starlark/starlarkproto/functions.go - infra/luci/luci-go - Git at Google

 // Copyright 2019 The LUCI Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 package starlarkproto

 import (
 	"bytes"
 	"encoding/json"
 	"fmt"

 	"go.starlark.net/starlark"
 	"go.starlark.net/starlarkstruct"

 	"google.golang.org/protobuf/encoding/protojson"
 	"google.golang.org/protobuf/encoding/prototext"
 	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/types/descriptorpb"
 	"google.golang.org/protobuf/types/dynamicpb"

 	"go.chromium.org/luci/common/errors"
 	"go.chromium.org/luci/common/proto/textpb"
 )

 // ToTextPB serializes a protobuf message to text proto.
 func ToTextPB(msg *Message) ([]byte, error) {
 	opts := prototext.MarshalOptions{
 		AllowPartial: true,
 		Indent:       " ",
 		Resolver:     msg.typ.loader.types, // used for google.protobuf.Any fields
 	}
 	blob, err := opts.Marshal(msg.ToProto())
 	if err != nil {
 		return nil, err
 	}
 	// prototext randomly injects spaces into the generate output. Pass it through
 	// a formatter to get rid of them.
 	return textpb.Format(blob, msg.MessageType().Descriptor())
 }

 // ToJSONPB serializes a protobuf message to JSONPB string.
 func ToJSONPB(msg *Message, useProtoNames bool) ([]byte, error) {
 	opts := protojson.MarshalOptions{
 		AllowPartial:  true,
 		Resolver:      msg.typ.loader.types, // used for google.protobuf.Any fields
 		UseProtoNames: useProtoNames,
 	}
 	blob, err := opts.Marshal(msg.ToProto())
 	if err != nil {
 		return nil, err
 	}
 	// protojson randomly injects spaces into the generate output. Pass it through
 	// a formatter to get rid of them.
 	var out bytes.Buffer
 	if err := json.Indent(&out, blob, "", "\t"); err != nil {
 		return nil, err
 	}
 	return bytes.TrimSpace(out.Bytes()), nil
 }

 // ToWirePB serializes a protobuf message to binary wire format.
 func ToWirePB(msg *Message) ([]byte, error) {
 	opts := proto.MarshalOptions{
 		AllowPartial:  true,
 		Deterministic: true,
 	}
 	return opts.Marshal(msg.ToProto())
 }

 // FromTextPB deserializes a protobuf message given in text proto form.
 //
 // Unlike the equivalent Starlark proto.from_textpb(...), this low-level native
 // function doesn't freeze returned messages, but also doesn't use the message
 // cache.
 func FromTextPB(typ *MessageType, blob []byte) (*Message, error) {
 	pb := dynamicpb.NewMessage(typ.desc)
 	opts := prototext.UnmarshalOptions{
 		AllowPartial: true,
 		Resolver:     typ.loader.types, // used for google.protobuf.Any fields
 	}
 	if err := opts.Unmarshal(blob, pb); err != nil {
 		return nil, err
 	}
 	return typ.MessageFromProto(pb), nil
 }

 // FromJSONPB deserializes a protobuf message given as JBONPB string.
 //
 // Unlike the equivalent Starlark proto.from_jsonpb(...), this low-level native
 // function doesn't freeze returned messages, but also doesn't use the message
 // cache.
 func FromJSONPB(typ *MessageType, blob []byte) (*Message, error) {
 	pb := dynamicpb.NewMessage(typ.desc)
 	opts := protojson.UnmarshalOptions{
 		AllowPartial:   true,
 		DiscardUnknown: true,
 		Resolver:       typ.loader.types, // used for google.protobuf.Any fields
 	}
 	if err := opts.Unmarshal(blob, pb); err != nil {
 		return nil, err
 	}
 	return typ.MessageFromProto(pb), nil
 }

 // FromWirePB deserializes a protobuf message given as a wire-encoded blob.
 //
 // Unlike the equivalent Starlark proto.from_wirepb(...), this low-level native
 // function doesn't freeze returned messages, but also doesn't use the message
 // cache.
 func FromWirePB(typ *MessageType, blob []byte) (*Message, error) {
 	pb := dynamicpb.NewMessage(typ.desc)
 	opts := proto.UnmarshalOptions{
 		AllowPartial:   true,
 		DiscardUnknown: true,
 		Resolver:       typ.loader.types, // used for google.protobuf.Any fields
 	}
 	if err := opts.Unmarshal(blob, pb); err != nil {
 		return nil, err
 	}
 	return typ.MessageFromProto(pb), nil
 }

