Add external code generator for RPC clients

Introduce generate_client.py to generate client code from the Bitcoin
Core RPC schema. This tool enables developers to easily update and
maintain client libraries in various languages by automatically
reflecting changes in the RPC interface.

contrib/codegen/generate_client.py

@@ -0,0 +1,66 @@
+#!/usr/bin/env python3
+
+import argparse
+import json
+import os
+import subprocess
+from jinja2 import Environment, FileSystemLoader
+
+def get_schema():
+    """Get the schema from the Bitcoin Core RPC help."""
+    try:
+        result = subprocess.run(['bitcoin-cli', 'schema'], capture_output=True, text=True, check=True)
+        schema = json.loads(result.stdout)
+        return schema
+    except Exception as e:
+        raise RuntimeError("Failed to get schema from bitcoin-cli: " + str(e))
+    
+def sanitize_argument_names(rpcs):
+    for rpc_name, details in rpcs.items():
+        if "argument_names" in details:
+            sanitized = []
+            for arg in details["argument_names"]:
+                sanitized.append(arg.split("|")[0])
+            details["argument_names"] = sanitized
+    
+    return rpcs
+    
+def generate_client(schema, language, output_dir):
+    """Generate client code using the specified language template."""
+    script_dir = os.path.dirname(os.path.abspath(__file__))
+    templates_path = os.path.join(script_dir, "templates")
+    env = Environment(loader=FileSystemLoader(templates_path))
+
+    # choose template based on target language
+    if language.lower() == "python":
+        template_file = env.get_template("python_client.jinja2")
+        output_file_name = "bitcoin_rpc_client.py"
+    elif language.lower() == "cpp":
+        template_file = env.get_template("cpp_client.jinja2")
+        output_file_name = "bitcoin_rpc_client.cpp"
+    else:
+        raise ValueError("Unsupported language: " + language)
+    
+    template = env.get_template(template_file)
+    rendered_code = template.render(rpcs=schema.get("rpcs", {}))
+
+    os.makedirs(output_dir, exist_ok=True)
+    output_path = os.path.join(output_dir, output_file_name)
+    with open(output_path, "w") as f:
+        f.write(rendered_code)
+    print(f"Generated {language.upper()} client code at {output_path}")
+
+def main():
+    parser = argparse.ArgumentParser(description="Generate Bitcoin Core RPC client code.")
+    parser.add_argument('--language', required=True, choices=["python", "cpp"], help="The target language for the client code.")
+    parser.add_argument('--output-dir', default="generated", help="The directory to write the generated code to.")
+    args = parser.parse_args()
+
+    print("Getting schema from Bitcoin Core RPC...")
+    schema = get_schema()
+    rpcs = schema.get("rpcs", {})
+    rpcs = sanitize_argument_names(rpcs)
+    generate_client(schema, args.language, args.output_dir)
+
+if __name__ == "__main__":
+    main()