GoToSocial/internal/cache/domain/domain.go

261 lines
5.9 KiB
Go

// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
package domain
import (
"fmt"
"strings"
"sync/atomic"
"unsafe"
"golang.org/x/exp/slices"
)
// Cache provides a means of caching domains in memory to reduce
// load on an underlying storage mechanism, e.g. a database.
//
// The in-memory domain list is kept up-to-date by means of a passed
// loader function during every call to .Matches(). In the case of
// a nil internal domain list, the loader function is called to hydrate
// the cache with the latest list of domains.
//
// The .Clear() function can be used to invalidate the cache,
// e.g. when an entry is added / deleted from the database.
type Cache struct {
// atomically updated ptr value to the
// current domain cache radix trie.
rootptr unsafe.Pointer
}
// Matches checks whether domain matches an entry in the cache.
// If the cache is not currently loaded, then the provided load
// function is used to hydrate it.
func (c *Cache) Matches(domain string, load func() ([]string, error)) (bool, error) {
// Load the current root pointer value.
ptr := atomic.LoadPointer(&c.rootptr)
if ptr == nil {
// Cache is not hydrated.
//
// Load domains from callback.
domains, err := load()
if err != nil {
return false, fmt.Errorf("error reloading cache: %w", err)
}
// Allocate new radix trie
// node to store matches.
root := new(root)
// Add each domain to the trie.
for _, domain := range domains {
root.Add(domain)
}
// Sort the trie.
root.Sort()
// Store the new node ptr.
ptr = unsafe.Pointer(root)
atomic.StorePointer(&c.rootptr, ptr)
}
// Look for a match in the trie node.
return (*root)(ptr).Match(domain), nil
}
// Clear will drop the currently loaded domain list,
// triggering a reload on next call to .Matches().
func (c *Cache) Clear() {
atomic.StorePointer(&c.rootptr, nil)
}
// String returns a string representation of stored domains in cache.
func (c *Cache) String() string {
if ptr := atomic.LoadPointer(&c.rootptr); ptr != nil {
return (*root)(ptr).String()
}
return "<empty>"
}
// root is the root node in the domain cache radix trie. this is the singular access point to the trie.
type root struct{ root node }
// Add will add the given domain to the radix trie.
func (r *root) Add(domain string) {
r.root.add(strings.Split(domain, "."))
}
// Match will return whether the given domain matches
// an existing stored domain in this radix trie.
func (r *root) Match(domain string) bool {
return r.root.match(strings.Split(domain, "."))
}
// Sort will sort the entire radix trie ensuring that
// child nodes are stored in alphabetical order. This
// MUST be done to finalize the domain cache in order
// to speed up the binary search of node child parts.
func (r *root) Sort() {
r.root.sort()
}
// String returns a string representation of node (and its descendants).
func (r *root) String() string {
buf := new(strings.Builder)
r.root.writestr(buf, "")
return buf.String()
}
type node struct {
part string
child []*node
}
func (n *node) add(parts []string) {
if len(parts) == 0 {
panic("invalid domain")
}
for {
// Pop next domain part.
i := len(parts) - 1
part := parts[i]
parts = parts[:i]
var nn *node
// Look for existing child node
// that matches next domain part.
for _, child := range n.child {
if child.part == part {
nn = child
break
}
}
if nn == nil {
// Alloc new child node.
nn = &node{part: part}
n.child = append(n.child, nn)
}
if len(parts) == 0 {
// Drop all children here as
// this is a higher-level domain
// than that we previously had.
nn.child = nil
return
}
// Re-iter with
// child node.
n = nn
}
}
func (n *node) match(parts []string) bool {
for len(parts) > 0 {
// Pop next domain part.
i := len(parts) - 1
part := parts[i]
parts = parts[:i]
// Look for existing child
// that matches next part.
nn := n.getChild(part)
if nn == nil {
// No match :(
return false
}
if len(nn.child) == 0 {
// It's a match!
return true
}
// Re-iter with
// child node.
n = nn
}
// Ran out of parts
// without a match.
return false
}
// getChild fetches child node with given domain part string
// using a binary search. THIS ASSUMES CHILDREN ARE SORTED.
func (n *node) getChild(part string) *node {
i, j := 0, len(n.child)
for i < j {
// avoid overflow when computing h
h := int(uint(i+j) >> 1)
// i ≤ h < j
if n.child[h].part < part {
// preserves:
// n.child[i-1].part != part
i = h + 1
} else {
// preserves:
// n.child[h].part == part
j = h
}
}
if i >= len(n.child) || n.child[i].part != part {
return nil // no match
}
return n.child[i]
}
func (n *node) sort() {
// Sort this node's slice of child nodes.
slices.SortFunc(n.child, func(i, j *node) bool {
return i.part < j.part
})
// Sort each child node's children.
for _, child := range n.child {
child.sort()
}
}
func (n *node) writestr(buf *strings.Builder, prefix string) {
if prefix != "" {
// Suffix joining '.'
prefix += "."
}
// Append current part.
prefix += n.part
// Dump current prefix state.
buf.WriteString(prefix)
buf.WriteByte('\n')
// Iterate through node children.
for _, child := range n.child {
child.writestr(buf, prefix)
}
}