Mantis SOAP-Error accessing mantisconnect.php (Eclipse Mylyn-Plugin) - php

Question

I installed Mantis BT 1.2.19 on my server and it works well. To benefit from it in my Eclipse-IDE (Mars) I installed the Task-Repo Plugin for Mantis and tried to add the connection.
When I click on "Validate settings" in Eclipse I get the following error:
SOAP-ERROR: Parsing WSDL: Couldn't load from '/var/www/vhosts/{myhost}/httpdocs/mantis/api/soap/mantisconnect.wsdl' : failed to load external entity "/var/www/vhosts/{myhost}/httpdocs/mantis/api/soap/mantisconnect.wsdl"
In my error-log on the server are the following entries
[14-Oct-2015 11:25:05 Europe/Berlin] [mantisconnect.php] Error Type: SYSTEM WARNING,
Error Description: SoapServer::SoapServer(): I/O warning : failed to load external entity "/var/www/vhosts/{myhost}/httpdocs/mantis/api/soap/mantisconnect.wsdl"
Stack Trace:
mantisconnect.php L121 SoapServer(<string>'mantisconnect.wsdl', <Array> { ['features'] => 5 })
[14-Oct-2015 11:25:05 Europe/Berlin] PHP Warning: Uncaught SoapFault exception: [Server] Error Type: SYSTEM WARNING,
Error Description: SoapServer::SoapServer(): I/O warning : failed to load external entity "/var/www/vhosts/{myhost}/httpdocs/mantis/api/soap/mantisconnect.wsdl" in /var/www/vhosts/{myhost}/httpdocs/mantis/api/soap/mc_api.php:107
Stack trace:
#0 /var/www/vhosts/{myhost}/httpdocs/mantis/api/soap/mc_api.php(530): SoapActions::sendSoapFault('Server', 'Error Type: SYS...')
#1 [internal function]: mc_error_handler(2, 'SoapServer::Soa...', '/var/www/vhosts...', 121, Array)
#2 /var/www/vhosts/{myhost}/httpdocs/mantis/api/soap/mantisconnect.php(121): SoapServer->SoapServer('mantisconnect.w...', Array)
#3 {main}
thrown in /var/www/vhosts/{myhost}/httpdocs/mantis/api/soap/mc_api.php on line 107
[14-Oct-2015 11:25:05 Europe/Berlin] PHP Fatal error: SOAP-ERROR: Parsing WSDL: Couldn't load from '/var/www/vhosts/{myhost}/httpdocs/mantis/api/soap/mantisconnect.wsdl' : failed to load external entity "/var/www/vhosts/{myhost}/httpdocs/mantis/api/soap/mantisconnect.wsdl"
in /var/www/vhosts/{myhost}/httpdocs/mantis/api/soap/mantisconnect.php on line 121
The errors above are produced by the Mantis plugin on accessing the URL
188.109.171.76 - - [14/Oct/2015:11:25:05 +0200] "POST /mantis/api/soap/mantisconnect.php HTTP/1.0" 500 1067 "-" "Mylyn/3.17.0 Mylyn-Mantis Connector/3.10.1 Apache Axis/1.4 Eclipse (org.eclipse.epp.package.jee.product) HttpClient/3.1 Java/1.8.0_60 (Oracle) Windows 7/6.1 (amd64; de_DE)"
But even a "normal" GET-access to the URL mentioned above produces the same error
https://{myhost}/mantis/api/soap/mantisconnect.php
No error is produced on accessing
https://{myhost}/mantis/api/soap/mantisconnect.php?wsdl
To solve the problem on my own I checked several ideas:
The file IS existant ... {myhost} is just a placeholder here obviously - placed by me
I switched to the context of the webserver www-data and tried accessing the file ... it IS accessible
So I´ve no idea...
PHP version is 5.5.9-1ubuntu4.13 on Ubuntu 14.04.3 LTS
€dit:
Tracked down the error to the following PHP-line in mantis/api/soap/mantisconnect.php
$server = new SoapServer("mantisconnect.wsdl",
array('features' => SOAP_USE_XSI_ARRAY_TYPE + SOAP_SINGLE_ELEMENT_ARRAYS)
);
I don´t understand why there an error is thrown - because as I said: it exists and is readable by the webserver...
€edit2:
I replaced the line
$server = new SoapServer("mantisconnect.wsdl",
with
$server = new SoapServer("http://{myhost}/mantis/api/soap/mantisconnect.wsdl",
THIS works... so I´ve a "solution" but I don´t know why the access via file does not work

Answer 1

I Think I found the answere on my own (my workaround failed some hours later - with same error again).
Seems to be a bug in PHP (on Ubuntu) as mentioned here
https://bugs.launchpad.net/ubuntu/+source/php5/+bug/1160336
Unresolved since 2013
:-(
My current workaround is disabling soap.wsdl_cache_enabled in php.ini which seems to help for the moment.