HTTP/2 Client

Overview

HTTP/2 is the binary successor to HTTP/1.1: a single multiplexed TLS connection carries any number of concurrent request / response streams, headers are compressed with HPACK, the server can push resources before the client asks for them, and stream priorities let the browser tell the server which response to deliver first. It is the wire protocol behind every modern browser, every public REST API at scale, and gRPC.

The sgcWebSockets TsgcHTTP2Client component is a native Delphi / C++ Builder / .NET HTTP/2 client implementation — no external libraries, no curl, no DLLs. It speaks RFC 9113 binary framing, HPACK header compression, ALPN protocol negotiation over TLS 1.2/1.3, and the full Get / Post / Put / Delete / Patch HTTP verb set, with both synchronous and asynchronous variants. Server push, stream priority and flow-control are exposed through events so your application can react in real time.

At a glance

Features

• RFC 9113 binary framing — full HTTP/2 wire protocol, no external dependencies.
• Multiplexed streams — many concurrent requests over a single TLS connection without head-of-line blocking.
• HPACK header compression — static and dynamic table per RFC 7541.
• ALPN over TLS 1.2 / 1.3 — protocol negotiation per RFC 7301, with OpenSSL and SChannel transports.
• Synchronous and asynchronous requests — Get, Post, Put, Delete, Patch plus their *Async counterparts; async returns immediately and fires OnHTTP2Response when the response arrives.
• Server push (PUSH_PROMISE) — receive pre-emptively pushed resources via OnHTTP2PushPromise; accept or cancel each push at the application level.
• Streaming response fragments — large bodies delivered chunk-by-chunk through OnHTTP2ResponseFragment; useful for downloads and SSE-style endpoints.
• Authentication helpers — Basic, Bearer (OAuth2 / JWT), Digest and custom-header schemes via Authentication.
• Stream prioritisation, flow control, settings — advertise window sizes, max concurrent streams, header table sizes; observe OnHTTP2GoAway and OnHTTP2RSTStream to react to peer-initiated tear-downs.
• Connection events — OnHTTP2Connect, OnHTTP2Disconnect, OnHTTP2Exception, OnHTTP2PendingRequests let you drive reconnect / retry logic.

Technical specification

Main properties

The principal published / public properties used to configure and drive the component. Consult the online help for the full list.

Main methods

The principal public methods exposed by the component.

Public events

The component exposes the following published events; consult the online help for full event-handler signatures.

Quick Start

Drop the component on a form, configure the properties below and activate it. The snippet that follows shows the typical TsgcHTTP2Client configuration sourced from the online help.

Delphi (VCL / FireMonkey)

oClient := TsgcHTTP2Client.Create(nil);
    oClient.OnHTTP2Response := OnHTTP2ResponseEvent;
    oClient.Get('https://www.google.com');

    procedure OnHTTP2ResponseEvent(Sender: TObject; const
    Connection: TsgcHTTP2ConnectionClient; const Request:
    TsgcHTTP2RequestProperty; const Response: TsgcHTTP2ResponseProperty);
    begin
    ShowMessage(Response.DataString);
    end;

C++ Builder

TsgcHTTP2Client *oClient = new TsgcHTTP2Client();
    oClient->OnHTTP2Response = OnHTTP2ResponseEvent;
    oClient->Get("https://www.google.com");

    void OnHTTP2ResponseEvent(TObject *Sender, const
    TsgcHTTP2ConnectionClient *Connection, const TsgcHTTP2RequestProperty *Request,
    	const TsgcHTTP2ResponseProperty *Response)
    {
    ShowMessage(Response->DataString);
    }

.NET (C#)

TsgcHTTP2Client oClient = new TsgcHTTP2Client();
    oClient.OnHTTP2Response += OnHTTP2ResponseEvent;
    oClient.Get("https://www.google.com");

    void OnHTTP2ResponseEvent(object Sender,
        TsgcHTTP2ConnectionClient Connection, TsgcHTTP2RequestProperty Request,
    	TsgcHTTP2ResponseProperty Response)
    {
    MessageBox.Show(Response.DataString);
    }

Common scenarios

The following scenarios are lifted verbatim from the online help. Each shows the configuration and method calls needed to drive the component through a specific real-world flow.

