func headLines(file *hdfs.FileReader, numLines int64) {
reader := bufio.NewReader(file)
var newlines, offset int64
for newlines < numLines {
b, err := reader.ReadByte()
if err == io.EOF {
offset = -1
break
} else if err != nil {
fatal(err)
}
if b == '\n' {
newlines++
}
offset++
}
_, err := file.Seek(0, 0)
if err != nil {
fatal(err)
}
if offset < 0 {
io.Copy(os.Stdout, file)
} else {
io.CopyN(os.Stdout, file, offset)
}
}
func tailLines(file *hdfs.FileReader, numLines int64) {
fileSize := file.Stat().Size()
searchPoint := file.Stat().Size() - tailSearchSize
if searchPoint < 0 {
searchPoint = 0
}
readSize := tailSearchSize
if readSize > fileSize {
readSize = fileSize
}
var printOffset int64
for searchPoint >= 0 {
section := bufio.NewReader(io.NewSectionReader(file, searchPoint, readSize))
off := searchPoint
newlines := make([]int64, 0, tailSearchSize/64)
b, err := section.ReadByte()
for err == nil {
if b == '\n' && (off+1 != fileSize) {
newlines = append(newlines, off)
}
off++
b, err = section.ReadByte()
}
if err != nil && err != io.EOF {
fatal(err)
}
foundNewlines := int64(len(newlines))
if foundNewlines >= numLines {
printOffset = newlines[foundNewlines-numLines] + 1
break
}
numLines -= foundNewlines
searchPoint -= tailSearchSize
}
_, err := file.Seek(printOffset, 0)
if err != nil {
fatal(err)
}
io.Copy(os.Stdout, file)
}