Скачать или смотреть Solving ImageSharp Caching Issues with a Custom Image Provider in Azure

Discover how to effectively implement a custom image provider with caching in Azure using `ImageSharp` and .NET 6, solving common issues like reloading images unnecessarily.
---
This video is based on the question https://stackoverflow.com/q/73352689/ asked by the user 'Bjarke' ( https://stackoverflow.com/u/597218/ ) and on the answer https://stackoverflow.com/a/73488334/ provided by the user 'James South' ( https://stackoverflow.com/u/427899/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Imagesharp custom image provider, cache not working

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the Caching Problem in ImageSharp

When working with image processing in .NET using the ImageSharp library, particularly in scenarios involving custom image providers and caching, developers might encounter challenges. One common issue is the failure of caching to function as expected. A developer recently faced this problem while attempting to implement a Proof of Concept (POC) that loaded images from a SQL database but ended up fetching images from the provider every time instead of utilizing cached versions in Azure.

What’s Happening?

In this case, the developer set up a custom image provider named LoadImageFromDatabaseProvider to retrieve images based on unique identifiers (GUIDs) provided in a URL. The images were supposed to be cached in Azure after they were loaded from a database. However, even after implementing caching, subsequent requests were still going to the provider instead of retrieving the images from the cache.

Let's explore how to resolve this issue.

How the Caching Mechanism Works

The essence of caching is to save frequently accessed data so that it can be quickly retrieved without needing to perform repetitive processes (like database access or file reading). In the case of ImageSharp, when an image is requested:

If the image is not in the cache, it is fetched from the provider.

After being fetched, the image is saved in the cache, and subsequent requests should ideally fetch from the cache instead.

Issue with Timestamp

The issue the developer faced stems from how the caching mechanism determines whether an image has changed:

Every Time a Request is Made: The developer's Get() method in the ImageRepository returned a new Metadata object containing the current timestamp when an image was requested. This timestamp is used to indicate when the image was created.

Implication of New Date: Since the timestamp was new with every request, ImageSharp assumed the image had been modified and thus bypassed the cache.

The Solution

To ensure that caching works effectively, it is crucial to return the actual “creation date” of the image, not just the current date. Here’s how to fix this:

Steps to Implement the Fix

Update ImageRepository.Get Method:

Adjust the Get method so that it retrieves and returns the actual creation date of the image.

Here’s a simple adjustment:

[[See Video to Reveal this Text or Code Snippet]]

Remove Unnecessary Metadata Updates:

Ensure that the CreatedOn property returns a consistent date that signifies when the image was first stored, rather than updating it each time the image is retrieved.

By implementing these changes, the cache will recognize that the image has not changed since it was first stored, avoiding unnecessary reloads and allowing efficient retrieval from the Azure cache.

Conclusion

Implementing a robust image caching mechanism using ImageSharp and Azure can be challenging, especially when dealing with metadata. By ensuring that the actual creation date is used instead of a new timestamp on each request, you can enhance your caching strategy, leading to improved performance and reduced loading times.

Next time you're setting up an image provider, remember the importance of stable metadata for effective caching!