Exception Suppression Mechanism (Silent Handling)

When initiating an HTTP remote request, the following exceptions may be encountered:

The target host is unreachable
The request is canceled
The request times out
Other network exceptions

By default, these exceptions interrupt program execution. Although developers typically use try/catch for exception handling, in certain scenarios we would rather silently return null when an exception occurs without interrupting the flow. To this end, the framework provides flexible exception suppression.

HTTP declarative requests suppress exceptions through the SuppressExceptionsAttribute attribute. The corresponding HTTP declarative extractor is implemented as the SuppressExceptionsDeclarativeExtractor type, which is responsible for parsing the SuppressExceptionsAttribute attribute and building the exception suppression configuration required by an HttpRequestBuilder instance.

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// Applied on the interface definition, affecting all methods[SuppressExceptions] // Suppress all exceptionspublic interface IHttpService : IHttpDeclarative{    [Get("https://furion.net/logo.png")]    Task<string> GetStringAsync();    // Applied on the method    [SuppressExceptions(typeof(TimeoutException), typeof(TaskCanceledException))]    // Suppress timeout and cancellation exceptions    [Get("https://furion.net/logo2.png")]    Task<string> GetStringAsync();    [SuppressExceptions(false)]    // Disable exception suppression (restore the default configuration)    [Get("https://furion.net/logo2.png")]    Task<string> GetStringAsync();}

After it is enabled, the exception suppression mechanism is automatically set when an HTTP remote request is sent.

SuppressExceptionsAttribute includes the following constructors and properties:

Constructors:
- new(): Applies to a method or interface; suppresses all exceptions.
- new(enable): Applies to a method or interface; indicates whether to enable exception suppression.
- new(types): Applies to a method or interface; suppresses exceptions of the specified types.
Properties:
- Types: The collection of exception suppression types (of type type[]; every element in the array must be of type System.Exception or a derived type).

Important Notes

When enabling exception suppression, note the following:

Override rule
When SuppressExceptions() or related configuration is invoked multiple times, only the last call takes effect.
Priority between status code checking and exception suppression
Even if EnsureSuccessStatusCode() is configured, a suppressed exception still returns null and does not trigger the status code checking logic.
Priority of exception suppression
Exception suppression has higher priority than status code checking. If both status code checking and exception suppression are enabled, exception suppression takes effect first.
Request interceptors remain available
If exceptions are captured via SetOnRequestFailed(ex, res) or other request handling mechanisms, the interceptor or callback method is still invoked even when the exception is suppressed.
Exception type selection advice
Carefully choose the exception types to suppress based on the specific business scenario, and avoid masking potential problems by over-suppressing exceptions.
Automatic suppression logging
When an exception is successfully suppressed, the framework automatically outputs a Warning-level log (for example "An exception occurred but was suppressed by SuppressExceptionPipelineHandler.") to facilitate troubleshooting.