
 #include <QCommandLineOption>
 #include <QCommandLineParser>
+#endif
+
 #include <QCoreApplication>
 #include <QHostAddress>
 #include <QRegExp>
@@ -37,6 +42,7 @@ int main(int argc, char * argv[])
 {
     QCoreApplication a(argc, argv);
 
+#if QT_VERSION >= 0x050000   
     // Build the command-line options
     QCommandLineParser parser;
     QCommandLineOption addressOption(
@@ -61,6 +67,10 @@ int main(int argc, char * argv[])
     // Obtain the values
     QHostAddress address = QHostAddress(parser.value(addressOption));
     quint16 port = parser.value(portOption).toInt();
+#else
+    QHostAddress address("127.0.0.1");
+    quint16 port = 8000;
+#endif
 
     // Build the hierarchy of handlers
     QFilesystemHandler handler(":/static");

examples/fileserver/main.cpp

@@ -20,8 +20,13 @@
  * IN THE SOFTWARE.
  */
 
+#include <QtGlobal>
+
+#if QT_VERSION >= 0x050000   
 #include <QCommandLineOption>
 #include <QCommandLineParser>
+#endif
+
 #include <QCoreApplication>
 #include <QDir>
 #include <QHostAddress>
@@ -34,6 +39,7 @@ int main(int argc, char * argv[])
 {
     QCoreApplication a(argc, argv);
 
+#if QT_VERSION >= 0x050000   
     // Build the command-line options
     QCommandLineParser parser;
     QCommandLineOption addressOption(
@@ -66,6 +72,11 @@ int main(int argc, char * argv[])
     QHostAddress address = QHostAddress(parser.value(addressOption));
     quint16 port = parser.value(portOption).toInt();
     QString dir = parser.value(dirOption);
+#else
+    QHostAddress address("127.0.0.1");
+    quint16 port = 8000;
+    QString dir = QDir::homePath();
+#endif
 
     // Create the filesystem handler and server
     QFilesystemHandler handler(dir);

src/CMakeLists.txt

@@ -14,6 +14,27 @@ set(SRC
     qlocalfile.cpp
     qobjecthandler.cpp
 )
+if (Qt4_FOUND)
+    set(SRC "${SRC}"
+        qjson-backport/qjsonarray.cpp
+        qjson-backport/qjson.cpp
+        qjson-backport/qjsondocument.cpp
+        qjson-backport/qjsonobject.cpp
+        qjson-backport/qjsonparser.cpp
+        qjson-backport/qjsonvalue.cpp
+        qjson-backport/qjsonwriter.cpp
+
+        mimetypes/src/mimetypes/qmimedatabase.cpp
+        mimetypes/src/mimetypes/qmimeglobpattern.cpp
+        mimetypes/src/mimetypes/qmimemagicrule.cpp
+        mimetypes/src/mimetypes/qmimemagicrulematcher.cpp
+        mimetypes/src/mimetypes/qmimeprovider.cpp
+        mimetypes/src/mimetypes/qmimetype.cpp
+        mimetypes/src/mimetypes/qmimetypeparser.cpp    
+        mimetypes/src/mimetypes/inqt5/qstandardpaths.cpp
+        mimetypes/src/mimetypes/inqt5/qstandardpaths_unix.cpp 
+    )
+endif()
 
 if(WIN32)
     configure_file(resource.rc.in "${CMAKE_CURRENT_BINARY_DIR}/resource.rc")
@@ -26,14 +47,24 @@ else()
     add_library(QHttpEngine SHARED ${HEADERS} ${SRC})
 endif()
 
-qt5_use_modules(QHttpEngine Network)
-
 target_include_directories(QHttpEngine PUBLIC
     "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>"
     "$<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}>"
     "$<INSTALL_INTERFACE:${INCLUDE_INSTALL_DIR}>"
 )
 
+if (Qt4_FOUND)
+    target_include_directories(QHttpEngine PRIVATE
+        "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/mimetypes/include/QtMimeTypes>"
+        "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/mimetypes/src/mimetypes/inqt5>"
+        "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/qjson-backport>"
+    )  
+
+    target_link_libraries(QHttpEngine Qt4::QtCore Qt4::QtNetwork Qt4::QtGui)      
+else()
+    qt5_use_modules(QHttpEngine Network)
+endif()
+
 set_target_properties(QHttpEngine PROPERTIES
     DEFINE_SYMBOL QT_NO_SIGNALS_SLOTS_KEYWORDS
     DEFINE_SYMBOL QHTTPENGINE_LIBRARY
@@ -68,3 +99,5 @@ configure_file(${PROJECT_NAME}.pc.in "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME
 install(FILES "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc"
     DESTINATION "${LIB_INSTALL_DIR}/pkgconfig"
 )
+
+

src/QHttpEngine/qibytearray.h

@@ -48,10 +48,22 @@ class QHTTPENGINE_EXPORT QIByteArray : public QByteArray
      */
     QIByteArray(const QByteArray &other);
 
+#if QT_VERSION >= 0x050000
     /**
      * @brief Create a QIByteArray from a const char *
      */
     QIByteArray(const char *data, int size = -1);
+#else
+    /**
+     * @brief Create a QIByteArray from a const char *
+     */
+    QIByteArray(const char *data);
+
+    /**
+     * @brief Create a QIByteArray from a const char *
+     */
+    QIByteArray(const char *data, int size);
+#endif
 };
 
 QHTTPENGINE_EXPORT bool operator==(const QIByteArray &a1, const QIByteArray &a2);

src/qfilesystemhandler.cpp

@@ -93,19 +93,26 @@ void QFilesystemHandlerPrivate::processFile(QHttpSocket *socket, const QString &
     copier->start();
 }
 
