Validation of invalid XML declarations

[bendrissou]

Description

The parser accepts incorrect XML declarations as valid, without raising an error. This is despite enabling the validator option "-v".

Input

<?xml version="1.0" var ?>  <a/>

There is an unassigned attribute var, which I expected to raise an error. The input is saved in a file named example.xml.

Code

./src/cli/cli.js -v example.xml

Output

{ '?xml': { '@_version': 1 }, a: '' }

My question is: Why the XML validator doesn't throw an error?
Please note that xmllint rejects the input example as invalid.

[bendrissou]

Hi @amitguptagwl

Can you please confirm if this is a valid issue?

[amitguptagwl]

Sorry I missed your original message. FXP validator checks for syntax error only, any other issue like scheme related, or the one you're highlighted are not covered.
I'm not sure about this issue but you can check it by disallowing boolean attributes. I guess it is by default is set to allow.

[bendrissou]

I believe this is a syntax error. The expression does not conform to the XML syntax, or the XML grammar. So I assume this is unintended behaviour?

[amitguptagwl]

Have you checked by disallowing boolean attributes?

[bendrissou]

Hi @amitguptagwl

As shown above, I have enabled the -v option.
I assume the -v flag should force the validation of the input before parsing. Is that correct?

[amitguptagwl]

Please try it from the code. I'm not sure if the CLI is updated with all the options. This docs can help you.

const {XMLValidator} = require("fast-xml-parser");
const result = XMLValidator.validate(xmlData, {
    allowBooleanAttributes: true
});

[bendrissou]

Hi @amitguptagwl

I have tried the code above:

#!/usr/bin/env node
const {XMLValidator} = require("../fxp");
const result = XMLValidator.validate('<?xml version="1.0" var ?>  <a/>', {
    allowBooleanAttributes: true
});
console.log(result);

Output is:

true

The XML input was accepted, despite having the unassigned attribute var.

[amitguptagwl]

As I remember, The validator has no check for xml description tag. same with v5

[Kristinita]

Type: Additional information ➕

1. Summary

fast-xml-parser validator doesn’t check non-valid XML declarations. It would be nice if fast-xml-parser will check declarations as xmllint.

2. Non-valid version in the declaration

KiraXMLNonValidDeclaration.xml:

<?xml version="kira-goddess" encoding="UTF-8"?>
	<kira>Goddess!</kira>

xmllint output:

D:\SashaDebugging\KiraFastXMLParser>xmllint --noout --pedantic KiraXMLNonValidDeclaration.xml
KiraXMLNonValidDeclaration.xml:1: parser error : String not closed expecting " or '
<?xml version="kira-goddess" encoding="UTF-8"?>
               ^
KiraXMLNonValidDeclaration.xml:1: parser error : Malformed declaration expecting version
<?xml version="kira-goddess" encoding="UTF-8"?>
               ^
KiraXMLNonValidDeclaration.xml:1: parser error : Blank needed here
<?xml version="kira-goddess" encoding="UTF-8"?>
               ^
KiraXMLNonValidDeclaration.xml:1: parser error : parsing XML declaration: '?>' expected
<?xml version="kira-goddess" encoding="UTF-8"?>
               ^

fast-xml-parser output:

D:\SashaDebugging\KiraFastXMLParser>fxparser -V KiraXMLNonValidDeclaration.xml
true

3. Non-valid encoding in the declaration

KiraXMLNonValidDeclaration.xml:

<?xml version="1.0" encoding="Kira-Goddess"?>
	<kira>Goddess!</kira>

xmllint output:

D:\SashaDebugging\KiraFastXMLParser>xmllint --noout --pedantic KiraXMLNonValidDeclaration.xml
KiraXMLNonValidDeclaration.xml:1: parser error : Unsupported encoding Kira-Goddess
<?xml version="1.0" encoding="Kira-Goddess"?>

fast-xml-parser output:

D:\SashaDebugging\KiraFastXMLParser>fxparser -V KiraXMLNonValidDeclaration.xml
true

Thanks.

[amitguptagwl]

I've separated CLI feature to fxp-cli. Please check. I hope the new features in CLI command will allow you to validate this. Otherwise please raise an issue in that repo and I'll look into.

[Kristinita]

Status: Not fixed 😿

The problem still persists for FXP CLI.

1. File

KiraXMLNonValidDeclaration.xml:

<?xml version="kira-goddess" encoding="UTF-8"?>
	<kira>Goddess!</kira>

2. Steps to reproduce

fxp val --file KiraXMLNonValidDeclaration.xml

3. Behavior

3.1. Expected

xmllint detects the error:

D:\SashaDebugging\KiraFastXMLParser>xmllint --noout --pedantic KiraXMLNonValidDeclaration.xml
KiraXMLNonValidDeclaration.xml:1: parser error : String not closed expecting " or '
<?xml version="kira-goddess" encoding="UTF-8"?>
               ^
KiraXMLNonValidDeclaration.xml:1: parser error : Malformed declaration expecting version
<?xml version="kira-goddess" encoding="UTF-8"?>
               ^
KiraXMLNonValidDeclaration.xml:1: parser error : Blank needed here
<?xml version="kira-goddess" encoding="UTF-8"?>
               ^
KiraXMLNonValidDeclaration.xml:1: parser error : parsing XML declaration: '?>' expected
<?xml version="kira-goddess" encoding="UTF-8"?>

3.2. Current

D:\SashaDebugging\KiraFastXMLParser>fxp val --file KiraXMLNonValidDeclaration.xml
Valid

FXP CLI shows Valid for non-valid file.

4. Environment

1. Windows 11 [Version 10.0.22621.3085]
2. Node.js 25.0.0
3. FXP CLI 0.0.2

Thanks.