implemented the E-mail sending functionality

util/freelist.go

@@ -0,0 +1,67 @@
+/*
+ * Amsterdam Web Communities System
+ * Copyright (c) 2025 Erbosoft Metaverse Design Solutions, All Rights Reserved
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+// Package util contains utility definitions.
+package util
+
+import "sync"
+
+// freeListElem is an element of the free list.
+type freeListElem[T any] struct {
+	next *freeListElem[T]
+	prev *freeListElem[T]
+	data *T
+}
+
+// FreeList defines a free list.
+type FreeList[T any] struct {
+	New     func() *T
+	mutex   sync.Mutex
+	listptr *freeListElem[T]
+}
+
+// Put adds a value to the free list.
+func (l *FreeList[T]) Put(value *T) {
+	l.mutex.Lock()
+	defer l.mutex.Unlock()
+	ne := freeListElem[T]{data: value}
+	if l.listptr == nil {
+		ne.next = &ne
+		ne.prev = &ne
+		l.listptr = &ne
+	} else {
+		ne.next = l.listptr
+		ne.prev = l.listptr.prev
+		ne.next.prev = &ne
+		ne.prev.next = &ne
+	}
+}
+
+// Get removes a value from the free list. If there are no values and New is specified, is calls that.
+func (l *FreeList[T]) Get() *T {
+	l.mutex.Lock()
+	defer l.mutex.Unlock()
+	var rc *T = nil
+	if l.listptr == nil {
+		if l.New != nil {
+			rc = l.New()
+		}
+	} else {
+		elt := l.listptr
+		rc = elt.data
+		l.listptr = elt.next
+		if l.listptr == elt {
+			l.listptr = nil
+		} else {
+			elt.prev.next = elt.next
+			elt.next.prev = elt.prev
+		}
+	}
+	return rc
+}