tec: Update the lib_opml (#4403)

* fix: Fix undefined GLOB_BRACE on Alpine

The manual states that:

> Note: The GLOB_BRACE flag is not available on some non GNU systems,
> like Solaris or Alpine Linux.

This generated an error on Alpine.

Reference: https://www.php.net/manual/function.glob.php

* fix: List details of feeds for OPML exportation

The details are necessary to export the XPath information, the CSS full
content path and read actions filters.

* Update LibOpml to 0.4.0

* Refactor OPML importation to be more robust

First, it fixes two regressions introduced by the update of lib_opml:

- title attribute is used when text attribute is missing;
- the OPML category attribute is used as a fallback for feeds categories.

In a related way, if also fixes a problem when a feed had both a parent
category outline and a category attribute. Before, it only considered the
attribute as its category, but now it considers the parent outline.

Then, it counts category limit correctly by not increasing
`$nb_categories` if the category already exists.

* Exclude lib_opml from the CodeSniffer

* Fix variable names when logging some errors

* Fix catch of LibOpml Exception

* Make sure to declare the category

* Exclude lib_opml from PHPStan analyze

* Disable markdownlint for lib_opml

* Fix typos

* Use auto-loading and allow updates via Composer

* Fix broken links to lib_opml

* Bring back the ability to import the OPML frss:opmlUrl attribute

* Refactor the logs of OPML errors

* Update lib_opml to the version 0.5.0

Co-authored-by: Alexandre Alapetite <alexandre@alapetite.fr>

1 files changed, 770 insertions, 0 deletions

diff --git a/lib/marienfressinaud/lib_opml/src/LibOpml/LibOpml.php b/lib/marienfressinaud/lib_opml/src/LibOpml/LibOpml.php
new file mode 100644
index 000000000..4ba0df821
--- /dev/null
+++ b/lib/marienfressinaud/lib_opml/src/LibOpml/LibOpml.php
@@ -0,0 +1,770 @@
+<?php
+
+namespace marienfressinaud\LibOpml;
+
+/**
+ * The LibOpml class provides the methods to read and write OPML files and
+ * strings. It transforms OPML files or strings to PHP arrays (or the reverse).
+ *
+ * How to read this file?
+ *
+ * The first methods are dedicated to the parsing, and the next ones to the
+ * reading. The three last methods are helpful methods, but you don't have to
+ * worry too much about them.
+ *
+ * The main methods are the public ones: parseFile, parseString and render.
+ * They call the other parse* and render* methods internally.
+ *
+ * These three main methods are available as functions (see the src/functions.php
+ * file).
+ *
+ * What's the array format?
+ *
+ * As said before, LibOpml transforms OPML to PHP arrays, or the reverse. The
+ * format is pretty simple. It contains four keys:
+ *
+ * - version: the version of the OPML;
+ * - namespaces: an array of namespaces used in the OPML, if any;
+ * - head: an array of OPML head elements, where keys are the names of the
+ *   elements;
+ * - body: an array of arrays representing OPML outlines, where keys are the
+ *   name of the attributes (the special @outlines key contains the sub-outlines).
+ *
+ * When rendering, only the body key is required (version will default to 2.0).
+ *
+ * Example:
+ *
+ * [
+ *     version => '2.0',
+ *     namespaces => [],
+ *     head => [
+ *         title => 'An OPML file'
+ *     ],
+ *     body => [
+ *         [
+ *             text => 'Newspapers',
+ *             @outlines => [
+ *                 [text => 'El País'],
+ *                 [text => 'Le Monde'],
+ *                 [text => 'The Guardian'],
+ *                 [text => 'The New York Times'],
+ *             ]
+ *         ]
+ *     ]
+ * ]
+ *
+ * @see http://opml.org/spec2.opml
+ *
+ * @author Marien Fressinaud <dev@marienfressinaud.fr>
+ * @link https://framagit.org/marienfressinaud/lib_opml
+ * @license MIT
+ */
+class LibOpml
+{
+    /**
+     * The list of valid head elements.
+     */
+    public const HEAD_ELEMENTS = [
+        'title', 'dateCreated', 'dateModified', 'ownerName', 'ownerEmail',
+        'ownerId', 'docs', 'expansionState', 'vertScrollState', 'windowTop',
+        'windowLeft', 'windowBottom', 'windowRight'
+    ];
+
+    /**
+     * The list of numeric head elements.
+     */
+    public const NUMERIC_HEAD_ELEMENTS = [
+        'vertScrollState',
+        'windowTop',
+        'windowLeft',
+        'windowBottom',
+        'windowRight',
+    ];
+
+    /** @var boolean */
+    private $strict = true;
+
+    /** @var string */
+    private $version = '2.0';
+
+    /** @var string[] */
+    private $namespaces = [];
+
+    /**
+     * @param bool $strict
+     *     Set to true (default) to check for violations of the specification,
+     *     false otherwise.
+     */
+    public function __construct($strict = true)
+    {
+        $this->strict = $strict;
+    }
+
+    /**
+     * Parse a XML file and return the corresponding array.
+     *
+     * @param string $filename
+     *     The XML file to parse.
+     *
+     * @throws \marienfressinaud\LibOpml\Exception
