// streamWriterAt writes the data to the provided io.Writer in
// sequential order.
//
+// streamWriterAt can also be wrapped with an io.OffsetWriter to
+// provide an asynchronous buffer: the caller can use the io.Writer
+// interface to write into a memory buffer and return without waiting
+// for the wrapped writer to catch up.
+//
// Close returns when all data has been written through.
type streamWriterAt struct {
writer io.Writer
buf []byte
+ writepos int // target offset if Write is called
partsize int // size of each part written through to writer
endpos int // portion of buf actually used, judging by WriteAt calls so far
partfilled []int // number of bytes written to each part so far
}
}
-// WriteAt implements io.WriterAt.
+// WriteAt implements io.WriterAt. WriteAt is goroutine-safe.
func (swa *streamWriterAt) WriteAt(p []byte, offset int64) (int, error) {
pos := int(offset)
n := 0