rpcgen: define entrypoint for running new rpcgen impl

The new program takes the form

  rpcgen [--mode source|header|repr] \
         [--header include] \
         xdr-file output-file

If '--mode' is not given it parses the XDR file but does not
generate anything, which is useful as a syntax check. The
'source' mode gives the '.c' file content, while 'header'
gives the '.h' file content. 'repr' gives a representation
of the abstract syntax tree, mostly useful for debugging
the parser.

If '--header' is given, it is added as a local #include ".."
statement in the output and is valid for either 'header'
or 'source' modes.

Either 'xdr-file' or 'output-file' can be omitted in which
case they default to stdin/stdout respectively.

This rpcgen program will directly include the 'config.h'
header in its output.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

diff --git a/scripts/rpcgen/main.py b/scripts/rpcgen/main.py
new file mode 100755 (executable)
index 0000000..bde6dcc
--- /dev/null
+++ b/scripts/rpcgen/main.py
@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+import argparse
+import os
+import sys
+
+from rpcgen.parser import XDRParser
+from rpcgen.generator import (
+    XDRTypeDeclarationGenerator,
+    XDRMarshallDeclarationGenerator,
+    XDRMarshallImplementationGenerator,
+)
+
+
+def parse_cli():
+    parser = argparse.ArgumentParser("RPC code generator")
+    parser.add_argument(
+        "-m",
+        "--mode",
+        choices=["header", "source", "repr"],
+        help="Output generation mode",
+    )
+    parser.add_argument(
+        "-r", "--header", default=[], action="append", help="Extra headers to include"
+    )
+    parser.add_argument("input", default="-", nargs="?", help="XDR input protocol file")
+    parser.add_argument("output", default="-", nargs="?", help="Generated output file")
+
+    return parser.parse_args()
+
+
+def main():
+    args = parse_cli()
+
+    infp = sys.stdin
+    outfp = sys.stdout
+    if args.input != "-":
+        infp = open(args.input, "r")
+    if args.output != "-":
+        # the old genprotocol.pl wrapper would make the
+        # output files mode 0444, which will prevent us
+        # from writing directly do them. Explicitly
+        # unlinking first gets rid of any old possibly
+        # read-only copy
+        #
+        # We can delete this in a few years, once we
+        # know users won't have a previously generated
+        # readonly copy lieing around.
+        try:
+            os.unlink(args.output)
+        except Exception:
+            pass
+        outfp = open(args.output, "w")
+
+    parser = XDRParser(infp)
+    spec = parser.parse()
+
+    if args.mode == "header":
+        print("/* This file is auto-generated from %s */\n" % args.input, file=outfp)
+        print("#include <rpc/rpc.h>", file=outfp)
+        for h in args.header:
+            print('#include "%s"' % h, file=outfp)
+        print("", file=outfp)
+        print("#pragma once\n", file=outfp)
+        generator = XDRTypeDeclarationGenerator(spec)
+        print(generator.visit(), file=outfp)
+        generator = XDRMarshallDeclarationGenerator(spec)
+        print(generator.visit(), file=outfp)
+    elif args.mode == "source":
+        print("/* This file is auto-generated from %s */\n" % args.input, file=outfp)
+        print("#include <config.h>", file=outfp)
+        for h in args.header:
+            print('#include "%s"' % h, file=outfp)
+        print("", file=outfp)
+        generator = XDRMarshallImplementationGenerator(spec)
+        print(generator.visit(), file=outfp)
+    elif args.mode == "repr":
+        print(spec, file=outfp)
+    else:
+        pass  # Just validates XDR input syntax
+
+
+main()