Copyright © tutorialspoint.com
rpcgen is a tool that generates C code to implement an RPC protocol. The input to rpcgen is a language similar to C known as RPC Language (Remote Procedure Call Language).
rpcgen is normally used as in the first synopsis where it takes an input file and generates up to four output files. If the infile is named proto.x, then rpcgen will generate a header file in proto.h, XDR routines in proto_xdr.c, server-side stubs in proto_svc.c, and client-side stubs in proto_clnt.c. With the -T option, it will also generate the RPC dispatch table in proto_tbl.i. With the -Sc option, it will also generate sample code which would illustrate how to use the remote procedures on the client side. This code would be created in proto_client.c. With the -Ss option, it will also generate a sample server code which would illustrate how to write the remote procedures. This code would be created in proto_server.c.
The server created can be started both by the port monitors (for example, inetd or listen) or by itself. When it is started by a port monitor, it creates servers only for the transport for which the file descriptor 0 was passed. The name of the transport must be specified by setting up the environmental variable PM_TRANSPORT. When the server generated by rpcgen is executed, it creates server handles for all the transports specified in NETPATH environment variable, or if it is unset, it creates server handles for all the visible transports from /etc/netconfig file. Note: the transports are chosen at run time and not at compile time. When the server is self-started, it backgrounds itself by default. A special define symbol RPC_SVC_FG can be used to run the server process in foreground.
The second synopsis provides special features which allow for the creation of more sophisticated RPC servers. These features include support for user provided #defines and RPC dispatch tables. The entries in the RPC dispatch table contain:
|o||pointers to the service routine corresponding to that procedure,|
|o||a pointer to the input and output arguments|
|o||the size of these routines|
The other three synopses shown above are used when one does not want to generate all the output files, but only a particular one. Some examples of their usage is described in the EXAMPLE section below. When rpcgen is executed with the -s option, it creates servers for that particular class of transports. When executed with the -n option, it creates a server for the transport specified by netid. If infile is not specified, rpcgen accepts the standard input.
The C preprocessor, cc -E [see cc(1)], is run on the input file before it is actually interpreted by rpcgen. For each type of output file, rpcgen defines a special preprocessor symbol for use by the rpcgen programmer:
|RPC_HDR||defined when compiling into header files|
|RPC_XDR||defined when compiling into XDR routines|
|RPC_SVC||defined when compiling into server-side stubs|
|RPC_CLNT||defined when compiling into client-side stubs|
|RPC_TBL||defined when compiling into RPC dispatch tables|
For every data type referred to in infile, rpcgen assumes that there exists a routine with the string xdr_ prepended to the name of the data type. If this routine does not exist in the RPC/XDR library, it must be provided. Providing an undefined data type allows customization of XDR routines.
The following options are available:
|-a||Generate all the files including sample code for client and server side.|
|-b||This generates code for the SunOS4.1 style of rpc. It is for backward compatibilty. This is the default.|
|-5||This generates code for the SysVr4 style of rpc. It is used by the Transport Independent RPC that is in Svr4 systems. By default rpcgen generates code for SunOS4.1 stype of rpc.|
|-c||Compile into XDR routines.|
|-C||Generate code in ANSI C. This option also generates code that could be compiled with the C++ compiler. This is the default.|
|-k||Generate code in K&R C. The default is ANSI C.|
|Define a symbol name. Equivalent to the #define directive in the source. If no value is given, value is defined as 1. This option may be specified more than once.|
|-h||Compile into C data-definitions (a header file). -T option can be used in conjunction to produce a header file which supports RPC dispatch tables.|
|-I||Generate a service that can be started from inetd. The default is to generate a static service that handles transports selected with -s. Using -I allows starting a service by either method.|
|By default, services created using rpcgen wait 120 seconds after servicing a request before exiting. That interval can be changed using the -K flag. To create a server that exits immediately upon servicing a request, -K 0 can be used. To create a server that never exits, the appropriate argument is -K -1.|
|When monitoring for a server, some portmonitors, like listen(1M), always spawn a new process in response to a service request. If it is known that a server will be used with such a monitor, the server should exit immediately on completion. For such servers, rpcgen should be used with -K -1.|
|-l||Compile into client-side stubs.|
|-m||Compile into server-side stubs, but do not generate a main routine. This option is useful for doing callback-routines and for users who need to write their own main routine to do initialization.|
|-n netid||Compile into server-side stubs for the transport specified by netid. There should be an entry for netid in the netconfig database. This option may be specified more than once, so as to compile a server that serves multiple transports.|
|-N||Use the newstyle of rpcgen. This allows procedures to have multiple arguments. It also uses the style of parameter passing that closely resembles C. So, when passing an argument to a remote procedure you do not have to pass a pointer to the argument but the argument itself. This behaviour is different from the oldstyle of rpcgen generated code. The newstyle is not the default case because of backward compatibility.|
|Specify the name of the output file. If none is specified, standard output is used (-c, -h, -l, -m, -n, -s, -sc, -ss and -t modes only).|
|Compile into server-side stubs for all the transports belonging to the class nettype. The supported classes are netpath, visible, circuit_n, circuit_v, datagram_n, datagram_v, tcp, and udp [see rpc(3N) for the meanings associated with these classes]. This option may be specified more than once. Note: the transports are chosen at run time and not at compile time.|
|-Sc||Generate sample code to show the use of remote procedure and how to bind to the server before calling the client side stubs generated by rpcgen.|
|-Ss||Generate skeleton code for the remote procedures on the server side. You would need to fill in the actual code for the remote procedures.|
|-t||Compile into RPC dispatch table.|
|-T||Generate the code to support RPC dispatch tables.|
Name clashes can occur when using program definitions, since the apparent scoping does not really apply. Most of these can be avoided by giving unique names for programs, versions, procedures and types.
The server code generated with -n option refers to the transport indicated by netid and hence is very site specific.
|$ rpcgen -T prot.x|
|generates the five files: prot.h, prot_clnt.c, prot_svc.c, prot_xdr.c and prot_tbl.i.|
|The following example sends the C data-definitions (header file) to the standard output.|
|$ rpcgen -h prot.x|
|To send the test version of the -DTEST, server side stubs for all the transport belonging to the class datagram_n to standard output, use:|
|$ rpcgen -s datagram_n -DTEST prot.x|
|To create the server side stubs for the transport indicated by netid tcp, use:|
|$ rpcgen -n tcp -o prot_svc.c prot.x|
Copyright © tutorialspoint.com