Add an I/O class to access a restricted range of bytes from another object

[libs/core.git] / source / io / slice.cpp

diff --git a/source/io/slice.cpp b/source/io/slice.cpp
new file mode 100644 (file)
index 0000000..423c1a6
--- /dev/null
+++ b/source/io/slice.cpp
@@ -0,0 +1,111 @@
+#include <stdexcept>
+#include "slice.h"
+
+using namespace std;
+
+namespace Msp {
+namespace IO {
+
+Slice::Slice(Seekable &b, SeekOffset s, SeekOffset l):
+       below(b),
+       start_offset(s),
+       length(l),
+       position(0),
+       sync_position(true)
+{
+       if(s<0 || l<0)
+               throw invalid_argument("Slice");
+
+       mode = below.get_mode()&M_RDWR;
+       below.signal_flush_required.connect(sigc::mem_fun(this, &Slice::flush));
+}
+
+void Slice::flush()
+{
+       sync_position = true;
+}
+
+unsigned Slice::prepare_op(unsigned size, Mode m)
+{
+       check_access(m);
+
+       if(sync_position)
+               seek(position, S_BEG);
+
+       SeekOffset remaining = start_offset+length-position;
+       if(size>remaining)
+               size = remaining;
+       if(!size && m==M_READ)
+               set_eof();
+
+       return size;
+}
+
+unsigned Slice::do_write(const char *data, unsigned size)
+{
+       size = prepare_op(size, M_WRITE);
+       if(!size)
+               return 0;
+
+       unsigned len = below.write(data, size);
+       position += len;
+       return len;
+}
+
+unsigned Slice::do_read(char *data, unsigned size)
+{
+       size = prepare_op(size, M_READ);
+       if(!size)
+               return 0;
+
+       unsigned len = below.read(data, size);
+       if(!len && below.eof())
+               set_eof();
+       position += len;
+       return len;
+}
+
+unsigned Slice::put(char c)
+{
+       if(!prepare_op(1, M_WRITE))
+               return 0;
+
+       unsigned len = below.put(c);
+       position += len;
+       return len;
+}
+
+int Slice::get()
+{
+       if(!prepare_op(1, M_READ))
+               return 0;
+
+       int c = below.get();
+       if(c==-1 && below.eof())
+               set_eof();
+       else
+               ++position;
+       return c;
+}
+
+SeekOffset Slice::seek(SeekOffset off, SeekType type)
+{
+       if(type==S_BEG)
+               off += start_offset;
+       else if(type==S_CUR)
+               off += position;
+       else if(type==S_END)
+               off += start_offset+length;
+
+       if(off<start_offset || off>start_offset+length)
+               throw bad_seek(off, type);
+
+       signal_flush_required.emit();
+
+       position = below.seek(off, S_BEG)-start_offset;
+       sync_position = false;
+       return position;
+}
+
+} // namespace IO
+} // namespace Msp