proto: wire decoding support

Add proto.Unmarshal.

Test cases all produce identical results to the v1 unmarshaller.

Change-Id: I42259266018a14e88a650c5d83a043cb17a3a15d
Reviewed-on: https://go-review.googlesource.com/c/153918
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
diff --git a/proto/decode_gen.go b/proto/decode_gen.go
new file mode 100644
index 0000000..130876f
--- /dev/null
+++ b/proto/decode_gen.go
@@ -0,0 +1,591 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style.
+// license that can be found in the LICENSE file.
+
+// Code generated by generate-types. DO NOT EDIT.
+
+package proto
+
+import (
+	"math"
+
+	"github.com/golang/protobuf/v2/internal/encoding/wire"
+	"github.com/golang/protobuf/v2/reflect/protoreflect"
+)
+
+// unmarshalScalar decodes a value of the given kind.
+//
+// Message values are decoded into a []byte which aliases the input data.
+func (o UnmarshalOptions) unmarshalScalar(b []byte, wtyp wire.Type, num wire.Number, kind protoreflect.Kind) (val protoreflect.Value, n int, err error) {
+	switch kind {
+	case protoreflect.BoolKind:
+		if wtyp != wire.VarintType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(wire.DecodeBool(v)), n, nil
+	case protoreflect.EnumKind:
+		if wtyp != wire.VarintType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(protoreflect.EnumNumber(v)), n, nil
+	case protoreflect.Int32Kind:
+		if wtyp != wire.VarintType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(int32(v)), n, nil
+	case protoreflect.Sint32Kind:
+		if wtyp != wire.VarintType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(int32(wire.DecodeZigZag(v & math.MaxUint32))), n, nil
+	case protoreflect.Uint32Kind:
+		if wtyp != wire.VarintType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(uint32(v)), n, nil
+	case protoreflect.Int64Kind:
+		if wtyp != wire.VarintType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(int64(v)), n, nil
+	case protoreflect.Sint64Kind:
+		if wtyp != wire.VarintType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(wire.DecodeZigZag(v)), n, nil
+	case protoreflect.Uint64Kind:
+		if wtyp != wire.VarintType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(v), n, nil
+	case protoreflect.Sfixed32Kind:
+		if wtyp != wire.Fixed32Type {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed32(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(int32(v)), n, nil
+	case protoreflect.Fixed32Kind:
+		if wtyp != wire.Fixed32Type {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed32(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(uint32(v)), n, nil
+	case protoreflect.FloatKind:
+		if wtyp != wire.Fixed32Type {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed32(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(math.Float32frombits(uint32(v))), n, nil
+	case protoreflect.Sfixed64Kind:
+		if wtyp != wire.Fixed64Type {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed64(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(int64(v)), n, nil
+	case protoreflect.Fixed64Kind:
+		if wtyp != wire.Fixed64Type {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed64(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(v), n, nil
+	case protoreflect.DoubleKind:
+		if wtyp != wire.Fixed64Type {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed64(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(math.Float64frombits(v)), n, nil
+	case protoreflect.StringKind:
+		if wtyp != wire.BytesType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeBytes(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(string(v)), n, nil
+	case protoreflect.BytesKind:
+		if wtyp != wire.BytesType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeBytes(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(append(([]byte)(nil), v...)), n, nil
+	case protoreflect.MessageKind:
+		if wtyp != wire.BytesType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeBytes(b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(v), n, nil
+	case protoreflect.GroupKind:
+		if wtyp != wire.StartGroupType {
+			return val, 0, errUnknown
+		}
+		v, n := wire.ConsumeGroup(num, b)
+		if n < 0 {
+			return val, 0, wire.ParseError(n)
+		}
+		return protoreflect.ValueOf(v), n, nil
+	default:
+		return val, 0, errUnknown
+	}
+}
+
+func (o UnmarshalOptions) unmarshalList(b []byte, wtyp wire.Type, num wire.Number, list protoreflect.List, kind protoreflect.Kind) (n int, err error) {
+	switch kind {
+	case protoreflect.BoolKind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeVarint(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(wire.DecodeBool(v)))
+			}
+			return n, nil
+		}
+		if wtyp != wire.VarintType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(wire.DecodeBool(v)))
+		return n, nil
+	case protoreflect.EnumKind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeVarint(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(protoreflect.EnumNumber(v)))
+			}
+			return n, nil
+		}
+		if wtyp != wire.VarintType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(protoreflect.EnumNumber(v)))
+		return n, nil
+	case protoreflect.Int32Kind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeVarint(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(int32(v)))
+			}
+			return n, nil
+		}
