Document extractor service (#15665)

* Document extractor service

* Fixing vendor modules

* Addressing PR Review comments

* Some small simplifications

* Fixing a linter complain

* simplifying a bit the code using package variables

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

vendor/github.com/levigross/exp-html/node.go

@@ -0,0 +1,154 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package html
+
+// A NodeType is the type of a Node.
+type NodeType int
+
+const (
+	ErrorNode NodeType = iota
+	TextNode
+	DocumentNode
+	ElementNode
+	CommentNode
+	DoctypeNode
+	scopeMarkerNode
+)
+
+// Section 12.2.3.3 says "scope markers are inserted when entering applet
+// elements, buttons, object elements, marquees, table cells, and table
+// captions, and are used to prevent formatting from 'leaking'".
+var scopeMarker = Node{Type: scopeMarkerNode}
+
+// A Node consists of a NodeType and some Data (tag name for element nodes,
+// content for text) and are part of a tree of Nodes. Element nodes may also
+// have a Namespace and contain a slice of Attributes. Data is unescaped, so
+// that it looks like "a<b" rather than "a&lt;b".
+//
+// An empty Namespace implies a "http://www.w3.org/1999/xhtml" namespace.
+// Similarly, "math" is short for "http://www.w3.org/1998/Math/MathML", and
+// "svg" is short for "http://www.w3.org/2000/svg".
+type Node struct {
+	Parent    *Node
+	Child     []*Node
+	Type      NodeType
+	Data      string
+	Namespace string
+	Attr      []Attribute
+}
+
+// Add adds a node as a child of n.
+// It will panic if the child's parent is not nil.
+func (n *Node) Add(child *Node) {
+	if child.Parent != nil {
+		panic("html: Node.Add called for a child Node that already has a parent")
+	}
+	child.Parent = n
+	n.Child = append(n.Child, child)
+}
+
+// Remove removes a node as a child of n.
+// It will panic if the child's parent is not n.
+func (n *Node) Remove(child *Node) {
+	if child.Parent == n {
+		child.Parent = nil
+		for i, m := range n.Child {
+			if m == child {
+				copy(n.Child[i:], n.Child[i+1:])
+				j := len(n.Child) - 1
+				n.Child[j] = nil
+				n.Child = n.Child[:j]
+				return
+			}
+		}
+	}
+	panic("html: Node.Remove called for a non-child Node")
+}
+
+// reparentChildren reparents all of src's child nodes to dst.
+func reparentChildren(dst, src *Node) {
+	for _, n := range src.Child {
+		if n.Parent != src {
+			panic("html: nodes have an inconsistent parent/child relationship")
+		}
+		n.Parent = dst
+	}
+	dst.Child = append(dst.Child, src.Child...)
+	src.Child = nil
+}
+
+// clone returns a new node with the same type, data and attributes.
+// The clone has no parent and no children.
+func (n *Node) clone() *Node {
+	m := &Node{
+		Type: n.Type,
+		Data: n.Data,
+		Attr: make([]Attribute, len(n.Attr)),
+	}
+	copy(m.Attr, n.Attr)
+	return m
+}
+
+// nodeStack is a stack of nodes.
+type nodeStack []*Node
+
+// pop pops the stack. It will panic if s is empty.
+func (s *nodeStack) pop() *Node {
+	i := len(*s)
+	n := (*s)[i-1]
+	*s = (*s)[:i-1]
+	return n
+}
+
+// top returns the most recently pushed node, or nil if s is empty.
+func (s *nodeStack) top() *Node {
+	if i := len(*s); i > 0 {
+		return (*s)[i-1]
+	}
+	return nil
+}
+
+// index returns the index of the top-most occurrence of n in the stack, or -1
+// if n is not present.
+func (s *nodeStack) index(n *Node) int {
+	for i := len(*s) - 1; i >= 0; i-- {
+		if (*s)[i] == n {
+			return i
+		}
+	}
+	return -1
+}
+
+// insert inserts a node at the given index.
+func (s *nodeStack) insert(i int, n *Node) {
+	(*s) = append(*s, nil)
+	copy((*s)[i+1:], (*s)[i:])
+	(*s)[i] = n
+}
+
+// remove removes a node from the stack. It is a no-op if n is not present.
+func (s *nodeStack) remove(n *Node) {
+	i := s.index(n)
+	if i == -1 {
+		return
+	}
+	copy((*s)[i:], (*s)[i+1:])
+	j := len(*s) - 1
+	(*s)[j] = nil
+	*s = (*s)[:j]
+}
+
+// TODO(nigeltao): forTag no longer used. Should it be deleted?
+
+// forTag returns the top-most element node with the given tag.
+func (s *nodeStack) forTag(tag string) *Node {
+	for i := len(*s) - 1; i >= 0; i-- {
+		n := (*s)[i]
+		if n.Type == ElementNode && n.Data == tag {
+			return n
+		}
+	}
+	return nil
+}