 // ProtoLib returns a dict with single struct named "proto" that holds public
 // Starlark API for working with proto messages.
 //
 // Exported functions:
 //
 //	def new_descriptor_set(name=None, blob=None, deps=None):
 //	  """Returns a new DescriptorSet.
 //
 //	  Args:
 //	    name: name of this set for debug and error messages, default is '???'.
 //	    blob: raw serialized FileDescriptorSet, if any.
 //	    deps: an iterable of DescriptorSet's with dependencies, if any.
 //
 //	  Returns:
 //	    New DescriptorSet.
 //	  """
 //
 //	def new_loader(*descriptor_sets):
 //	  """Returns a new proto loader."""
 //
 //	def default_loader():
 //	  """Returns a loader used by default when registering descriptor sets."""
 //
 //	def message_type(msg):
 //	  """Returns proto.MessageType of the given message."""
 //
 //	def to_textpb(msg):
 //	  """Serializes a protobuf message to text proto.
 //
 //	  Args:
 //	    msg: a *Message to serialize.
 //
 //	  Returns:
 //	    A str representing msg in text format.
 //	  """
 //
 //	def to_jsonpb(msg, use_proto_names = None):
 //	  """Serializes a protobuf message to JSONPB string.
 //
 //	  Args:
 //	    msg: a *Message to serialize.
 //	    use_proto_names: boolean, whether to use snake_case in field names
 //	      instead of camelCase. The default is False.
 //
 //	  Returns:
 //	    A str representing msg in JSONPB format.
 //	  """
 //
 //	def to_wirepb(msg):
 //	  """Serializes a protobuf message to a string using binary wire encoding.
 //
 //	  Args:
 //	    msg: a *Message to serialize.
 //
 //	  Returns:
 //	    A str representing msg in binary wire format.
 //	  """
 //
 //	def from_textpb(ctor, body):
 //	  """Deserializes a protobuf message given in text proto form.
 //
 //	  Unknown fields are not allowed.
 //
 //	  Args:
 //	    ctor: a message constructor function.
 //	    body: a string with serialized message.
 //
 //	  Returns:
 //	    Deserialized frozen message constructed via `ctor`.
 //	  """
 //
 //	def from_jsonpb(ctor, body):
 //	  """Deserializes a protobuf message given as JBONPB string.
 //
 //	  Unknown fields are silently skipped.
 //
 //	  Args:
 //	    ctor: a message constructor function.
 //	    body: a string with serialized message.
 //
 //	  Returns:
 //	    Deserialized frozen message constructed via `ctor`.
 //	  """
 //
 //	def from_wirepb(ctor, body):
 //	  """Deserializes a protobuf message given its wire serialization.
 //
 //	  Unknown fields are silently skipped.
 //
 //	  Args:
 //	    ctor: a message constructor function.
 //	    body: a string with serialized message.
 //
 //	  Returns:
 //	    Deserialized frozen message constructed via `ctor`.
 //	  """
 //
 //	def struct_to_textpb(s):
 //	  """Converts a struct to a text proto string.
 //
 //	  Args:
 //	    s: a struct object. May not contain dicts.
 //
 //	  Returns:
 //	    A str containing a text format protocol buffer message.
 //	  """
 //
 //	def clone(msg):
 //	  """Returns a deep copy of a given proto message.
 //
 //	  Args:
 //	    msg: a proto message to make a copy of.
 //
 //	  Returns:
 //	    A deep copy of the message
 //	  """
 //
 //	def has(msg, field):
 //	  """Checks if a proto message has the given optional field set.
 //
 //	  Args:
 //	    msg: a message to check.
 //	    field: a string name of the field to check.
 //
 //	  Returns:
 //	    True if the message has the field set.
 //	  """
 func ProtoLib() starlark.StringDict {
 	return starlark.StringDict{
 		"proto": starlarkstruct.FromStringDict(starlark.String("proto"), starlark.StringDict{
 			"new_descriptor_set": starlark.NewBuiltin("new_descriptor_set", newDescriptorSet),
 			"new_loader":         starlark.NewBuiltin("new_loader", newLoader),
 			"default_loader":     starlark.NewBuiltin("default_loader", defaultLoader),
 			"message_type":       starlark.NewBuiltin("message_type", messageType),
 			"to_textpb":          marshallerBuiltin("to_textpb", ToTextPB),
 			"to_jsonpb":          toJSONPBBuiltin("to_jsonpb"),
 			"to_wirepb":          marshallerBuiltin("to_wirepb", ToWirePB),
 			"from_textpb":        unmarshallerBuiltin("from_textpb", FromTextPB),
 			"from_jsonpb":        unmarshallerBuiltin("from_jsonpb", FromJSONPB),
 			"from_wirepb":        unmarshallerBuiltin("from_wirepb", FromWirePB),
 			"struct_to_textpb":   starlark.NewBuiltin("struct_to_textpb", structToTextPb),
 			"clone":              starlark.NewBuiltin("clone", clone),
 			"has":                starlark.NewBuiltin("has", has),
 		}),
 	}
 }

