How to generate zip / 7z archive on the fly in a HTTP server using Gin?

Question

I use Gin to create a HTTP server and I want to give a dynamically generated zip archive to the user.

Theoretically I could first generate a zip file on a file system and then serve it. But that is really a bad way (to wait 5 mins before starting download). I want start giving it to a user immediately and push content as it is generated.

I've found DataFromReader (example) but ContentLength is not known until archive is done.

func DownloadEndpoint(c *gin.Context) {
    ...
    c.DataFromReader(
        http.StatusOK,
        ContentLength,
        ContentType,
        Body,
        map[string]string{
            "Content-Disposition": "attachment; filename=\"archive.zip\""),
        },
    )
}

How can I do that?

Answer 1

Using the stream method and archive/zip you can create zip on the fly and stream them to the server.

package main

import (
    "os"

    "archive/zip"

    "github.com/gin-gonic/gin"
)

func main() {

    r := gin.Default()
    r.GET("/", func(c *gin.Context) {

        c.Writer.Header().Set("Content-type", "application/octet-stream")
        c.Stream(func(w io.Writer) bool {

            // Create a zip archive.
            ar := zip.NewWriter(w)

            file1, _ := os.Open("filename1")
            file2, _ := os.Open("filename2")
            c.Writer.Header().Set("Content-Disposition", "attachment; filename='filename.zip'")

            f1, _ := ar.Create("filename1")
            io.Copy(f1, file1)
            f2, _ := ar.Create("filename2")
            io.Copy(f2, file2)

            ar.Close()

            return false
        })
    })
    r.Run()
}

By using directly ResponseWriter

package main

import (
    "io"
    "os"

    "archive/zip"

    "github.com/gin-gonic/gin"
)


func main() {

    r := gin.Default()
    r.GET("/", func(c *gin.Context) {
        c.Writer.Header().Set("Content-type", "application/octet-stream")
        c.Writer.Header().Set("Content-Disposition", "attachment; filename='filename.zip'")
        ar :=  zip.NewWriter(c.Writer)
        file1, _ := os.Open("filename1")
        file2, _ := os.Open("filename2")
        f1, _ := ar.Create("filename1")
        io.Copy(f1, file1)
        f2, _ := ar.Create("filename1")
        io.Copy(f1, file2)
        ar.Close()
    })
    r.Run()
}