From 7e0f021a9aec35fd8e6725e87e3313b101d26f5e Mon Sep 17 00:00:00 2001 From: Tobias Klauser Date: Sun, 27 Jan 2008 11:37:44 +0100 Subject: Initial import (2.0.2-6) --- reference/C/CONCEPT/rpc.html | 356 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 356 insertions(+) create mode 100644 reference/C/CONCEPT/rpc.html (limited to 'reference/C/CONCEPT/rpc.html') diff --git a/reference/C/CONCEPT/rpc.html b/reference/C/CONCEPT/rpc.html new file mode 100644 index 0000000..e45041c --- /dev/null +++ b/reference/C/CONCEPT/rpc.html @@ -0,0 +1,356 @@ +RPC + +
+

Remote Procedure Calls (RPC).

+
+In the normal scope of things, a program can only call a function +that is linked into the executable or provided by a shared library. +RPC allows programs to execute functions in another executing program, cool! +

+RPC has a concept of clients and servers. +

    +
  1. The client issues requests to the server. +
  2. Servers perform the requests and return the results. +
  3. The data that flows between client and server includes +int, float, strings and structures. +
  4. The client and server can be on the same host or different hosts +connected via a network. +
  5. The hosts do not have to be the same artitechture. +
+ +The RPC API has three levels of support. +By using the highest level +RPC is responcable for most of the code but is not too flexable. The lowest +level requres more coding but gives the programmer more control over how RPC +functions. +

+The easiest way to start with RPC is to use a program called rpcgen +this reads a file that describes the required interface between client and server +and generates C code that you can include in your client and server. + +

+
+	prog.x --> rpcgen ---> prog.h        Header file
+                          ---> prog_clnt.c   Client stubs file
+                          ---> prog_svc.c    Server stubs file
+                          ---> prog_xdr.c    XDR routines (more later).
+
+
+You write prog.x and rpcgen generates +prog.h prog_clnt.c prog_svc.c prog_xdr.c + +You then write the client and server and link them with the rpcgen code +to complete the RPC system. + +
+
+	client.c    -----> client executable
+        prog.h      ---|
+        prog_clnt.c ---|
+        prog_xdr.c  ---|
+
+        server.c    -----> Server executable
+        prog.h      ---|
+        prog_svc.c  ---|
+        prog_xdr.c  ---|
+
+
+
+ +Ok, time for some examples. + +

Calling an RPC server function without passing any arguments.

+This is the simplest form of RPC. + +

+

+ + + + + +
+void.x +
+
+
+  /* RPCGEN code decribing the client/server API. */
+ 
+  program MJLPROG
+  {
+    version MJLVERS
+    {
+      void VOID(void) = 1;
+    
+    } = 1;
+  } = 0x20000001;
+
+
+
+

+ +void.x describes the RPC interface between the client +and server. There are some important items to note here. +

+ + + + + + + + + + + + +
+
+program MJLPROG
+{
+} = 0x20000001;
+
This is the RPC program number. It is used by the client to +identify the server it intends to use. +It is important that you provide a unique number here. You can see +which values are in use with the Unix command rpcinfo -p or +by looking at /etc/rpc. Please note that the number is supplied +in void.x as a hex value but shown as a decimal value by rpcinfo +One other point, you should only use values in the range 0x20000000 +0x3FFFFFFF as these have been reserved for use local use. +
+
+version MJLVERS
+{
+} = 1;
+
The RPC Version number.
void VOID(void) = 1;
This defines the only RPC function that the server will provide.
+

+ +

+ + + + + +
+void_client.c +
+
+
+  #include <rpc/rpc.h>
+  #include "void.h"
+
+  main()
+  {
+      CLIENT *pclnt;
+      void   *pVoid;
+    
+      char    Host[256];
+
+      /* Get the name of the host running the server. */
+    
+      gethostname(Host, 256);
+
+      /* Connect to the server. */
+    
+      pclnt = clnt_create(Host, MJLPROG, MJLVERS, "udp");
+
+      /* Issue a request to the server. */
+    
+      void_1(pVoid, pclnt);
+
+      /* Disconnect from the server. */
+    
+      clnt_destroy(pclnt);
+
+  }
+
+
+
+ +

+ + + + + + + + + + + + + + + + + + + + + +
+
+#include <rpc/rpc.h>
+
+
+		 +Include the standard RPC headers. +
+
+#include "void.h"
+
+		 +Include the header file generated by rpcgen +
+
+pclnt = clnt_create();
+
+		Connect to the server MJLPROG on Host and return a +pointer to the CLIENT control structure. +
+
+void_1(pVoid, pclnt);
+
+		 +Call the remote function. +
+
+clnt_destroy();
+
+		 +Disconnect from the server. +
+

+ +

+ + + + + +
+void_server.c +
+
+
+  #include 
+  #include "void.h"
+
+  void *void_1_svc(void *pVoid,  struct svc_req *X)
+  {
+      printf("Function called without passing arguments\n");
+  }
+
+
+
+
+ +

+ + + + + +
+
+void *void_1_svc()
+
+		 +The server function that will be run for the client. +
+

+ +Please note that the server does not have a main(), rpcgen +generates it for you. +

+The code can be compiled with the following commands + +

+  gcc void_server.c void_svc.c -o void_server
+  gcc void_client.c void_clnt.c -o void_client
+
+

+In theory you should be able to start the server and it will +respond everytime the client is executed. I have not included any +error recovery into this example as it makes the code harder to +read. As an exercise try adding the error recovery code yourself :-) + +

Transfer integers between the client and server

+ + +

+

+ + + + + +
+integer.x +
+
+
+  /* RPCGEN code decribing the client/server API. */
+ 
+  program MJLPROG
+  {
+    version MJLVERS
+    {
+      int INTEGER(int) = 1;
+    
+    } = 1;
+  } = 0x20000001;
+
+
+
+ +

+ + + + + +
+
+int INTEGER(int) = 1;
+
+		 +Server function now accepts an integer and returns an integer. +
+ + + + +

+ +

+

See Also:

+ + +VOID keyword. +
+

+

+ + + + +
+Top + +Master Index + +Keywords + +Functions +
+
+

+ +

+29-Dec-97 +
Martin Leslie + + + -- cgit v1.2.3-54-g00ecf