Cache the DSN resolution result to avoid repeated lookup

[AayushTyagi1]

Describe the problem this PR is solving

Short description of the changes

[gemini-code-assist]

Summary of Changes

Hello @AayushTyagi1, 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 significantly improves the efficiency and reliability of network connections by introducing a robust DNS resolution caching system. It intelligently caches DNS SRV lookup results, including handling for private endpoints, to minimize redundant network calls. Additionally, it bolsters the application's stability by adding critical input validation for connection parameters and ensuring proper cache invalidation upon connection removal.

Highlights

• DNS Resolution Caching: Implemented a caching mechanism for DNS Service (SRV) record lookups in NSLookup.ts to reduce repeated network requests and improve performance. The cache has a 5-minute TTL.
• Private Endpoint Handling: The DNS caching logic now intelligently handles private endpoints by skipping SRV lookups for URLs identified as private or for those that previously resulted in an ENOTFOUND error, caching this information to prevent future failed attempts.
• Robust Connection URL Handling: Enhanced CouchbaseRestAPI.ts to include explicit checks for valid server URLs returned by getServerURL, and added comprehensive input validation for connection URLs and usernames in connections.ts during connection setup and testing.
• DNS Cache Invalidation: Added functionality to clear specific DNS cache entries when a connection is removed, ensuring that stale or incorrect DNS information is not retained for deleted connections.

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[gemini-code-assist]

Code Review

This pull request introduces a valuable caching layer for DNS resolution to improve performance and adds several input validations to increase robustness. However, it also introduces a critical security vulnerability: connection URLs, which can contain embedded credentials, are logged in error or debug messages, potentially leading to sensitive information leakage in the VS Code output channel. Furthermore, there are high-severity issues including a bug in the new caching logic causing unnecessary network lookups, and an issue with the SDK Doctor utility call leading to incorrect connection diagnostics. Addressing these concerns, particularly sanitizing URLs before logging, is crucial for a solid and reliable improvement.

[gemini-code-assist]

The current cache-checking logic has a flaw. If a DNS SRV lookup for a non-private endpoint successfully returns an empty list of servers, this result is cached. However, on subsequent calls, the condition if (cachedEntry.servers.length > 0) will be false, causing the code to fall through and perform the DNS lookup again. This defeats the purpose of caching for this scenario.

The logic can be simplified to correctly handle all cached cases, including empty server lists for non-private endpoints. By returning cachedEntry.servers directly when a valid cache entry is found, you ensure that all successful lookups (even those with no results) are properly cached and served.

    if (cachedEntry && isCacheValid(cachedEntry)) {
        logger.debug(`Using cached DNS result for: ${url}`);
        return cachedEntry.servers;
    }

[AayushTyagi1]

This I will put as a part of MCP release

It was emergency review for a customer but not being reviewed properly. Need to get it reviewed.