Convention

The thumbnails are placed in a folder “thumbnails” at the same place as original file.

The thumbnail size is appended to filename, right before the extention part. For example:

bucket/
└── folder/
    ├── photo.jpg
    └── thumbnails/
        ├── photo_128x128.jpg
        └── photo_512x512.jpg
    ├── photo-missing-extension
    └── thumbnails/
        ├── photo-missing-extension_128x128
        └── photo-missing-extension_512x512

The function expects these environment variables to be set:

• THUMB_SIZES: Size of thumbnails to be generated. Example: 512x512,128x128.

• MONITORED_PATHS: Folders (and theirs children) where the function will process the uploaded images. Muliple paths are separated by “:”, like user-docs:user-profiles. If you want to monitor all over the bucket, set it as /.

• NOTIFY_THUMBNAIL_GENERATED (optional): Tell Thunagen to notify after thumbnails are created.

The variables can be passed via .env file in the working directory.

Get notified when thumbnails are generated

Other applications may want to be informed when the thumbnails are created. We support this by leveraging Google Cloud Pub/Sub service.

After finishing generating thumbnail, if the NOTIFY_THUMBNAIL_GENERATED environment variable is set (with non-empty value), the function will publish a message to Pub/Sub. The message is sent to topic thumbnail-generated/{bucket_name}/{image_path}, with the content being JSON string of thumbnail info (size and path). Example:

• Topic: thumbnail-generated%2Fbucket%2Ffolder%2Fphoto.jpg (URL-encoded of “thumbnail-generated/bucket/folder/photo.jpg”)

• Message:

  {
      "128x128": "folder/thumbnails/photo_128x128.jpg",
      "512x512": "folder/thumbnails/photo_512x512.jpg"
  }

Other applications can subscribe to that topic to get notified. Google doesnot allow slash (“/”) in topic name, so subscribed applications have to take care of URL-encode, decode the topic.

Why Thunagen

I’m aware that there is already a Firebase extension for the same purpose. But that extension, when doing its job, need to create a temporary file and in many cases, falling into race condition when the temporary file is deleted by another execution of the same cloud function. Thunagen, on the other hand, generates the file and uploads (back to Storage) on-the-fly (in memory), so it doesn’t get into that issue.

Installation

Thunagen is distributed via PyPI. You can install it with pip:

pip install thunagen

Include to your project

Thunagen is provided without a main.py file, for you to incorporate more easily to your project, where you may have your own way to configure deployment environment (different bucket for “staging” and “production”, for example).

To include Thunagen, from your main.py, do:

from thunagen.functions import generate_gs_thumbnail

Credit

Thunagen is brought to you by Nguyễn Hồng Quân, from SunshineTech (Việt Nam).