How to Ensure Your HTTP Requests are Sent Asynchronously in Rust

Discover how to modify your Rust code to send `HTTP requests` asynchronously, ensuring that the responses are handled efficiently and effectively.
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This video is based on the question https://stackoverflow.com/q/70772751/ asked by the user 'iustin' ( https://stackoverflow.com/u/14149793/ ) and on the answer https://stackoverflow.com/a/70777909/ provided by the user 'battlmonstr' ( https://stackoverflow.com/u/1009546/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Sending HTTP Requests Asynchronously in Rust

When building a program that sends multiple HTTP requests, managing concurrency effectively is essential for performance. One common issue many encounter is unintentionally sending requests sequentially instead of asynchronously. In this post, we will investigate a specific example in Rust and learn how to modify the code to achieve true asynchronous behavior for HTTP requests.

Understanding the Problem

The initial setup involves sending a list of URLs, retrieving their StatusCode and body. However, the code snippet below reveals that the requests are being sent one by one due to a couple of issues in the implementation:

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The output indicates that the program seems to wait for each request's complete response before proceeding to the next. This situation can be frustrating, especially when working with numerous URLs.

Analyzing the Code

The following two points explain why the requests are not being sent asynchronously and how to address the issue:

Unintended Blocking with .map()
The line:

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

inadvertently forces the program to complete each future before moving on to the next one. This behavior locks the process into a sequential manner, rendering the buffer_unordered() function ineffective.

Request Conversion
The requests within filter_map produce a Result, but since those are not categorized as futures directly, this also restricts them from being handled in an asynchronous manner correctly.

Solution: Modifying the Code

To correct this, the following adjustments are recommended:

Step 1: Replace filter_map with map

Instead of using filter_map, utilize map to convert URLs into asynchronous tasks (futures):

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Step 2: Update the Buffering Technique

You should then buffer the futures that are ready to run without blocking:

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

Step 3: Post-Processing of Errors

If there is a need to filter out any errors gracefully, it can be done after buffering:

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

Conclusion

By making these simple changes, you can enhance the performance of Rust applications that are responsible for making multiple HTTP requests. The key takeaway is to ensure that you manage the futures properly and allow them to operate independently rather than locking them into a sequential order.

Don’t let poor concurrency practices slow your application down; consider implementing these adjustments in your own code and observe the benefits of true asynchronous processing. Happy coding!