Inconsistent compressed output between tarsum and direct gzip Writer

gzip-inconsistency.go

package main

import (
        "compress/gzip"
        "io"
        "os"

        "github.com/docker/docker/pkg/tarsum"
)

func main() {
        gzippedFile, err := os.Create("normal.gz")
        if err != nil {
                panic(err.Error())
        }
        tarsumFile, err := os.Create("tarsum.gz")
        if err != nil {
                panic(err.Error())
        }
        gzipWriter := gzip.NewWriter(gzippedFile)
        if err != nil {
                panic(err.Error())
        }
        
        tarsumLayer, err := tarsum.NewTarSum(io.TeeReader(os.Stdin, gzipWriter), false, tarsum.Version0)
        if err != nil {
                panic(err.Error())
        }
        _, err = io.Copy(tarsumFile, tarsumLayer)
        if err != nil {
                panic(err.Error())
        }

        gzipWriter.Close()
        gzippedFile.Close()
        tarsumFile.Close()
}