ENH: add OFstream rewind() method.

- truncates output file, handles compressed streams

applications/test/OCountStream/Test-OCountStream.C

@@ -105,6 +105,18 @@ int main(int argc, char *argv[])
         printInfo(os1);
         printInfo(os2);
         printInfo(os3);
+
+        // Rewind and test single output
+        os1.rewind(); generateOutput(os1);
+        os2.rewind(); generateOutput(os2);
+        os3.rewind(); generateOutput(os3);
+
+        Info<< nl
+            << "single output" << nl;
+
+        printInfo(os1);
+        printInfo(os2);
+        printInfo(os3);
     }
 
     Info<< "\nEnd\n" << endl;

src/OpenFOAM/db/IOstreams/Fstreams/IFstream.C

@@ -123,13 +123,10 @@ const std::istream& Foam::IFstream::stdStream() const
 
 void Foam::IFstream::rewind()
 {
-    lineNumber_ = 1;  // Reset line number
-
     if (IOstreamOption::COMPRESSED == ifstreamPointer::whichCompression())
     {
-        // Special treatment for compressed stream
+        lineNumber_ = 1;  // Reset line number
         ifstreamPointer::reopen_gz(this->name() + ".gz");
-
         setState(ifstreamPointer::get()->rdstate());
     }
     else

src/OpenFOAM/db/IOstreams/Fstreams/IFstream.H

@@ -104,7 +104,8 @@ public:
         //- Const access to underlying std::istream
         virtual const std::istream& stdStream() const;
 
-        //- Rewind the stream so that it may be read again
+        //- Rewind the stream so that it may be read again.
+        //  Includes special handling for compressed streams.
         virtual void rewind();
 
 

src/OpenFOAM/db/IOstreams/Fstreams/OFstream.C

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -129,6 +129,37 @@ const std::ostream& Foam::OFstream::stdStream() const
 }
 
 
+void Foam::OFstream::rewind()
+{
+    if (IOstreamOption::COMPRESSED == ofstreamPointer::whichCompression())
+    {
+        ofstreamPointer::reopen_gz(this->name() + ".gz");
+    }
+    else
+    {
+        // Reopen (truncate)
+        ofstreamPointer::reopen(this->name());
+    }
+
+    // As per OSstream::rewind()
+
+    lineNumber_ = 1;  // Reset line number
+    setState(ofstreamPointer::get()->rdstate());
+
+    if (good())
+    {
+        setOpened();
+    }
+    else
+    {
+        setClosed();
+        setBad();
+    }
+
+    stdStream().rdbuf()->pubseekpos(0, std::ios_base::out);
+}
+
+
 void Foam::OFstream::print(Ostream& os) const
 {
     os  << "OFstream: ";

src/OpenFOAM/db/IOstreams/Fstreams/OFstream.H

@@ -108,6 +108,10 @@ public:
         //- Const access to underlying std::ostream
         virtual const std::ostream& stdStream() const;
 
+        //- Rewind the stream so that it may be written again.
+        //- Reopens the file (truncation)
+        virtual void rewind();
+
 
     // Print
 

src/OpenFOAM/db/IOstreams/Fstreams/fstreamPointer.H

@@ -167,6 +167,16 @@ class ofstreamPointer
         //- The stream pointer (ofstream | ogzstream | ocountstream)
         std::unique_ptr<std::ostream> ptr_;
 
+protected:
+
+    // Protected Member Functions
+
+        //- Special 'rewind' method for compressed stream
+        void reopen_gz(const std::string& pathname_gz);
+
+        //- General 'rewind' method (non-compressed)
+        void reopen(const std::string& pathname);
+
 public:
 
     // Generated Methods

src/OpenFOAM/db/IOstreams/Fstreams/fstreamPointers.C

@@ -207,6 +207,38 @@ void Foam::ifstreamPointer::reopen_gz(const std::string& pathname_gz)
 }
 
 
+void Foam::ofstreamPointer::reopen_gz(const std::string& pathname_gz)
+{
+    #ifdef HAVE_LIBZ
+    ogzstream* gz = dynamic_cast<ogzstream*>(ptr_.get());
+
+    if (gz)
+    {
+        // Special treatment for gzstream
+        gz->close();
+        gz->clear();
+        gz->open(pathname_gz);
+    }
+    #endif /* HAVE_LIBZ */
+}
+
+
+void Foam::ofstreamPointer::reopen(const std::string& pathname)
+{
+    std::ofstream* file = dynamic_cast<std::ofstream*>(ptr_.get());
+
+    if (file)
+    {
+        if (file->is_open())
+        {
+            file->close();
+        }
+        file->clear();
+        file->open(pathname);
+    }
+}
+
+
 Foam::IOstreamOption::compressionType
 Foam::ifstreamPointer::whichCompression() const
 {