Allow offloading of label printing to the configured plugin

InvenTree/label/api.py

@@ -1,12 +1,15 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
+from io import BytesIO
+from PIL import Image
+
 from django.utils.translation import ugettext_lazy as _
 
 from django.conf import settings
 from django.conf.urls import url, include
 from django.core.exceptions import ValidationError, FieldError
-from django.http import HttpResponse
+from django.http import HttpResponse, JsonResponse
 
 from django_filters.rest_framework import DjangoFilterBackend
 
@@ -14,6 +17,7 @@ from rest_framework import generics, filters
 from rest_framework.response import Response
 
 import InvenTree.helpers
+from InvenTree.tasks import offload_task
 import common.models
 
 from plugin.registry import registry
@@ -102,6 +106,8 @@ class LabelPrintMixin:
 
         label_name = "label.pdf"
 
+        label_names = []
+
         # Merge one or more PDF files into a single download
         for item in items_to_print:
             label = self.get_object()
@@ -109,6 +115,8 @@ class LabelPrintMixin:
 
             label_name = label.generate_filename(request)
 
+            label_names.append(label_name)
+
             if debug_mode:
                 outputs.append(label.render_as_string(request))
             else:
@@ -117,7 +125,46 @@ class LabelPrintMixin:
         if not label_name.endswith(".pdf"):
             label_name += ".pdf"
 
-        if debug_mode:
+        if plugin is not None:
+            """
+            Label printing is to be handled by a plugin,
+            rather than being exported to PDF.
+
+            In this case, we do the following:
+            
+            - Individually generate each label, exporting as an image file
+            - Pass all the images through to the label printing plugin
+            - Return a JSON response indicating that the printing has been offloaded
+            
+            """
+
+            for output in outputs:
+                """
+                For each output, we generate a temporary image file,
+                which will then get sent to the printer
+                """
+
+                # Generate a png image at 300dpi
+                (img_data, w, h) = output.get_document().write_png(resolution=300)
+
+                # Construct a BytesIO object, which can be read by pillow
+                img_bytes = BytesIO(img_data)
+
+                image = Image.open(img_bytes)
+
+                # Offload a background task to print the provided label
+                offload_task(
+                    'plugin.events.print_label',
+                    plugin.plugin_slug(),
+                    image
+                )
+
+            return JsonResponse({
+                'plugin': plugin.plugin_slug(),
+                'labels': label_names,
+            })
+
+        elif debug_mode:
             """
             Contatenate all rendered templates into a single HTML string,
             and return the string as a HTML response.
@@ -126,6 +173,7 @@ class LabelPrintMixin:
             html = "\n".join(outputs)
 
             return HttpResponse(html)
+
         else:
             """
             Concatenate all rendered pages into a single PDF object,

InvenTree/plugin/builtin/integration/mixins.py

@@ -415,15 +415,6 @@ class LabelPrintingMixin:
     def get_printer_name(self):
         return self.PRINTER_NAME
 
-    def print_labels(self, labels, **kwargs):
-        """
-        Print multiple labels.
-        Default implementation is to call print_label() for each label,
-        but it can be overridden if desired.
-        """
-        for label in labels:
-            self.print_label(label, **kwargs)
-
     def print_label(self, label, **kwargs):
         """
         Callback to print a single label

InvenTree/plugin/events.py

@@ -95,7 +95,11 @@ def process_event(plugin_slug, event, *args, **kwargs):
 
     logger.info(f"Plugin '{plugin_slug}' is processing triggered event '{event}'")
 
-    plugin = registry.plugins[plugin_slug]
+    plugin = registry.plugins.get(plugin_slug, None)
+    
+    if plugin is None:
+        logger.error(f"Could not find matching plugin for '{plugin_slug}'")
+        return
 
     plugin.process_event(event, *args, **kwargs)
 
@@ -186,3 +190,25 @@ def after_delete(sender, instance, **kwargs):
         model=sender.__name__,
         table=table,
     )
+
+
+def print_label(plugin_slug, label_image, **kwargs):
+    """
+    Print label with the provided plugin.
+
+    This task is nominally handled by the background worker.
+
+    Arguments:
+        plugin_slug: The unique slug (key) of the plugin
+        label_image: A PIL.Image image object to be printed
+    """
+
+    logger.info(f"Plugin '{plugin_slug}' is printing a label")
+
+    plugin = registry.plugins.get(plugin_slug, None)
+    
+    if plugin is None:
+        logger.error(f"Could not find matching plugin for '{plugin_slug}'")
+        return
+
+    plugin.print_label(label_image)

InvenTree/templates/js/translated/label.js

@@ -14,11 +14,41 @@
 */
 
 /* exported
+    printLabels,
     printPartLabels,
     printStockItemLabels,
     printStockLocationLabels,
 */
 
+
+/*
+ * Perform the "print" action.
+ */
+function printLabels(url, plugin=null) {
+
+    if (plugin) {
+        // If a plugin is provided, do not redirect the browser.
+        // Instead, perform an API request and display a message
+
+        url = url + `plugin=${plugin}`;
+
+        inventreeGet(url, {}, {
+            success: function(response) {
+                showMessage(
+                    '{% trans "Labels sent to printer" %}',
+                    {
+                        style: 'success',
+                    }
+                );
+            }
+        });
+    } else {
+        window.location.href = url;
+    }
+
+}
+
+
 function printStockItemLabels(items) {
     /**
      * Print stock item labels for the given stock items
@@ -67,11 +97,7 @@ function printStockItemLabels(items) {
                                 href += `items[]=${item}&`;
                             });
 
-                            if (data.plugin) {
-                                href += `plugin=${data.plugin}`;
-                            }
-
-                            window.location.href = href;
+                            printLabels(href, data.plugin);
                         }
                     }
                 );
@@ -80,6 +106,7 @@ function printStockItemLabels(items) {
     );
 }
 
+
 function printStockLocationLabels(locations) {
 
     if (locations.length == 0) {
@@ -124,11 +151,7 @@ function printStockLocationLabels(locations) {
                                 href += `locations[]=${location}&`;
                             });
 
-                            if (data.plugin) {
-                                href += `plugin=${data.plugin}`;
-                            }
-
-                            window.location.href = href;
+                            printLabels(href, data.plugin);
                         }
                     }
                 );
@@ -186,11 +209,7 @@ function printPartLabels(parts) {
                                 url += `parts[]=${part}&`;
                             });
 
-                            if (data.plugin) {
-                                href += `plugin=${data.plugin}`;
-                            }
-
-                            window.location.href = url;
+                            printLabels(href, data.plugin);
                         }
                     }
                 );
@@ -234,7 +253,6 @@ function selectLabel(labels, items, options={}) {
 
     var plugin_selection = '';
     
-    
     if (plugins.length > 0) {
         plugin_selection =`
         <div class='form-group'>