1 files changed, 142 insertions, 0 deletions
diff --git a/lib/proto/cmd/star2proto/star2proto.go b/lib/proto/cmd/star2proto/star2proto.go
new file mode 100644
index 0000000..7911723
--- /dev/null
+++ b/lib/proto/cmd/star2proto/star2proto.go
@@ -0,0 +1,142 @@
+// The star2proto command executes a Starlark file and prints a protocol
+// message, which it expects to find in a module-level variable named 'result'.
+//
+// THIS COMMAND IS EXPERIMENTAL AND ITS INTERFACE MAY CHANGE.
+package main
+
+// TODO(adonovan): add features to make this a useful tool for querying,
+// converting, and building messages in proto, JSON, and YAML.
+// - define operations for reading and writing files.
+// - support (e.g.) querying a proto file given a '-e expr' flag.
+//   This will need a convenient way to put the relevant descriptors in scope.
+
+import (
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"strings"
+
+	starlarkproto "go.starlark.net/lib/proto"
+	"go.starlark.net/resolve"
+	"go.starlark.net/starlark"
+	"go.starlark.net/starlarkjson"
+	"google.golang.org/protobuf/encoding/protojson"
+	"google.golang.org/protobuf/encoding/prototext"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/reflect/protodesc"
+	"google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/reflect/protoregistry"
+	"google.golang.org/protobuf/types/descriptorpb"
+)
+
+// flags
+var (
+	outputFlag  = flag.String("output", "text", "output format (text, wire, json)")
+	varFlag     = flag.String("var", "result", "the variable to output")
+	descriptors = flag.String("descriptors", "", "comma-separated list of names of files containing proto.FileDescriptorProto messages")
+)
+
+// Starlark dialect flags
+func init() {
+	flag.BoolVar(&resolve.AllowFloat, "fp", true, "allow floating-point numbers")
+	flag.BoolVar(&resolve.AllowSet, "set", resolve.AllowSet, "allow set data type")
+	flag.BoolVar(&resolve.AllowLambda, "lambda", resolve.AllowLambda, "allow lambda expressions")
+	flag.BoolVar(&resolve.AllowNestedDef, "nesteddef", resolve.AllowNestedDef, "allow nested def statements")
+}
+
+func main() {
+	log.SetPrefix("star2proto: ")
+	log.SetFlags(0)
+	flag.Parse()
+	if len(flag.Args()) != 1 {
+		fatalf("requires a single Starlark file name")
+	}
+	filename := flag.Args()[0]
+
+	// By default, use the linked-in descriptors
+	// (very few in star2proto, e.g. descriptorpb itself).
+	pool := protoregistry.GlobalFiles
+
+	// Load a user-provided FileDescriptorSet produced by a command such as:
+	// $ protoc --descriptor_set_out=foo.fds foo.proto
+	if *descriptors != "" {
+		var fdset descriptorpb.FileDescriptorSet
+		for i, filename := range strings.Split(*descriptors, ",") {
+			data, err := ioutil.ReadFile(filename)
+			if err != nil {
+				log.Fatalf("--descriptors[%d]: %s", i, err)
+			}
+			// Accumulate into the repeated field of FileDescriptors.
+			if err := (proto.UnmarshalOptions{Merge: true}).Unmarshal(data, &fdset); err != nil {
+				log.Fatalf("%s does not contain a proto2.FileDescriptorSet: %v", filename, err)
+			}
+		}
+
+		files, err := protodesc.NewFiles(&fdset)
+		if err != nil {
+			log.Fatalf("protodesc.NewFiles: could not build FileDescriptor index: %v", err)
+		}
+		pool = files
+	}
+
+	// Execute the Starlark file.
+	thread := &starlark.Thread{
+		Print: func(_ *starlark.Thread, msg string) { fmt.Println(msg) },
+	}
+	starlarkproto.SetPool(thread, pool)
+	predeclared := starlark.StringDict{
+		"proto": starlarkproto.Module,
+		"json":  starlarkjson.Module,
+	}
+	globals, err := starlark.ExecFile(thread, filename, nil, predeclared)
+	if err != nil {
+		if evalErr, ok := err.(*starlark.EvalError); ok {
+			fatalf("%s", evalErr.Backtrace())
+		} else {
+			fatalf("%s", err)
+		}
+	}
+
+	// Print the output variable as a message.
+	// TODO(adonovan): this is clumsy.
+	// Let the user call print(), or provide an expression on the command line.
+	result, ok := globals[*varFlag]
+	if !ok {
+		fatalf("%s must define a module-level variable named %q", filename, *varFlag)
+	}
+	msgwrap, ok := result.(*starlarkproto.Message)
+	if !ok {
+		fatalf("got %s, want proto.Message, for %q", result.Type(), *varFlag)
+	}
+	msg := msgwrap.Message()
+
+	// -output
+	var marshal func(protoreflect.ProtoMessage) ([]byte, error)
+	switch *outputFlag {
+	case "wire":
+		marshal = proto.Marshal
+
+	case "text":
+		marshal = prototext.MarshalOptions{Multiline: true, Indent: "\t"}.Marshal
+
+	case "json":
+		marshal = protojson.MarshalOptions{Multiline: true, Indent: "\t"}.Marshal
+
+	default:
+		fatalf("unsupported -output format: %s", *outputFlag)
+	}
+	data, err := marshal(msg)
+	if err != nil {
+		fatalf("%s", err)
+	}
+	os.Stdout.Write(data)
+}
+
+func fatalf(format string, args ...interface{}) {
+	fmt.Fprintf(os.Stderr, "star2proto: ")
+	fmt.Fprintf(os.Stderr, format, args...)
+	fmt.Fprintln(os.Stderr)
+	os.Exit(1)
+}