ClosedFileInputSource: add method to keep file open

During periods of intensive operation on a specific file, this method
can reduce the overhead of repeated open/close operations.

ChangeLog

@@ -1,3 +1,10 @@
+2018-08-04  Jay Berkenbilt  <ejb@ql.org>
+
+	* Add ClosedFileInputSource::stayOpen method, enabling a
+	ClosedFileInputSource to stay open during manually indicated
+	periods of high activity, thus reducing the overhead of frequent
+	open/close operations.
+
 2018-06-23  Jay Berkenbilt  <ejb@ql.org>
 
 	* 8.1.0: release

include/qpdf/ClosedFileInputSource.hh

@@ -55,6 +55,13 @@ class ClosedFileInputSource: public InputSource
     QPDF_DLL
     virtual void unreadCh(char ch);
 
+    // The file stays open between calls to stayOpen(true) and
+    // stayOpen(false). You can use this to surround multiple
+    // operations on a single ClosedFileInputSource to reduce the
+    // overhead of a separate open/close on each call.
+    QPDF_DLL
+    void stayOpen(bool);
+
   private:
     ClosedFileInputSource(ClosedFileInputSource const&);
     ClosedFileInputSource& operator=(ClosedFileInputSource const&);
@@ -76,6 +83,7 @@ class ClosedFileInputSource: public InputSource
         std::string filename;
         qpdf_offset_t offset;
         FileInputSource* fis;
+        bool stay_open;
     };
     PointerHolder<Members> m;
 };

libqpdf/ClosedFileInputSource.cc

@@ -4,7 +4,8 @@
 ClosedFileInputSource::Members::Members(char const* filename) :
     filename(filename),
     offset(0),
-    fis(0)
+    fis(0),
+    stay_open(false)
 {
 }
 
@@ -42,6 +43,10 @@ ClosedFileInputSource::after()
 {
     this->last_offset = this->m->fis->getLastOffset();
     this->m->offset = this->m->fis->tell();
+    if (this->m->stay_open)
+    {
+        return;
+    }
     delete this->m->fis;
     this->m->fis = 0;
 }
@@ -82,6 +87,10 @@ void
 ClosedFileInputSource::rewind()
 {
     this->m->offset = 0;
+    if (this->m->fis)
+    {
+        this->m->fis->rewind();
+    }
 }
 
 size_t
@@ -101,3 +110,13 @@ ClosedFileInputSource::unreadCh(char ch)
     // Don't call after -- the file has to stay open after this
     // operation.
 }
+
+void
+ClosedFileInputSource::stayOpen(bool val)
+{
+    this->m->stay_open = val;
+    if ((! val) && this->m->fis)
+    {
+        after();
+    }
+}

libtests/closed_file_input_source.cc

@@ -65,6 +65,11 @@ int main()
     std::cout << "testing with ClosedFileInputSource\n";
     ClosedFileInputSource cf("input");
     do_tests(&cf);
+    std::cout << "testing with ClosedFileInputSource in stay open mode\n";
+    ClosedFileInputSource cf2("input");
+    cf2.stayOpen(true);
+    do_tests(&cf2);
+    cf2.stayOpen(false);
     std::cout << "testing with FileInputSource\n";
     FileInputSource f;
     f.setFilename("input");

libtests/qtest/closedfile/output

@@ -1,3 +1,4 @@
 testing with ClosedFileInputSource
+testing with ClosedFileInputSource in stay open mode
 testing with FileInputSource
 all assertions passed