Add StreamBuffer to optimize save/load from memory

CMakeLists.txt

@@ -66,6 +66,8 @@ add_library(XISF
   libXISF_global.h
   libxisf.cpp
   libxisf.h
+  streambuffer.cpp
+  streambuffer.h
   utils.cpp
   variant.cpp
   ${THIRD_PARTY_SRC}

libxisf.cpp

@@ -27,6 +27,7 @@
 #include <lz4hc.h>
 #include <pugixml.hpp>
 #include <zlib.h>
+#include "streambuffer.h"
 
 namespace LibXISF
 {
@@ -532,6 +533,7 @@ private:
     Image parseImage(const pugi::xml_node &node);
 
     std::unique_ptr<std::istream> _io;
+    std::unique_ptr<StreamBuffer> _buffer;
     std::vector<Image> _images;
     Image _thumbnail;
     std::vector<Property> _properties;
@@ -548,8 +550,8 @@ void XISFReaderPrivate::open(const String &name)
 void XISFReaderPrivate::open(const ByteArray &data)
 {
     close();
-    std::string str((char*)data.data(), data.size());
+    _buffer = std::make_unique<StreamBuffer>(data);
-    _io = std::make_unique<std::istringstream>(str, std::ios_base::in | std::ios_base::binary);
+    _io = std::make_unique<std::istream>(_buffer.get());
     readSignature();
     readXISFHeader();
 }
@@ -565,6 +567,7 @@ void XISFReaderPrivate::open(std::istream *io)
 void XISFReaderPrivate::close()
 {
     _io.reset();
+    _buffer.reset();
     _images.clear();
     _properties.clear();
 }
@@ -839,10 +842,10 @@ void XISFWriterPrivate::save(const String &name)
 
 void XISFWriterPrivate::save(ByteArray &data)
 {
-    std::ostringstream oss;
+    StreamBuffer buffer;
+    std::ostream oss(&buffer);
     save(oss);
-    std::string str = oss.str();
+    data = buffer.byteArray();
-    data = ByteArray(str.data(), str.size());
 }
 
 void XISFWriterPrivate::save(std::ostream &io)

streambuffer.cpp

@@ -0,0 +1,144 @@
+#include "streambuffer.h"
+
+namespace LibXISF
+{
+
+StreamBuffer::StreamBuffer()
+{
+    setg(nullptr, nullptr, nullptr);
+    setp(nullptr, nullptr);
+}
+
+StreamBuffer::StreamBuffer(const ByteArray &byteArray) :
+    _size(byteArray.size()),
+    _byteArray(byteArray)
+{
+    if(_byteArray.size())
+    {
+        char *ptr = _byteArray.data();
+        setg(ptr, ptr, ptr + _size);
+        setp(ptr, ptr + _size);
+    }
+    else
+    {
+        setg(nullptr, nullptr, nullptr);
+        setp(nullptr, nullptr);
+    }
+}
+
+ByteArray StreamBuffer::byteArray()
+{
+    return _byteArray;
+}
+
+StreamBuffer::pos_type StreamBuffer::seekoff(off_type off, std::ios_base::seekdir dir, std::ios_base::openmode mode)
+{
+    pos_type ret = pos_type(off_type(-1));
+    off_type newoffi = off;
+    off_type newoffo = off;
+    if(dir == std::ios_base::cur)
+    {
+        newoffi += gptr() - eback();
+        newoffo += pptr() - pbase();
+    }
+    else if(dir == std::ios_base::end)
+        newoffo = newoffi = _byteArray.size() - off;
+
+    char *ptr = _byteArray.data();
+    if(mode & std::ios_base::in && newoffi >= 0 && newoffi <= _size)
+    {
+        setg(ptr, ptr + newoffi, ptr + _size);
+        ret = pos_type(newoffi);
+    }
+
+    if(mode & std::ios_base::out && newoffo >= 0 && newoffo <= _size)
+    {
+        setp(ptr, ptr + _size);
+        pbump(newoffo);
+        ret = pos_type(newoffo);
+    }
+
+    return ret;
+}
+
+StreamBuffer::pos_type StreamBuffer::seekpos(pos_type pos, std::ios_base::openmode mode)
+{
+    pos_type ret = pos_type(off_type(-1));
+    off_type off = pos;
+
+    if(off >= 0 && off <= (off_type)_byteArray.size())
+    {
+        char *ptr = _byteArray.data();
+        if(mode & std::ios_base::in)
+            setg(ptr, ptr + pos, ptr + _size);
+
+        if(mode & std::ios_base::out)
+        {
+            setp(ptr, ptr + _size);
+            pbump(pos);
+        }
+
+        ret = pos;
+    }
+    return ret;
+}
+
+std::streamsize StreamBuffer::xsgetn(char_type *s, std::streamsize n)
+{
+    std::streamsize ret = 0;
+    std::streamsize len = egptr() - gptr();
+    if(len > 0)
+    {
+        std::streamsize c = std::min(n, len);
+        std::memcpy(s, gptr(), c);
+        gbump(c);
+        ret = c;
+    }
+    return ret;
+}
+
+StreamBuffer::int_type StreamBuffer::underflow()
+{
+    if(gptr() < egptr())
+        return traits_type::to_int_type(*gptr());
+    else
+        return traits_type::eof();
+}
+
+std::streamsize StreamBuffer::xsputn(const char_type *s, std::streamsize n)
+{
+    off_type len = epptr() - pptr();
+    if(len < n)
+    {
+        _size += n - len;
+        _byteArray.resize(_size);
+        update_ptrs();
+    }
+    std::memcpy(pptr(), s, n);
+    pbump(n);
+    return n;
+}
+
+StreamBuffer::int_type StreamBuffer::overflow(int_type c)
+{
+    if(traits_type::eq_int_type(traits_type::eof(), c))
+        return traits_type::eof();
+
+    _byteArray.append(c);
+    _size++;
+    pbump(1);
+    update_ptrs();
+    return c;
+}
+
+void StreamBuffer::update_ptrs()
+{
+    off_type ipos = gptr() - eback();
+    off_type opos = pptr() - pbase();
+    char *ptr = _byteArray.data();
+    setg(ptr, ptr + ipos, ptr + _size);
+    setp(ptr, ptr + _size);
+    pbump(opos);
+}
+
+}

streambuffer.h

@@ -0,0 +1,33 @@
+#ifndef STREAMBUFFER_H
+#define STREAMBUFFER_H
+
+#include <streambuf>
+#include "libxisf.h"
+
+namespace LibXISF
+{
+
+class StreamBuffer : public std::streambuf
+{
+public:
+    StreamBuffer();
+    StreamBuffer(const ByteArray &byteArray);
+    ByteArray byteArray();
+protected:
+    pos_type seekoff(off_type off, std::ios_base::seekdir dir, std::ios_base::openmode mode = std::ios_base::in | std::ios_base::out) override;
+    pos_type seekpos(pos_type pos, std::ios_base::openmode mode = std::ios_base::in | std::ios_base::out) override;
+
+    std::streamsize xsgetn(char_type *s, std::streamsize n) override;
+    int_type underflow() override;
+
+    std::streamsize xsputn(const char_type *s, std::streamsize n) override;
+    int_type overflow(int_type c = traits_type::eof()) override;
+private:
+    void update_ptrs();
+    off_type _size = 0;
+    ByteArray _byteArray;
+};
+
+}
+
+#endif // STREAMBUFFER_H