+     *     Raised if the file cannot be read. See also exceptions raised by the
+     *     parseString method.
+     *
+     * @return array
+     *     An array reflecting the OPML (the structure is described above).
+     */
+    public function parseFile($filename)
+    {
+        $file_content = @file_get_contents($filename);
+
+        if ($file_content === false) {
+            throw new Exception("OPML file {$filename} cannot be found or read");
+        }
+
+        return $this->parseString($file_content);
+    }
+
+    /**
+     * Parse a XML string and return the corresponding array.
+     *
+     * @param string $xml
+     *     The XML string to parse.
+     *
+     * @throws \marienfressinaud\LibOpml\Exception
+     *     Raised if the XML cannot be parsed, if version is missing or
+     *     invalid, if head is missing or contains invalid (or not parsable)
+     *     elements, or if body is missing, empty or contain non outline
+     *     elements. The exceptions (except XML parsing errors) are not raised
+     *     if strict is false. See also exceptions raised by the parseOutline
+     *     method.
+     *
+     * @return array
+     *     An array reflecting the OPML (the structure is described above).
+     */
+    public function parseString($xml)
+    {
+        $dom = new \DOMDocument();
+        $dom->recover = true;
+        $dom->encoding = 'UTF-8';
+
+        try {
+            $result = @$dom->loadXML($xml);
+        } catch (\Exception | \Error $e) {
+            $result = false;
+        }
+
+        if (!$result) {
+            throw new Exception('OPML string is not valid XML');
+        }
+
+        $opml_element = $dom->documentElement;
+
+        // Load the custom namespaces of the document
+        $xpath = new \DOMXPath($dom);
+        $this->namespaces = [];
+        foreach ($xpath->query('//namespace::*') as $node) {
+            if ($node->prefix === 'xml') {
+                // This is the base namespace, we don't need to store it
+                continue;
+            }
+
+            $this->namespaces[$node->prefix] = $node->namespaceURI;
+        }
+
+        // Get the version of the document
+        $version = $opml_element->getAttribute('version');
+        if (!$version) {
+            $this->throwExceptionIfStrict('OPML version attribute is required');
+        }
+
+        $version = trim($version);
+        if ($version === '1.1') {
+            $version = '1.0';
+        }
+
+        if ($version !== '1.0' && $version !== '2.0') {
+            $this->throwExceptionIfStrict('OPML supported versions are 1.0 and 2.0');
+        }
+
+        $this->version = $version;
+
+        // Get head and body child elements
+        $head_elements = $opml_element->getElementsByTagName('head');
+        $child_head_elements = [];
+        if (count($head_elements) === 1) {
+            $child_head_elements = $head_elements[0]->childNodes;
+        } else {
+            $this->throwExceptionIfStrict('OPML must contain one and only one head element');
+        }
+
+        $body_elements = $opml_element->getElementsByTagName('body');
+        $child_body_elements = [];
+        if (count($body_elements) === 1) {
+            $child_body_elements = $body_elements[0]->childNodes;
+        } else {
+            $this->throwExceptionIfStrict('OPML must contain one and only one body element');
+        }
+
+        $array = [
+            'version' => $this->version,
+            'namespaces' => $this->namespaces,
+            'head' => [],
+            'body' => [],
+        ];
+
+        // Load the child head elements in the head array
+        foreach ($child_head_elements as $child_head_element) {
+            if ($child_head_element->nodeType !== XML_ELEMENT_NODE) {
+                continue;
+            }
+
+            $name = $child_head_element->nodeName;
+            $value = $child_head_element->nodeValue;
+            $namespaced = $child_head_element->namespaceURI !== null;
+
+            if (!in_array($name, self::HEAD_ELEMENTS) && !$namespaced) {
+                $this->throwExceptionIfStrict(
+                    "OPML head {$name} element is not part of the specification"
+                );
+            }
+
+            if ($name === 'dateCreated' || $name === 'dateModified') {
+                try {
+                    $value = $this->parseDate($value);
+                } catch (\DomainException $e) {
+                    $this->throwExceptionIfStrict(
+                        "OPML head {$name} element must be a valid RFC822 or RFC1123 date"
+                    );
+                }
+            } elseif ($name === 'ownerEmail') {
+                // Testing email validity is hard. PHP filter_var() function is
+                // too strict compared to the RFC 822, so we can't use it.
+                if (strpos($value, '@') === false) {
+                    $this->throwExceptionIfStrict(
+                        'OPML head ownerEmail element must be an email address'
