SendAsync

SendAsync is a method name used in programming libraries to send a request or message to a remote endpoint in an asynchronous fashion. It is commonly used in network I/O to avoid blocking the calling thread while the operation completes. The pattern is widespread across frameworks that perform I/O-bound work, including HTTP requests and messaging systems.

In the .NET ecosystem, HttpClient exposes a public SendAsync method that takes a HttpRequestMessage and a CancellationToken and returns a Task<HttpResponseMessage>. The actual sending occurs through a pipeline of HttpMessageHandler instances; the core extension point is a protected virtual SendAsync(HttpRequestMessage, CancellationToken) method that can be overridden by custom handlers. This design allows developers to customize how requests are dispatched and how responses are processed.

Usage typically involves constructing an HttpRequestMessage with the desired HTTP method, URI, headers, and optional content, then calling SendAsync and awaiting the result. The response is represented by an HttpResponseMessage, which can be inspected for status codes and content. Good practice includes disposing resources as appropriate, handling exceptions, and using a reusable HttpClient instance to avoid socket exhaustion. CancellationToken support enables responsive cancellation of in-flight requests.

Design considerations for SendAsync include adherence to asynchronous programming patterns, proper error handling, and avoiding common pitfalls such as deadlocks or blocking calls. In many libraries, SendAsync serves as the central entry point for dispatching requests, with the ability to customize or extend behavior through handler pipelines.

See also: HttpClient, HttpMessageHandler, Task, CancellationToken.