 // newDescriptorSet constructs *DescriptorSet.
 func newDescriptorSet(_ *starlark.Thread, fn *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 	var name string
 	var blob string
 	var deps starlark.Value
 	err := starlark.UnpackArgs("new_descriptor_set", args, kwargs,
 		"name?", &name,
 		"blob?", &blob,
 		"deps?", &deps,
 	)
 	if err != nil {
 		return nil, err
 	}

 	// Name is optional.
 	if name == "" {
 		name = "???"
 	}

 	// Blob is also optional. If given, it is a serialized FileDescriptorSet.
 	var fdps []*descriptorpb.FileDescriptorProto
 	if blob != "" {
 		fds := &descriptorpb.FileDescriptorSet{}
 		if err := proto.Unmarshal([]byte(blob), fds); err != nil {
 			return nil, fmt.Errorf("new_descriptor_set: for parameter \"blob\": %s", err)
 		}
 		fdps = fds.GetFile()
 	}

 	// Collect []*DescriptorSet from 'deps'.
 	var sets []*DescriptorSet
 	if deps != nil && deps != starlark.None {
 		iter := starlark.Iterate(deps)
 		if iter == nil {
 			return nil, fmt.Errorf("new_descriptor_set: for parameter \"deps\": got %s, want an iterable", deps.Type())
 		}
 		defer iter.Done()
 		var x starlark.Value
 		for iter.Next(&x) {
 			ds, ok := x.(*DescriptorSet)
 			if !ok {
 				return nil, fmt.Errorf("new_descriptor_set: for parameter \"deps\" #%d: got %s, want proto.DescriptorSet", len(sets), x.Type())
 			}
 			sets = append(sets, ds)
 		}
 	}

 	// Checks all imports can be resolved.
 	ds, err := NewDescriptorSet(name, fdps, sets)
 	if err != nil {
 		return nil, fmt.Errorf("new_descriptor_set: %s", err)
 	}
 	return ds, nil
 }

 // newLoader constructs *Loader and populates it with given descriptor sets.
 func newLoader(_ *starlark.Thread, fn *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 	if len(kwargs) > 0 {
 		return nil, errors.New("new_loader: unexpected keyword arguments")
 	}
 	sets := make([]*DescriptorSet, len(args))
 	for i, v := range args {
 		ds, ok := v.(*DescriptorSet)
 		if !ok {
 			return nil, fmt.Errorf("new_loader: for parameter %d: got %s, want proto.DescriptorSet", i+1, v.Type())
 		}
 		sets[i] = ds
 	}
 	l := NewLoader()
 	for _, ds := range sets {
 		if err := l.AddDescriptorSet(ds); err != nil {
 			return nil, fmt.Errorf("new_loader: %s", err)
 		}
 	}
 	return l, nil
 }

 // defaultLoader returns *Loader installed in the thread via SetDefaultLoader.
 func defaultLoader(th *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 	if err := starlark.UnpackArgs("default_loader", args, kwargs); err != nil {
 		return nil, err
 	}
 	if l := DefaultLoader(th); l != nil {
 		return l, nil
 	}
 	return starlark.None, nil
 }

 // messageType returns MessageType of the given message.
 func messageType(th *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 	var msg *Message
 	if err := starlark.UnpackArgs("message_type", args, kwargs, "msg", &msg); err != nil {
 		return nil, err
 	}
 	return msg.MessageType(), nil
 }

 // marshallerBuiltin implements Starlark shim for To*PB() functions.
 func marshallerBuiltin(name string, impl func(*Message) ([]byte, error)) *starlark.Builtin {
 	return starlark.NewBuiltin(name, func(_ *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 		var msg *Message
 		if err := starlark.UnpackArgs(name, args, kwargs, "msg", &msg); err != nil {
 			return nil, err
 		}
 		blob, err := impl(msg)
 		if err != nil {
 			return nil, fmt.Errorf("%s: %s", name, err)
 		}
 		return starlark.String(blob), nil
 	})
 }

 // toJSONPBBuiltin implements Starlark shim for the ToJSONPB function.
 func toJSONPBBuiltin(name string) *starlark.Builtin {
 	return starlark.NewBuiltin(name, func(_ *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 		var msg *Message
 		var useProtoNames starlark.Bool
 		if err := starlark.UnpackArgs(name, args, kwargs, "msg", &msg, "use_proto_names?", &useProtoNames); err != nil {
 			return nil, err
 		}
 		blob, err := ToJSONPB(msg, bool(useProtoNames))
 		if err != nil {
 			return nil, fmt.Errorf("%s: %s", name, err)
 		}
 		return starlark.String(blob), nil
 	})
 }