+		if wtyp != wire.VarintType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(int32(v)))
+		return n, nil
+	case protoreflect.Sint32Kind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeVarint(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(int32(wire.DecodeZigZag(v & math.MaxUint32))))
+			}
+			return n, nil
+		}
+		if wtyp != wire.VarintType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(int32(wire.DecodeZigZag(v & math.MaxUint32))))
+		return n, nil
+	case protoreflect.Uint32Kind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeVarint(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(uint32(v)))
+			}
+			return n, nil
+		}
+		if wtyp != wire.VarintType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(uint32(v)))
+		return n, nil
+	case protoreflect.Int64Kind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeVarint(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(int64(v)))
+			}
+			return n, nil
+		}
+		if wtyp != wire.VarintType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(int64(v)))
+		return n, nil
+	case protoreflect.Sint64Kind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeVarint(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(wire.DecodeZigZag(v)))
+			}
+			return n, nil
+		}
+		if wtyp != wire.VarintType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(wire.DecodeZigZag(v)))
+		return n, nil
+	case protoreflect.Uint64Kind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeVarint(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(v))
+			}
+			return n, nil
+		}
+		if wtyp != wire.VarintType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeVarint(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(v))
+		return n, nil
+	case protoreflect.Sfixed32Kind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeFixed32(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(int32(v)))
+			}
+			return n, nil
+		}
+		if wtyp != wire.Fixed32Type {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed32(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(int32(v)))
+		return n, nil
+	case protoreflect.Fixed32Kind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeFixed32(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(uint32(v)))
+			}
+			return n, nil
+		}
+		if wtyp != wire.Fixed32Type {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed32(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(uint32(v)))
+		return n, nil
+	case protoreflect.FloatKind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeFixed32(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(math.Float32frombits(uint32(v))))
+			}
+			return n, nil
+		}
+		if wtyp != wire.Fixed32Type {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed32(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(math.Float32frombits(uint32(v))))
+		return n, nil
+	case protoreflect.Sfixed64Kind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeFixed64(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(int64(v)))
+			}
+			return n, nil
+		}
+		if wtyp != wire.Fixed64Type {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed64(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(int64(v)))
+		return n, nil
+	case protoreflect.Fixed64Kind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeFixed64(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(v))
+			}
+			return n, nil
+		}
+		if wtyp != wire.Fixed64Type {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed64(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(v))
+		return n, nil
+	case protoreflect.DoubleKind:
+		if wtyp == wire.BytesType {
+			buf, n := wire.ConsumeBytes(b)
+			if n < 0 {
+				return 0, wire.ParseError(n)
+			}
+			for len(buf) > 0 {
+				v, n := wire.ConsumeFixed64(buf)
+				if n < 0 {
+					return 0, wire.ParseError(n)
+				}
+				buf = buf[n:]
+				list.Append(protoreflect.ValueOf(math.Float64frombits(v)))
+			}
+			return n, nil
+		}
+		if wtyp != wire.Fixed64Type {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeFixed64(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(math.Float64frombits(v)))
+		return n, nil
+	case protoreflect.StringKind:
+		if wtyp != wire.BytesType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeBytes(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(string(v)))
+		return n, nil
+	case protoreflect.BytesKind:
+		if wtyp != wire.BytesType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeBytes(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		list.Append(protoreflect.ValueOf(append(([]byte)(nil), v...)))
+		return n, nil
+	case protoreflect.MessageKind:
+		if wtyp != wire.BytesType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeBytes(b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		m := list.NewMessage().ProtoReflect()
+		if err := o.unmarshalMessage(v, m); err != nil {
+			return 0, err
+		}
+		list.Append(protoreflect.ValueOf(m))
+		return n, nil
+	case protoreflect.GroupKind:
+		if wtyp != wire.StartGroupType {
+			return 0, errUnknown
+		}
+		v, n := wire.ConsumeGroup(num, b)
+		if n < 0 {
+			return 0, wire.ParseError(n)
+		}
+		m := list.NewMessage().ProtoReflect()
+		if err := o.unmarshalMessage(v, m); err != nil {
+			return 0, err
+		}
+		list.Append(protoreflect.ValueOf(m))
+		return n, nil
+	default:
+		return 0, errUnknown
+	}
+}