1 · TsgcHTTP2Client | HTTP/2 Headers

TsgcHTTP2Client allows customizing Headers sent to server when client connects

procedure OnHTTP2BeforeRequest(Sender: TObject; const Connection: TsgcHTTP2ConnectionClient; 
 var Headers: TStringList);
begin
Headers.Add('Client: sgcWebSockets');
end;

void OnHTTP2BeforeRequest(TObject *Sender, const TsgcHTTP2ConnectionClient *Connection, 
 ref TStringList *Headers)
{
Headers->Add("Client: sgcWebSockets");
}

void OnHTTP2BeforeRequest(object Sender, TsgcHTTP2ConnectionClient Connection, 
  ref string Headers)
{
Headers = Headers + Environment.NewLine + "Client: sgcWebSockets";
}

2 · TsgcHTTP2Client | HTTP/2 Partial Responses

Usually when you send an HTTP Request, server sends a response with the file requested, sometimes, instead of sending a single response, the server can send multiple responses like a stream, in these cases you can use OnHTTP2ResponseFragment event to capture these responses and show to user.

oClient := TsgcHTTP2Client.Create(nil);
oClient.OnHTTP2ResponseFragment := OnHTTP2ResponseFragmentEvent;
oClient.Get('https://http2.golang.org/clockstream');
...
procedure OnHTTP2ResponseFragmentEvent(Sender: TObject; const Connection: TsgcHTTP2ConnectionClient; 
 const Request: TsgcHTTP2RequestProperty; const Fragment: TsgcHTTP2ResponseFragmentProperty);
begin
ShowMessage(Fragment.DataString);
end;

TsgcHTTP2Client *oClient = new TsgcHTTP2Client();
oClient->OnHTTP2ResponseFragment = OnHTTP2ResponseFragmentEvent;
oClient->Get("https://http2.golang.org/clockstream");
...
void OnHTTP2ResponseFragmentEvent(TObject *Sender, const TsgcHTTP2ConnectionClient *Connection, 
 const TsgcHTTP2RequestProperty *Request, const TsgcHTTP2ResponseFragmentProperty *Fragment)
{
ShowMessage(Fragment->DataString);
}

TsgcHTTP2Client oClient = new TsgcHTTP2Client();
oClient.OnHTTP2ResponseFragment += OnHTTP2ResponseFragmentEvent;
oClient.Get("https://http2.golang.org/clockstream");
...
void OnHTTP2ResponseFragmentEvent(object Sender, TsgcHTTP2ConnectionClient Connection, 
  TsgcHTTP2RequestProperty Request, TsgcHTTP2ResponseFragmentProperty Fragment)
{
MessageBox.Show(Fragment.DataString);
}

3 · Basic Authentication

If server returns a header requesting Basic Authentication, set OnHTTP2Authorization the username and password.

oClient := TsgcHTTP2Client.Create(nil);
oClient.OnHTTP2Authorization := OnHTTP2AuthorizationEvent;
...
procedure OnHTTP2AuthorizationEvent(Sender: TObject; const Connection: TsgcHTTP2ConnectionClient; const AuthType, AuthData: string; var UserName, Password, aToken: string; var Handled: Boolean);
begin
if AuthType = 'Basic' then
begin
UserName := 'user';
	Password := 'secret';
end;
end;

TsgcHTTP2Client *oClient = new TsgcHTTP2Client();
oClient->OnHTTP2Authorization = OnHTTP2AuthorizationEvent;
...
void OnHTTP2AuthorizationEvent(TObject *Sender, const TsgcHTTP2ConnectionClient *Connection, const string AuthType, const string AuthData, string &UserName, string &Password, string &aToken, bool &Handled)
{
if (AuthType == "Basic")
{
UserName = "user";
	Password = "secret";
}
}