 // unmarshallerBuiltin implements Starlark shim for From*PB() functions.
 //
 // It also knows how to use the message cache in the thread to cache
 // deserialized messages.
 func unmarshallerBuiltin(name string, impl func(*MessageType, []byte) (*Message, error)) *starlark.Builtin {
 	return starlark.NewBuiltin(name, func(th *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 		var ctor starlark.Value
 		var body string
 		if err := starlark.UnpackArgs(name, args, kwargs, "ctor", &ctor, "body", &body); err != nil {
 			return nil, err
 		}
 		typ, ok := ctor.(*MessageType)
 		if !ok {
 			return nil, fmt.Errorf("%s: got %s, expecting a proto message constructor", name, ctor.Type())
 		}

 		cache := messageCache(th)
 		if cache != nil {
 			cached, err := cache.Fetch(th, name, body, typ)
 			if err != nil {
 				return nil, fmt.Errorf("%s: internal message cache error when fetching: %s", name, err)
 			}
 			if cached != nil {
 				if cached.MessageType() != typ {
 					panic(fmt.Sprintf("the message cache returned message of type %s, but %s was expected", cached.MessageType(), typ))
 				}
 				if !cached.IsFrozen() {
 					panic("the message cache returned non-frozen message")
 				}
 				return cached, nil
 			}
 		}

 		msg, err := impl(typ, []byte(body))
 		if err != nil {
 			return nil, fmt.Errorf("%s: %s", name, err)
 		}
 		msg.Freeze()

 		if cache != nil {
 			if err := cache.Store(th, name, body, msg); err != nil {
 				return nil, fmt.Errorf("%s: internal message cache error when storing: %s", name, err)
 			}
 		}

 		return msg, nil
 	})
 }

 // clone returns a copy of a given message.
 func clone(th *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 	var msg *Message
 	if err := starlark.UnpackArgs("clone", args, kwargs, "msg", &msg); err != nil {
 		return nil, err
 	}
 	return msg.MessageType().MessageFromProto(proto.Clone(msg.ToProto())), nil
 }

 // has checks a presence of an optional field.
 func has(th *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 	var msg *Message
 	var field string
 	if err := starlark.UnpackArgs("has", args, kwargs, "msg", &msg, "field", &field); err != nil {
 		return nil, err
 	}
 	return starlark.Bool(msg.HasProtoField(field)), nil
 }

 // TODO(vadimsh): Remove once users switch to protos.

 // structToTextPb takes a struct and returns a string containing a text format
 // protocol buffer.
 func structToTextPb(_ *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 	var val starlark.Value
 	if err := starlark.UnpackArgs("struct_to_textpb", args, kwargs, "struct", &val); err != nil {
 		return nil, err
 	}
 	s, ok := val.(*starlarkstruct.Struct)
 	if !ok {
 		return nil, fmt.Errorf("struct_to_textpb: got %s, expecting a struct", val.Type())
 	}
 	var buf bytes.Buffer
 	err := writeProtoStruct(&buf, 0, s)
 	if err != nil {
 		return nil, err
 	}
 	return starlark.String(buf.String()), nil
 }

 // Based on
 // https://github.com/google/starlark-go/blob/32ce6ec36500ded2e2340a430fae42bc43da8467/starlarkstruct/struct.go
 func writeProtoStruct(out *bytes.Buffer, depth int, s *starlarkstruct.Struct) error {
 	for _, name := range s.AttrNames() {
 		val, err := s.Attr(name)
 		if err != nil {
 			return err
 		}
 		if err = writeProtoField(out, depth, name, val); err != nil {
 			return err
 		}
 	}
 	return nil
 }

 func writeProtoField(out *bytes.Buffer, depth int, field string, v starlark.Value) error {
 	if depth > 16 {
 		return fmt.Errorf("struct_to_textpb: depth limit exceeded")
 	}

 	switch v := v.(type) {
 	case *starlarkstruct.Struct:
 		fmt.Fprintf(out, "%*s%s: <\n", 2*depth, "", field)
 		if err := writeProtoStruct(out, depth+1, v); err != nil {
 			return err
 		}
 		fmt.Fprintf(out, "%*s>\n", 2*depth, "")
 		return nil

 	case *starlark.List, starlark.Tuple:
 		iter := starlark.Iterate(v)
 		defer iter.Done()
 		var elem starlark.Value
 		for iter.Next(&elem) {
 			if err := writeProtoField(out, depth, field, elem); err != nil {
 				return err
 			}
 		}
 		return nil
 	}

