Add QPDFObjectHandle::getUniqueResourceName

ChangeLog

@@ -1,5 +1,9 @@
 2019-01-25  Jay Berkenbilt  <ejb@ql.org>
 
+	* Add new method QPDFObjectHandle::getUniqueResourceName() to
+	return an unused key available to be used in a resource
+	dictionary.
+
 	* Add new method QPDFPageObjectHelper::getAttribute() that
 	properly handles inherited attributes and allows for creation of a
 	copy of shared attributes. This is very useful if you are getting

include/qpdf/QPDFObjectHandle.hh

@@ -600,6 +600,18 @@ class QPDFObjectHandle
     QPDF_DLL
     std::set<std::string> getResourceNames();
 
+    // Find a unique name within a resource dictionary starting with a
+    // given prefix. This method works by appending a number to the
+    // given prefix. It searches starting with min_suffix and sets
+    // min_suffix to selected value upon return. This can be used to
+    // increase efficiency if adding multiple items with the same
+    // prefix. (Why doesn't it set min_suffix to the next number?
+    // Well, maybe you aren't going to actually use the name it
+    // returns.)
+    QPDF_DLL
+    std::string getUniqueResourceName(std::string const& prefix,
+                                      int& min_suffix);
+
     // Return the QPDF object that owns an indirect object.  Returns
     // null for a direct object.
     QPDF_DLL

libqpdf/QPDFObjectHandle.cc

@@ -931,6 +931,30 @@ QPDFObjectHandle::getResourceNames()
     return result;
 }
 
+std::string
+QPDFObjectHandle::getUniqueResourceName(std::string const& prefix,
+                                        int& min_suffix)
+{
+    std::set<std::string> names = getResourceNames();
+    int max_suffix = min_suffix + names.size();
+    while (min_suffix <= max_suffix)
+    {
+        std::string candidate = prefix + QUtil::int_to_string(min_suffix);
+        if (names.count(candidate) == 0)
+        {
+            return candidate;
+        }
+        // Increment after return; min_suffix should be the value
+        // used, not the next value.
+        ++min_suffix;
+    }
+    // This could only happen if there is a coding error.
+    // The number of candidates we test is more than the
+    // number of keys we're checking against.
+    throw std::logic_error("unable to find unconflicting name in"
+                           " QPDFObjectHandle::getUniqueResourceName");
+}
+
 // Indirect object accessors
 QPDF*
 QPDFObjectHandle::getOwningQPDF()

libqpdf/QPDFPageDocumentHelper.cc

@@ -155,35 +155,15 @@ QPDFPageDocumentHelper::flattenAnnotationsForPage(
             {
                 QTC::TC("qpdf", "QPDFPageDocumentHelper non-widget annotation");
             }
-            std::set<std::string> names = resources.getResourceNames();
-            std::string name;
-            int max_fx = next_fx + names.size() + 1;
-            while (next_fx <= max_fx)
-            {
-                std::string candidate = "/Fxo" + QUtil::int_to_string(next_fx);
-                if (names.count(candidate) == 0)
-                {
-                    name = candidate;
-                    break;
-                }
-                ++next_fx;
-            }
-            if (name.empty())
-            {
-                // This could only happen if there is a coding error.
-                // The number of candidates we test is more than the
-                // number of keys we're checking against.
-                name = "/FxConflict";
-            }
+            std::string name = resources.getUniqueResourceName(
+                "/Fxo", next_fx);
             std::string content = aoh.getPageContentForAppearance(
                 name, rotate, required_flags, forbidden_flags);
             if (! content.empty())
             {
                 resources.mergeResources(
-                    QPDFObjectHandle::parse(
-                        "<< /XObject << " + name + " null >> >>"));
+                    QPDFObjectHandle::parse("<< /XObject << >> >>"));
                 resources.getKey("/XObject").replaceKey(name, as);
-                names.insert(name);
                 ++next_fx;
             }
             new_content += content;