(rpc rpc types) module provides a representation of the
various XDR types defined in the standard to represent RPC messages
(see References). We only describe the most important ones as
well as procedures from the
(rpc rpc) module that help use it.
This variable contains a XDR struct type representing all possible RPC
rpc_msg struct type defined in RFC 1831. By
“rpc message” we mean the header that is transmitted before the
actual procedure argument to describe the procedure call being made.
Roughly, this header contains a transaction ID allowing clients to match call/reply pairs, plus information describing either the call or the reply being made. Calls essentially contain a program, version and procedure numbers. Replies, on the other hand, can be more complex since they can describe a large class of errors.
This variable is bound to an XDR enumeration. Its two possible values
REPLY (both represented in Scheme using
symbols), denoting a procedure call and a reply to a procedure call,
rpc-message datum. type should be either
REPLY (the two values of the
rpc-message-type enumeration). The arguments args are
message-type-specific. For example, a message denoting a procedure
call to procedure number 5 of version 1 of program 77 can be created
(define my-call-msg (make-rpc-message #x123 ;; the transaction ID 'CALL ;; the message type 77 1 5))
It can then be encoded in the usual way (see XDR Encoding and Decoding):
(let* ((size (xdr-type-size rpc-message my-call-msg)) (bv (make-bytevector size))) (xdr-encode! bv 0 rpc-message my-call-msg) ;;; ... )
Likewise, a reply message denoting a successful RPC call can be produced as follows:
(make-rpc-message xid 'REPLY 'MSG_ACCEPTED 'SUCCESS)
It is worth noting that in practice, “messages” of type
rpc-message are followed by additional data representing either
the procedure call arguments (if the message is a
or the procedure return value (if the message is a
Return true if rpc-msg (an RPC message as returned by a previous
(xdr-decode rpc-message port) call) is a valid reply for the
invocation labeled with transaction ID xid indicating that it
was accepted. If xid is
#t, any reply transaction ID is
accepted and it is returned (provided the rest of the message denotes
an accepted message). On failure, an appropriate error condition is
The error conditions that may be raised obey
rpc-call-error?. More precisely, error conditions include the
If rpc-msg denotes the fact that the program requested by the corresponding RPC call is not available.
If the corresponding RPC call requested a program version that is not
available. The procedures
rpc-program-mismatch-error:high-version return, respectively,
the lowest and highest version numbers supported by the remote server.
If the corresponding RPC call requested a procedure that is not available.
If the remote server failed to decode the procedure arguments.
If the remote server failed to allocate enough memory for argument decoding, for instance.