Sniffs buffer to determine its Content-Type.
The result may also be influenced by the Content-Type declared in msg's response headers.
the message to sniff
a buffer containing the start of msg's response body
return location for Content-Type parameters (eg, "charset"), or null
the sniffed Content-Type of buffer; this will never be null, but may be application/octet-stream.
Sniffs buffer to determine its Content-Type.
The result may also be influenced by the Content-Type declared in msg's response headers.