Http Client in Pascal

Here’s an idiomatic Pascal code example demonstrating the HTTP client concept:

program HTTPClient;

uses
  SysUtils, Classes, IdHTTP;

var
  HTTPClient: TIdHTTP;
  ResponseStream: TStringStream;
  ResponseText: TStringList;
  i: Integer;

begin
  HTTPClient := TIdHTTP.Create(nil);
  ResponseStream := TStringStream.Create('');
  ResponseText := TStringList.Create;
  try
    // Send an HTTP GET request
    try
      HTTPClient.Get('https://example.com', ResponseStream);
      WriteLn('Response status: ', HTTPClient.ResponseCode, ' ', HTTPClient.ResponseText);

      // Print the first 5 lines of the response body
      ResponseText.LoadFromStream(ResponseStream);
      for i := 0 to Min(4, ResponseText.Count - 1) do
        WriteLn(ResponseText[i]);
    except
      on E: Exception do
        WriteLn('Error: ', E.Message);
    end;
  finally
    HTTPClient.Free;
    ResponseStream.Free;
    ResponseText.Free;
  end;
end.

This Pascal program demonstrates how to create a simple HTTP client using the Indy components, which are commonly used for network operations in Pascal. Here’s an explanation of the code:

1. We use the IdHTTP unit, which provides HTTP client functionality.

2. We create three main objects:

   • HTTPClient: An instance of TIdHTTP for making HTTP requests.
   • ResponseStream: A TStringStream to store the response body.
   • ResponseText: A TStringList to easily process the response lines.

3. We use a try-finally block to ensure proper resource management.

4. Inside a try-except block, we send a GET request to ‘https://example.com’ using HTTPClient.Get().

5. We print the response status using HTTPClient.ResponseCode and HTTPClient.ResponseText.

6. We load the response body into ResponseText and print the first 5 lines (or fewer if the response is shorter).

7. If an exception occurs, we catch it and print the error message.

8. Finally, we free all created objects to prevent memory leaks.

To compile and run this program:

1. Make sure you have Free Pascal or Delphi installed.

2. Save the code in a file named HTTPClient.pas.

3. If using Free Pascal, compile and run the program with:

   fpc HTTPClient.pas
   ./HTTPClient

4. If using Delphi, you can compile and run directly from the IDE.

Note that this example uses Indy components, which might need to be installed separately depending on your Pascal development environment. The Indy components provide a cross-platform networking solution for Pascal and are widely used in the Pascal community for HTTP and other network operations.

This example demonstrates basic HTTP client functionality in Pascal, including sending a GET request, handling the response, and basic error management. It follows Pascal conventions and best practices, such as proper resource management and exception handling.