How to Abort a Go HTTP Client POST Request Before Completion?

Aborting a Go HTTP Client POST Request Prematurely

In Go, the http.Client library is commonly used for client-side HTTP requests. When performing long-polling operations, it may be necessary to prematurely abort the request due to user actions or other events.

The standard approach to pre-empt or cancel a client-side request is by setting a timeout using http.Transport. However, this mechanism only allows for cancellation based on timeouts, not user-initiated actions.

A more flexible solution is to utilize the http.Request.WithContext function. This function allows the request to be associated with a context.Context. The context can then be canceled or set with a deadline, allowing for cancellation at any point.

To implement this approach:

1. Create an http.Request as usual.
2. Use req.WithContext(ctx) to associate the request with a context. The context can be created using context.WithDeadline or context.WithCancel.
3. Use the modified request object (req) to make the request using the client.Do method.

Example:

import (
    "context"
    "net/http"
)

// Create a context with a user-specified timeout or cancellation.
ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel() // Remember to cancel the context when done.

// Create an HTTP request.
req, err := http.NewRequest("POST", "http://example.com", nil)
if err != nil {
    // Handle error.
}

// Add headers or other request-specific information.

// Associate the request with the context.
req = req.WithContext(ctx)

// Perform the request.
resp, err := client.Do(req)
if err != nil {
    // Handle error.
}
// ... // Handle the response as usual.

Using this approach, the request will be automatically aborted if the context is canceled or if the deadline expires.

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