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head.go
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head.go
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package filter
import (
"bufio"
"bytes"
"io"
"github.com/koron/nvgd/resource"
)
func init() {
MustRegister("head", newHead)
}
func newHead(r *resource.Resource, p Params) (*resource.Resource, error) {
start := p.Int("start", 0)
if start < 0 {
start = 0
}
limit := p.Int("limit", 10)
if limit <= 0 {
limit = 10
}
return r.Wrap(NewHead(r, uint(start), uint(limit))), nil
}
// Head is "head" like filter.
type Head struct {
Base
start uint
last uint
curr uint
}
var (
_ io.ReadCloser = (*Head)(nil)
)
// NewHead creates an instance of head filter.
func NewHead(r io.ReadCloser, start, limit uint) *Head {
h := &Head{
start: start,
last: start + limit,
}
h.Base.Init(r, h.readNext)
return h
}
func (h *Head) readNext(buf *bytes.Buffer) error {
for h.curr < h.last {
lnum := h.curr
b, err := h.Reader.ReadSlice('\n')
if err != nil {
if err != bufio.ErrBufferFull {
return err
}
} else {
h.curr++
}
if lnum >= h.start {
if _, err := buf.Write(b); err != nil {
return err
}
return nil
}
}
return io.EOF
}