Send mail via EWS: Schema validation: invalid child element 'Body' - c++

Question

I'm trying to send an e-mail from within a C++ application via a Microsoft Exchange 2010 server. For this, I use the EWS protocol using the library ews-cpp.
The following trivial example, based on the one from https://github.com/otris/ews-cpp/blob/master/examples/send_message.cpp, is failing (mail addresses and credentials stripped from my actual code):
#include <iostream>
#include <ews/ews.hpp>
struct {
std::string domain = "mailserver";
std::string username = "...";
std::string password = "...";
std::string server_uri = "https://mailserver/EWS/Exchange.asmx";
} env;
int main()
{
ews::set_up();
try
{
auto service = ews::service(env.server_uri, env.domain, env.username,
env.password);
service.set_request_server_version(ews::server_version::exchange_2010_sp2);
auto message = ews::message();
message.set_subject("Test mail from outer space");
std::vector<ews::mailbox> recipients;
recipients.push_back(ews::mailbox("..."));
message.set_to_recipients(recipients);
auto text = ews::body("This is a test.");
message.set_body(text);
service.create_item(message,
ews::message_disposition::send_and_save_copy);
}
catch (ews::schema_validation_error& exc)
{
std::cout << exc.what() << std::endl;
std::cout << exc.violation() << std::endl;
}
ews::tear_down();
return 0;
}
The raw SOAP request is as follows (indentation added by me):
<m:CreateItem MessageDisposition="SendAndSaveCopy">
<m:Items>
<t:Message>
<t:Subject>Test mail from outer space</t:Subject>
<t:ToRecipients>
<t:Mailbox>
<t:EmailAddress>...</t:EmailAddress>
</t:Mailbox>
</t:ToRecipients>
<t:Body BodyType="Text">This is a test.</t:Body>
</t:Message>
</m:Items>
</m:CreateItem>
The function create_item throws an ews::schema_validation_error which is caught in the above code, printing:
The request failed schema validation
The element 'Message' in namespace ‘http://schemas.microsoft.com/exchange/services/2006/types’ has invalid child element 'Body' in namespace 'http://schemas.microsoft.com/exchange/services/2006/types'. List of possible elements expected: 'CcRecipients, BccRecipients, IsReadReceiptRequested, IsDeliveryReceiptRequested, ConversationIndex, ConversationTopic, From, InternetMessageId, IsRead, IsResponseRequested, References, ReplyTo, ReceivedBy, ReceivedRepresenting' in Namespace 'http://schemas.microsoft.com/exchange/services/2006/types'.
In other words, EWS doesn't expect <t:Body> within <t:Message>.
So, when leaving out that element in the SOAP request (comment out message.set_body(text)), the mail is sent smoothly. However, a mail without a body doesn't make much sense, does it?
I thought that the problem might be the fact that ews-cpp was written for Exchange 2013 (and that the schema changed between 2010 and 2013 in this regard). So I digged into the schema, which each Exchange server serves at /ews/types.xsd, to see if the schema allows such a child element.
In the schema definition file, I found the definition of the type MessageType (which is the type of the Message element we are talking about):
<xs:complexType name="MessageType">
<xs:complexContent>
<xs:extension base="t:ItemType">
<xs:sequence>
<xs:element name="Sender" minOccurs="0" type="t:SingleRecipientType"/>
<xs:element name="ToRecipients" type="t:ArrayOfRecipientsType" minOccurs="0"/>
<xs:element name="CcRecipients" type="t:ArrayOfRecipientsType" minOccurs="0"/>
<xs:element name="BccRecipients" type="t:ArrayOfRecipientsType" minOccurs="0"/>
<xs:element name="IsReadReceiptRequested" type="xs:boolean" minOccurs="0"/>
<xs:element name="IsDeliveryReceiptRequested" type="xs:boolean" minOccurs="0"/>
<xs:element name="ConversationIndex" type="xs:base64Binary" minOccurs="0"/>
<xs:element name="ConversationTopic" type="xs:string" minOccurs="0"/>
<xs:element name="From" type="t:SingleRecipientType" minOccurs="0"/>
<xs:element name="InternetMessageId" type="xs:string" minOccurs="0"/>
<xs:element name="IsRead" type="xs:boolean" minOccurs="0"/>
<xs:element name="IsResponseRequested" type="xs:boolean" minOccurs="0"/>
<xs:element name="References" type="xs:string" minOccurs="0"/>
<xs:element name="ReplyTo" type="t:ArrayOfRecipientsType" minOccurs="0"/>
<xs:element name="ReceivedBy" type="t:SingleRecipientType" minOccurs="0"/>
<xs:element name="ReceivedRepresenting" type="t:SingleRecipientType" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
As you can see, there is no Body child element, but MessageType is based on ItemType, which is defined as follows (excerpt):
<xs:complexType name="ItemType">
<xs:sequence>
<xs:element name="MimeContent" type="t:MimeContentType" minOccurs="0"/>
<xs:element name="ItemId" type="t:ItemIdType" minOccurs="0"/>
<xs:element name="ParentFolderId" type="t:FolderIdType" minOccurs="0"/>
<xs:element name="ItemClass" type="t:ItemClassType" minOccurs="0"/>
<xs:element name="Subject" type="xs:string" minOccurs="0"/>
<xs:element name="Sensitivity" type="t:SensitivityChoicesType" minOccurs="0"/>
<xs:element name="Body" type="t:BodyType" minOccurs="0"/>
<xs:element name="Attachments" type="t:NonEmptyArrayOfAttachmentsType" minOccurs="0"/>
[...]
</xs:sequence>
</xs:complexType>
As you can see, it accepts the Body element as a child.
Note that the Subject element is also defined in the ItemType and not in MessageType, and that is accepted by EWS in the above code snippet.
What might be the cause of this strange validation failure?

Answer 1

Found the solution myself:
For the element Message, which is based on Item according to the schema definition, EWS first expects all child elements for Item, followed by the Message-specific child elements.
This sounds very insane (to me), but swapping <t:ToRecipients> and <t:Body> in the <t:Message> element indeed solved the problem.
I did this by swapping the two corresponding setters in my code:
auto message = ews::message();
// First, set properties of the general "item":
message.set_subject("Test mail from outer space");
auto text = ews::body("This is a test.");
message.set_body(text);
// Then, set properties of the concrete "message":
std::vector<ews::mailbox> recipients;
recipients.push_back(ews::mailbox("..."));
message.set_to_recipients(recipients);
I'm not sure if this is a bug in ews-cpp, in EWS / Exchange server, or in the EWS schema definition.