Url Parsing in Pascal

Here’s the translation of the Go URL parsing example to Pascal, formatted in Markdown suitable for Hugo:

program URLParsing;

uses
  SysUtils, Classes, StrUtils;

type
  TURL = record
    Scheme: string;
    User: string;
    Password: string;
    Host: string;
    Port: string;
    Path: string;
    Query: string;
    Fragment: string;
  end;

function ParseURL(const URL: string): TURL;
var
  SchemeDelimiter, UserInfoDelimiter, HostPortDelimiter, PathDelimiter, 
  QueryDelimiter, FragmentDelimiter: Integer;
begin
  // Initialize result
  Result := Default(TURL);

  // Find scheme
  SchemeDelimiter := Pos('://', URL);
  if SchemeDelimiter > 0 then
  begin
    Result.Scheme := Copy(URL, 1, SchemeDelimiter - 1);
    SchemeDelimiter := SchemeDelimiter + 3;
  end
  else
    SchemeDelimiter := 1;

  // Find user info
  UserInfoDelimiter := PosEx('@', URL, SchemeDelimiter);
  if UserInfoDelimiter > 0 then
  begin
    Result.User := Copy(URL, SchemeDelimiter, UserInfoDelimiter - SchemeDelimiter);
    HostPortDelimiter := UserInfoDelimiter + 1;
    
    // Split user and password
    UserInfoDelimiter := Pos(':', Result.User);
    if UserInfoDelimiter > 0 then
    begin
      Result.Password := Copy(Result.User, UserInfoDelimiter + 1, Length(Result.User));
      Result.User := Copy(Result.User, 1, UserInfoDelimiter - 1);
    end;
  end
  else
    HostPortDelimiter := SchemeDelimiter;

  // Find path
  PathDelimiter := PosEx('/', URL, HostPortDelimiter);
  if PathDelimiter = 0 then
    PathDelimiter := Length(URL) + 1;

  // Extract host and port
  Result.Host := Copy(URL, HostPortDelimiter, PathDelimiter - HostPortDelimiter);
  HostPortDelimiter := Pos(':', Result.Host);
  if HostPortDelimiter > 0 then
  begin
    Result.Port := Copy(Result.Host, HostPortDelimiter + 1, Length(Result.Host));
    Result.Host := Copy(Result.Host, 1, HostPortDelimiter - 1);
  end;

  // Find query
  QueryDelimiter := PosEx('?', URL, PathDelimiter);
  if QueryDelimiter = 0 then
    QueryDelimiter := Length(URL) + 1;

  // Extract path
  Result.Path := Copy(URL, PathDelimiter, QueryDelimiter - PathDelimiter);

  // Find fragment
  FragmentDelimiter := PosEx('#', URL, QueryDelimiter);
  if FragmentDelimiter = 0 then
    FragmentDelimiter := Length(URL) + 1;

  // Extract query
  Result.Query := Copy(URL, QueryDelimiter + 1, FragmentDelimiter - QueryDelimiter - 1);

  // Extract fragment
  Result.Fragment := Copy(URL, FragmentDelimiter + 1, Length(URL));
end;

var
  URL: string;
  ParsedURL: TURL;
begin
  // We'll parse this example URL, which includes a
  // scheme, authentication info, host, port, path,
  // query params, and query fragment.
  URL := 'postgres://user:pass@host.com:5432/path?k=v#f';

  // Parse the URL
  ParsedURL := ParseURL(URL);

  // Output the parsed components
  WriteLn('Scheme: ', ParsedURL.Scheme);
  WriteLn('User: ', ParsedURL.User);
  WriteLn('Password: ', ParsedURL.Password);
  WriteLn('Host: ', ParsedURL.Host);
  WriteLn('Port: ', ParsedURL.Port);
  WriteLn('Path: ', ParsedURL.Path);
  WriteLn('Query: ', ParsedURL.Query);
  WriteLn('Fragment: ', ParsedURL.Fragment);
end.

This Pascal program demonstrates URL parsing. Here’s a breakdown of what it does:

We define a TURL record to hold the different components of a URL.
The ParseURL function takes a URL string and breaks it down into its components, returning a TURL record.
In the main program, we use an example URL that includes various components: scheme, authentication info, host, port, path, query params, and fragment.
We call ParseURL to parse our example URL.
Finally, we print out each component of the parsed URL.

To run this program, you would typically save it as a .pas file (e.g., urlparsing.pas) and compile it with a Pascal compiler like Free Pascal:

$ fpc urlparsing.pas
$ ./urlparsing

The output would show each component of the parsed URL:

Scheme: postgres
User: user
Password: pass
Host: host.com
Port: 5432
Path: /path
Query: k=v
Fragment: f

This example demonstrates how to handle URL parsing in Pascal. While Pascal doesn’t have built-in URL parsing libraries like some modern languages, we can implement the functionality ourselves using string manipulation techniques.

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Url Parsing in Pascal