 	// scalars
 	fmt.Fprintf(out, "%*s%s: ", 2*depth, "", field)
 	switch v := v.(type) {
 	case starlark.Bool:
 		fmt.Fprintf(out, "%t", v)

 	case starlark.Int:
 		out.WriteString(v.String())

 	case starlark.Float:
 		fmt.Fprintf(out, "%g", v)

 	case starlark.String:
 		fmt.Fprintf(out, "%q", string(v))

 	default:
 		return fmt.Errorf("struct_to_textpb: cannot convert %s to proto", v.Type())
 	}
 	out.WriteByte('\n')
 	return nil
 }
	// Copyright 2019 The LUCI Authors.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	package starlarkproto

	import (
	"bytes"
	"encoding/json"
	"fmt"

	"go.starlark.net/starlark"
	"go.starlark.net/starlarkstruct"

	"google.golang.org/protobuf/encoding/protojson"
	"google.golang.org/protobuf/encoding/prototext"
	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/types/descriptorpb"
	"google.golang.org/protobuf/types/dynamicpb"

	"go.chromium.org/luci/common/errors"
	"go.chromium.org/luci/common/proto/textpb"
	)

	// ToTextPB serializes a protobuf message to text proto.
	func ToTextPB(msg *Message) ([]byte, error) {
	opts := prototext.MarshalOptions{
	AllowPartial: true,
	Indent: " ",
	Resolver: msg.typ.loader.types, // used for google.protobuf.Any fields
	}
	blob, err := opts.Marshal(msg.ToProto())
	if err != nil {
	return nil, err
	}
	// prototext randomly injects spaces into the generate output. Pass it through
	// a formatter to get rid of them.
	return textpb.Format(blob, msg.MessageType().Descriptor())
	}

	// ToJSONPB serializes a protobuf message to JSONPB string.
	func ToJSONPB(msg *Message, useProtoNames bool) ([]byte, error) {
	opts := protojson.MarshalOptions{
	AllowPartial: true,
	Resolver: msg.typ.loader.types, // used for google.protobuf.Any fields
	UseProtoNames: useProtoNames,
	}
	blob, err := opts.Marshal(msg.ToProto())
	if err != nil {
	return nil, err
	}
	// protojson randomly injects spaces into the generate output. Pass it through
	// a formatter to get rid of them.
	var out bytes.Buffer
	if err := json.Indent(&out, blob, "", "\t"); err != nil {
	return nil, err
	}
	return bytes.TrimSpace(out.Bytes()), nil
	}

	// ToWirePB serializes a protobuf message to binary wire format.
	func ToWirePB(msg *Message) ([]byte, error) {
	opts := proto.MarshalOptions{
	AllowPartial: true,
	Deterministic: true,
	}
	return opts.Marshal(msg.ToProto())
	}

	// FromTextPB deserializes a protobuf message given in text proto form.
	//
	// Unlike the equivalent Starlark proto.from_textpb(...), this low-level native
	// function doesn't freeze returned messages, but also doesn't use the message
	// cache.
	func FromTextPB(typ MessageType, blob []byte) (Message, error) {
	pb := dynamicpb.NewMessage(typ.desc)
	opts := prototext.UnmarshalOptions{
	AllowPartial: true,
	Resolver: typ.loader.types, // used for google.protobuf.Any fields
	}
	if err := opts.Unmarshal(blob, pb); err != nil {
	return nil, err
	}
	return typ.MessageFromProto(pb), nil
	}

	// FromJSONPB deserializes a protobuf message given as JBONPB string.
	//
	// Unlike the equivalent Starlark proto.from_jsonpb(...), this low-level native
	// function doesn't freeze returned messages, but also doesn't use the message
	// cache.
	func FromJSONPB(typ MessageType, blob []byte) (Message, error) {
	pb := dynamicpb.NewMessage(typ.desc)
	opts := protojson.UnmarshalOptions{
	AllowPartial: true,
	DiscardUnknown: true,
	Resolver: typ.loader.types, // used for google.protobuf.Any fields
	}
	if err := opts.Unmarshal(blob, pb); err != nil {
	return nil, err
	}
	return typ.MessageFromProto(pb), nil
	}

	// FromWirePB deserializes a protobuf message given as a wire-encoded blob.
	//
	// Unlike the equivalent Starlark proto.from_wirepb(...), this low-level native
	// function doesn't freeze returned messages, but also doesn't use the message
	// cache.
	func FromWirePB(typ MessageType, blob []byte) (Message, error) {
	pb := dynamicpb.NewMessage(typ.desc)
	opts := proto.UnmarshalOptions{
	AllowPartial: true,
	DiscardUnknown: true,
	Resolver: typ.loader.types, // used for google.protobuf.Any fields
	}
	if err := opts.Unmarshal(blob, pb); err != nil {
	return nil, err
	}
	return typ.MessageFromProto(pb), nil
	}

