Module io 

I/O

Reading streams

• A stream is Read.
• Currently, read buffer is 16 KiB.
• Reading stops until the stream returns 0 bytes.
• ErrorKind::WouldBlock will be ignored. It then waits for 10 milliseconds, and retries.

Reading /dev/urandom

• limit must be larger than zero. Or an error is returned.
• If data read from that file is not equal to limit, an error is returned.