Add cache headers to document URLs endpoint (#3766)

Author: Copilot

src/Swashbuckle.AspNetCore.SwaggerUI/SwaggerUIMiddleware.cs

@@ -159,14 +159,6 @@ private async Task RespondWithFile(
 
             await response.WriteAsync(text, Encoding.UTF8, cancellationToken);
         }
-
-        static string HashText(string text)
-        {
-            var buffer = Encoding.UTF8.GetBytes(text);
-            var hash = SHA1.HashData(buffer);
-
-            return Convert.ToBase64String(hash);
-        }
     }
 
     [UnconditionalSuppressMessage(
@@ -192,9 +184,20 @@ private async Task RespondWithDocumentUrls(HttpResponse response)
 
         json ??= JsonSerializer.Serialize(_options.ConfigObject, _jsonSerializerOptions);
 
+        var etag = HashText(json);
+        SetHeaders(response, _options, etag);
+
         await response.WriteAsync(json, Encoding.UTF8);
     }
 
+    private static string HashText(string text)
+    {
+        var buffer = Encoding.UTF8.GetBytes(text);
+        var hash = SHA1.HashData(buffer);
+
+        return Convert.ToBase64String(hash);
+    }
+
     [UnconditionalSuppressMessage(
         "AOT",
         "IL2026:RequiresUnreferencedCode",

test/Swashbuckle.AspNetCore.IntegrationTests/SwaggerUIIntegrationTests.cs

@@ -381,4 +381,35 @@ public async Task SwaggerUIMiddleware_Returns_ExpectedAssetContents_NotModified(
         using var stream = await cached.Content.ReadAsStreamAsync(cancellationToken);
         Assert.Equal(0, stream.Length);
     }
+
+    [Fact]
+    public async Task DocumentUrlsEndpoint_ReturnsJsonWithCacheHeaders()
+    {
+        // Arrange
+        var cancellationToken = TestContext.Current.CancellationToken;
+
+        var site = new TestSite(typeof(MultipleVersions.Startup), outputHelper);
+        using var client = site.BuildClient();
+
+        // Act
+        using var response = await client.GetAsync("/swagger/documentUrls", cancellationToken);
+
+        // Assert
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        Assert.Equal("application/javascript; charset=utf-8", response.Content.Headers.ContentType.ToString());
+
+        var content = await response.Content.ReadAsStringAsync(cancellationToken);
+        Assert.NotEmpty(content);
+        Assert.Contains("Version 1.0", content);
+        Assert.Contains("Version 2.0", content);
+
+        // Verify cache headers are set
+        Assert.NotNull(response.Headers.ETag);
+        Assert.True(response.Headers.ETag.IsWeak);
+        Assert.NotEmpty(response.Headers.ETag.Tag);
+
+        Assert.NotNull(response.Headers.CacheControl);
+        Assert.True(response.Headers.CacheControl.Private);
+        Assert.Equal(TimeSpan.FromDays(7), response.Headers.CacheControl.MaxAge);
+    }
 }