Return string from webapi gives an unwanted extra character

Question

I am using a webapi observer.

In the model, I am requiring a legacy file that echo a well-formed XML for SOAP communication. However, Magento2 echo the result of the Model method, and it does it after the XML document. The resulting output is a badly formatted XML document.

One way I have tried to tackle that issue is to buffer the output of the legacy file, and return the resulting string. However, the resulting string is escaped by magento2 to become a json.

How to get only the legacy XML well-formatted result (with no extra character printed from Magento itself)?

etc/webapi.xml

<?xml version="1.0"?>
<routes xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Webapi:etc/webapi.xsd">
    <route url="/v1/liaison/:serial_code" method="POST">
        <service class="\MyCompany\MyModule\Api\Liaison" method="fromOldModule"/>
        <resources>
            <resource ref="anonymous"/>
        </resources>
    </route>
</routes>

etc/di.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <virtualType name="moduleConfig" type="Magento\Core\Model\Config">
        <arguments>
            <argument name="type" xsi:type="string">system</argument>
        </arguments>
    </virtualType>
    <type name="Magento\Core\Model\App">
        <arguments>
            <argument name="config" xsi:type="object">moduleConfig</argument>
        </arguments>
    </type>
</config>

Api/Liaison.php

namespace MyCompany\MyModule\Api;

class Liaison {
    /**
     * @param string $serial_code
     * @return array le XML est déjà affiché via distant.php, donc on n'a pas besoni d'afficher (returnà n'importe quelle autre information
     */
    public function fromOldModule($serial_code) {
        require __DIR__ . '/../v1/liaison/legacyFile.php'; // <-- This legacy code outputs a well-formated XML document
        return '';
    }
}

Result : (the "" at the very end are the characters printed by Magento that should be removed)

<?xml version="1.0" encoding="UTF-8"?>
<env:Envelope xmlns:env="http://www.w3.org/2003/05/soap-envelope" xmlns:ns1="urn:Liaison" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:enc="http://www.w3.org/2003/05/soap-encoding"><env:Body xmlns:rpc="http://www.w3.org/2003/05/soap-rpc"><ns1:ReceiverResponse env:encodingStyle="http://www.w3.org/2003/05/soap-encoding"><rpc:result>return</rpc:result><return xsi:type="xsd:boolean">true</return></ns1:ReceiverResponse></env:Body></env:Envelope>
""

I have tried to return null or an empty sting with no success. I have tried to transform the legacy SOAP return statement into an array so that Magento will use it and print it, but that was not successful.

Answer 1

Magento will convert the returned result from the methode fromOldModule from the file Api/Liaison.php into json.

One simple hack is to end this method with :

die('string to return');

This will return plain text through the api result.

Before that, any output should be captured. This is the result :

    ob_start();
    require __DIR__ . '/../v1/liaison/legacyFile.php'; // <-- This legacy code outputs a well-formated XML document
    $xml = ob_get_flush();
    die($xml);