I think the original intention was to find a way to replay InputStream bodies in case of a retry (connection crash), but I don't think it can work:

• it sets the readlimit to 0, meaning that the mark becomes invalid after the first read
• reset behavior is completely inconsistent across implementations. A ByteArrayInputStream will always be able to reset as everything is in memory, but a BufferedInputStream will crash on reset if the mark moved out of the buffer, while markSupported always return true (so there's no way to detect that reset will fail beforehand).

Dropping this non feature that cannot work.