Different behavior of golang's scanner depending on the file passed

I am writing a simple fxn that counts line numbers:

func GetNumberOfLines(file io.Reader) (numberOfLines int, err error) {      scanner := bufio.NewScanner(file)      scanner.Split(bufio.ScanLines)      for scanner.Scan() {          numberOfLines++      }      return numberOfLines, nil  }  

In a test run, when I dynamically create a temporary file the fxn fails to count the number and returns 0

const fileContents = `Here is a line  and here is another line  and a third one`    func main() {      file, err := ioutil.TempFile("/tmp", "")      if err != nil {          panic(err)      }        _, err = file.Write([]byte(fileContents))      if err != nil {          panic(err)      }        lineNo, err := GetNumberOfLines(file)      if err != nil {          panic(err)      }      print(lineNo)  }  

▶ go run main.go                        0         

If However I pass the file that was previously created explicitly, the fxn does count the numbers correctly:

func main() {        file, err := os.Open("/tmp/742665138")      if err != nil {          panic(err)      }        lineNo, err := GetNumberOfLines(file)      if err != nil {          panic(err)      }      print(lineNo)  }  

▶ go run main.go   3        

Why in the case of the dynamic tmp file creation the GetNumberOfLines fails to count the lines?

https://stackoverflow.com/questions/66631162/different-behavior-of-golangs-scanner-depending-on-the-file-passed March 15, 2021 at 09:05AM