Attachment size is wrong in msgraph api - microsoft-graph-api

Question

The property size of FileAttachment is larger than the actrually size of binary.
{
"#odata.type": "#microsoft.graph.fileAttachment",
"#odata.mediaContentType": "application/octet-stream",
"id": "<the attachment id>",
"lastModifiedDateTime": "2020-10-26T09:57:36Z",
"name": "test.bin",
"contentType": "application/octet-stream",
"size": 245,
"isInline": false,
"contentId": null,
"contentLocation": null,
"contentBytes": "aGVsbG8gd29ybGQ="
}
Here is a piece of java code create above json data:
IGraphServiceClient graphClient = GraphServiceClient.builder().authenticationProvider(provider).buildClient();
FileAttachment attachment = new FileAttachment();
attachment.oDataType = "#microsoft.graph.fileAttachment";
attachment.name = "test.bin";
attachment.contentBytes = "hello world".getBytes();
Attachment att = graphClient.users().byId(userId).messages().byId(mailId).attachments().buildRequest().post(attachment);
System.out.println(att.size);

Answer 1

The attachment size in the Graph should just be the PidTagAttachSize property https://learn.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-oxprops/917d8d18-adee-4f14-9f2a-9a1d37fff41e . The size returned is basically made up of the size of all the attachment properties (not just the underlying attachment size) in the Attachment object. So it will always be bigger then the actual attachment size. There's another description https://learn.microsoft.com/en-us/office/client-developer/outlook/mapi/pidtagattachsize-canonical-property
This property can be used to check the approximate size of the attachment before performing a remote transfer by modem and to display progress indicators when saving the attachment to disk. It is particularly useful with attached OLE objects.
Given they talk about modems its a little dated.