Enabling ETag Response Caching

ETag (entity tag) is a mechanism in the HTTP protocol used to identify the version of a resource. The server returns the resource's ETag value in the response headers (for example, "abc123"), and the client can carry that value via the If-None-Match header in subsequent requests. If the resource has not changed, the server returns 304 Not Modified without retransmitting the content; otherwise it returns the new content along with a new ETag.

After enabling ETag caching, the framework handles this process automatically: the first request caches the response and the ETag, and subsequent requests automatically attach If-None-Match; when a 304 status code is received, the cached content is reused directly, reducing data transfer and improving request efficiency. In weak network environments or mobile data-metering scenarios, this mechanism can significantly reduce bandwidth consumption while speeding up response times.

HTTP declarative requests enable ETag response caching through the UseETagAttribute attribute. The corresponding HTTP declarative extractor is implemented as the UseETagDeclarativeExtractor type, which is responsible for parsing the UseETagAttribute attribute and building the ETag response caching configuration needed for the HttpRequestBuilder instance.

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// Applied on the interface definition, affecting all methods[UseETag]public interface IHttpService : IHttpDeclarative{    // Applied on a method    [UseETag]    [Get("https://furion.net/")]    Task<string> GetStringAsync();    [UseETag(false)]   // Disable this feature    [Get("https://furion.net/")]    Task<string> GetStringAsync();}

ETag Response Caching Notes

Only takes effect for GET and HEAD requests.
If the request explicitly calls DisableCache(), the ETag feature is automatically skipped.
The cache is stored in memory by default, and can be replaced with a distributed cache (such as Redis) by implementing the IHttpETagCache interface.
The default in-memory cache does not limit the number of cache entries or the size of a single response; a large number of unique URLs or large responses may cause memory to grow continuously. To avoid this, it is recommended to implement the IHttpETagCache interface and replace the default implementation, for example:
cs
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1
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services.Replace(ServiceDescriptor.Singleton<IHttpETagCache, CustomETagCache>());
If the global request profiler (AddProfilerDelegatingHandler) is also enabled and you find that the response content is not printed, explicitly call the Profiler() method on the request to resolve it.

UseETagAttribute contains the following constructors and properties:

Constructors:
- new(): applies to methods or interfaces, enabling ETag response caching.
- new(enabled): applies to methods or interfaces, setting whether to enable ETag response caching.
Properties:
- Enabled: whether to enable (type bool), with a default value of true (enabled).