+                    );
+                }
+            } elseif ($name === 'ownerId' || $name === 'docs') {
+                if (!$this->checkHttpAddress($value)) {
+                    $this->throwExceptionIfStrict(
+                        "OPML head {$name} element must be a HTTP address"
+                    );
+                }
+            } elseif ($name === 'expansionState') {
+                $numbers = explode(',', $value);
+                $value = array_map(function ($str_number) {
+                    if (is_numeric($str_number)) {
+                        return intval($str_number);
+                    } else {
+                        $this->throwExceptionIfStrict(
+                            'OPML head expansionState element must be a list of numbers'
+                        );
+                        return $str_number;
+                    }
+                }, $numbers);
+            } elseif (in_array($name, self::NUMERIC_HEAD_ELEMENTS)) {
+                if (is_numeric($value)) {
+                    $value = intval($value);
+                } else {
+                    $this->throwExceptionIfStrict("OPML head {$name} element must be a number");
+                }
+            }
+
+            $array['head'][$name] = $value;
+        }
+
+        // Load the child body elements in the body array
+        foreach ($child_body_elements as $child_body_element) {
+            if ($child_body_element->nodeType !== XML_ELEMENT_NODE) {
+                continue;
+            }
+
+            if ($child_body_element->nodeName === 'outline') {
+                $array['body'][] = $this->parseOutline($child_body_element);
+            } else {
+                $this->throwExceptionIfStrict(
+                    'OPML body element can only contain outline elements'
+                );
+            }
+        }
+
+        if (empty($array['body'])) {
+            $this->throwExceptionIfStrict(
+                'OPML body element must contain at least one outline element'
+            );
+        }
+
+        return $array;
+    }
+
+    /**
+     * Parse a XML element as an outline element and return the corresponding array.
+     *
+     * @param \DOMElement $outline_element
+     *     The element to parse.
+     *
+     * @throws \marienfressinaud\LibOpml\Exception
+     *     Raised if the outline contains non-outline elements, if it doesn't
+     *     contain a text attribute (or if empty), if a special attribute is
+     *     not parsable, or if type attribute requirements are not met. The
+     *     exceptions are not raised if strict is false. The exception about
+     *     missing text attribute is not raised if version is 1.0.
+     *
+     * @return array
+     *     An array reflecting the OPML outline (the structure is described above).
+     */
+    private function parseOutline($outline_element)
+    {
+        $outline = [];
+
+        // Load the element attributes in the outline array
+        foreach ($outline_element->attributes as $outline_attribute) {
+            $name = $outline_attribute->nodeName;
+            $value = $outline_attribute->nodeValue;
+
+            if ($name === 'created') {
+                try {
+                    $value = $this->parseDate($value);
+                } catch (\DomainException $e) {
+                    $this->throwExceptionIfStrict(
+                        'OPML outline created attribute must be a valid RFC822 or RFC1123 date'
+                    );
+                }
+            } elseif ($name === 'category') {
+                $categories = explode(',', $value);
+                $categories = array_map(function ($category) {
+                    return trim($category);
+                }, $categories);
+                $value = $categories;
+            } elseif ($name === 'isComment' || $name === 'isBreakpoint') {
+                if ($value === 'true' || $value === 'false') {
+                    $value = $value === 'true';
+                } else {
+                    $this->throwExceptionIfStrict(
+                        "OPML outline {$name} attribute must be a boolean (true or false)"
+                    );
+                }
+            } elseif ($name === 'type') {
+                // type attribute is case-insensitive
+                $value = strtolower($value);
+            }
+
+            $outline[$name] = $value;
+        }
+
+        if (empty($outline['text']) && $this->version !== '1.0') {
+            $this->throwExceptionIfStrict(
+                'OPML outline text attribute is required'
+            );
+        }
+
+        // Perform additional check based on the type of the outline
+        $type = $outline['type'] ?? '';
+        if ($type === 'rss') {
+            if (empty($outline['xmlUrl'])) {
+                $this->throwExceptionIfStrict(
+                    'OPML outline xmlUrl attribute is required when type is "rss"'
+                );
+            } elseif (!$this->checkHttpAddress($outline['xmlUrl'])) {
+                $this->throwExceptionIfStrict(
