Problem

The TryMatchAgainstResources method in ResourceOutgoingPeerResolver was returning true on the first resource match, even when multiple resources had matching addresses. This could lead to ambiguous peer resolution where the method would return different results depending on the order of resources in the collection.

Solution

Updated TryMatchAgainstResources to:

• Count all matching resources before returning a result
• Return true only if exactly one resource matches
• Return false if zero or multiple resources match (ambiguous case)
• Set out parameters to null when returning false for multiple matches

Changes

Core Logic Update

// Before: returned immediately on first match
if (DoesAddressMatch(resourceAddress, peerAddress))
{
    name = ResourceViewModel.GetResourceName(resource, resources);
    resourceMatch = resource;
    return true; // ← Problem: returned without checking for other matches
}

// After: counts all matches before deciding
if (DoesAddressMatch(resourceAddress, peerAddress))
{
    if (foundResource is null)
    {
        foundResource = resource;
    }
    matchCount++;
    break; // No need to check other addresses for this resource
}
// Returns true only if matchCount == 1

Comprehensive Test Coverage

Added unit tests covering realistic scenarios:

• SQL Server addresses: Multiple resources with localhost:1433 addresses
• Redis addresses: Multiple resources with localhost:6379 addresses
• SQL Server comma format: Resources matching localhost,1433 format
• Mixed port formats: Resources with same logical address but different formats
• Address transformation: Scenarios showing how 127.0.0.1 ↔ localhost transformations work
• Single match validation: Ensuring positive cases still work correctly

Test Results

• ✅ All 24 ResourceOutgoingPeerResolver tests passing (17 existing + 7 new)
• ✅ All 269 Dashboard tests passing (verified no regressions)
• ✅ Covers realistic SQL Server and Redis endpoint scenarios

Files Changed

• src/Aspire.Dashboard/Model/ResourceOutgoingPeerResolver.cs - Updated core matching logic
• tests/Aspire.Dashboard.Tests/ResourceOutgoingPeerResolverTests.cs - Added comprehensive test scenarios

This fix ensures deterministic peer resolution behavior and prevents ambiguous matches from returning inconsistent results.

This pull request was created as a result of the following prompt from Copilot chat.

Update TryMatchAgainstResources to return false if multiple resources match, and update/add tests with realistic addresses. Only return true if exactly one match is found. If more than one resource matches, set out parameters to null and return false. Update or add unit tests in Aspire.Dashboard.Tests to cover: (1) no match, (2) single match, (3) multiple matches (ambiguous), using realistic resource addresses like SQL and Redis endpoints.

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