FFDHE: add NamedGroups method for getting a list of supported named groups.

Also updates TestFFDHE to exercise the new method (and, in doing so,
refactors the tests a bit).

The core check logic from exercise() is moved into a tryFFDHELookupByName
function, which is now used by both the exercise() test, as well as the
namedGroupsMethod() test that is added by this commit.

src/FFDHE.cpp

@@ -8,6 +8,16 @@
 #include "FFDHE.h"
 #include "FFDHETable.h"
 
+QStringList FFDHE::NamedGroups() {
+	QStringList ng;
+	ng << QLatin1String("ffdhe2048");
+	ng << QLatin1String("ffdhe3072");
+	ng << QLatin1String("ffdhe4096");
+	ng << QLatin1String("ffdhe6144");
+	ng << QLatin1String("ffdhe8192");
+	return ng;
+}
+
 QByteArray FFDHE::PEMForNamedGroup(QString name) {
 	name = name.toLower();
 

src/FFDHE.h

@@ -9,6 +9,10 @@
 /// FFDHE provides access to the Diffie-Hellman parameters from RFC 7919.
 class FFDHE {
 	public:
+		/// NamedGroups returns a list of the supported named
+		/// groups for PEMForNamedGroup.
+		static QStringList NamedGroups();
+
 		/// PEMForNamedGroup returns the PEM-encoded
 		/// Diffie-Hellman parameters for the RFC 7919
 		/// group with the given name, such as "ffdhe2048",

src/tests/TestFFDHE/TestFFDHE.cpp

@@ -22,6 +22,7 @@ class TestFFDHE : public QObject {
 #if defined(USE_QSSLDIFFIEHELLMANPARAMETERS)
 		void exercise_data();
 		void exercise();
+		void namedGroupsMethod();
 #endif
 };
 
@@ -51,10 +52,7 @@ void TestFFDHE::exercise_data() {
 	QTest::newRow("trailingspace") << QString(QLatin1String("ffdhe2048 ")) << false;
 }
 
-void TestFFDHE::exercise() {
-	QFETCH(QString, name);
-	QFETCH(bool, expectedToWork);
-
+static bool tryFFDHELookupByName(QString name) {
 	bool ok = true;
 
 	QByteArray pem = FFDHE::PEMForNamedGroup(name);
@@ -69,7 +67,19 @@ void TestFFDHE::exercise() {
 		}
 	}
 
-	QCOMPARE(ok, expectedToWork);
+	return ok;
+}
+
+void TestFFDHE::exercise() {
+	QFETCH(QString, name);
+	QFETCH(bool, expectedToWork);
+	QCOMPARE(tryFFDHELookupByName(name), expectedToWork);
+}
+
+void TestFFDHE::namedGroupsMethod() {
+	foreach (QString name, FFDHE::NamedGroups()) {
+		QCOMPARE(tryFFDHELookupByName(name), true);
+	}
 }
 #endif