THE PROBLEM
There is a web page with students' schedules: https://education.khai.edu/union/schedule/.
When I make a request by the link I get "empty" HTML. It means that responded HTML contains JS-scripts only, no schedule HTML:
<!DOCTYPE html>
<html lang="ru-UA">
<head>
...
<!--Blazor:{"sequence":1,"type":"server","descriptor":"CfDJ8MBhIHG65FtKlX56pWtbUtQZ6T285HAgOYeCRtbbe9JO4U4cZsYQJ9xvkrUrO01rnP\u002BgDnPMCl0MnI0E/fW58mYoqDZ3J1ztRz/DKm9\u002BABDrmL5ArBFfTFdeO82HHavNnd1E10j7gHBU9uqKmOW2otP1y5s/a\u002BnMT/P2jvdetcCcDQvdfLnX2/w747D4dYNA1MuoeBRlst63xJlks\u002BYeAfhhNMi1s961JEi777JANAEi\u002B9g\u002BNf7aS9sLn\u002BbJZ4m0IBrUnCcHbu3idntWrD/GDpgDVCwhrIhUIPhs8ITgqZHJdQprUnffKWflcMbJ6YyyWBBABTi2eOX/VMHvtFWxT8ABDgmXbyqC3vTfRe6VlwN5ibDYH/UKDkULoJuX\u002Bw\u002BQB2e3sSP1OddN/ud8pWe5\u002BuCo3\u002BkQ9OG6x2GLMXJHWgah"}-->
</head>
<body class="x-background">
<!--Blazor:{"sequence":0,"type":"server","descriptor":"CfDJ8MBhIHG65FtKlX56pWtbUtTdcyRUeUr\u002BhT344Mo3B4Gc0Gg3YwX1FY0c9owxv7oR1MDnLFR1BTJFjhuwYAjnROc3JT8UhSCkRbOdLVMuG0iwpNvwHNc47\u002BrguaHCTkDZKvZ9GKc0Jp\u002BCX0hcssqhCnp6eka\u002BG9Q7XF2B4ARhWnuJDKvUT\u002BbuWra063kFqG0Ixs4eWc4KrPRNS1KnTVu3QZrmx8r9dx6iyQXHjN/YgTqJhcv9LoQqWTfncbhBLwGm9l0BCTBLn3fGdJsOB6ES0lRwvVygmY7DA/2OGzhY7jGppr6UNaUXhdgo4xZDi3FkZgY3OL5xGS1p0bkc14UU9TM="}-->
<script async src="/ui/app.js?v=3hNtGnhO8Vl6rh70OirKX4BnS6mxiiS5k9p3XAvofZA"></script>
<script src="_framework/blazor.server.js" autostart="false"></script>
<script src="_content/Blazor-Analytics/blazor-analytics.js"></script>
<script>
async function connectionDown() {
console.log("Blazor disconnected");
location.reload();
}
function connectionUp() {
console.log("Blazor connected");
}
window.Blazor.start({
reconnectionOptions: {
maxRetries: 10,
retryIntervalMilliseconds: 500,
},
reconnectionHandler: {
onConnectionDown: e => connectionDown(e),
onConnectionUp: e => connectionUp(e)
}
});
</script>
</body>
</html>
When I open the web page from a browser, the website starts SignalR-stream and load the needed schedule HTML.
How I can get a similar result from .NET?
SOME SUCCESSES
I found that the site uses the blazor.server.js script for manipulations with the SignalR-stream. There is its source code: click.
CONNECTION
I tried to rewrite the JS connection code to C# and I had success. JS:
...
async function initializeConnection(options: CircuitStartOptions, logger: Logger, circuit: CircuitDescriptor): Promise<HubConnection> {
const hubProtocol = new MessagePackHubProtocol();
(hubProtocol as unknown as { name: string }).name = 'blazorpack';
const connectionBuilder = new HubConnectionBuilder()
.withUrl('_blazor')
.withHubProtocol(hubProtocol);
options.configureSignalR(connectionBuilder);
const connection = connectionBuilder.build();
...
