Make delegator blocking with a waiting http server

slim-containers-files/delegator_template.py

@@ -1,16 +1,48 @@
 #!/usr/bin/env python
 import sys
 import subprocess
+from http.server import BaseHTTPRequestHandler, HTTPServer
 
-# Later the address (or rather the port) should be dynamic
 processing_server_address = "http://localhost:{{ OCRD_PS_PORT }}"
 processor_name = "{{ processor_name }}"
 
-args = list(sys.argv)
+STOP_WAITING_SERVER = False
 
 
-cmd = [
-    "ocrd", "network", "client", "processing", "processor",
-    processor_name, "--address", processing_server_address
-]
-subprocess.run(cmd + args[1:])
+class CallbackReceiver(BaseHTTPRequestHandler):
+    """Simple http-server to wait for a processor to finish working.
+
+    The OCR-D processor is started with a callback-url which points to this server. The processor
+    starts working in the background but the call is returned immediately. When the processor is
+    finished it sends a request to the callback-url. The purpose of this server is to wait for the
+    processor to finish and print its result.
+    """
+    def do_POST(self):
+        self.send_response(200)
+        self.send_header("Content-Type", "text/plain")
+        self.end_headers()
+        self.wfile.write("finished".encode("utf-8"))
+        len = int(self.headers.get("Content-Length", 0))
+        data = self.rfile.read(len).decode("utf-8")
+        # TODO: how should the callback-content be handled/printed
+        print(f"Processor finished: {data}")
+        global STOP_WAITING_SERVER
+        STOP_WAITING_SERVER = True
+
+
+def call_processor_and_wait():
+    server = HTTPServer(("0.0.0.0", 0), CallbackReceiver)
+    callback_url = f"http://172.17.0.1:{server.server_address[1]}"
+    cmd = [
+        "ocrd", "network", "client", "processing", "processor",
+        processor_name, "--address", processing_server_address,
+        "--callback-url", callback_url
+    ]
+    args = list(sys.argv)
+    subprocess.run(cmd + args[1:])
+    while not STOP_WAITING_SERVER:
+        server.handle_request()
+
+
+if __name__ == "__main__":
+    call_processor_and_wait()