main/logtail.go (31 lines of code) (raw):
package main
import (
"io"
"io/ioutil"
"os"
"github.com/pkg/errors"
)
// tailFile returns the last max bytes (or the entire file if the file size is
// smaller than max) from the file at path. If the file does not exist, it
// returns a nil slice and no error.
func tailFile(path string, max int64) ([]byte, error) {
f, err := os.Open(path)
if err != nil && os.IsNotExist(err) {
return nil, nil
} else if err != nil {
return nil, errors.Wrap(err, "error opening file")
}
defer f.Close()
fi, err := f.Stat()
if err != nil {
return nil, errors.Wrap(err, "error retrieving file info")
}
size := fi.Size()
n := max
if size < n {
n = size
}
_, err = f.Seek(-n, io.SeekEnd)
if err != nil {
return nil, errors.Wrapf(err, "error seeking file: offset=%d whence=%v", n, io.SeekEnd)
}
b, err := ioutil.ReadAll(io.LimitReader(f, max))
return b, errors.Wrap(err, "error reading from file")
}