The soap application supports the sending and receiving of SOAP attachments
in accordance with the W3C standard.
Attachments are included in the messages using MIME. Each attachment has
its own set of MIME headers (comparable to HTTP headers). On the Erlang
side (both client and server), MIME messages are represented as a list
[{[Header], Body}], where each Header is a tuple {Name, Value}, and
Name and Value are strings and Body is a binary.
To generate a client that supports the sending of attachments in the
service request, a special option must be passed to erlang2wsdl:
{attachments, true}. In this case the generated functions will have an
additional 4th argument to pass the attachments.
Any attachments that are received from the server will always be available
in the soap_response tuple, irrespective of the value for the
attachments option (except in the case of an HTTP error response,
which cannot contain an attachment).
On the server side the attachments are made available via the soap_req.
Attachments that are received from the client can be inspected using
soap_req:req_attachments/1; attachments that should be sent to the server
can be added to the request using soap_req:set_resp_attachments/2.