Add robust error handling and logging to print endpoint

app.py

@@ -1,9 +1,12 @@
+import logging
+import subprocess
 from enum import Enum
 from pathlib import Path
 
-from fastapi import FastAPI, File, Form, UploadFile
+from fastapi import FastAPI, File, Form, UploadFile, HTTPException
 from fastapi.responses import FileResponse
 from fastapi.staticfiles import StaticFiles
+from PIL import UnidentifiedImageError
 
 from imaging.process import to_1bit
 from printer.cups import spool_raw
@@ -34,6 +37,8 @@ class Lang(str, Enum):
 static_dir = Path(__file__).parent / "static"
 app.mount("/static", StaticFiles(directory=static_dir), name="static")
 
+logger = logging.getLogger(__name__)
+
 
 @app.get("/")
 async def index() -> FileResponse:
@@ -46,12 +51,22 @@ async def print_image(
     media: Media = Form(...),
     lang: Lang = Form(...),
 ) -> dict:
-    img_bytes = await file.read()
-    width = MEDIA_WIDTHS[media]
-    img = to_1bit(img_bytes, width)
-    if lang == Lang.EPL:
-        payload = img_to_epl_gw(img)
-    else:
-        payload = img_to_zpl_gf(img)
-    spool_raw(PRINTER_NAME, payload)
+    try:
+        img_bytes = await file.read()
+        width = MEDIA_WIDTHS[media]
+        img = to_1bit(img_bytes, width)
+        if lang == Lang.EPL:
+            payload = img_to_epl_gw(img)
+        else:
+            payload = img_to_zpl_gf(img)
+        spool_raw(PRINTER_NAME, payload)
+    except UnidentifiedImageError:
+        logger.exception("Failed to process uploaded image")
+        raise HTTPException(status_code=400, detail="Invalid image file")
+    except subprocess.CalledProcessError:
+        logger.exception("Printing failed")
+        raise HTTPException(status_code=500, detail="Failed to spool print job")
+    except Exception:
+        logger.exception("Unexpected error during printing")
+        raise HTTPException(status_code=500, detail="Internal server error")
     return {"status": "ok"}