Reads data from a blob into a new blob
Device + Agent
The number of bytes to read
This method reads the specified number of bytes from the blob and returns them as a new blob.
Only those bytes up to the end the source blob are read; if the call asks for 256 bytes but the read/write pointer is 128 bytes from the end, the new blob will be 128 bytes long.
The size of the new blob can be verified using the len() method.