fix(xds): add mutiple async connections to the server

[hanshal101]

Fixes #20
Closes #20

Description

This PR adds the functionality to connect multiple clients to the XDS Server.

[kmesh-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign hzxuzhonghu for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[gemini-code-assist]

Summary of Changes

Hello @hanshal101, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the XDS server's internal communication mechanism to support multiple asynchronous client connections. Previously, the server used tokio::sync::mpsc::channel which only allows a single consumer. This change migrates to tokio::sync::broadcast::channel, enabling multiple clients to subscribe to resource updates from the server simultaneously, addressing the limitation of single-client connectivity.

Highlights

• Migration to tokio::sync::broadcast::channel: Replaced mpsc::channel with broadcast::channel for delta_resource_tx and stream_resource_tx in the XDS server and its examples, allowing multiple clients to receive resource updates concurrently.
• Adaptation of Server Logic: The AggregateServer struct and its methods were updated to use tokio::sync::broadcast::Sender and Receiver (obtained via subscribe()), removing the need for atomic_take and enabling multi-client support.
• Updated Example Servers: All four example server files (server.rs, server_routes_and_loads.rs, server_secret_rotation.rs, server_secret_rotation_simple.rs) were modified to reflect the new channel types and their usage, including cloning senders and removing .await from send() calls.
• ServerAction Trait Implementations: The ServerAction enum now derives Debug and Clone, which is a requirement for messages sent over tokio::sync::broadcast::channel.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point in your pull request via creating an issue comment (i.e. comment on the pull request page) using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in issue comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request successfully refactors the XDS server to use tokio::sync::broadcast channels, enabling multiple clients to connect simultaneously. The transition from mpsc to broadcast channels is implemented correctly across the server logic and most of the examples. However, I've identified an issue in the server_secret_rotation_simple.rs example where the newly created channel sender is not utilized, rendering the example non-functional. Overall, the change is a solid improvement for the server's capabilities.

[hanshal101]

Thanks for rectifying the issue @YaoZengzeng , it seems like I understood the communication between the client and server. I changed the type of the aggregated_server from Send to Receive.

[hanshal101]

Also I am not sure why the CI failed, I even did cargo fmt --all and pushed the updated code.
I see few things here, I noticed that the code which is being scanned for format belongs to the main branch which doesn't match the PR. I think we should do something about this.

[hzxuzhonghu]

Also I am not sure why the CI failed, I even did cargo fmt --all and pushed the updated code.

Maybe related to your rust version

[hzxuzhonghu]

I am not familiar with this patch. defer to @YaoZengzeng

[hanshal101]

Hello @YaoZengzeng can you help us here please.

[Eeshu-Yadav]

Also I am not sure why the CI failed, I even did cargo fmt --all and pushed the updated code. I see few things here, I noticed that the code which is being scanned for format belongs to the main branch which doesn't match the PR. I think we should do something about this.

ci is faling during the formating in your case , so when you update anything then in the last run this cargo fmt --all. yeah there is issue in the ci but not during the formatting , the ci fail during the clippy , i have pushed code mutliple times today there is no such case found in the formating so please try instruction as above told .