Update dependencies

vendor/tailscale.com/util/race/race.go

@@ -0,0 +1,115 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package race contains a helper to "race" two functions, returning the first
+// successful result. It also allows explicitly triggering the
+// (possibly-waiting) second function when the first function returns an error
+// or indicates that it should be retried.
+package race
+
+import (
+	"context"
+	"errors"
+	"time"
+)
+
+type resultType int
+
+const (
+	first resultType = iota
+	second
+)
+
+// queryResult is an internal type for storing the result of a function call
+type queryResult[T any] struct {
+	ty  resultType
+	res T
+	err error
+}
+
+// Func is the signature of a function to be called.
+type Func[T any] func(context.Context) (T, error)
+
+// Race allows running two functions concurrently and returning the first
+// non-error result returned.
+type Race[T any] struct {
+	func1, func2  Func[T]
+	d             time.Duration
+	results       chan queryResult[T]
+	startFallback chan struct{}
+}
+
+// New creates a new Race that, when Start is called, will immediately call
+// func1 to obtain a result. After the timeout d or if triggered by an error
+// response from func1, func2 will be called.
+func New[T any](d time.Duration, func1, func2 Func[T]) *Race[T] {
+	ret := &Race[T]{
+		func1:         func1,
+		func2:         func2,
+		d:             d,
+		results:       make(chan queryResult[T], 2),
+		startFallback: make(chan struct{}),
+	}
+	return ret
+}
+
+// Start will start the "race" process, returning the first non-error result or
+// the errors that occurred when calling func1 and/or func2.
+func (rh *Race[T]) Start(ctx context.Context) (T, error) {
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	// func1 is started immediately
+	go func() {
+		ret, err := rh.func1(ctx)
+		rh.results <- queryResult[T]{first, ret, err}
+	}()
+
+	// func2 is started after a timeout
+	go func() {
+		wait := time.NewTimer(rh.d)
+		defer wait.Stop()
+
+		// Wait for our timeout, trigger, or context to finish.
+		select {
+		case <-ctx.Done():
+			// Nothing to do; we're done
+			var zero T
+			rh.results <- queryResult[T]{second, zero, ctx.Err()}
+			return
+		case <-rh.startFallback:
+		case <-wait.C:
+		}
+
+		ret, err := rh.func2(ctx)
+		rh.results <- queryResult[T]{second, ret, err}
+	}()
+
+	// For each possible result, get it off the channel.
+	var errs []error
+	for range 2 {
+		res := <-rh.results
+
+		// If this was an error, store it and hope that the other
+		// result gives us something.
+		if res.err != nil {
+			errs = append(errs, res.err)
+
+			// Start the fallback function immediately if this is
+			// the first function's error, to avoid having
+			// to wait.
+			if res.ty == first {
+				close(rh.startFallback)
+			}
+			continue
+		}
+
+		// Got a valid response! Return it.
+		return res.res, nil
+	}
+
+	// If we get here, both raced functions failed. Return whatever errors
+	// we have, joined together.
+	var zero T
+	return zero, errors.Join(errs...)
+}