TUN-528: Move cloudflared into a separate repo

vendor/zombiezen.com/go/capnproto2/internal/fulfiller/fulfiller.go

@@ -0,0 +1,329 @@
+// Package fulfiller provides a type that implements capnp.Answer that
+// resolves by calling setter methods.
+package fulfiller
+
+import (
+	"errors"
+	"sync"
+
+	"zombiezen.com/go/capnproto2"
+	"zombiezen.com/go/capnproto2/internal/queue"
+)
+
+// callQueueSize is the maximum number of pending calls.
+const callQueueSize = 64
+
+// Fulfiller is a promise for a Struct.  The zero value is an unresolved
+// answer.  A Fulfiller is considered to be resolved once Fulfill or
+// Reject is called.  Calls to the Fulfiller will queue up until it is
+// resolved.  A Fulfiller is safe to use from multiple goroutines.
+type Fulfiller struct {
+	once     sync.Once
+	resolved chan struct{} // initialized by init()
+
+	// Protected by mu
+	mu     sync.RWMutex
+	answer capnp.Answer
+	queue  []pcall // initialized by init()
+}
+
+// init initializes the Fulfiller.  It is idempotent.
+// Should be called for each method on Fulfiller.
+func (f *Fulfiller) init() {
+	f.once.Do(func() {
+		f.resolved = make(chan struct{})
+		f.queue = make([]pcall, 0, callQueueSize)
+	})
+}
+
+// Fulfill sets the fulfiller's answer to s.  If there are queued
+// pipeline calls, the capabilities on the struct will be embargoed
+// until the queued calls finish.  Fulfill will panic if the fulfiller
+// has already been resolved.
+func (f *Fulfiller) Fulfill(s capnp.Struct) {
+	f.init()
+	f.mu.Lock()
+	if f.answer != nil {
+		f.mu.Unlock()
+		panic("Fulfiller.Fulfill called more than once")
+	}
+	f.answer = capnp.ImmediateAnswer(s)
+	queues := f.emptyQueue(s)
+	ctab := s.Segment().Message().CapTable
+	for capIdx, q := range queues {
+		ctab[capIdx] = newEmbargoClient(ctab[capIdx], q)
+	}
+	close(f.resolved)
+	f.mu.Unlock()
+}
+
+// emptyQueue splits the queue by which capability it targets and
+// drops any invalid calls.  Once this function returns, f.queue will
+// be nil.
+func (f *Fulfiller) emptyQueue(s capnp.Struct) map[capnp.CapabilityID][]ecall {
+	qs := make(map[capnp.CapabilityID][]ecall, len(f.queue))
+	for i, pc := range f.queue {
+		c, err := capnp.TransformPtr(s.ToPtr(), pc.transform)
+		if err != nil {
+			pc.f.Reject(err)
+			continue
+		}
+		in := c.Interface()
+		if !in.IsValid() {
+			pc.f.Reject(capnp.ErrNullClient)
+			continue
+		}
+		cn := in.Capability()
+		if qs[cn] == nil {
+			qs[cn] = make([]ecall, 0, len(f.queue)-i)
+		}
+		qs[cn] = append(qs[cn], pc.ecall)
+	}
+	f.queue = nil
+	return qs
+}
+
+// Reject sets the fulfiller's answer to err.  If there are queued
+// pipeline calls, they will all return errors.  Reject will panic if
+// the error is nil or the fulfiller has already been resolved.
+func (f *Fulfiller) Reject(err error) {
+	if err == nil {
+		panic("Fulfiller.Reject called with nil")
+	}
+	f.init()
+	f.mu.Lock()
+	if f.answer != nil {
+		f.mu.Unlock()
+		panic("Fulfiller.Reject called more than once")
+	}
+	f.answer = capnp.ErrorAnswer(err)
+	for i := range f.queue {
+		f.queue[i].f.Reject(err)
+		f.queue[i] = pcall{}
+	}
+	close(f.resolved)
+	f.mu.Unlock()
+}
+
+// Done returns a channel that is closed once f is resolved.
+func (f *Fulfiller) Done() <-chan struct{} {
+	f.init()
+	return f.resolved
+}
+
+// Peek returns f's resolved answer or nil if f has not been resolved.
+// The Struct method of an answer returned from Peek returns immediately.
+func (f *Fulfiller) Peek() capnp.Answer {
+	f.init()
+	f.mu.RLock()
+	a := f.answer
+	f.mu.RUnlock()
+	return a
+}
+
+// Struct waits until f is resolved and returns its struct if fulfilled
+// or an error if rejected.
+func (f *Fulfiller) Struct() (capnp.Struct, error) {
+	<-f.Done()
+	return f.Peek().Struct()
+}
+
+// PipelineCall calls PipelineCall on the fulfilled answer or queues the
+// call if f has not been fulfilled.
+func (f *Fulfiller) PipelineCall(transform []capnp.PipelineOp, call *capnp.Call) capnp.Answer {
+	f.init()
+
+	// Fast path: pass-through after fulfilled.
+	if a := f.Peek(); a != nil {
+		return a.PipelineCall(transform, call)
+	}
+
+	f.mu.Lock()
+	// Make sure that f wasn't fulfilled.