	// ProtoLib returns a dict with single struct named "proto" that holds public
	// Starlark API for working with proto messages.
	//
	// Exported functions:
	//
	// def new_descriptor_set(name=None, blob=None, deps=None):
	// """Returns a new DescriptorSet.
	//
	// Args:
	// name: name of this set for debug and error messages, default is '???'.
	// blob: raw serialized FileDescriptorSet, if any.
	// deps: an iterable of DescriptorSet's with dependencies, if any.
	//
	// Returns:
	// New DescriptorSet.
	// """
	//
	// def new_loader(*descriptor_sets):
	// """Returns a new proto loader."""
	//
	// def default_loader():
	// """Returns a loader used by default when registering descriptor sets."""
	//
	// def message_type(msg):
	// """Returns proto.MessageType of the given message."""
	//
	// def to_textpb(msg):
	// """Serializes a protobuf message to text proto.
	//
	// Args:
	// msg: a *Message to serialize.
	//
	// Returns:
	// A str representing msg in text format.
	// """
	//
	// def to_jsonpb(msg, use_proto_names = None):
	// """Serializes a protobuf message to JSONPB string.
	//
	// Args:
	// msg: a *Message to serialize.
	// use_proto_names: boolean, whether to use snake_case in field names
	// instead of camelCase. The default is False.
	//
	// Returns:
	// A str representing msg in JSONPB format.
	// """
	//
	// def to_wirepb(msg):
	// """Serializes a protobuf message to a string using binary wire encoding.
	//
	// Args:
	// msg: a *Message to serialize.
	//
	// Returns:
	// A str representing msg in binary wire format.
	// """
	//
	// def from_textpb(ctor, body):
	// """Deserializes a protobuf message given in text proto form.
	//
	// Unknown fields are not allowed.
	//
	// Args:
	// ctor: a message constructor function.
	// body: a string with serialized message.
	//
	// Returns:
	// Deserialized frozen message constructed via `ctor`.
	// """
	//
	// def from_jsonpb(ctor, body):
	// """Deserializes a protobuf message given as JBONPB string.
	//
	// Unknown fields are silently skipped.
	//
	// Args:
	// ctor: a message constructor function.
	// body: a string with serialized message.
	//
	// Returns:
	// Deserialized frozen message constructed via `ctor`.
	// """
	//
	// def from_wirepb(ctor, body):
	// """Deserializes a protobuf message given its wire serialization.
	//
	// Unknown fields are silently skipped.
	//
	// Args:
	// ctor: a message constructor function.
	// body: a string with serialized message.
	//
	// Returns:
	// Deserialized frozen message constructed via `ctor`.
	// """
	//
	// def struct_to_textpb(s):
	// """Converts a struct to a text proto string.
	//
	// Args:
	// s: a struct object. May not contain dicts.
	//
	// Returns:
	// A str containing a text format protocol buffer message.
	// """
	//
	// def clone(msg):
	// """Returns a deep copy of a given proto message.
	//
	// Args:
	// msg: a proto message to make a copy of.
	//
	// Returns:
	// A deep copy of the message
	// """
	//
	// def has(msg, field):
	// """Checks if a proto message has the given optional field set.
	//
	// Args:
	// msg: a message to check.
	// field: a string name of the field to check.
	//
	// Returns:
	// True if the message has the field set.
	// """
	func ProtoLib() starlark.StringDict {
	return starlark.StringDict{
	"proto": starlarkstruct.FromStringDict(starlark.String("proto"), starlark.StringDict{
	"new_descriptor_set": starlark.NewBuiltin("new_descriptor_set", newDescriptorSet),
	"new_loader": starlark.NewBuiltin("new_loader", newLoader),
	"default_loader": starlark.NewBuiltin("default_loader", defaultLoader),
	"message_type": starlark.NewBuiltin("message_type", messageType),
	"to_textpb": marshallerBuiltin("to_textpb", ToTextPB),
	"to_jsonpb": toJSONPBBuiltin("to_jsonpb"),
	"to_wirepb": marshallerBuiltin("to_wirepb", ToWirePB),
	"from_textpb": unmarshallerBuiltin("from_textpb", FromTextPB),
	"from_jsonpb": unmarshallerBuiltin("from_jsonpb", FromJSONPB),
	"from_wirepb": unmarshallerBuiltin("from_wirepb", FromWirePB),
	"struct_to_textpb": starlark.NewBuiltin("struct_to_textpb", structToTextPb),
	"clone": starlark.NewBuiltin("clone", clone),
	"has": starlark.NewBuiltin("has", has),
	}),
	}
	}

