Record-Marking Standard

When RPC messages are passed on top of a byte stream transport (like TCP), it is necessary, or at least desirable, to delimit one message from another to detect and possibly recover from user protocol errors. This is called record marking (RM). One RPC message fits into one RM record.

A record is composed of one or more record fragments. A record fragment is a four-byte header followed by 0 to (2**31) - 1 bytes of fragment data. The bytes encode an unsigned binary number; as with XDR integers, the byte order is the network byte order.

The header encodes two values:

• A Boolean that specifies whether the fragment is the last fragment of the record (bit value 1 implies the fragment is the last fragment).

• A 31-bit unsigned binary value that is the length in bytes of the fragment's data. The Boolean value is the highest-order bit of the header; the length is the 31 low-order bits. (This record specification is not in XDR standard form).