Remove Indy dependency and replace connectivity check with System.Net.HttpClient

[jimmckeeth]

Overview

The training uses Indy (IdTCPClient) solely to check internet connectivity by opening a TCP connection to www.embarcadero.com:80. Indy is a legacy networking library; Delphi has included the modern System.Net.HttpClient stack since XE8. The Indy dependency should be removed and replaced with a native connectivity check.

Background

Current Pattern

uses IdComponent, IdTCPClient;

function IsConnected: Boolean;
var
  TCP: TIdTCPClient;
begin
  TCP := TIdTCPClient.Create(nil);
  try
    TCP.Host := 'www.embarcadero.com';
    TCP.Port := 80;
    TCP.Connect;
    Result := TCP.Connected;
  except
    Result := False;
  finally
    TCP.Free;
  end;
end;

This is wrapped in a TTask.Future<Boolean> for async execution.

Problems

• Indy is installed with Delphi but is increasingly unmaintained and flagged by static analysis tools.
• TCP port 80 connections are often blocked by corporate firewalls; HTTP/HTTPS is more reliable.
• System.Net.HttpClient (already used elsewhere in the project for the Maps API) achieves the same goal with a HEAD request and no extra dependency.

Replacement Strategy

Use TNetHTTPClient with a HEAD request to a reliable endpoint (e.g., https://www.google.com or https://connectivitycheck.gstatic.com/generate_204). The async wrapper via TTask can remain unchanged.

Files Affected

lab-src/Lab*/forms/formMain.pas  (connectivity check call site)
lab-src/Lab*/units/  (wherever Indy units are referenced)
All FieldLogger.dproj files (remove Indy package references if explicit)

Steps to Address

1. Locate all uses clauses referencing IdComponent, IdTCPClient, IdBaseComponent and remove them.
2. Replace the connectivity check function body with:

   uses System.Net.HttpClient;
   
   function IsConnected: Boolean;
   var
     HTTP: THTTPClient;
     Resp: IHTTPResponse;
   begin
     HTTP := THTTPClient.Create;
     try
       try
         Resp := HTTP.Head('https://connectivitycheck.gstatic.com/generate_204');
         Result := Resp.StatusCode < 500;
       except
         Result := False;
       end;
     finally
       HTTP.Free;
     end;
   end;

3. Wrap the call in TTask.Run (or keep the existing TTask.Future<Boolean> wrapper) for async execution.
4. Verify no other Indy units (IdSSLOpenSSL, etc.) remain in the codebase.
5. Remove explicit Indy package references from .dproj files if present.

Test Plan

• Code compiles without any Id*.pas unit in the uses clause.
• On Android emulator with Wi-Fi enabled: connectivity check returns True and the Maps API image loads.
• On Android emulator with Wi-Fi disabled (airplane mode): connectivity check returns False and the app shows the "no internet" message gracefully.
• Same two scenarios verified on iOS simulator.
• No Indy-related packages appear in the project's package list.
• Connectivity check completes within 5 seconds (no blocking the UI thread).