How to read the zipfile in chunks using multipart formdata in golang

Question

I am trying to read the zip file in chunks. The scenario is, I am uploading the large file through our endpoint and trying to read that zip file in smaller chunks. I have been following this code but it throws as error stating that not a valid zip file.

package main

import (
    "archive/zip"
    "bytes"
    "io"
    "log"
    "mime/multipart"
    "net/http"
    "os"

    "github.com/labstack/echo/v4"
)

func main() {
    e := echo.New()

    // Route to handle file uploads
    e.POST("/upload", uploadHandler)

    // Start the server
    e.Logger.Fatal(e.Start(":8080"))
}

func uploadHandler(c echo.Context) error {
    // Read the form data including the file
    form, err := c.MultipartForm()
    if err != nil {
        return err
    }

    // Get the file from form data
    fileHeaders := form.File["zipFile"]
    if len(fileHeaders) == 0 {
        return c.String(http.StatusBadRequest, "No file uploaded")
    }

    // Open the uploaded file
    file, err := fileHeaders[0].Open()
    if err != nil {
        return err
    }
    defer file.Close()

    // Create a new zip file to write the extracted contents
    outFile, err := os.Create("extracted.zip")
    if err != nil {
        return err
    }
    defer outFile.Close()

    // Create a zip writer for the output file
    zipWriter := zip.NewWriter(outFile)
    defer zipWriter.Close()

    // Accumulate chunks of data until we have a complete zip file
    var buf bytes.Buffer
    _, err := io.CopyN(&buf, file, 8192) // Read 8KB chunks
        if err != nil {
            if err == io.EOF {
                break
            }
            return err
        }

        // Create a zip reader for the current chunk of data
        zipReader, err := zip.NewReader(bytes.NewReader(buf.Bytes()), int64(buf.Len()))
        if err != nil {
            return err
        }

        // Iterate over each file in the zip file
        for _, f := range zipReader.File {
            // Open the file in the zip archive
            rc, err := f.Open()
            if err != nil {
                return err
            }
            defer rc.Close()

            // Create a new file in the output zip
            outFile, err := zipWriter.Create(f.Name)
            if err != nil {
                return err
            }

            // Copy the file contents to the output zip
            _, err = io.Copy(outFile, rc)
            if err != nil {
                return err
            }
        }

    // Return success response
    return c.String(http.StatusOK, "Files extracted and written to extracted.zip")
}

This below code block throwing the error:

// Create a zip reader for the current chunk of data
   zipReader, err := zip.NewReader(bytes.NewReader(buf.Bytes()), int64(buf.Len()))
  if err != nil {
     return err
  }

The intention of this code is reading the zip file into smaller chunks and write it into another zip file.