package kit: Add BAbstractBufferedDataReader

It doesn't do much in terms of buffering, but defines an interface
buffered readers can implement, namely the additional
ReadDataToOutput() which currently BPackageDataReader specifies.

headers/os/package/hpkg/DataReader.h

@@ -14,6 +14,9 @@ namespace BPackageKit {
 namespace BHPKG {
 
 
+class BDataOutput;
+
+
 class BDataReader {
 public:
 	virtual						~BDataReader();
@@ -23,6 +26,17 @@ public:
 };
 
 
+class BAbstractBufferedDataReader : public BDataReader {
+public:
+	virtual						~BAbstractBufferedDataReader();
+
+	virtual	status_t			ReadData(off_t offset, void* buffer,
+									size_t size);
+	virtual	status_t			ReadDataToOutput(off_t offset, size_t size,
+									BDataOutput* output) = 0;
+};
+
+
 class BFDDataReader : public BDataReader {
 public:
 								BFDDataReader(int fd);

src/kits/package/hpkg/DataReader.cpp

@@ -6,6 +6,8 @@
 
 #include <package/hpkg/DataReader.h>
 
+#include <package/hpkg/DataOutput.h>
+
 #include <string.h>
 
 
@@ -22,6 +24,22 @@ BDataReader::~BDataReader()
 }
 
 
+// #pragma mark - BAbstractBufferedDataReader
+
+
+BAbstractBufferedDataReader::~BAbstractBufferedDataReader()
+{
+}
+
+
+status_t
+BAbstractBufferedDataReader::ReadData(off_t offset, void* buffer, size_t size)
+{
+	BBufferDataOutput output(buffer, size);
+	return ReadDataToOutput(offset, size, &output);
+}
+
+
 // #pragma mark - BBufferDataReader