	// newDescriptorSet constructs *DescriptorSet.
	func newDescriptorSet(_ starlark.Thread, fn starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
	var name string
	var blob string
	var deps starlark.Value
	err := starlark.UnpackArgs("new_descriptor_set", args, kwargs,
	"name?", &name,
	"blob?", &blob,
	"deps?", &deps,
	)
	if err != nil {
	return nil, err
	}

	// Name is optional.
	if name == "" {
	name = "???"
	}

	// Blob is also optional. If given, it is a serialized FileDescriptorSet.
	var fdps []*descriptorpb.FileDescriptorProto
	if blob != "" {
	fds := &descriptorpb.FileDescriptorSet{}
	if err := proto.Unmarshal([]byte(blob), fds); err != nil {
	return nil, fmt.Errorf("new_descriptor_set: for parameter \"blob\": %s", err)
	}
	fdps = fds.GetFile()
	}

	// Collect []*DescriptorSet from 'deps'.
	var sets []*DescriptorSet
	if deps != nil && deps != starlark.None {
	iter := starlark.Iterate(deps)
	if iter == nil {
	return nil, fmt.Errorf("new_descriptor_set: for parameter \"deps\": got %s, want an iterable", deps.Type())
	}
	defer iter.Done()
	var x starlark.Value
	for iter.Next(&x) {
	ds, ok := x.(*DescriptorSet)
	if !ok {
	return nil, fmt.Errorf("new_descriptor_set: for parameter \"deps\" #%d: got %s, want proto.DescriptorSet", len(sets), x.Type())
	}
	sets = append(sets, ds)
	}
	}

	// Checks all imports can be resolved.
	ds, err := NewDescriptorSet(name, fdps, sets)
	if err != nil {
	return nil, fmt.Errorf("new_descriptor_set: %s", err)
	}
	return ds, nil
	}

	// newLoader constructs *Loader and populates it with given descriptor sets.
	func newLoader(_ starlark.Thread, fn starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
	if len(kwargs) > 0 {
	return nil, errors.New("new_loader: unexpected keyword arguments")
	}
	sets := make([]*DescriptorSet, len(args))
	for i, v := range args {
	ds, ok := v.(*DescriptorSet)
	if !ok {
	return nil, fmt.Errorf("new_loader: for parameter %d: got %s, want proto.DescriptorSet", i+1, v.Type())
	}
	sets[i] = ds
	}
	l := NewLoader()
	for _, ds := range sets {
	if err := l.AddDescriptorSet(ds); err != nil {
	return nil, fmt.Errorf("new_loader: %s", err)
	}
	}
	return l, nil
	}

	// defaultLoader returns *Loader installed in the thread via SetDefaultLoader.
	func defaultLoader(th starlark.Thread, _ starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
	if err := starlark.UnpackArgs("default_loader", args, kwargs); err != nil {
	return nil, err
	}
	if l := DefaultLoader(th); l != nil {
	return l, nil
	}
	return starlark.None, nil
	}

	// messageType returns MessageType of the given message.
	func messageType(th starlark.Thread, _ starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
	var msg *Message
	if err := starlark.UnpackArgs("message_type", args, kwargs, "msg", &msg); err != nil {
	return nil, err
	}
	return msg.MessageType(), nil
	}

	// marshallerBuiltin implements Starlark shim for To*PB() functions.
	func marshallerBuiltin(name string, impl func(Message) ([]byte, error)) starlark.Builtin {
	return starlark.NewBuiltin(name, func(_ starlark.Thread, _ starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
	var msg *Message
	if err := starlark.UnpackArgs(name, args, kwargs, "msg", &msg); err != nil {
	return nil, err
	}
	blob, err := impl(msg)
	if err != nil {
	return nil, fmt.Errorf("%s: %s", name, err)
	}
	return starlark.String(blob), nil
	})
	}

	// toJSONPBBuiltin implements Starlark shim for the ToJSONPB function.
	func toJSONPBBuiltin(name string) *starlark.Builtin {
	return starlark.NewBuiltin(name, func(_ starlark.Thread, _ starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
	var msg *Message
	var useProtoNames starlark.Bool
	if err := starlark.UnpackArgs(name, args, kwargs, "msg", &msg, "use_proto_names?", &useProtoNames); err != nil {
	return nil, err
	}
	blob, err := ToJSONPB(msg, bool(useProtoNames))
	if err != nil {
	return nil, fmt.Errorf("%s: %s", name, err)
	}
	return starlark.String(blob), nil
	})
	}

