Support appending pre-encoded data when serializing (#510)

* add print_job data

* Apply suggestions from code review

---------

Co-authored-by: Chris Talkington <chris@talkingtontech.com>

examples/print_example.py

@@ -0,0 +1,34 @@
+# pylint: disable=W0621
+"""Asynchronous Python client for IPP."""
+import asyncio
+
+from pyipp import IPP
+from pyipp.enums import IppOperation
+
+
+async def main() -> None:
+
+    pdf_file = '/path/to/pdf.pfd'
+    with open(pdf_file, 'rb') as f:
+        content = f.read()
+
+    """Show example of executing operation against your IPP print server."""
+    async with IPP("ipp://192.168.1.92:631/ipp/print") as ipp:
+        response = await ipp.execute(
+            IppOperation.PRINT_JOB,
+            {
+                "operation-attributes-tag": {
+                    "requesting-user-name": "Me",
+                    "job-name": "My Test Job",
+                    "document-format": "application/pdf",
+                },
+                'data': content,
+            },
+        )
+
+        print(response)
+
+
+if __name__ == "__main__":
+    loop = asyncio.get_event_loop()
+    loop.run_until_complete(main())

src/pyipp/serializer.py

@@ -93,4 +93,7 @@ def encode_dict(data: dict[str, Any]) -> bytes:
 
     encoded += struct.pack(">b", IppTag.END.value)
 
+    if "data" in data:
+        encoded += data["data"]
+
     return encoded