COMMON: Set and implement a seekable base for file writer streams

src/common/writefile.cpp

@@ -94,8 +94,9 @@ size_t WriteFile::write(const void *dataPtr, size_t dataSize) {
 
 	assert(dataPtr);
 
+	const size_t oldPos = pos();
 	const size_t written = std::fwrite(dataPtr, 1, dataSize, _handle);
-	_size += written;
+	_size += MAX<size_t>(0, -size() + oldPos + written);
 
 	return written;
 }
@@ -104,4 +105,21 @@ size_t WriteFile::size() const {
 	return _size;
 }
 
+size_t WriteFile::pos() const {
+	return std::ftell(_handle);
+}
+
+size_t WriteFile::seek(ptrdiff_t offset, SeekableWriteStream::Origin whence) {
+	const size_t oldPos = pos();
+	const size_t newPos = evalSeek(offset, whence, pos(), 0, size());
+
+	if (newPos > _size)
+		throw Exception(kSeekError);
+
+	if (std::fseek(_handle, newPos, SEEK_SET))
+		throw Exception(kSeekError);
+
+	return oldPos;
+}
+
 } // End of namespace Common

src/common/writefile.h

@@ -37,7 +37,7 @@ namespace Common {
 class UString;
 
 /** A simple streaming file writing class. */
-class WriteFile : boost::noncopyable, public WriteStream {
+class WriteFile : boost::noncopyable, public SeekableWriteStream {
 public:
 	WriteFile();
 	WriteFile(const UString &fileName);
@@ -66,6 +66,12 @@ class WriteFile : boost::noncopyable, public WriteStream {
 	/** Return the number of bytes written to the current file in total. */
 	size_t size() const;
 
+	/** Return the current position ot the stream in the file. */
+	size_t pos() const;
+
+	/** Seek to the speciied offset from the specified origin. */
+	size_t seek(ptrdiff_t offset, Origin whence = SeekableWriteStream::kOriginBegin);
+
 protected:
 	std::FILE *_handle; ///< The actual file handle.