	// unmarshallerBuiltin implements Starlark shim for From*PB() functions.
	//
	// It also knows how to use the message cache in the thread to cache
	// deserialized messages.
	func unmarshallerBuiltin(name string, impl func(MessageType, []byte) (Message, error)) *starlark.Builtin {
	return starlark.NewBuiltin(name, func(th starlark.Thread, _ starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
	var ctor starlark.Value
	var body string
	if err := starlark.UnpackArgs(name, args, kwargs, "ctor", &ctor, "body", &body); err != nil {
	return nil, err
	}
	typ, ok := ctor.(*MessageType)
	if !ok {
	return nil, fmt.Errorf("%s: got %s, expecting a proto message constructor", name, ctor.Type())
	}

	cache := messageCache(th)
	if cache != nil {
	cached, err := cache.Fetch(th, name, body, typ)
	if err != nil {
	return nil, fmt.Errorf("%s: internal message cache error when fetching: %s", name, err)
	}
	if cached != nil {
	if cached.MessageType() != typ {
	panic(fmt.Sprintf("the message cache returned message of type %s, but %s was expected", cached.MessageType(), typ))
	}
	if !cached.IsFrozen() {
	panic("the message cache returned non-frozen message")
	}
	return cached, nil
	}
	}

	msg, err := impl(typ, []byte(body))
	if err != nil {
	return nil, fmt.Errorf("%s: %s", name, err)
	}
	msg.Freeze()

	if cache != nil {
	if err := cache.Store(th, name, body, msg); err != nil {
	return nil, fmt.Errorf("%s: internal message cache error when storing: %s", name, err)
	}
	}

	return msg, nil
	})
	}

	// clone returns a copy of a given message.
	func clone(th starlark.Thread, _ starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
	var msg *Message
	if err := starlark.UnpackArgs("clone", args, kwargs, "msg", &msg); err != nil {
	return nil, err
	}
	return msg.MessageType().MessageFromProto(proto.Clone(msg.ToProto())), nil
	}

	// has checks a presence of an optional field.
	func has(th starlark.Thread, _ starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
	var msg *Message
	var field string
	if err := starlark.UnpackArgs("has", args, kwargs, "msg", &msg, "field", &field); err != nil {
	return nil, err
	}
	return starlark.Bool(msg.HasProtoField(field)), nil
	}

	// TODO(vadimsh): Remove once users switch to protos.

	// structToTextPb takes a struct and returns a string containing a text format
	// protocol buffer.
	func structToTextPb(_ starlark.Thread, _ starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
	var val starlark.Value
	if err := starlark.UnpackArgs("struct_to_textpb", args, kwargs, "struct", &val); err != nil {
	return nil, err
	}
	s, ok := val.(*starlarkstruct.Struct)
	if !ok {
	return nil, fmt.Errorf("struct_to_textpb: got %s, expecting a struct", val.Type())
	}
	var buf bytes.Buffer
	err := writeProtoStruct(&buf, 0, s)
	if err != nil {
	return nil, err
	}
	return starlark.String(buf.String()), nil
	}

	// Based on
	// https://github.com/google/starlark-go/blob/32ce6ec36500ded2e2340a430fae42bc43da8467/starlarkstruct/struct.go
	func writeProtoStruct(out bytes.Buffer, depth int, s starlarkstruct.Struct) error {
	for _, name := range s.AttrNames() {
	val, err := s.Attr(name)
	if err != nil {
	return err
	}
	if err = writeProtoField(out, depth, name, val); err != nil {
	return err
	}
	}
	return nil
	}

	func writeProtoField(out *bytes.Buffer, depth int, field string, v starlark.Value) error {
	if depth > 16 {
	return fmt.Errorf("struct_to_textpb: depth limit exceeded")
	}

	switch v := v.(type) {
	case *starlarkstruct.Struct:
	fmt.Fprintf(out, "%s%s: <\n", 2depth, "", field)
	if err := writeProtoStruct(out, depth+1, v); err != nil {
	return err
	}
	fmt.Fprintf(out, "%s>\n", 2depth, "")
	return nil

	case *starlark.List, starlark.Tuple:
	iter := starlark.Iterate(v)
	defer iter.Done()
	var elem starlark.Value
	for iter.Next(&elem) {
	if err := writeProtoField(out, depth, field, elem); err != nil {
	return err
	}
	}
	return nil
	}

	// scalars
	fmt.Fprintf(out, "%s%s: ", 2depth, "", field)
	switch v := v.(type) {
	case starlark.Bool:
	fmt.Fprintf(out, "%t", v)

	case starlark.Int:
	out.WriteString(v.String())

	case starlark.Float:
	fmt.Fprintf(out, "%g", v)

	case starlark.String:
	fmt.Fprintf(out, "%q", string(v))

	default:
	return fmt.Errorf("struct_to_textpb: cannot convert %s to proto", v.Type())
	}
	out.WriteByte('\n')
	return nil
	}