.NET - BlazorPackHubProtocol.cs (I couldn't find any other way to change the protocol name, so I created a shell for MessagePackHubProtocol):
using System;
using System.Buffers;
using Microsoft.AspNetCore.Connections;
using Microsoft.AspNetCore.SignalR;
using Microsoft.AspNetCore.SignalR.Protocol;
using Microsoft.Extensions.Options;
namespace KuzCode.SignalR.Protocols.BlazorPack
{
public class BlazorPackHubProtocol : IHubProtocol
{
private MessagePackHubProtocol _protocol;
public string Name => "blazorpack"; // if the protocol has another name, connection fails
public int Version => _protocol.Version;
public TransferFormat TransferFormat => _protocol.TransferFormat;
public BlazorPackHubProtocol(IOptions<MessagePackHubProtocolOptions> options)
{
_protocol = new(options);
}
public BlazorPackHubProtocol() : this(Options.Create(new MessagePackHubProtocolOptions())) { }
public bool IsVersionSupported(int version) => _protocol.IsVersionSupported(version);
public bool TryParseMessage(ref ReadOnlySequence<byte> input, IInvocationBinder binder, out HubMessage message)
=> _protocol.TryParseMessage(ref input, binder, out message);
public void WriteMessage(HubMessage message, IBufferWriter<byte> output)
=> _protocol.WriteMessage(message, output);
public ReadOnlyMemory<byte> GetMessageBytes(HubMessage message) => _protocol.GetMessageBytes(message);
}
}
.NET - BlazorPackProtocolDependencyInjectionExtensions.cs (for easy use in connection builder):
using KuzCode.SignalR.Protocols.BlazorPack;
using Microsoft.AspNetCore.SignalR;
using Microsoft.AspNetCore.SignalR.Protocol;
using Microsoft.Extensions.DependencyInjection.Extensions;
using System;
namespace Microsoft.Extensions.DependencyInjection
{
public static class BlazorPackProtocolDependencyInjectionExtensions
{
public static TBuilder AddBlazorPackProtocol<TBuilder>(this TBuilder builder) where TBuilder : ISignalRBuilder
=> builder.AddBlazorPackProtocol(_ => { });
public static TBuilder AddBlazorPackProtocol<TBuilder>(this TBuilder builder, Action<MessagePackHubProtocolOptions> configure)
where TBuilder : ISignalRBuilder
{
builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IHubProtocol, BlazorPackHubProtocol>());
builder.Services.Configure(configure);
return builder;
}
}
}
.NET - KhaiClient.cs (main class with connection):
using Microsoft.AspNetCore.Http.Connections;
using Microsoft.AspNetCore.SignalR.Client;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using System;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace KuzCode.KhaiApiClient
{
public class KhaiClient
{
private HubConnection _hubConnection;
public KhaiClient()
{
_hubConnection = new HubConnectionBuilder()
.WithUrl("wss://education.khai.edu/_blazor", configuration =>
{
configuration.SkipNegotiation = false;
configuration.Transports = HttpTransportType.WebSockets;
})
.AddBlazorPackProtocol()
.ConfigureLogging(logging =>
{
logging.AddConsole();
logging.SetMinimumLevel(LogLevel.Debug);
})
.Build();
}
public async Task ConnectAsync() => await _hubConnection.StartAsync();
public async Task DisconnectAsync() => await _hubConnection.StopAsync();
}
}
.NET - Program.cs (for testing):
var khaiClient = new KhaiClient();
khaiClient.ConnectAsync().Wait();
while (true) {}
It's working! I had the next log:
...
info: Microsoft.AspNetCore.Http.Connections.Client.Internal.WebSocketsTransport[1]
Starting transport. Transfer mode: Binary. Url: 'wss://education.khai.edu/_blazor?id=_f5aporohBDfopQF-CExsA'.
...
info: Microsoft.AspNetCore.SignalR.Client.HubConnection[24]
Using HubProtocol 'blazorpack v1'.
dbug: Microsoft.AspNetCore.SignalR.Client.HubConnection[28]
Sending Hub Handshake.
...
dbug: Microsoft.AspNetCore.SignalR.Client.HubConnection[47]
Receive loop starting.
info: Microsoft.AspNetCore.SignalR.Client.HubConnection[44]
HubConnection started.
WHAT NEXT?
Now I tried to recreate some requests but had no success.
Select another group request (I selected group 613п):
First response:
Source code: https://github.com/iiKuzmychov/KhaiApiClient.
Update:
I found a hub implementation I want, I can copy-paste code, but I don`t know how to initialize it.