Content-Transfer-Encoding in file uploading request

Xavier's answer doesn't sound right. RFC2616 also has this to say (section 3.7):

In general, HTTP treats a multipart message-body no differently than
any other media type: strictly as payload. The one exception is the
"multipart/byteranges"

It seems to me that section 19.4 of RFC2616 is talking about HTTP as a whole, in the sense that it uses a syntax similar to MIME (like headers format), but is not MIME-compliant.

Also, there is RFC2388. In section 3, last paragraph, it says:

Each part may be encoded and the "content-transfer-encoding" header
supplied if the value of that part does not conform to the default
encoding.

Section 4.3 elaborates on this:

4.3 Encoding

While the HTTP protocol can transport arbitrary binary data, the default for mail transport is the 7BIT encoding. The value supplied for a part may need to be encoded and the "content-transfer-encoding" header supplied if the value does not conform to the default encoding. [See section 5 of RFC 2046 for more details.]