Browser viewer: Do not fail if the book contains javascript that has errors. Fixes #1715781 [Private bug](https://bugs.launchpad.net/calibre/+bug/1715781)

src/pyj/read_book/iframe.pyj

@@ -69,6 +69,7 @@ class IframeBoss:
         self.replace_history_on_next_cfi_update = True
         self.encrypted_communications = False
         self.blob_url_map = {}
+        self.resource_urls = {}
         self.content_ready = False
         self.last_window_width = self.last_window_height = -1
         window.addEventListener('message', self.handle_message, False)
@@ -145,15 +146,19 @@ class IframeBoss:
             # type of error
             console.log(f'Unhandled error from external javascript, ignoring: {msg} {script_url} {line_number}')
             return
-        console.log(error_object)
-        try:
-            fname = script_url.rpartition('/')[-1] or script_url
-            msg = msg + '<br><span style="font-size:smaller">' + 'Error at {}:{}:{}'.format(fname, line_number, column_number or '') + '</span>'
-            details = traceback.format_exception(error_object).join('') if error_object else ''
-            self.send_message('error', title=_('Unhandled error'), details=details, msg=msg)
-            return True
-        except:
-            console.log('There was an error in the iframe unhandled exception handler')
+        is_internal_error = not self.resource_urls[script_url]
+        if is_internal_error:  # dont report errors from scripts in the book itself
+            console.log(error_object)
+            try:
+                fname = script_url.rpartition('/')[-1] or script_url
+                msg = msg + '<br><span style="font-size:smaller">' + 'Error at {}:{}:{}'.format(fname, line_number, column_number or '') + '</span>'
+                details = traceback.format_exception(error_object).join('') if error_object else ''
+                self.send_message('error', title=_('Unhandled error'), details=details, msg=msg)
+                return True
+            except:
+                console.log('There was an error in the iframe unhandled exception handler')
+        else:
+            (console.error or console.log)('There was an error in the JavaScript from within the book')
 
     def display(self, data):
         self.length_before = None
@@ -186,7 +191,7 @@ class IframeBoss:
         for name in self.blob_url_map:
             window.URL.revokeObjectURL(self.blob_url_map[name])
         root_data, self.mathjax, self.blob_url_map = finalize_resources(self.book, data.name, data.resource_data)
-        unserialize_html(root_data, self.content_loaded)
+        self.resource_urls = unserialize_html(root_data, self.content_loaded)
 
     def handle_gesture(self, gesture):
         if gesture.type is 'show-chrome':

src/pyj/read_book/resources.pyj

@@ -185,7 +185,7 @@ def apply_attributes(src, elem, ns_map):
         else:
             elem.setAttribute(a[0], a[1])
 
-def process_stack(stack, tag_map, ns_map, load_required, onload):
+def process_stack(stack, tag_map, ns_map, load_required, onload, resource_urls):
     while stack.length:
         node, parent = stack.pop()
         src = tag_map[node[0]]
@@ -194,13 +194,14 @@ def process_stack(stack, tag_map, ns_map, load_required, onload):
         else:
             elem = document.createElement(src.n)
         loadable = False
-        if src.n in resource_tag_names:
-            attr = resource_tag_names[src.n]
+        attr = resource_tag_names[src.n]
+        if attr:
             if attr.indexOf(':') != -1:
                 attr = attr.replace('xlink:', '')
             for a in (src.a or v'[]'):
                 if a[0] is attr:
                     loadable = a[1].startswith('blob:')
+                    resource_urls[a[1]] = True
                     break
         if loadable:
             load_required.add(node[0])
@@ -227,6 +228,7 @@ def unserialize_html(serialized_data, proceed):
     apply_attributes(html, document.documentElement, ns_map)
     head, body = tree[1], tree[2]  # noqa: unused-local
     clear(document.head, document.body)
+    resource_urls = {}
     load_required = set()
     proceeded = False
     hang_timeout = 5
@@ -248,14 +250,14 @@ def unserialize_html(serialized_data, proceed):
     stack = v'[]'
     for v'var i = head.length - 1; i >= 1; i--':
         stack.push(v'[head[i], document.head]')
-    process_stack(stack, tag_map, ns_map, load_required, onload)
+    process_stack(stack, tag_map, ns_map, load_required, onload, resource_urls)
     bnode = tag_map[body[0]]
     apply_attributes(bnode, document.body, ns_map)
     if bnode.x:
         document.body.appendChild(document.createTextNode(bnode.x))
     for v'var i = body.length - 1; i >= 1; i--':  # noqa: unused-local
         stack.push(v'[body[i], document.body]')
-    process_stack(stack, tag_map, ns_map, load_required, onload)
+    process_stack(stack, tag_map, ns_map, load_required, onload, resource_urls)
     ev = document.createEvent('Event')
     ev.initEvent('DOMContentLoaded', True, True)
     document.dispatchEvent(ev)
@@ -264,6 +266,7 @@ def unserialize_html(serialized_data, proceed):
     else:
         proceeded = True
         proceed()
+    return resource_urls
 
 def text_from_serialized_html(data):
     serialized_data = JSON.parse(data)