Have you ever found yourself in a situation where you need to read a file or another readable source from the end to the start? While bufio.Scanner only supports reading from the start, rscanner.Scanner offers the capability to read from the end.

rscanner.Scanner is an exceptionally efficient and thoroughly tested reverse scanner, even in production.

The rscanner package intentionally maintains the same interface as bufio.Scanner for reading, including scanner.Scan(),scanner.Bytes(), and scanner.Text(). However, rscanner introduces some slight differences to offer enhanced configurability, such as scanner.Buffer(), scanner.MaxTokenSize(), and scanner.MaxConsecutiveEmptyReads().

To achieve superior performance, it minimizes memory allocation and reuses the same block of memory for multiple reads.

go get -t github.com/vallerion/rscanner

const text = "run\nforrest\nrun"
sc := rscanner.NewScanner(strings.NewReader(text), int64(len(text)))
for sc.Scan() {
    log.Println(sc.Text())
}
if sc.Err() != nil {
    log.Fatalf("woops! err: %v", sc.Err())
}

f, err := os.Open("service.log")
if err != nil {
    log.Fatalln(err)
}
defer f.Close()

fs, err := f.Stat()
if err != nil {
    log.Fatalln(err)
}

sc := rscanner.NewScanner(f, fs.Size())
for sc.Scan() {
    log.Println(sc.Text())
}

if sc.Err() != nil {
    log.Fatalf("woops! err: %v", sc.Err())
}

log.Println("File is finished!")