implement HttpBrowserCapabilities.IsBrowser

src/Microsoft.AspNetCore.SystemWebAdapters/Adapters/Features/IHttpBrowserCapabilityFeature.cs

@@ -15,6 +15,8 @@ namespace Microsoft.AspNetCore.SystemWebAdapters.Features;
 public interface IHttpBrowserCapabilityFeature
 {
     string? this[string key] { get; }
+
+    bool IsBrowser(string browserName);
 }
 
 #endif

src/Microsoft.AspNetCore.SystemWebAdapters/Configuration/BrowserCapabilitiesFactory.cs

@@ -652,18 +652,19 @@ private bool UcbrowserProcess(string userAgent, ParsedBrowserResult dictionary)
 
     private sealed class ParsedBrowserResult : Dictionary<string, string?>, IHttpBrowserCapabilityFeature
     {
+        private readonly HashSet<string> _browsers = new(StringComparer.OrdinalIgnoreCase);
+
         public ParsedBrowserResult()
             : base(StringComparer.OrdinalIgnoreCase)
         {
         }
 
-        [Conditional("NotNeededYet")]
-        [Diagnostics.CodeAnalysis.SuppressMessage("Performance", "CA1822:Mark members as static", Justification = "Retained in case we need the data later")]
-        public void AddBrowser(string browser)
-        {
-        }
+        public void AddBrowser(string browser) => _browsers.Add(browser);
 
         string? IHttpBrowserCapabilityFeature.this[string key] => TryGetValue(key, out var value) ? value : null;
+
+        bool IHttpBrowserCapabilityFeature.IsBrowser(string browserName)
+            => !string.IsNullOrEmpty(browserName) && _browsers.Contains(browserName);
     }
 
     private readonly struct RegexResult
@@ -724,5 +725,7 @@ private sealed class EmptyBrowserFeatures : IHttpBrowserCapabilityFeature
         public static IHttpBrowserCapabilityFeature Instance { get; } = new EmptyBrowserFeatures();
 
         public string? this[string key] => null;
+
+        public bool IsBrowser(string browserName) => false;
     }
 }

src/Microsoft.AspNetCore.SystemWebAdapters/Configuration/HttpCapabilitiesBase.cs

@@ -64,6 +64,8 @@ private IHttpBrowserCapabilityFeature Capability
 
     public bool IsMobileDevice => GetBoolean("isMobileDevice");
 
+    public bool IsBrowser(string browserName) => Capability.IsBrowser(browserName);
+
     private int GetInt(string key) => int.TryParse(Capability[key], NumberStyles.Integer, CultureInfo.InvariantCulture, out var result) ? result : throw new HttpUnhandledException($"Invalid string from browser capabilities '{key}'");
 
     private bool GetBoolean(string key) => bool.TryParse(Capability[key], out var result) && result;

src/Microsoft.AspNetCore.SystemWebAdapters/HttpBrowserCapabilitiesBase.cs

@@ -19,4 +19,6 @@ public class HttpBrowserCapabilitiesBase
     public virtual bool Crawler => throw new NotImplementedException();
 
     public virtual bool IsMobileDevice => throw new NotImplementedException();
+
+    public virtual bool IsBrowser(string browserName) => throw new NotImplementedException();
 }

src/Microsoft.AspNetCore.SystemWebAdapters/HttpBrowserCapabilitiesWrapper.cs

@@ -27,4 +27,6 @@ public HttpBrowserCapabilitiesWrapper(HttpBrowserCapabilities capabilities)
     public override bool Crawler => _capabilities.Crawler;
 
     public override bool IsMobileDevice => _capabilities.IsMobileDevice;
+
+    public override bool IsBrowser(string browserName) => _capabilities.IsBrowser(browserName);
 }

test/Microsoft.AspNetCore.SystemWebAdapters.Tests/Configuration/BrowserCapabilitiesFactoryTests.cs