+	if a := f.answer; a != nil {
+		f.mu.Unlock()
+		return a.PipelineCall(transform, call)
+	}
+	if len(f.queue) == cap(f.queue) {
+		f.mu.Unlock()
+		return capnp.ErrorAnswer(errCallQueueFull)
+	}
+	cc, err := call.Copy(nil)
+	if err != nil {
+		f.mu.Unlock()
+		return capnp.ErrorAnswer(err)
+	}
+	g := new(Fulfiller)
+	f.queue = append(f.queue, pcall{
+		transform: transform,
+		ecall: ecall{
+			call: cc,
+			f:    g,
+		},
+	})
+	f.mu.Unlock()
+	return g
+}
+
+// PipelineClose waits until f is resolved and then calls PipelineClose
+// on the fulfilled answer.
+func (f *Fulfiller) PipelineClose(transform []capnp.PipelineOp) error {
+	<-f.Done()
+	return f.Peek().PipelineClose(transform)
+}
+
+// pcall is a queued pipeline call.
+type pcall struct {
+	transform []capnp.PipelineOp
+	ecall
+}
+
+// EmbargoClient is a client that flushes a queue of calls.
+// Fulfiller will create these automatically when pipelined calls are
+// made on unresolved answers.  EmbargoClient is exported so that rpc
+// can avoid making calls on its own Conn.
+type EmbargoClient struct {
+	client capnp.Client
+
+	mu    sync.RWMutex
+	q     queue.Queue
+	calls ecallList
+}
+
+func newEmbargoClient(client capnp.Client, queue []ecall) capnp.Client {
+	ec := &EmbargoClient{
+		client: client,
+		calls:  make(ecallList, callQueueSize),
+	}
+	ec.q.Init(ec.calls, copy(ec.calls, queue))
+	go ec.flushQueue()
+	return ec
+}
+
+func (ec *EmbargoClient) push(cl *capnp.Call) capnp.Answer {
+	f := new(Fulfiller)
+	cl, err := cl.Copy(nil)
+	if err != nil {
+		return capnp.ErrorAnswer(err)
+	}
+	i := ec.q.Push()
+	if i == -1 {
+		return capnp.ErrorAnswer(errCallQueueFull)
+	}
+	ec.calls[i] = ecall{cl, f}
+	return f
+}
+
+// flushQueue is run in its own goroutine.
+func (ec *EmbargoClient) flushQueue() {
+	var c ecall
+	ec.mu.Lock()
+	if i := ec.q.Front(); i != -1 {
+		c = ec.calls[i]
+	}
+	ec.mu.Unlock()
+	for c.call != nil {
+		ans := ec.client.Call(c.call)
+		go func(f *Fulfiller, ans capnp.Answer) {
+			s, err := ans.Struct()
+			if err == nil {
+				f.Fulfill(s)
+			} else {
+				f.Reject(err)
+			}
+		}(c.f, ans)
+		ec.mu.Lock()
+		ec.q.Pop()
+		if i := ec.q.Front(); i != -1 {
+			c = ec.calls[i]
+		} else {
+			c = ecall{}
+		}
+		ec.mu.Unlock()
+	}
+}
+
+// Client returns the underlying client if the embargo has been lifted
+// and nil otherwise.
+func (ec *EmbargoClient) Client() capnp.Client {
+	ec.mu.RLock()
+	ok := ec.isPassthrough()
+	ec.mu.RUnlock()
+	if !ok {
+		return nil
+	}
+	return ec.client
+}
+
+func (ec *EmbargoClient) isPassthrough() bool {
+	return ec.q.Len() == 0
+}
+
+// Call either queues a call to the underlying client or starts a call
+// if the embargo has been lifted.
+func (ec *EmbargoClient) Call(cl *capnp.Call) capnp.Answer {
+	// Fast path: queue is flushed.
+	ec.mu.RLock()
+	ok := ec.isPassthrough()
+	ec.mu.RUnlock()
+	if ok {
+		return ec.client.Call(cl)
+	}
+
+	// Add to queue.
+	ec.mu.Lock()
+	// Since we released the lock, check that the queue hasn't been flushed.
+	if ec.isPassthrough() {
+		ec.mu.Unlock()
+		return ec.client.Call(cl)
+	}
+	ans := ec.push(cl)
+	ec.mu.Unlock()
+	return ans
+}
+
+// TryQueue will attempt to queue a call or return nil if the embargo
+// has been lifted.
+func (ec *EmbargoClient) TryQueue(cl *capnp.Call) capnp.Answer {
+	ec.mu.Lock()
+	if ec.isPassthrough() {
+		ec.mu.Unlock()
+		return nil
+	}
+	ans := ec.push(cl)
+	ec.mu.Unlock()
+	return ans
+}
+
+// Close closes the underlying client, rejecting any queued calls.
+func (ec *EmbargoClient) Close() error {
+	ec.mu.Lock()
+	// reject all queued calls
+	for ec.q.Len() > 0 {
+		ec.calls[ec.q.Front()].f.Reject(errQueueCallCancel)
+		ec.q.Pop()
+	}
+	ec.mu.Unlock()
+	return ec.client.Close()
+}
+
+// ecall is an queued embargoed call.
+type ecall struct {
+	call *capnp.Call
+	f    *Fulfiller
+}
+
+type ecallList []ecall
+
+func (el ecallList) Len() int {
+	return len(el)
+}
+
+func (el ecallList) Clear(i int) {
+	el[i] = ecall{}
+}
+
+var (
+	errCallQueueFull   = errors.New("capnp: promised answer call queue full")
+	errQueueCallCancel = errors.New("capnp: queued call canceled")
+)