xml-lexer4delphi

Simple Delphi Lexer for XML documents

Features

• Very small and simple! (~400 sloc)
• Cross-platform
• Event driven API (SAX-like)
• Fault tolerant
• Handles CDATA
• Easy to extend and fine tune (state machine is exposed in Lexer instances)

Examples

Happy case

var LEvent: TEvent := procedure(AType: TType; AData: string)
begin
  // Write to console
end;
  
const xml = '<hello color="blue">'
          + '  <greeting>Hello, world!</greeting>'
          + '</hello>';

var LLexer := TLexer.Create(LEvent);
try
  LLexer.Write(xml);
finally
  LLexer.Free();
end;

/*
Console output:

{ type: 'open-tag', value: 'hello' }
{ type: 'attribute-name', value: 'color' }
{ type: 'attribute-value', value: 'blue' }
{ type: 'open-tag', value: 'greeting' }
{ type: 'data', value: 'Hello, world!' }
{ type: 'close-tag', value: 'greeting' }
{ type: 'close-tag', value: 'hello' }
*/

Chunked processing

const chunk1 = '<hello><greet'; // note this
const chunk2 = 'ing>Hello, world!</greeting></hello>';

LLexer := TLexer.Create(LEvent);
try
  LLexer.Write(chunk1);
  LLexer.Write(chunk2);
finally
  LLexer.Free();
end;

/*
Console output:

{ type: 'open-tag', value: 'hello' }
{ type: 'open-tag', value: 'greeting' }
{ type: 'data', value: 'Hello, world!' }
{ type: 'close-tag', value: 'greeting' }
{ type: 'close-tag', value: 'hello' }
*/

Document with errors

LLexer := TLexer.Create(LEvent);
try
  LLexer.Write('<<hello">hi</hello attr="value">');
finally
  LLexer.Free();
end;

/*
Console output (note the open-tag value):

{ type: 'open-tag', value: '<hello"' }
{ type: 'data', value: 'hi' }
{ type: 'close-tag', value: 'hello' }
*/

Update state machine to fix document errors

LLexer := TLexer.Create(LEvent);
try
  LLexer.StateMachine[TState.tagBegin].AddOrSetValue(TAction.lt, procedure(AChar: char)
  begin 
    //
  end);
  LLexer.StateMachine[TState.tagName].AddOrSetValue(TAction.error, procedure(AChar: char) 
  begin 
    //
  end);

  LLexer.Build(); //Builds the indexed state machine
  LLexer.Write('<<hello">hi</hello attr="value">');
finally
  LLexer.Free();
end;

/*
Console output (note the fixed open-tag value):

{ type: 'open-tag', value: 'hello' }
{ type: 'data', value: 'hi' }
{ type: 'close-tag', value: 'hello' }
*/

License

MIT