TUN-1350: Enhance error messages with cloudflarestatus.com link, if relevant

vendor/github.com/cloudflare/golibs/lrucache/list.go

@@ -0,0 +1,238 @@
+// Copyright 2009 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.
+
+/* This file is a slightly modified file from the go package sources
+and is released on the following license:
+
+Copyright (c) 2012 The Go Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+// Package list implements a doubly linked list.
+//
+// To iterate over a list (where l is a *List):
+//	for e := l.Front(); e != nil; e = e.Next() {
+//		// do something with e.Value
+//	}
+//
+
+package lrucache
+
+// Element is an element of a linked list.
+type element struct {
+	// Next and previous pointers in the doubly-linked list of elements.
+	// To simplify the implementation, internally a list l is implemented
+	// as a ring, such that &l.root is both the next element of the last
+	// list element (l.Back()) and the previous element of the first list
+	// element (l.Front()).
+	next, prev *element
+
+	// The list to which this element belongs.
+	list *list
+
+	// The value stored with this element.
+	Value interface{}
+}
+
+// Next returns the next list element or nil.
+func (e *element) Next() *element {
+	if p := e.next; e.list != nil && p != &e.list.root {
+		return p
+	}
+	return nil
+}
+
+// Prev returns the previous list element or nil.
+func (e *element) Prev() *element {
+	if p := e.prev; e.list != nil && p != &e.list.root {
+		return p
+	}
+	return nil
+}
+
+// List represents a doubly linked list.
+// The zero value for List is an empty list ready to use.
+type list struct {
+	root element // sentinel list element, only &root, root.prev, and root.next are used
+	len  int     // current list length excluding (this) sentinel element
+}
+
+// Init initializes or clears list l.
+func (l *list) Init() *list {
+	l.root.next = &l.root
+	l.root.prev = &l.root
+	l.len = 0
+	return l
+}
+
+// New returns an initialized list.
+// func New() *list { return new(list).Init() }
+
+// Len returns the number of elements of list l.
+// The complexity is O(1).
+func (l *list) Len() int { return l.len }
+
+// Front returns the first element of list l or nil
+func (l *list) Front() *element {
+	if l.len == 0 {
+		return nil
+	}
+	return l.root.next
+}
+
+// Back returns the last element of list l or nil.
+func (l *list) Back() *element {
+	if l.len == 0 {
+		return nil
+	}
+	return l.root.prev
+}
+
+// insert inserts e after at, increments l.len, and returns e.
+func (l *list) insert(e, at *element) *element {
+	n := at.next
+	at.next = e
+	e.prev = at
+	e.next = n
+	n.prev = e
+	e.list = l
+	l.len++
+	return e
+}
+
+// insertValue is a convenience wrapper for insert(&Element{Value: v}, at).
+func (l *list) insertValue(v interface{}, at *element) *element {
+	return l.insert(&element{Value: v}, at)
+}
+
+// remove removes e from its list, decrements l.len, and returns e.
+func (l *list) remove(e *element) *element {
+	e.prev.next = e.next
+	e.next.prev = e.prev
+	e.next = nil // avoid memory leaks
+	e.prev = nil // avoid memory leaks
+	e.list = nil
+	l.len--
+	return e
+}
+
+// Remove removes e from l if e is an element of list l.
+// It returns the element value e.Value.
+func (l *list) Remove(e *element) interface{} {
+	if e.list == l {
+		// if e.list == l, l must have been initialized when e was inserted
+		// in l or l == nil (e is a zero Element) and l.remove will crash
+		l.remove(e)
+	}
+	return e.Value
+}
+
+// PushFront inserts a new element e with value v at the front of list l and returns e.
+func (l *list) PushFront(v interface{}) *element {
+	return l.insertValue(v, &l.root)
+}
+
+// PushBack inserts a new element e with value v at the back of list l and returns e.
+func (l *list) PushBack(v interface{}) *element {
+	return l.insertValue(v, l.root.prev)
+}
+
+// InsertBefore inserts a new element e with value v immediately before mark and returns e.
+// If mark is not an element of l, the list is not modified.
+func (l *list) InsertBefore(v interface{}, mark *element) *element {
+	if mark.list != l {
+		return nil
+	}
+	// see comment in List.Remove about initialization of l
+	return l.insertValue(v, mark.prev)
+}
+
+// InsertAfter inserts a new element e with value v immediately after mark and returns e.
+// If mark is not an element of l, the list is not modified.
+func (l *list) InsertAfter(v interface{}, mark *element) *element {
+	if mark.list != l {
+		return nil
+	}
+	// see comment in List.Remove about initialization of l
+	return l.insertValue(v, mark)
+}
+
+// MoveToFront moves element e to the front of list l.
+// If e is not an element of l, the list is not modified.
+func (l *list) MoveToFront(e *element) {
+	if e.list != l || l.root.next == e {
+		return
+	}
+	// see comment in List.Remove about initialization of l
+	l.insert(l.remove(e), &l.root)
+}
+
+// MoveToBack moves element e to the back of list l.
+// If e is not an element of l, the list is not modified.
+func (l *list) MoveToBack(e *element) {
+	if e.list != l || l.root.prev == e {
+		return
+	}
+	// see comment in List.Remove about initialization of l
+	l.insert(l.remove(e), l.root.prev)
+}
+
+// MoveBefore moves element e to its new position before mark.
+// If e is not an element of l, or e == mark, the list is not modified.
+func (l *list) MoveBefore(e, mark *element) {
+	if e.list != l || e == mark {
+		return
+	}
+	l.insert(l.remove(e), mark.prev)
+}
+
+// MoveAfter moves element e to its new position after mark.
+// If e is not an element of l, or e == mark, the list is not modified.
+func (l *list) MoveAfter(e, mark *element) {
+	if e.list != l || e == mark {
+		return
+	}
+	l.insert(l.remove(e), mark)
+}
+
+// PushBackList inserts a copy of an other list at the back of list l.
+// The lists l and other may be the same.
+func (l *list) PushBackList(other *list) {
+	for i, e := other.Len(), other.Front(); i > 0; i, e = i-1, e.Next() {
+		l.insertValue(e.Value, l.root.prev)
+	}
+}
+
+// PushFrontList inserts a copy of an other list at the front of list l.
+// The lists l and other may be the same.
+func (l *list) PushFrontList(other *list) {
+	for i, e := other.Len(), other.Back(); i > 0; i, e = i-1, e.Prev() {
+		l.insertValue(e.Value, &l.root)
+	}
+}