server.lib.turbotunnel.go Maven / Gradle / Ivy
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package snowflake_server
import (
"net"
"sync"
"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/turbotunnel"
)
// clientIDMap is a fixed-capacity mapping from ClientIDs to a net.Addr.
// Adding a new entry using the Set method causes the oldest existing entry to
// be forgotten.
//
// This data type is meant to be used to remember the IP address associated with
// a ClientID, during the short period of time between when a WebSocket
// connection with that ClientID began, and when a KCP session is established.
//
// The design requirements of this type are that it needs to remember a mapping
// for only a short time, and old entries should expire so as not to consume
// unbounded memory. It is not a critical error if an entry is forgotten before
// it is needed; better to forget entries than to use too much memory.
type clientIDMap struct {
lock sync.Mutex
// entries is a circular buffer of (ClientID, addr) pairs.
entries []struct {
clientID turbotunnel.ClientID
addr net.Addr
}
// oldest is the index of the oldest member of the entries buffer, the
// one that will be overwritten at the next call to Set.
oldest int
// current points to the index of the most recent entry corresponding to
// each ClientID.
current map[turbotunnel.ClientID]int
}
// newClientIDMap makes a new clientIDMap with the given capacity.
func newClientIDMap(capacity int) *clientIDMap {
return &clientIDMap{
entries: make([]struct {
clientID turbotunnel.ClientID
addr net.Addr
}, capacity),
oldest: 0,
current: make(map[turbotunnel.ClientID]int),
}
}
// Set adds a mapping from clientID to addr, replacing any previous mapping for
// clientID. It may also cause the clientIDMap to forget at most one other
// mapping, the oldest one.
func (m *clientIDMap) Set(clientID turbotunnel.ClientID, addr net.Addr) {
m.lock.Lock()
defer m.lock.Unlock()
if len(m.entries) == 0 {
// The invariant m.oldest < len(m.entries) does not hold in this
// special case.
return
}
// m.oldest is the index of the entry we're about to overwrite. If it's
// the current entry for any ClientID, we need to delete that clientID
// from the current map (that ClientID is now forgotten).
if i, ok := m.current[m.entries[m.oldest].clientID]; ok && i == m.oldest {
delete(m.current, m.entries[m.oldest].clientID)
}
// Overwrite the oldest entry.
m.entries[m.oldest].clientID = clientID
m.entries[m.oldest].addr = addr
// Add the overwritten entry to the quick-lookup map.
m.current[clientID] = m.oldest
// What was the oldest entry is now the newest.
m.oldest = (m.oldest + 1) % len(m.entries)
}
// Get returns a previously stored mapping. The second return value indicates
// whether clientID was actually present in the map. If it is false, then the
// returned address will be nil.
func (m *clientIDMap) Get(clientID turbotunnel.ClientID) (net.Addr, bool) {
m.lock.Lock()
defer m.lock.Unlock()
if i, ok := m.current[clientID]; ok {
return m.entries[i].addr, true
} else {
return nil, false
}
}