+                    'OPML outline xmlUrl attribute must be a HTTP address when type is "rss"'
+                );
+            }
+        } elseif ($type === 'link' || $type === 'include') {
+            if (empty($outline['url'])) {
+                $this->throwExceptionIfStrict(
+                    "OPML outline url attribute is required when type is \"{$type}\""
+                );
+            } elseif (!$this->checkHttpAddress($outline['url'])) {
+                $this->throwExceptionIfStrict(
+                    "OPML outline url attribute must be a HTTP address when type is \"{$type}\""
+                );
+            }
+        }
+
+        // Load the sub-outlines in a @outlines array
+        foreach ($outline_element->childNodes as $child_outline_element) {
+            if ($child_outline_element->nodeType !== XML_ELEMENT_NODE) {
+                continue;
+            }
+
+            if ($child_outline_element->nodeName === 'outline') {
+                $outline['@outlines'][] = $this->parseOutline($child_outline_element);
+            } else {
+                $this->throwExceptionIfStrict(
+                    'OPML body element can only contain outline elements'
+                );
+            }
+        }
+
+        return $outline;
+    }
+
+    /**
+     * Parse a value as a date.
+     *
+     * @param string $value
+     *
+     * @throws \DomainException
+     *     Raised if the value cannot be parsed.
+     *
+     * @return \DateTime
+     */
+    private function parseDate($value)
+    {
+        $formats = [
+            \DateTimeInterface::RFC822,
+            \DateTimeInterface::RFC1123,
+        ];
+
+        foreach ($formats as $format) {
+            $date = date_create_from_format($format, $value);
+            if ($date !== false) {
+                return $date;
+            }
+        }
+
+        throw new \DomainException('The argument cannot be parsed as a date');
+    }
+
+    /**
+     * Render an OPML array as a string or a \DOMDocument.
+     *
+     * @param array $array
+     *     The array to render, it must follow the structure defined above.
+     * @param bool $as_dom_document
+     *     Set to false (default) to return the array as a string, true to
+     *     return as a \DOMDocument.
+     *
+     * @throws \marienfressinaud\LibOpml\Exception
+     *     Raised if the `head` array contains unknown or invalid elements
+     *     (i.e. not of correct type), or if the `body` array is missing or
+     *     empty. The exceptions are not raised if strict is false. See also
+     *     exceptions raised by the renderOutline method.
+     *
+     * @return string|\DOMDocument
+     *     The XML string or DOM document corresponding to the given array.
+     */
+    public function render($array, $as_dom_document = false)
+    {
+        $dom = new \DOMDocument('1.0', 'UTF-8');
+        $opml_element = new \DOMElement('opml');
+        $dom->appendChild($opml_element);
+
+        // Set the version attribute of the OPML document
+        $version = $array['version'] ?? '2.0';
+
+        if ($version === '1.1') {
+            $version = '1.0';
+        }
+
+        if ($version !== '1.0' && $version !== '2.0') {
+            $this->throwExceptionIfStrict('OPML supported versions are 1.0 and 2.0');
+        }
+
+        $this->version = $version;
+        $opml_element->setAttribute('version', $this->version);
+
+        // Declare the namespace on the opml element
+        $this->namespaces = $array['namespaces'] ?? [];
+        foreach ($this->namespaces as $prefix => $namespace) {
+            $opml_element->setAttributeNS(
+                'http://www.w3.org/2000/xmlns/',
+                "xmlns:{$prefix}",
+                $namespace
+            );
+        }
+
+        // Add the head element to the OPML document. $array['head'] is
+        // optional but head tag will always exist in the final XML.
+        $head_element = new \DOMElement('head');
+        $opml_element->appendChild($head_element);
+        if (isset($array['head'])) {
+            foreach ($array['head'] as $name => $value) {
+                $namespace = $this->getNamespace($name);
+
+                if (!in_array($name, self::HEAD_ELEMENTS, true) && !$namespace) {
+                    $this->throwExceptionIfStrict(
+                        "OPML head {$name} element is not part of the specification"
+                    );
+                }
+
+                if ($name === 'dateCreated' || $name === 'dateModified') {
+                    if ($value instanceof \DateTimeInterface) {
+                        $value = $value->format(\DateTimeInterface::RFC1123);
+                    } else {
+                        $this->throwExceptionIfStrict(
+                            "OPML head {$name} element must be a DateTime"
+                        );
+                    }
+                } elseif ($name === 'ownerEmail') {
+                    // Testing email validity is hard. PHP filter_var() function is
