implement print queue

printer/print_queue.py

@@ -0,0 +1,36 @@
+import subprocess
+import time
+import logging
+
+class PrintQueue:
+    _queue = []
+
+    def add(self, file_name):
+        self._queue.append(file_name)
+
+    def in_queue(self, file_name):
+        return file_name in self._queue
+
+    def actual_queue_available(self):
+        proc = subprocess.Popen(
+            'lpstat -o',
+            shell=True,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            text=True,
+        )
+
+        printer_job_count = str(proc.stdout.read()).count("\n")
+
+        return printer_job_count <= 2
+
+    def feed_into_printer(self):
+        while True:
+            time.sleep(1)
+
+            if self._queue.__len__() == 0:
+                continue
+
+            if self.actual_queue_available():
+                logging.info("FED REQUEST INTO PRINTER")
+                self._queue.pop(0)

printer/server.py

@@ -7,6 +7,8 @@
 import time
 import uuid
 import collector
+import asyncio
+from print_queue import PrintQueue
 
 from fastapi import FastAPI, File, Form, HTTPException, UploadFile
 from fastapi.middleware.cors import CORSMiddleware
@@ -17,6 +19,8 @@
 from metrics import MetricsHandler
 
 
+print_queue = PrintQueue()
+printer_lock = asyncio.Lock()
 metrics_handler = MetricsHandler.instance()
 app = FastAPI()
 
@@ -35,7 +39,6 @@
 logging.getLogger("uvicorn.access").setLevel(logging.WARNING)
 logging.getLogger("uvicorn.error").setLevel(logging.WARNING)
 
-
 def get_args() -> argparse.Namespace:
     parser = argparse.ArgumentParser()
     parser.add_argument(
@@ -113,6 +116,7 @@ def send_file_to_printer(
     PRINTER_NAME = os.environ.get("RIGHT_PRINTER_NAME")
     command = f"lp -n {num_copies} {maybe_page_range} -o sides={sides} -o media=na_letter_8.5x11in -d {PRINTER_NAME} {file_path}"
     metrics_handler.print_jobs_recieved.inc()
+
     if args.development:
         logging.warning(
             f"server is in development mode, command would've been `{command}`"
@@ -126,6 +130,7 @@ def send_file_to_printer(
         stderr=subprocess.PIPE,
         text=True,
     )
+
     print_job.wait()
 
     if print_job.returncode != 0:
@@ -145,16 +150,14 @@ def send_file_to_printer(
         # with code 0 but the output could not be parsed for a job id.
         return ''
 
-
 def maybe_delete_pdf(file_path):
     if args.dont_delete_pdfs:
         logging.info(
-            f"--dont-delete-pdfs is set, skipping deletion of file {file_path}"
+           f"--dont-delete-pdfs is set, skipping deletion of file {file_path}"
         )
         return
     pathlib.Path(file_path).unlink()
 
-
 @app.get("/healthcheck/printer")
 def api():
     metrics_handler.last_health_check_request.set(int(time.time()))
@@ -178,30 +181,42 @@ async def read_item(
       "sides": string value from user input on clark frontend; we insert this into the lp command,
     }
     """
-    try:
-        base = pathlib.Path("/tmp")
-        file_id = str(uuid.uuid4())
-        file_path = str(base / file_id)
-        with open(file_path, "wb") as f:
-            f.write(await file.read())
-        print_id = send_file_to_printer(
-            str(file_path),
-            copies,
-            sides=sides,
-        )
+    async with printer_lock:
+        if not args.development and not print_queue.actual_queue_available():
+            print_queue.add(file.filename)
+            timeout = 0
+            while print_queue.in_queue(file.filename):
+                timeout += 1
 
-        maybe_delete_pdf(file_path)
+                if timeout > 300:
+                    raise Exception("/print TIMED OUT AFTER 300 SECONDS WHILE WAITING IN THE PRINTER QUEUE")
+
+                await asyncio.sleep(1)
 
-        if not args.development and print_id is None:
-            raise Exception("unable to extract print id from print request")
-        return {"print_id": print_id}
-    except Exception:
-        logging.exception("printing failed!")
-        return HTTPException(
-            status_code=500,
-            detail="printing failed, check logs",
-        )
+        try:
+            base = pathlib.Path("/tmp")
+            file_id = str(uuid.uuid4())
+            file_path = str(base / file_id)
+            with open(file_path, "wb") as f:
+                f.write(await file.read())
+            print_id = send_file_to_printer(
+                str(file_path),
+                copies,
+                sides=sides,
+            )
 
+            maybe_delete_pdf(file_path)
+
+            if not args.development and print_id is None:
+                raise Exception("unable to extract print id from print request")
+            return {"print_id": print_id}
+        except Exception:
+            logging.exception("printing failed!")
+            return HTTPException(
+                status_code=500,
+                detail="printing failed, check logs",
+            )
+
 
 # we have a separate __name__ check here due to how FastAPI starts
 # a server. the file is first ran (where __name__ == "__main__")
@@ -212,6 +227,13 @@ async def read_item(
 # the thread interacts with an instance different than the one the
 # server uses
 if __name__ == "server":
+    if not args.development:
+        queue_thread = threading.Thread(
+            target=print_queue.feed_into_printer,
+            daemon=True
+        )
+        queue_thread.start()
+
     if not args.development:
         # set the last time we opened an ssh tunnel to now because
         # when the script runs for the first time, we did so in what.sh