writer.go

package bigqueue

import (
	"github.com/grandecola/mmap"
)

// writer knows how to copy data of given length to arena.
type writer interface {
	// len returns the length of the data that writer holds.
	len() int

	// writeTo writes the data to arena starting at given offset. It is possible that the
	// whole data that writer holds may not fit in the given arena. Hence, an index
	// into the data is provided. The data is copied starting from index until either
	// no more data is left, or no space is left in the given arena to write more data.
	writeTo(aa *mmap.File, offset, index int) int
}

// bytesWriter holds a slice of bytes and satisfies the bigqueue.writer interface.
type bytesWriter struct {
	b []byte
}

// len returns the length of data that bytesWriter holds.
func (bw *bytesWriter) len() int {
	return len(bw.b)
}

// writeTo writes data that it holds from index to end of
// the data or arena, into the arena starting at the offset.
func (bw *bytesWriter) writeTo(aa *mmap.File, offset, index int) int {
	n, _ := aa.WriteAt(bw.b[index:], int64(offset))
	return n
}

// stringWriter holds a string and satisfies bigqueue.writer interface.
type stringWriter struct {
	s string
}

// len returns the length of string that stringWriter holds.
func (sw *stringWriter) len() int {
	return len(sw.s)
}

// writeTo writes the string starting from index into arena
// starting at offset until either arena lasts or string lasts.
func (sw *stringWriter) writeTo(aa *mmap.File, offset, index int) int {
	return aa.WriteStringAt(sw.s[index:], int64(offset))
}