+                    // too strict compared to the RFC 822, so we can't use it.
+                    if (strpos($value, '@') === false) {
+                        $this->throwExceptionIfStrict(
+                            'OPML head ownerEmail element must be an email address'
+                        );
+                    }
+                } elseif ($name === 'ownerId' || $name === 'docs') {
+                    if (!$this->checkHttpAddress($value)) {
+                        $this->throwExceptionIfStrict(
+                            "OPML head {$name} element must be a HTTP address"
+                        );
+                    }
+                } elseif ($name === 'expansionState') {
+                    if (is_array($value)) {
+                        foreach ($value as $number) {
+                            if (!is_int($number)) {
+                                $this->throwExceptionIfStrict(
+                                    'OPML head expansionState element must be an array of integers'
+                                );
+                            }
+                        }
+
+                        $value = implode(', ', $value);
+                    } else {
+                        $this->throwExceptionIfStrict(
+                            'OPML head expansionState element must be an array of integers'
+                        );
+                    }
+                } elseif (in_array($name, self::NUMERIC_HEAD_ELEMENTS)) {
+                    if (!is_int($value)) {
+                        $this->throwExceptionIfStrict(
+                            "OPML head {$name} element must be an integer"
+                        );
+                    }
+                }
+
+                $child_head_element = new \DOMElement($name, $value, $namespace);
+                $head_element->appendChild($child_head_element);
+            }
+        }
+
+        // Check body is set and contains at least one element
+        if (!isset($array['body'])) {
+            $this->throwExceptionIfStrict('OPML array must contain a body key');
+        }
+
+        $array_body = $array['body'] ?? [];
+        if (count($array_body) <= 0) {
+            $this->throwExceptionIfStrict(
+                'OPML body element must contain at least one outline array'
+            );
+        }
+
+        // Create outline elements in the body element
+        $body_element = new \DOMElement('body');
+        $opml_element->appendChild($body_element);
+        foreach ($array_body as $outline) {
+            $this->renderOutline($body_element, $outline);
+        }
+
+        // And return the final result
+        if ($as_dom_document) {
+            return $dom;
+        } else {
+            $dom->formatOutput = true;
+            return $dom->saveXML();
+        }
+    }
+
+    /**
+     * Transform an outline array to a \DOMElement and add it to a parent element.
+     *
+     * @param \DOMElement $parent_element
+     *     The DOM parent element of the current outline.
+     * @param array $outline
+     *     The outline array to transform in a \DOMElement, it must follow the
+     *     structure defined above.
+     *
+     * @throws \marienfressinaud\LibOpml\Exception
+     *     Raised if the outline is not an array, if it doesn't contain a text
+     *     attribute (or if empty), if the `@outlines` key is not an array, if
+     *     a special attribute does not match its corresponding type, or if
+     *     `type` key requirements are not met. The exceptions (except errors
+     *     about outline or suboutlines not being arrays) are not raised if
+     *     strict is false. The exception about missing text attribute is not
+     *     raised if version is 1.0.
+     */
+    private function renderOutline($parent_element, $outline)
+    {
+        // Perform initial checks to verify the outline is correctly declared
+        if (!is_array($outline)) {
+            throw new Exception(
+                'OPML outline element must be defined as an array'
+            );
+        }
+
+        if (empty($outline['text']) && $this->version !== '1.0') {
+            $this->throwExceptionIfStrict(
+                'OPML outline text attribute is required'
+            );
+        }
+
+        if (isset($outline['type'])) {
+            $type = strtolower($outline['type']);
+
+            if ($type === 'rss') {
+                if (empty($outline['xmlUrl'])) {
+                    $this->throwExceptionIfStrict(
+                        'OPML outline xmlUrl attribute is required when type is "rss"'
+                    );
+                } elseif (!$this->checkHttpAddress($outline['xmlUrl'])) {
+                    $this->throwExceptionIfStrict(
+                        'OPML outline xmlUrl attribute must be a HTTP address when type is "rss"'
+                    );
+                }
+            } elseif ($type === 'link' || $type === 'include') {
+                if (empty($outline['url'])) {
+                    $this->throwExceptionIfStrict(