TsgcHTTP2Client oClient = new TsgcHTTP2Client();
oClient.OnHTTP2Authorization += OnHTTP2AuthorizationEvent;
...
void OnHTTP2AuthorizationEvent(object Sender, TsgcHTTP2ConnectionClient Connection, string AuthType, string AuthData, ref string UserName, ref string Password, ref string aToken, ref bool Handled)
{
if (AuthType == "Basic")
{
UserName = "user";
	Password = "secret";
}
}

4 · Asynchronous Mode

Get the following url: https://www.google.com and be notified when client receives the full response. After you call GETASYNC method, the process continues and OnHTTP2Response event is called when response is received.

oClient := TsgcHTTP2Client.Create(nil);
oClient.OnHTTP2Response := OnHTTP2ResponseEvent;
oClient.GetAsync('https://www.gooogle.com');
procedure OnHTTP2ResponseEvent(Sender: TObject; const Connection: TsgcHTTP2ConnectionClient; 
 const Request: TsgcHTTP2RequestProperty; const Response: TsgcHTTP2ResponseProperty);
begin
ShowMessage(Response.Headers.Text + #13#10 + Response.DataString);
end;

TsgcHTTP2Client *oClient = new TsgcHTTP2Client();
oClient->OnHTTP2Response = OnHTTP2ResponseEvent;
oClient->GetAsync("https://www.gooogle.com");
void OnHTTP2ResponseEvent(TObject *Sender, const TsgcHTTP2ConnectionClient *Connection, 
 const TsgcHTTP2RequestProperty *Request, const TsgcHTTP2ResponseProperty *Response)
{
ShowMessage(Response->Headers->Text + #13#10 + Response->DataString);
}

TsgcHTTP2Client oClient = new TsgcHTTP2Client();
oClient.OnHTTP2Response += OnHTTP2ResponseEvent;
oClient.GetAsync("https://www.gooogle.com");
void OnHTTP2ResponseEvent(object Sender, TsgcHTTP2ConnectionClient Connection, 
  TsgcHTTP2RequestProperty Request, TsgcHTTP2ResponseProperty Response)
{
MessageBox.Show(Response.Headers.Text + #13#10 + Response.DataString);
}

5 · HeartBeat

HeartBeat property allows you to send a Ping every X seconds to maintain connection alive. Some servers, close TCP connections if there is no data exchanged between peers. HeartBeat solves this problem, sending a ping every a specific interval. Usually this is enough to maintain a connection active.

oClient := TsgcHTTP2Client.Create(nil);
oClient.HeartBeat.Interval := 30;
oClient.HeartBeat.Enabled := true;
oClient.Active := true;

oClient = new TsgcHTTP2Client();
oClient->HeartBeat->Interval = 30;
oClient->HeartBeat->Enabled = true;
oClient->Active = true;

oClient = new TsgcHTTP2Client();
oClient.HeartBeat.Interval = 30;
oClient.HeartBeat.Enabled = true;
oClient.Active = true;

6 · Large File Downloads

When downloading large files (hundreds of MB or more), set HTTP2Options.ReadTimeout to 0 (no timeout) to ensure the transfer completes without being interrupted by the default 60-second timeout:

oClient := TsgcHTTP2Client.Create(nil);
oClient.HTTP2Options.ReadTimeout := 0; // no timeout for large files
oClient.Get('https://server/largefile', oStream);

TsgcHTTP2Client *oClient = new TsgcHTTP2Client();
oClient->HTTP2Options->ReadTimeout = 0; // no timeout for large files
oClient->Get("https://server/largefile", oStream);

TsgcHTTP2Client oClient = new TsgcHTTP2Client();
oClient.HTTP2Options.ReadTimeout = 0; // no timeout for large files
oClient.Get("https://server/largefile", oStream);

Sources used to build this document

Every external claim links back to a primary source. The online-help references decode the canonical deep-link the company maintains for this component.