Outlook Mail REST API: send message with attachment - outlook-restapi

Question

I'm trying to use next API method: https://msdn.microsoft.com/office/office365/APi/mail-rest-operations#SendMessages. Sending messages without attachments works just fine, but I can not understand how to send message with attachments.
According to docs, Message structure can contain array of Attachments with items of type https://msdn.microsoft.com/office/office365/APi/complex-types-for-mail-contacts-calendar#RESTAPIResourcesFileAttachment . Problem is in the field ContentBytes -- it is impossible to dump bytes to JSON before sending request to this API method (actually dumping any BLOB to JSON is nonsense).
How should I pass Attachments using REST API at all?
Thanks.

Answer 1

There's an example of passing the attachment on that page: https://msdn.microsoft.com/office/office365/APi/mail-rest-operations#SendMessageOnTheFly

Answer 2

I know I'm 3 years late but, you can look at this example:
https://msdn.microsoft.com/office/office365/APi/mail-rest-operations#create-and-send-messages (if you don't get forwarded to the section "Create and send messages", please scroll manually).
I know it is 365 and not Microsoft Graph but request is absolutely same.
This is basically how JSON representation of the post method looks:
https://outlook.office.com/api/v2.0/me/sendmail
{
"Message":
{
"Subject": "Meet for lunch?",
"Body": {
"ContentType": "Text",
"Content": "The new cafeteria is open."
},
"ToRecipients": [
{
"EmailAddress": {
"Address": "garthf#a830edad9050849NDA1.onmicrosoft.com"
}
}
],
"Attachments": [
{
"#odata.type": "#Microsoft.OutlookServices.FileAttachment",
"Name": "menu.txt",
"ContentBytes": "bWFjIGFuZCBjaGVlc2UgdG9kYXk="
}
]
}
}