+                        "OPML outline url attribute is required when type is \"{$type}\""
+                    );
+                } elseif (!$this->checkHttpAddress($outline['url'])) {
+                    $this->throwExceptionIfStrict(
+                        "OPML outline url attribute must be a HTTP address when type is \"{$type}\""
+                    );
+                }
+            }
+        }
+
+        // Create the outline element and add it to the parent
+        $outline_element = new \DOMElement('outline');
+        $parent_element->appendChild($outline_element);
+
+        // Load the sub-outlines as child elements
+        if (isset($outline['@outlines'])) {
+            $outline_children = $outline['@outlines'];
+
+            if (!is_array($outline_children)) {
+                throw new Exception(
+                    'OPML outline element must be defined as an array'
+                );
+            }
+
+            foreach ($outline_children as $outline_child) {
+                $this->renderOutline($outline_element, $outline_child);
+            }
+
+            // We don't want the sub-outlines to be loaded as attributes, so we
+            // remove the key from the array.
+            unset($outline['@outlines']);
+        }
+
+        // Load the other elements of the array as attributes
+        foreach ($outline as $name => $value) {
+            $namespace = $this->getNamespace($name);
+
+            if ($name === 'created') {
+                if ($value instanceof \DateTimeInterface) {
+                    $value = $value->format(\DateTimeInterface::RFC1123);
+                } else {
+                    $this->throwExceptionIfStrict(
+                        'OPML outline created attribute must be a DateTime'
+                    );
+                }
+            } elseif ($name === 'isComment' || $name === 'isBreakpoint') {
+                if (is_bool($value)) {
+                    $value = $value ? 'true' : 'false';
+                } else {
+                    $this->throwExceptionIfStrict(
+                        "OPML outline {$name} attribute must be a boolean"
+                    );
+                }
+            } elseif (is_array($value)) {
+                $value = implode(', ', $value);
+            }
+
+            $outline_element->setAttributeNS($namespace, $name, $value);
+        }
+    }
+
+    /**
+     * Return wether a value is a valid HTTP address or not.
+     *
+     * HTTP address is not strictly defined by the OPML spec, so it is assumed:
+     *
+     * - it can be parsed by parse_url
+     * - it has a host part
+     * - scheme is http or https
+     *
+     * filter_var is not used because it would reject internationalized URLs
+     * (i.e. with non ASCII chars). An alternative would be to punycode such
+     * URLs, but it's more work to do it properly, and lib_opml needs to stay
+     * simple.
+     *
+     * @param string $value
+     *
+     * @return boolean
+     *     Return true if the value is a valid HTTP address, false otherwise.
+     */
+    public function checkHttpAddress($value)
+    {
+        $value = trim($value);
+        $parsed_url = parse_url($value);
+        if (!$parsed_url) {
+            return false;
+        }
+
+        if (
+            !isset($parsed_url['scheme']) ||
+            !isset($parsed_url['host'])
+        ) {
+            return false;
+        }
+
+        if (
+            $parsed_url['scheme'] !== 'http' &&
+            $parsed_url['scheme'] !== 'https'
+        ) {
+            return false;
+        }
+
+        return true;
+    }
+
+    /**
+     * Return the namespace of a qualified name. An empty string is returned if
+     * the name is not namespaced.
+     *
+     * @param string $qualified_name
+     *
+     * @throws \marienfressinaud\LibOpml\Exception
+     *     Raised if the namespace prefix isn't declared.
+     *
+     * @return string
+     */
+    private function getNamespace($qualified_name)
+    {
+        $split_name = explode(':', $qualified_name, 2);
+        // count will always be 1 or 2.
+        if (count($split_name) === 1) {
+            // If 1, there's no prefix, thus no namespace
+            return '';
+        } else {
+            // If 2, it means it has a namespace prefix, so we get the
+            // namespace from the declared ones.
+            $namespace_prefix = $split_name[0];
+            if (!isset($this->namespaces[$namespace_prefix])) {
+                throw new Exception(
+                    "OPML namespace {$namespace_prefix} is not declared"
+                );
+            }
+
+            return $this->namespaces[$namespace_prefix];
+        }
+    }
+
+    /**
+     * Raise an exception only if strict is true.
+     *
+     * @param string $message
+     *
+     * @throws \marienfressinaud\LibOpml\Exception
+     */
+    private function throwExceptionIfStrict($message)
+    {
+        if ($this->strict) {
+            throw new Exception($message);
+        }
+    }
+}