Multipart and Pipe file stream

multipart-pipe.go

// This example shows how to send files via pipe using multipart package

package main

import (
	"errors"
	"fmt"
	"io"
	"mime/multipart"
	"os"
	"path/filepath"
)

func main() {
	pipeReader, pipeWriter, err := os.Pipe()
	if err != nil {
		panic(err)
	}
	defer pipeReader.Close()

	form := multipart.NewWriter(pipeWriter)
	defer form.Close()

	go func() {
		defer pipeWriter.Close()

		files := []string{"file1.txt", "file2.txt"}

		for i := range files {
			filePart, err := form.CreateFormFile("file", files[i])
			if err != nil {
				panic(err)
			}

			copyToWriter(filePart, files[i])
		}
	}()

	reader := multipart.NewReader(pipeReader, form.Boundary())
	for {
		part, err := reader.NextPart()
		if err != nil {
			break
		}

		fileName := filepath.Join("./uploads/" + part.FileName())
		copyToFile(fileName, part)
	}
}

func copyToWriter(dst io.Writer, src string) {
	file, err := os.Open(src)
	if err != nil {
		panic(err)
	}
	defer file.Close()

	_, err = io.Copy(dst, file)
	if err != nil {
		panic(err)
	}
}

func copyToFile(dst string, src io.Reader) {
	tempFile, err := os.Create(dst)
	if err != nil {
		panic(err)
	}
	defer tempFile.Close()

	_, err = io.Copy(tempFile, src)
	if err != nil {
		if errors.Is(err, io.ErrUnexpectedEOF) {
			fmt.Println("File upload complete")
			os.Exit(0)
		}

		panic(err)
	}
}