One thing I find very elegant about working with golang is that it is very open minded about where data is flowing in from or going out to. I recently built an application that downloaded an audio file from one location and pushed it to s3 – and golang makes it very easy to do that without needing to write an intermediate file and then upload that. Here’s my code, in case I need to do this again some day :)

Downloading a File

By creating an HTTP request, I get a basic request object that I can change other parameters of if I need to. This example sets an Authorization header too, to give you an idea of how the other configuration works.

    req, _ := http.NewRequest("GET", RecordingURL, nil)
    req.Header.Set("Authorization", "Bearer "+jwt)
    client := &http.Client{}
    resp, err := client.Do(req)
    if err != nil {
        panic(err)
    }
    defer resp.Body.Close()

We haven’t actually done anything with the request yet, but by deferring the close we can access the resp.Body as a stream when we come to send the file over to S3.

Uploading to S3

It turns out that AWS already has a very nice SDK for working with Golang – it’s not as popular as some of the other SDKs so I didn’t find lots of code examples for working with it, but it was a very easy starting point! The SDK has a few ways to supply credentials but I like to use environment variables:

• AWS_ACCESS_KEY_ID
• AWS_SECRET_ACCESS_KEY

With these credentials set, and the resp from the section above to read from, I can upload the file to S3. This is a .mp3 file so the ContentType is set accordingly – change this for other file types in your own applications.

        format := "audio/mpeg"
        sess, err := session.NewSession(&aws.Config{
            Region: aws.String("us-east-1")},
        )
        if err != nil {
            panic(err)
        }

        uploader := s3manager.NewUploader(sess)
        _, err = uploader.Upload(&s3manager.UploadInput{
            Bucket:      aws.String("my-bucket"),
            Key:         aws.String("uploaded-file.mp3"),
            Body:        resp.Body,
            ContentType: &format,
        })

I don’t need to do anything with the response here, but if there’s an error I do want to catch it and respond, so I’ve assigned err in the example above.

Just a very quick and simple example but it took me a little while to line up all the pieces I needed so I thought I’d share what I did!