Dynamic Path

Although directories are an illusion in S3, they're still useful due to the prefix filtering capabilities of the S3 API. There are a lot of common strategies for organizing objects in S3, but the most important rule is:

Organization matters.

Schema architecture matters in a SQL database, and prefix architecture matters in S3. We always want to group objects in a way that makes sense for our case, because often we'll want to operate on a group of objects at once.

For example, pretend you do the naive thing and upload all your images to the root of your bucket. What happens if...

you want to delete all the images for a specific user?
a feature changed and you need to resize all the images it uses?
you want to change the permissions of all the images associated with a specific organization?

If you don't have any prefixes (directories) to group objects, you might find yourself iterating over every object in the bucket to find the ones you care about. That's slow and expensive.

Assignment

Tubely's software architect has decided on the following prefix "schema" for our video uploads:

landscape (16:9 aspect ratio)
portrait (9:16 aspect ratio)
other (everything else)

Install ffmpeg (which will also install ffprobe):

# mac
brew install ffmpeg

# linux
sudo apt install ffmpeg

Ensure that the installation worked and the commands are available in your PATH:

ffprobe -version
ffmpeg -version

Use ffprobe manually to get the aspect ratio of a video file.

ffprobe -v error -print_format json -show_streams PATH_TO_VIDEO

You should see a streams array containing information about the video. We care about the width and height fields of the first stream.

Create a function getVideoAspectRatio(filePath string) (string, error) that takes a file path and returns the aspect ratio as a string.
- It should use exec.Command to run the same ffprobe command as above. In this case, the command is ffprobe and the arguments are -v, error, -print_format, json, -show_streams, and the file path.
- Set the resulting exec.Cmd's Stdout field to a pointer to a new bytes.Buffer.
- .Run() the command
- Unmarshal the stdout of the command from the buffer's .Bytes into a JSON struct so that you can get the width and height fields.
- I did a bit of math to determine the ratio, then returned one of three strings: 16:9, 9:16, or other.

Aspect ratios might be slightly off due to rounding errors. You can use a tolerance range (or just use integer division and call it a day).

Update the handlerUploadVideo to get the aspect ratio of the video file from the temporary file once it's saved to disk. Depending on the aspect ratio, add a "landscape", "portrait", or "other" prefix to the key before uploading it to S3.
Test your code by using both the provided horizontal (16:9) and portrait (9:16) videos. You should see the correct prefix in the S3 bucket.
Delete all the videos from your [email protected] account, and recreate them in this order (the tests retrieve videos sorted by most recent first):
1. Vertical video:
  - Title: "Boots Vertical"
  - Description: "A vertical video of boots"
  - Use the vertical video
2. Horizontal video:
  - Title: "Boots Horizontal"
  - Description: "A horizontal video of boots"
  - Use the horizontal video (this one might take a bit to upload)

Run and submit the CLI tests.