Golang : Read large file with bufio.Scanner cause token too long error



Tags : golang token-too-long bufio-scanner bufio-reader

There are couple of ways to read files with Golang and one of the common way to read in file is with bufio.NewScanner() function. For example :

 package main

 import (
  "bufio"
  "fmt"
  "os"
 )

 func main() {
  file, err := os.Open("somefile.dat")

  if err != nil {
 panic(err.Error())
  }

  defer file.Close()

  reader := bufio.NewReader(file)
  scanner := bufio.NewScanner(reader)

  scanner.Split(bufio.ScanBytes)

  for scanner.Scan() {
 fmt.Println(scanner.Bytes())
  }
 if err := scanner.Err(); err != nil {
 fmt.Println("error while reading :", err)
  }
 }

Most of the time, things should be fine and dandy. However, there will be cases when the program attempts to read in a very large file and it will throw out this error message :

"bufio.Scanner: token too long"

This error message was caused by the input token size that exceeded the bufio.MaxScanTokenSize buffer size. The allocated size is MaxScanTokenSize = 64 * 1024

To read in large files, it is recommended to use bufio.Reader.ReadLine instead.

References :

bufio.MaxTokenSize

Golang Bufio NewScanner example

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  See also : Golang : Scanf function weird error in Windows



Tags : golang token-too-long bufio-scanner bufio-reader

By Adam Ng

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