XmlReaderTask fails on an empty file and silently emits an empty DOMDocument on invalid XML #202

Description

XmlReaderTask (through CleverAge\ProcessBundle\Filesystem\XmlFile::read()) does not handle bad input files:

• Empty file: the task crashes with a low-level ValueError: SplFileObject::fread(): Argument #1 ($length) must be greater than 0.
• Invalid XML: the result of DOMDocument::loadXML() is ignored. Only a PHP warning is raised, and an empty \DOMDocument (documentElement = null, no child nodes) is passed to the next tasks. In debug mode the Symfony error handler turns the warning into an exception, so the process fails; without debug (production), the process goes on silently with an empty document.

Reproduction

clever_age_process:
    configurations:
        demo.xml_reader_invalid:
            tasks:
                read:
                    service: '@CleverAge\ProcessBundle\Task\File\Xml\XmlReaderTask'
                    options:
                        file_path: '{{ file_path }}'
                    outputs: [dump]
                dump:
                    service: '@CleverAge\ProcessBundle\Task\Debug\DebugTask'

printf '' > var/data/empty.xml
printf '<root><a>1</a>' > var/data/invalid.xml
bin/console cleverage:process:execute demo.xml_reader_invalid -c file_path:"'/var/www/var/data/empty.xml'"
bin/console cleverage:process:execute --no-debug demo.xml_reader_invalid -c file_path:"'/var/www/var/data/invalid.xml'"

Empty file:

CRITICAL  [cleverage_process_task] SplFileObject::fread(): Argument #1 ($length) must be greater than 0
In XmlFile.php line 33:
  Process demo.xml_reader_invalid has failed during process read with message
  : 'SplFileObject::fread(): Argument #1 ($length) must be greater than 0'.

Invalid XML (--no-debug): the process does not fail, and the dumped document is empty:

ERROR     [php] Warning: DOMDocument::loadXML(): Premature end of data in tag root line 1 in Entity, line: 1
  +childNodes: DOMNodeList {
    +length: 0
  +documentElement: null

Tested on main (c1a2804), PHP 8.5, Symfony 7.4.

Cause

In XmlFile::read():

• the file size is passed to fread() without a check, and fread(0) throws a ValueError (L33);
• the return value of $dom->loadXML() is ignored (L35), and libxml errors are only reported as PHP warnings.

Proposed fix

• an empty file throws an explicit \UnexpectedValueException('XML file "<path>" is empty');
• loadXML() runs with libxml_use_internal_errors(true); the collected libxml errors are cleared and the previous setting is restored;
• if the load fails, or libxml reports an error or a fatal error, an \UnexpectedValueException('Invalid XML in file "<path>": <libxml message> (line L, column C); ...') is thrown; libxml warnings are still tolerated;
• update the XmlReaderTask reference documentation (Notes), add unit tests for XmlFile.

Requirements

• Documentation updates
  • Reference
  • Cookbooks
  • Changelog
• Unit tests

Breaking changes

Bug fix: XmlReaderTask now throws an \UnexpectedValueException when the XML is invalid, instead of passing an empty or partial \DOMDocument to the next tasks with only a PHP warning. This includes XML that parses but has libxml errors, such as an undefined namespace prefix (<root><x:a/></root>), which used to give a partial document. An empty file now throws an \UnexpectedValueException instead of a \ValueError. Processes relying on the silent empty document (e.g. in production, without the Symfony debug error handler) will now fail at the reader task: use error_strategy to handle these files.