@@ -225,4 +225,113 @@ public static IEnumerable<object[]> UserAgentTestData
             };
         }
     }
+
+    [Theory]
+    [MemberData(nameof(IsBrowserTestData))]
+    [System.Diagnostics.CodeAnalysis.SuppressMessage("Design", "CA1062:Validate arguments of public methods", Justification = "Used for tests")]
+    public void IsBrowserMatchesHierarchy(string userAgent, string[] expectedMatches, string[] expectedNonMatches)
+    {
+        // Arrange
+        var browserFactory = new BrowserCapabilitiesFactory();
+
+        // Act
+        var result = browserFactory.Parse(userAgent);
+
+        // Assert
+        foreach (var name in expectedMatches)
+        {
+            Assert.True(result.IsBrowser(name), $"Expected IsBrowser(\"{name}\") to be true for '{userAgent}'");
+        }
+
+        foreach (var name in expectedNonMatches)
+        {
+            Assert.False(result.IsBrowser(name), $"Expected IsBrowser(\"{name}\") to be false for '{userAgent}'");
+        }
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData(null)]
+    public void IsBrowserRejectsEmpty(string? browserName)
+    {
+        // Arrange
+        var browserFactory = new BrowserCapabilitiesFactory();
+
+        // Act
+        var result = browserFactory.Parse(
+            "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.5005.63 Safari/537.36");
+
+        // Assert
+        Assert.False(result.IsBrowser(browserName!));
+    }
+
+    [Fact]
+    public void IsBrowserCaseInsensitive()
+    {
+        // Arrange
+        var browserFactory = new BrowserCapabilitiesFactory();
+
+        // Act
+        var result = browserFactory.Parse(
+            "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:120.0) Gecko/20100101 Firefox/120.0");
+
+        // Assert
+        Assert.True(result.IsBrowser("firefox"));
+        Assert.True(result.IsBrowser("FIREFOX"));
+        Assert.True(result.IsBrowser("Firefox"));
+    }
+
+    public static IEnumerable<object[]> IsBrowserTestData
+    {
+        get
+        {
+            // Chrome desktop -> Default, Mozilla, WebKit, Chrome
+            yield return new object[]
+            {
+                "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.5005.63 Safari/537.36",
+                new[] { "Default", "Mozilla", "WebKit", "Chrome" },
+                new[] { "Firefox", "IE", "Safari", "Opera" },
+            };
+
+            // Firefox desktop -> Default, Mozilla, Firefox
+            yield return new object[]
+            {
+                "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:120.0) Gecko/20100101 Firefox/120.0",
+                new[] { "Default", "Mozilla", "Firefox" },
+                new[] { "Chrome", "WebKit", "IE", "Safari" },
+            };
+
+            // MSIE 10 -> Default, Mozilla, IE
+            yield return new object[]
+            {
+                "Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; Trident/6.0; MDDCJS)",
+                new[] { "Default", "Mozilla", "IE" },
+                new[] { "Chrome", "Firefox", "WebKit", "Safari" },
+            };
+
+            // iPhone CriOS (no "Chrome/" token in UA, Safari branch wins) -> Default, Mozilla, WebKit, Safari
+            yield return new object[]
+            {
+                "Mozilla/5.0 (iPhone; CPU iPhone OS 15_5 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) CriOS/102.0.5005.87 Mobile/15E148 Safari/604.1",
+                new[] { "Default", "Mozilla", "WebKit", "Safari" },
+                new[] { "Chrome", "Firefox", "IE" },
+            };
+
+            // Opera (handled before Mozilla, no Mozilla node added) -> Default, Opera
+            yield return new object[]
+            {
+                "Opera/9.80 (Windows NT 6.0) Presto/2.12.388 Version/12.14",
+                new[] { "Default", "Opera" },
+                new[] { "Mozilla", "Chrome", "Firefox", "IE" },
+            };
+
+            // Empty UA via Parse still runs DefaultProcess -> only Default is added
+            yield return new object[]
+            {
+                string.Empty,
+                new[] { "Default" },
+                new[] { "Mozilla", "Chrome", "Firefox", "IE" },
+            };
+        }
+    }
 }