I reproduced it with the following code:
<?php
error_reporting(E_ALL);
include('/var/www/dump/xmlrpc/lib/xmlrpc.inc');
$c = new xmlrpc_client('/dump/dokuwiki/lib/exe/xmlrpc.php', 'localhost', 80);
$c->setDebug = 1;
$m = new xmlrpcmsg('wiki.putAttachment');
$m->addParam(new xmlrpcval("datei.jpg", "string"));
$m->addParam(new xmlrpcval("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", "base64"));
$m->addParam(new xmlrpcval(array("ow" => new xmlrpcval(true, "boolean")), "struct"));
$r = $c->send($m);
var_dump($r);
if($r == false) die('foo!');
if(!$r->faultCode()) {
$v = php_xmlrpc_decode($r->value());
echo $v;
}
?>
The problem is that the extension of the file is *.jpg but inside the file the first bytes start with the following:
�PNG
^Z
^@^@^@
IHDR^@^@^@0^@^@^@0^H
and "file" gives the following output
lupo49@WS6 ~ $ file Downloads/Auto-Bild-Logo_normal.jpg
Downloads/Auto-Bild-Logo_normal.jpg: PNG image data, 48 x 48, 8-bit/color RGB, non-interlaced
So there's a mismatch between the given extension of the file and the real type of the file. After renaming the file to *.png in the xmlrpcval-filename,
$m->addParam(new xmlrpcval("datei.png", "string"));
the file can be successfully uploaded through the XMLRPC interface.