diff --git a/types/iox/io.go b/types/iox/io.go
new file mode 100644
index 000000000..a5ca1be43
--- /dev/null
+++ b/types/iox/io.go
@@ -0,0 +1,23 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Package iox provides types to implement [io] functionality.
+package iox
+
+// TODO(https://go.dev/issue/21670): Deprecate or remove this functionality
+// once the Go language supports implementing an 1-method interface directly
+// using a function value of a matching signature.
+
+// ReaderFunc implements [io.Reader] using the underlying function value.
+type ReaderFunc func([]byte) (int, error)
+
+func (f ReaderFunc) Read(b []byte) (int, error) {
+	return f(b)
+}
+
+// WriterFunc implements [io.Writer] using the underlying function value.
+type WriterFunc func([]byte) (int, error)
+
+func (f WriterFunc) Write(b []byte) (int, error) {
+	return f(b)
+}
diff --git a/types/iox/io_test.go b/types/iox/io_test.go
new file mode 100644
index 000000000..9fba39605
--- /dev/null
+++ b/types/iox/io_test.go
@@ -0,0 +1,39 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package iox
+
+import (
+	"bytes"
+	"io"
+	"testing"
+	"testing/iotest"
+
+	"tailscale.com/util/must"
+)
+
+func TestCopy(t *testing.T) {
+	const testdata = "the quick brown fox jumped over the lazy dog"
+	src := testdata
+	bb := new(bytes.Buffer)
+	if got := must.Get(io.Copy(bb, ReaderFunc(func(b []byte) (n int, err error) {
+		n = copy(b[:min(len(b), 7)], src)
+		src = src[n:]
+		if len(src) == 0 {
+			err = io.EOF
+		}
+		return n, err
+	}))); int(got) != len(testdata) {
+		t.Errorf("copy = %d, want %d", got, len(testdata))
+	}
+	var dst []byte
+	if got := must.Get(io.Copy(WriterFunc(func(b []byte) (n int, err error) {
+		dst = append(dst, b...)
+		return len(b), nil
+	}), iotest.OneByteReader(bb))); int(got) != len(testdata) {
+		t.Errorf("copy = %d, want %d", got, len(testdata))
+	}
+	if string(dst) != testdata {
+		t.Errorf("copy = %q, want %q", dst, testdata)
+	}
+}