如何将文件保留在内存中-在服务器之间传输文件而不将其存储在本地

Question

I am in the process of writing a simple deployment tool which needs to take tar files from s3, extract them and then upload them to our staging server. I would like to do this without storing the files locally, keeping them in memory.

Here is my code to download files from s3

func s3downloadFile(downloader *s3manager.Downloader, item string) {
    localitem := strings.Replace(item, s3base, "", -1)
    os.MkdirAll(path.Dir(localitem), os.ModePerm)
    file, err := os.Create(localitem)
    if err != nil {
        exitErrorf("Unable to open file %q, %v", err)
    }

    defer file.Close()

    numBytes, err := downloader.Download(file,
        &s3.GetObjectInput{
            Bucket: aws.String(s3bucket),
            Key:    aws.String(item),
        })
    if err != nil {
        exitErrorf("Unable to download item %q, %v", item, err)
    }

    fmt.Println("Downloaded", file.Name(), numBytes, "bytes")
}

I would like to avoid having to create the directories and files in this example and just keep everything in memory. I left out the step that extracts the files from my code. The next step would be to upload the files with go-scp like so:

// Finaly, copy the file over
// Usage: CopyFile(fileReader, remotePath, permission)

client.CopyFile(f, "/path/to/remote/file", "0655")

My question would then focus on the file, err := os.Create(localitem) part of this code, how can I keep a filereader in memory instead of storing the file locally.

Answer 1

This is mentioned in the docs for Download:

The w io.WriterAt can be satisfied by an os.File to do multipart concurrent downloads, or in memory []byte wrapper using aws.WriteAtBuffer.

So use an aws.WriteAtBuffer instead of an *os.File:

buf := new(aws.WriteAtBuffer)

numBytes, err := downloader.Download(buf, &s3.GetObjectInput{
    Bucket: aws.String(s3bucket),
    Key:    aws.String(item),
})

tr := tar.NewReader(bytes.NewReader(buf.Bytes()))
// ...