I need to know how to parse attachment data

[Darrell Huang]

Hi, everyone, I got some trouble in reading the attachment data from 
documents with the HTTP API. When an attachment is downloaded with the API, 
some extra data is found before and after the attachment data, and the data 
can be different at different times.
For example, when I downloaded an attachment with the jpg format several 
weeks ago, there is a character sequence "dbc\r\n" preceding the actual file 
data, but when I did that today, it was "a24\r\n".
I don't know what this extra data means. Can someone tell me how to parse 
the packet content and extract the actual attachment data from it?