TUN-528: Move cloudflared into a separate repo

vendor/zombiezen.com/go/capnproto2/internal/capnptool/BUILD.bazel

@@ -0,0 +1,8 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["capnptool.go"],
+    importpath = "zombiezen.com/go/capnproto2/internal/capnptool",
+    visibility = ["//:__subpackages__"],
+)

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

@@ -0,0 +1,76 @@
+// Package capnptool provides an API for calling the capnp tool in tests.
+package capnptool
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os/exec"
+	"strings"
+	"sync"
+)
+
+// Tool is the path to the capnp command-line tool.
+// It can be used from multiple goroutines.
+type Tool string
+
+var cache struct {
+	init sync.Once
+	tool Tool
+	err  error
+}
+
+// Find searches PATH for the capnp tool.
+func Find() (Tool, error) {
+	cache.init.Do(func() {
+		path, err := exec.LookPath("capnp")
+		if err != nil {
+			cache.err = err
+			return
+		}
+		cache.tool = Tool(path)
+	})
+	return cache.tool, cache.err
+}
+
+// Run executes the tool with the given stdin and arguments returns the stdout.
+func (tool Tool) Run(stdin io.Reader, args ...string) ([]byte, error) {
+	c := exec.Command(string(tool), args...)
+	c.Stdin = stdin
+	stderr := new(bytes.Buffer)
+	c.Stderr = stderr
+	out, err := c.Output()
+	if err != nil {
+		return nil, fmt.Errorf("run `%s`: %v; stderr:\n%s", strings.Join(c.Args, " "), err, stderr)
+	}
+	return out, nil
+}
+
+// Encode encodes Cap'n Proto text into the binary representation.
+func (tool Tool) Encode(typ Type, text string) ([]byte, error) {
+	return tool.Run(strings.NewReader(text), "encode", typ.SchemaPath, typ.Name)
+}
+
+// Decode decodes a Cap'n Proto message into text.
+func (tool Tool) Decode(typ Type, r io.Reader) (string, error) {
+	out, err := tool.Run(r, "decode", "--short", typ.SchemaPath, typ.Name)
+	if err != nil {
+		return "", err
+	}
+	return string(out), nil
+}
+
+// DecodePacked decodes a packed Cap'n Proto message into text.
+func (tool Tool) DecodePacked(typ Type, r io.Reader) (string, error) {
+	out, err := tool.Run(r, "decode", "--short", "--packed", typ.SchemaPath, typ.Name)
+	if err != nil {
+		return "", err
+	}
+	return string(out), nil
+}
+
+// Type is a reference to a Cap'n Proto type in a schema.
+type Type struct {
+	SchemaPath string
+	Name       string
+}