Golang : How to split or chunking a file to smaller pieces?

Problem :

You have a big file and you want to split / chunk the file into smaller pieces. How to do that in Golang?

Solution :

  1. Calculate the size of each chunk that you want to split the file into.
  2. Read the file content into a buffer(created according to the calculated chunk size).
  3. Write the buffer content into individual pieces.

Here you go :

 package main

 import (

 func main() {

 fileToBeChunked := "./somebigfile"

 file, err := os.Open(fileToBeChunked)

 if err != nil {

 defer file.Close()

 fileInfo, _ := file.Stat()

 var fileSize int64 = fileInfo.Size()

 const fileChunk = 1 * (1 << 20) // 1 MB, change this to your requirement

 // calculate total number of parts the file will be chunked into

 totalPartsNum := uint64(math.Ceil(float64(fileSize) / float64(fileChunk)))

 fmt.Printf("Splitting to %d pieces.\n", totalPartsNum)

 for i := uint64(0); i < totalPartsNum; i++ {

 partSize := int(math.Min(fileChunk, float64(fileSize-int64(i*fileChunk))))
 partBuffer := make([]byte, partSize)


 // write to disk
 fileName := "somebigfile_" + strconv.FormatUint(i, 10)
 _, err := os.Create(fileName)

 if err != nil {

 // write/save buffer to disk
 ioutil.WriteFile(fileName, partBuffer, os.ModeAppend)

 fmt.Println("Split to : ", fileName)

Sample output :

Splitting to 5 pieces.

Split to : somebigfile_1

Split to : somebigfile_2

Split to : somebigfile_3

Split to : somebigfile_4

References :



  See also : Golang : Upload big file (larger than 100MB) to AWS S3 with multipart upload

By Adam Ng

IF you gain some knowledge or the information here solved your programming problem. Please consider donating to the less fortunate or some charities that you like. Apart from donation, planting trees, volunteering or reducing your carbon footprint will be great too.