errreader.go

package shp

import (
	"fmt"
	"io"
)

// errReader is a helper to perform multiple successive read from another reader
// and do the error checking only once afterwards. It will not perform any new
// reads in case there was an error encountered earlier.
type errReader struct {
	io.Reader
	e error
	n int64
}

func (er *errReader) Read(p []byte) (n int, err error) {
	if er.e != nil {
		return 0, fmt.Errorf("unable to read after previous error: %v", er.e)
	}
	n, er.e = er.Reader.Read(p)
	er.n += int64(n)
	return n, er.e
}