Update

vendor/tailscale.com/util/bufiox/bufiox.go

@@ -0,0 +1,31 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package bufiox provides extensions to the standard bufio package.
+package bufiox
+
+import "io"
+
+// BufferedReader is an interface for readers that support peeking
+// into an internal buffer, like [bufio.Reader].
+type BufferedReader interface {
+	Peek(n int) ([]byte, error)
+	Discard(n int) (discarded int, err error)
+}
+
+// ReadFull reads exactly len(buf) bytes from r into buf, like
+// [io.ReadFull], but without heap allocations. It uses Peek to
+// access the buffered data directly, copies it into buf, then
+// discards the consumed bytes. If an error occurs,
+// discard is not called and the buffer is left unchanged.
+func ReadFull(r BufferedReader, buf []byte) (int, error) {
+	b, err := r.Peek(len(buf))
+	if err != nil {
+		if len(b) > 0 && err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		return 0, err
+	}
+	defer r.Discard(len(buf))
+	return copy(buf, b), nil
+}