Increase random data provider support

Add a method to get the current random data provider, and document and
test the method for resetting it.

ChangeLog

@@ -1,3 +1,10 @@
+2013-12-16  Jay Berkenbilt  <ejb@ql.org>
+
+	* Document and make explicit that passing null to
+	QUtil::setRandomDataProvider() resets the random data provider.
+
+	* Provide QUtil::getRandomDataProvider().
+
 2013-12-14  Jay Berkenbilt  <ejb@ql.org>
 
 	* Allow anyspace rather than just newline to follow xref header.

include/qpdf/QUtil.hh

@@ -142,9 +142,20 @@ namespace QUtil
     // memory for the RandomDataProvider.  This method modifies a
     // static variable.  If you are providing your own random data
     // provider, you should call this at the beginning of your program
-    // before creating any QPDF objects.
+    // before creating any QPDF objects.  Passing a null to this
+    // method will reset the library back to whichever of the built-in
+    // random data handlers is appropriate basedon how qpdf was
+    // compiled.
     QPDF_DLL
     void setRandomDataProvider(RandomDataProvider*);
+
+    // This returns the random data provider that would be used the
+    // next time qpdf needs random data.  It will never return null.
+    // If no random data provider has been provided and the library
+    // was not compiled with any random data provider available, an
+    // exception will be thrown.
+    QPDF_DLL
+    RandomDataProvider* getRandomDataProvider();
 };
 
 #endif // __QUTIL_HH__

libqpdf/QUtil.cc

@@ -423,6 +423,8 @@ initialize_random_data_provider()
             random_data_provider = insecure_random_data_provider;
         }
     }
+    // QUtil.hh has comments indicating that getRandomDataProvider(),
+    // which calls this method, never returns null.
     if (random_data_provider == 0)
     {
         throw std::logic_error("QPDF has no random data provider");
@@ -435,6 +437,13 @@ QUtil::setRandomDataProvider(RandomDataProvider* p)
     random_data_provider = p;
 }
 
+RandomDataProvider*
+QUtil::getRandomDataProvider()
+{
+    initialize_random_data_provider();
+    return random_data_provider;
+}
+
 void
 QUtil::initializeWithRandomBytes(unsigned char* data, size_t len)
 {

libtests/random.cc

@@ -24,6 +24,7 @@ class BogusRandomDataProvider: public RandomDataProvider
 
 int main()
 {
+    RandomDataProvider* orig_rdp = QUtil::getRandomDataProvider();
     long r1 = QUtil::random();
     long r2 = QUtil::random();
     if (r1 == r2)
@@ -48,6 +49,11 @@ int main()
 #endif
     BogusRandomDataProvider brdp;
     QUtil::setRandomDataProvider(&brdp);
+    if (QUtil::getRandomDataProvider() != &brdp)
+    {
+        std::cout << "fail: getRandomDataProvider didn't"
+            " return our provider\n";
+    }
     r1 = QUtil::random();
     r2 = QUtil::random();
     if (r1 != r2)
@@ -63,6 +69,12 @@ int main()
     {
         std::cout << "fail: bogus random didn't provide correct bytes\n";
     }
+    QUtil::setRandomDataProvider(0);
+    if (QUtil::getRandomDataProvider() != orig_rdp)
+    {
+        std::cout << "fail: passing null to setRandomDataProvider "
+            "didn't reset the random data provider\n";
+    }
     std::cout << "random: end of tests\n";
     return 0;
 }