I am trying to use ISession in a .net Blazor web app server side only. My problem is that the ISession in very unstable as it disappear and comeback when it feels like it.

First in the program.cs i added the session like so :

builder.Services.AddDistributedMemoryCache();
builder.Services.AddSession(options =>
{
    options.IdleTimeout = TimeSpan.FromMinutes(30); // Set timeout
    options.Cookie.HttpOnly = true;
    options.Cookie.IsEssential = true;
});

builder.Services.AddHttpContextAccessor();

And right after the build :

var app = builder.Build();

I added the session to it

app.UseSession();

Now here the default home page that comes in an empty project and i added a button to demonstrate with console write to see what is happening :

@page "/"
@page "/Home"
@inject IHttpContextAccessor hca

<PageTitle>Home</PageTitle>

<h1>Hello, world!</h1>

Welcome to your new app.

<button @onclick="Click">click</button>

@code{   
    protected override void OnInitialized()
    {
        Console.WriteLine($@"Home.Initialized - SessionId = {hca.HttpContext.Session.Id}");
        Console.WriteLine($@"Home.Initialized - Keys.Count = {hca.HttpContext.Session.Keys.ToList().Count}");
     
        hca.HttpContext.Session.SetString("test", "tesatassad");
    }

    private void Click()
    {
        hca.HttpContext.Session.SetString("test1", "tesatassad");
        hca.HttpContext.Session.SetString("test2", "tesatassad");

        Console.WriteLine($@"Home.Click - SessionId = {hca.HttpContext.Session.Id}");
        Console.WriteLine($@"Home.Click - Keys.Count = {hca.HttpContext.Session.Keys.ToList().Count}");    
    }    
}

The whole idea is to log the session id and the amount of keys in it on initialized and when i click the button. Now just running the page i have the first issue. The pages always trigger OnInitialized twice.

I made the log purposely before the new key is created to see it so the log shows that the second trigger is valid (which make sense)

Home.Initialized - SessionId = 3c3f9a90-7273-f76f-0368-843e3f01f374
Home.Initialized - Keys.Count = 0
Home.Initialized - SessionId = 3c3f9a90-7273-f76f-0368-843e3f01f374
Home.Initialized - Keys.Count = 1

Now lets click the button. The button set 2 new key and display the count after and check the full log again

Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 0
Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 1
Home.Click - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Click - Keys.Count = 3

Now this make sense, i have my double load and i have the log after the set in the button showing addition of 2 keys for a total of 3.

Now let’s refresh the page with F5 and check the log :

Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 0
Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 1
Home.Click - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Click - Keys.Count = 3
Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 1
Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 3

Again you see the double log but the first is wrong. It lost all the key but the session id is still the same. What is this coming from ? how can you tell when to try to read session only on the second OnInitialized ?

Now this is even weirder, Let’s click F5 again to refresh the page once more

Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 0
Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 1
Home.Click - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Click - Keys.Count = 3
Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 1
Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 3
Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 3
Home.Initialized - SessionId = 846bc865-7b0f-de46-c4d0-f015eb1b4389
Home.Initialized - Keys.Count = 3

Now the second F5 the session keys exist in both call of OnInitialized. From now on it will work for any navigation combination you want and the session is always up to date.

My major problem is that i need to load data in the page in the OnInitialized but it need to use values stored server side in the ISession. Being so unstable there must be something i am missing