perf(images): support conditional ETag responses

allstarr.Tests/ImageConditionalRequestHelperTests.cs

@@ -0,0 +1,64 @@
+using Microsoft.AspNetCore.Http;
+using allstarr.Services.Common;
+
+namespace allstarr.Tests;
+
+public class ImageConditionalRequestHelperTests
+{
+    [Fact]
+    public void ComputeStrongETag_SamePayload_ReturnsStableQuotedHash()
+    {
+        var payload = new byte[] { 1, 2, 3, 4 };
+
+        var first = ImageConditionalRequestHelper.ComputeStrongETag(payload);
+        var second = ImageConditionalRequestHelper.ComputeStrongETag(payload);
+
+        Assert.Equal(first, second);
+        Assert.StartsWith("\"", first);
+        Assert.EndsWith("\"", first);
+    }
+
+    [Fact]
+    public void MatchesIfNoneMatch_WithExactMatch_ReturnsTrue()
+    {
+        var headers = new HeaderDictionary
+        {
+            ["If-None-Match"] = "\"ABC123\""
+        };
+
+        Assert.True(ImageConditionalRequestHelper.MatchesIfNoneMatch(headers, "\"ABC123\""));
+    }
+
+    [Fact]
+    public void MatchesIfNoneMatch_WithMultipleValues_ReturnsTrueForMatchingEntry()
+    {
+        var headers = new HeaderDictionary
+        {
+            ["If-None-Match"] = "\"stale\", \"fresh\""
+        };
+
+        Assert.True(ImageConditionalRequestHelper.MatchesIfNoneMatch(headers, "\"fresh\""));
+    }
+
+    [Fact]
+    public void MatchesIfNoneMatch_WithWildcard_ReturnsTrue()
+    {
+        var headers = new HeaderDictionary
+        {
+            ["If-None-Match"] = "*"
+        };
+
+        Assert.True(ImageConditionalRequestHelper.MatchesIfNoneMatch(headers, "\"anything\""));
+    }
+
+    [Fact]
+    public void MatchesIfNoneMatch_WithoutMatch_ReturnsFalse()
+    {
+        var headers = new HeaderDictionary
+        {
+            ["If-None-Match"] = "\"ABC123\""
+        };
+
+        Assert.False(ImageConditionalRequestHelper.MatchesIfNoneMatch(headers, "\"XYZ789\""));
+    }
+}