+#if QT_VERSION >= 0x050000
+#    define HTMLESCAPE(x) ((x).toHtmlEscaped())
+#else
+#    include <QtGui/qtextdocument.h>
+#    define HTMLESCAPE(x) (Qt::escape(x))
+#endif
+
 void QFilesystemHandlerPrivate::processDirectory(QHttpSocket *socket, const QString &path, const QString &absolutePath)
 {
     // Add entries for each of the files
     QString listing;
     foreach(QFileInfo info, QDir(absolutePath).entryInfoList()) {
         listing.append(QString("<li><a href=\"%1%2\">%1%2</a></li>")
-                .arg(info.fileName().toHtmlEscaped())
+                .arg(HTMLESCAPE(info.fileName()))
                 .arg(info.isDir() ? "/" : ""));
     }
 
     // Build the response and convert the string to UTF-8
     QByteArray data = ListTemplate
-            .arg("/" + path.toHtmlEscaped())
+            .arg("/" + HTMLESCAPE(path))
             .arg(listing)
             .arg(QHTTPENGINE_VERSION)
             .toUtf8();

src/qhttphandler.cpp

@@ -46,6 +46,8 @@ void QHttpHandler::addSubHandler(const QRegExp &pattern, QHttpHandler *handler)
     d->subHandlers.append(SubHandler(pattern, handler));
 }
 
+#include <QStringList>
+
 void QHttpHandler::route(QHttpSocket *socket, const QString &path)
 {
     // Check each of the redirects for a match

src/qibytearray.cpp

@@ -31,6 +31,12 @@ QIByteArray::QIByteArray(const QByteArray &other)
     : QByteArray(other)
 {}
 
+#if QT_VERSION < 0x050000
+QIByteArray::QIByteArray(const char *data)
+    : QByteArray(data)
+{}
+#endif
+
 QIByteArray::QIByteArray(const char *data, int size)
     : QByteArray(data, size)
 {}

src/qobjecthandler.cpp

@@ -20,9 +20,8 @@
  * IN THE SOFTWARE.
  */
 
-#include <QJsonDocument>
-#include <QJsonObject>
-#include <QJsonParseError>
+#include <qjsondocument.h>
+#include <qjsonobject.h>
 #include <QMetaMethod>
 #include <QMetaObject>
 #include <QMetaType>
@@ -107,7 +106,12 @@ void QObjectHandler::process(QHttpSocket *socket, const QString &path)
 
     // Ensure that the return type of the slot is QVariantMap
     QMetaMethod method = metaObject()->method(index);
+
+#if QT_VERSION >= 0x050000   
     if(method.returnType() != QMetaType::QVariantMap) {
+#else
+    if(!method.typeName() || strcmp(method.typeName(), "QVariantMap") != 0) {
+#endif
         socket->writeError(QHttpSocket::InternalServerError);
         return;
     }

tests/CMakeLists.txt

@@ -1,23 +1,46 @@
-find_package(Qt5Test 5.1 REQUIRED)
+if (Qt4_FOUND)
+    find_package(Qt4 4.8 REQUIRED QtTest)
+else()
+    find_package(Qt5Test 5.1 REQUIRED)
+endif()
 
 add_subdirectory(common)
 
 set(TESTS
-    TestQFilesystemHandler
-    TestQHttpHandler
     TestQHttpParser
-    TestQHttpServer
-    TestQHttpSocket
     TestQIByteArray
-    TestQIODeviceCopier
     TestQLocalFile
-    TestQObjectHandler
 )
 
+# These don't work with Qt4
+if (NOT Qt4_FOUND)
+    set(TESTS ${TESTS}
+        TestQFilesystemHandler
+        TestQHttpHandler
+        TestQHttpServer
+        TestQHttpSocket
+        TestQIODeviceCopier
+        TestQObjectHandler
+    )
+endif()
+
 foreach(TEST ${TESTS})
     add_executable(${TEST} ${TEST}.cpp)
+
+if (Qt4_FOUND)
+    target_link_libraries(${TEST} Qt4::QtTest)   
+
+    target_include_directories(${TEST} PRIVATE
+        "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/../src/mimetypes/include/QtMimeTypes>"
+        "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/../src/mimetypes/src/mimetypes/inqt5>"
+        "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/../src/qjson-backport>"
+    )  
+else()
     qt5_use_modules(${TEST} Test)
+endif()
+
     target_link_libraries(${TEST} QHttpEngine common)
+
     add_test(NAME ${TEST}
         COMMAND ${TEST}
     )

tests/TestQHttpParser.cpp

@@ -30,6 +30,7 @@
 typedef QList<QByteArray> QByteArrayList;
 
 Q_DECLARE_METATYPE(QHttpHeaderMap)
+Q_DECLARE_METATYPE(QList<QByteArray>)
 
 const QIByteArray Key1 = "a";
 const QByteArray Value1 = "b";

tests/TestQObjectHandler.cpp

@@ -20,8 +20,8 @@
  * IN THE SOFTWARE.
  */
 
-#include <QJsonDocument>
-#include <QJsonObject>
+#include <qjsondocument.h>
+#include <qjsonobject.h>
 #include <QObject>
 #include <QTest>
 #include <QVariantMap>

tests/common/CMakeLists.txt

@@ -6,4 +6,8 @@ set(SRC
 add_library(common STATIC ${SRC})
 target_link_libraries(common QHttpEngine)
 
-qt5_use_modules(common Network)
+if (Qt4_FOUND)
+    target_link_libraries(common Qt4::QtNetwork)  
+else()
+    qt5_use_modules(common Network)
+endif()