SupplyParameterFromSession support for Blazor

[dariatiurina]

SupplyParameterFromSession support for Blazor

Summary

Adds a new [SupplyParameterFromSession] attribute that allows Blazor SSR components to declaratively read and write HTTP session data, following the same pattern as [SupplyParameterFromQuery] and [SupplyParameterFromForm].

Motivation

Currently, Blazor SSR lacks a simple, declarative way to access session data. Developers who want to persist user-specific data across HTTP requests (like shopping cart contents or multi-step form state) must:

• Inject IHttpContextAccessor and manually interact with ISession
• Handle serialization/deserialization manually
• Write boilerplate code for each session value

This creates inconsistent patterns across applications and increases the likelihood of errors.

Changes

• SupplyParameterFromSessionAttribute (Components.Web) — A new public attribute inheriting from CascadingParameterAttributeBase with an optional Name property to specify the session key (defaults to the property name). SingleDelivery is false, so values are re-supplied on each render.
• SessionCascadingValueSupplier (Components.Endpoints) — Internal scoped service that:
  • Reads values from ISession via ISessionFeature and deserializes them using System.Text.Json (with JsonSerializerDefaults.Web)
  • Registers a Response.OnStarting callback to persist all tracked property values back to the session before the response is sent
  • Uses case-insensitive session keys (lowercased via ToLowerInvariant())
  • Caches PropertyGetter instances per component type/property pair using a ConcurrentDictionary
  • Logs warnings (without throwing) when serialization or deserialization fails
  • Enforces unique session keys — throws InvalidOperationException if multiple components register the same key
• SessionSubscription (inner class of SessionCascadingValueSupplier) — On the first GetCurrentValue() call, reads from the session; on subsequent calls, returns the current component property value (enabling two-way binding). Removes the value callback on Dispose.
• DI registration — AddRazorComponents() now registers SessionCascadingValueSupplier as a scoped service and wires it as a cascading value supplier for SupplyParameterFromSessionAttribute.
• EndpointHtmlRenderer — Calls SessionCascadingValueSupplier.SetRequestContext(httpContext) during standard service initialization.
• Public API surface — Added to PublicAPI.Unshipped.txt: SupplyParameterFromSessionAttribute class, its constructor, and Name property.

Usage

Developers must configure session middleware in their application:

builder.Services.AddDistributedMemoryCache();
builder.Services.AddSession(options =>
{
    options.Cookie.HttpOnly = true;
    options.Cookie.IsEssential = true;
});

app.UseSession();

Then use the attribute on component properties:

@code {
    [SupplyParameterFromSession]
    public string? Email { get; set; }

    [SupplyParameterFromSession(Name = "user_email")]
    public string? UserEmail { get; set; }

    [SupplyParameterFromSession]
    public ShoppingCart? Cart { get; set; }
}

Values are read from the session on first render and automatically persisted back when the response starts.

Testing

• Unit tests (SessionCascadingValueSupplierTest) — 10 tests covering: callback registration, duplicate key rejection, value persistence to session, null value removal, multiple keys, exception resilience (both callback and serialization errors), key lowercasing, no-op when session is unavailable, callback deletion, and OnStarting integration.
• Unit tests (SessionSubscriptionTest) — 8 tests covering: null when HttpContext not set, null for missing keys, value retrieval, key lowercasing, enum deserialization, null on deserialization failure, component-value passthrough on subsequent calls, and full CreateSubscription round-trip.
• E2E tests (SupplyParameterFromSessionAttributeTest) — 5 Selenium tests covering: reading from session, null for missing keys, redirect persistence, complex type serialization, and cross-navigation persistence.
• Test infrastructure — Refactored RazorComponentEndpointsNoInteractivityStartup to separate session middleware configuration (--UseSession) from TempData session storage (--UseSessionStorageTempDataProvider), added Microsoft.AspNetCore.Session reference to test server project, and added two test Razor components.

Fixes #64422

[Copilot]

Pull request overview

Adds [SupplyParameterFromSession] support for Blazor SSR by introducing a session-backed cascading value supplier and request-scoped session value mapper, plus test assets and E2E/unit tests to validate behavior.

Changes:

• Introduces SupplyParameterFromSessionAttribute, session value provider, and ISessionValueMapper/SessionValueMapper.
• Wires session value mapper into EndpointHtmlRenderer request initialization and registers services via AddRazorComponents().
• Adds test server pages and E2E/unit tests for reading/writing session-backed parameters across navigations.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
src/Components/test/testassets/Components.TestServer/RazorComponents/Pages/SupplyParameterFromSessionNavigationComponent.razor	Adds navigation test page used to validate session persistence across redirects.
src/Components/test/testassets/Components.TestServer/RazorComponents/Pages/SupplyParameterFromSessionComponent.razor	Adds SSR test page exercising primitive, named-key, null, and complex session values.
src/Components/test/testassets/Components.TestServer/RazorComponentEndpointsNoInteractivityStartup.cs	Adds conditional session service/middleware setup for the tests.
src/Components/test/testassets/Components.TestServer/Components.TestServer.csproj	Adds Session assembly reference for the test server.
src/Components/test/E2ETest/Tests/SupplyParameterFromSessionAttributeTest.cs	Adds E2E coverage for session parameter read/write and navigation persistence.
src/Components/Endpoints/test/SessionValueMapperTest.cs	Adds unit tests for SessionValueMapper serialization, persistence, and error handling.
src/Components/Endpoints/src/Session/SupplyParameterFromSessionValueProvider.cs	Implements the cascading value supplier that binds component properties to session keys.
src/Components/Endpoints/src/Session/SupplyParameterFromSessionServiceCollectionExtensions.cs	Adds DI extension to register the session value supplier.
src/Components/Endpoints/src/Session/SessionValueMapper.cs	Implements session read/write with JSON serialization and response on-start persistence.
src/Components/Endpoints/src/Session/ISessionValueMapper.cs	Adds public contract for session value mapping and persistence callbacks.
src/Components/Endpoints/src/Rendering/EndpointHtmlRenderer.cs	Initializes the session mapper with the current request HttpContext.
src/Components/Endpoints/src/Rendering/EndpointHtmlRenderer.Prerendering.cs	Widens accessibility of overrides (likely to enable cross-assembly usage).
src/Components/Endpoints/src/Rendering/EndpointComponentState.cs	Widens accessibility of GetComponentKey override.
src/Components/Endpoints/src/PublicAPI.Unshipped.txt	Declares newly added public APIs for the Endpoints assembly.
src/Components/Endpoints/src/DependencyInjection/RazorComponentsServiceCollectionExtensions.cs	Registers ISessionValueMapper and session value provider in AddRazorComponents().
src/Components/Components/src/SupplyParameterFromSessionAttribute.cs	Adds the public attribute for supplying values from session.
src/Components/Components/src/PublicAPI.Unshipped.txt	Declares newly added public APIs for the Components assembly.
src/Components/Components/src/Microsoft.AspNetCore.Components.csproj	Adds internals visibility to allow Endpoints to consume internal attribute members.