DCErpc详解

– Naming (X.500,DNS) – Authentication (Kerberos) – Data sharing (AFS) – Clock Synchronization (NTP) – Distributed applications (RPC) – Thread support (POSIX based)
• Caller and callee may have different data representations
– Byte order – Structure – Character Set
• One solution: Convert to canonical form
– Conversion done everywhere
DCE RPC
• System independent
– Runs over multiple protocols – Core feature set implemented on each system
• Language independent
– Procedures declared in Interface Description Language
[out, string] char server_reply[REPLY_SIZE]
);
• First parameter is binding
– Explicit (if first parameter is type handle_t)
– From configuration file
– Automatic
• At-most-once
• Idempotent (safe to call more than once)
– Broadcast – try all servers, only one result to client
– Maybe – no response, no guarantee or notice of completion
);
}
Interface Attributes
[uuid(3d6ead56-06e3-11ca-8dd1-826901beabcd), version(1.0)]
• Uuid is required global unique identifier, created with ‘uuidgen’ command
Environment
• DCE: Evolved from CMU research project
– Same folks that produced AFS – Incorporates Kerberos, other research projects
• Includes several components for building distributed systems
• Compiles into stubs that are viewed as local procedures on each host
DCE RPC Run-time System
• Directory Services
– RPC not tied to specific machine name
Using defined interface:
Client
/* greet_client.c - Client of "greet" interface. usage: greet_client <CDS pathname>*/ #include <stdio.h> #include <dce/rpc.h> #include "greet.h“ #include "util.h" Int main(int argc, char *argv[]) {
/* greet.idl
* The "greet" interface. */
[uuid(3d6ead56-06e3-11ca-8dd1-826901beabcd), versic_includes.idl” */
/* type declarations (typedef) */
CS603 Communication Mechanisms
18 January 2002
What is coming
• Remote procedure call – specific systems
– DCE RPC – Java RMI – SOAP
• First project
Distributed Computing
rpc_ns_handle_t import_context; handle_t binding_h; error_status_t status; idl_char reply[REPLY_SIZE]; /* Start importing servers using the name specified on the command line. */ rpc_ns_binding_import_begin(rpc_c_ns_syntax_default, (unsigned_char_p_t) argv[1],
unsigned32 status; rpc_binding_vector_t *binding_vector; /* Register interface with RPC runtime. */
rpc_server_register_if(greetif_v1_0_s_ifspec, NULL, NULL, &status); ERROR_CHECK(status, "Can't register interface"); /* Use all protocol sequences that are available. */ rpc_server_use_all_protseqs(rpc_c_protseq_max_reqs_default, &status); ERROR_CHECK(status, "Can't use protocol sequences"); /* Get the binding handles generated by the runtime. */ rpc_server_inq_bindings(&binding_vector, &status); ERROR_CHECK(status, "Can't get bindings for server");
• DCE RPC: Leave in native form
– Tag with description of native form – Convert on demand – Conversion handled by stub
Building a DCE RPC Application
Sample IDL for message/reply RPC
greetif_v1_0_c_ifspec, NULL, &import_context, &status); ERROR_CHECK(status, "Can't begin import"); /* Import the first server (we could iterate here, but we'll just take the first one). */ rpc_ns_binding_import_next(import_context, &binding_h, &status); ERROR_CHECK(status, "Can't import"); /* Make the remote call. */ greet(binding_h, (idl_char *) "hello, server", reply); printf("The Greet Server said: %s\n", reply); }
Using defined interface:
Server
/* Register assigned endpoints with endpoint mapper. */ rpc_ep_register(greetif_v1_0_s_ifspec, binding_vector, NULL, (unsigned_char_p_t) "greet server version 1.0", &status); ERROR_CHECK(status, "Can't register with endpoint map");
• Includes some special network support
– Example: “Autobind” – declares that procedure will find an execute on another server should the first one fail
• Run-time
– Responds to requests by stubs
• Data Conversion
– Handles differences between systems
IDL Compiler
• IDL is C-like language for specifying semantics of a procedure
– Produces stubs that “stand in” for procedure on local system