95 lines
2.7 KiB
Go
95 lines
2.7 KiB
Go
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// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
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// SPDX-License-Identifier: MIT
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// Package server accepts connections from NFS clients.
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//
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// Each accepted connection reaches the Handle hook, which owns the
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// connection for its whole lifetime; a nil Handle closes it at once. The
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// nfsd command wires the hook to the NFSv4.2 dispatcher.
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package server
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import (
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"context"
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"errors"
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"net"
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"sync/atomic"
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"syscall"
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"time"
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)
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// acceptRetryPause is the pause before the next accept after a
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// transient resource error, so a connection storm cannot spin the loop.
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const acceptRetryPause = 10 * time.Millisecond
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// A Server accepts connections from NFS clients.
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type Server struct {
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// Handle serves one accepted connection. It runs on its own goroutine
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// and owns the connection for its whole lifetime, closing it when the
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// session ends. A nil Handle closes the connection at once.
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Handle func(conn net.Conn)
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// MaxConns caps the connections served at once. Zero means no cap. A
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// connection offered above the cap closes at once, and the client
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// sees an immediate end of file.
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MaxConns int
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live atomic.Int64
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}
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// transientAccept reports whether the accept error is survivable: the
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// listener stays usable and the next accept is worth trying. A storm of
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// aborted connections or a momentary file table exhaustion must not
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// take the daemon down with every client on it.
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func transientAccept(err error) bool {
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return errors.Is(err, syscall.ECONNABORTED) ||
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errors.Is(err, syscall.EMFILE) ||
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errors.Is(err, syscall.ENFILE) ||
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errors.Is(err, syscall.EAGAIN) ||
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errors.Is(err, syscall.EINTR)
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}
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// Serve accepts connections on ln until the listener fails or ctx is
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// cancelled. A cancellation closes the listener and Serve returns nil;
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// a closed listener returns nil; a transient accept error is waited out;
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// any other listener failure returns the error as is. In flight
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// connections are not drained: NFS clients retry through their session
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// replay caches, so an immediate return is the correct shutdown.
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func (s *Server) Serve(ctx context.Context, ln net.Listener) error {
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stop := make(chan struct{})
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defer close(stop)
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go func() {
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select {
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case <-ctx.Done():
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ln.Close()
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case <-stop:
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}
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}()
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for {
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conn, err := ln.Accept()
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if err == nil {
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if s.Handle == nil {
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conn.Close()
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continue
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}
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if s.MaxConns > 0 && s.live.Load() >= int64(s.MaxConns) {
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conn.Close()
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continue
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}
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s.live.Add(1)
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go func() {
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defer s.live.Add(-1)
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s.Handle(conn)
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}()
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continue
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}
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if ctx.Err() != nil || errors.Is(err, net.ErrClosed) {
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return nil
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}
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if transientAccept(err) {
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time.Sleep(acceptRetryPause)
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continue
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}
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return err
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}
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}
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