go/proto/msgpack: Fix Error -> ErrorCode is int on the wire and not extension type

It was already 'int' before the migration to msgpack:

https://lab.nexedi.com/nexedi/neoppod/-/blob/6332112cb/neo/lib/protocol.py#L653

It is 'int' after the migration to msgpack:

https://lab.nexedi.com/nexedi/neoppod/-/blob/9d0bf97a1/neo/lib/protocol.py#L842

(it's explicitly cast into an integer here)

Another verification that 'ErrorCode' is 'int' on the wire can be found
here:

https://lab.nexedi.com/nexedi/neoppod/-/blob/3ddb6663b/neo/tests/protocol#L76

In the Nexedi NEO protocol specification document v1 this is however not
specified (or I couldn't find it):

https://neo.nexedi.com/P-NEO-Protocol.Specification.2019

go/neo/proto/proto_test.go

@@ -176,7 +176,7 @@ func TestMsgMarshal(t *testing.T) {
 		// uint32(N)/enum(M), string
 		{&Error{Code: 0x00000045, Message: "hello"},
 			"\x00\x00\x00\x45\x00\x00\x00\x05hello",
-			hex("92") + hex("d40245") + "\xc4\x05hello",
+			hex("92") + hex("45") + "\xc4\x05hello",
 		},
 
 		// Oid, Tid, bool, Checksum, []byte

go/neo/proto/protogen.go

@@ -985,6 +985,12 @@ func (s *sizerM) genBasic(path string, typ *types.Basic, userType types.Type) {
 		return
 	}
 
+	// Code argument of Error packet is not encoded as enum, but as int
+	if typeName(userType) == "ErrorCode" {
+		s.size.AddExpr("msgpack.Uint32Size(%s)", upath)
+		return
+	}
+
 	// enums are encoded as extensions
 	if _, isEnum := enumRegistry[userType]; isEnum {
 		s.size.Add(1+1+1) // fixext1 enumType value
@@ -1030,17 +1036,6 @@ func (e *encoderM) genBasic(path string, typ *types.Basic, userType types.Type)
 		return
 	}
 
-	// enums are encoded as `fixext1 enumType fixint<value>`
-	if enum, ok := enumRegistry[userType]; ok {
-		e.emit("data[%v] = byte(msgpack.FixExt1)", e.n);  e.n++
-		e.emit("data[%v] = %d", e.n, enum);               e.n++
-		e.emit("if !(0 <= %s && %s <= 0x7f) {", path, path) // mposfixint
-		e.emit(`  panic("%s: invalid %s enum value)")`, path, typeName(userType))
-		e.emit("}")
-		e.emit("data[%v] = byte(%s)", e.n, path);  e.n++
-		return
-	}
-
 	// mputint emits mput<kind>int<size>(path)
 	mputint := func(kind string, size int) {
 		KI := "I" // I or <Kind>i
@@ -1054,6 +1049,23 @@ func (e *encoderM) genBasic(path string, typ *types.Basic, userType types.Type)
 		e.n = 0
 	}
 
+	// Code argument of Error packet is not encoded as enum, but as int
+	if typeName(userType) == "ErrorCode" {
+		mputint("U", 32)
+		return
+	}
+
+	// enums are encoded as `fixext1 enumType fixint<value>`
+	if enum, ok := enumRegistry[userType]; ok {
+		e.emit("data[%v] = byte(msgpack.FixExt1)", e.n);  e.n++
+		e.emit("data[%v] = %d", e.n, enum);               e.n++
+		e.emit("if !(0 <= %s && %s <= 0x7f) {", path, path) // mposfixint
+		e.emit(`  panic("%s: invalid %s enum value)")`, path, typeName(userType))
+		e.emit("}")
+		e.emit("data[%v] = byte(%s)", e.n, path);  e.n++
+		return
+	}
+
 	switch typ.Kind() {
 	case types.Bool:
 		e.emit("data[%v] = byte(msgpack.Bool(%s))", e.n, path)
@@ -1105,43 +1117,6 @@ func (d *decoderM) expectEnum(assignto string, enumType int) {
 }
 
 func (d *decoderM) genBasic(assignto string, typ *types.Basic, userType types.Type) {
-	// zodb.Tid and zodb.Oid are encoded as [8]bin or Nil
-	if userType == zodbTid || userType == zodbOid {
-		d.resetPos()
-		d.overflowCheck()
-		defer d.overflowCheck()
-
-		// Size depends on if we have an INVALID_{TID,OID}
-		// which is encoded as NIL or if we have a valid
-		// {TID,OID} which is encdoed as Bin8Fix.
-		d.overflow.AddExpr("msgpack.TidOrOidSize(data)")
-		d.emit("if data[%v] == byte(msgpack.Nil) {", d.n)
-		d.emit("%s = %s(%v)", assignto, typeName(userType), INVALID_ID)
-		d.n += 1
-		d.resetPos()
-		d.emit("} else {")
-		d.expectBin8Fix(assignto, 8, false)
-		d.emit("%s= %s(binary.BigEndian.Uint64(data[%v:]))", assignto, typeName(userType), d.n)
-		d.n += 8
-		d.resetPos()
-		d.emit("}")
-		return
-	}
-
-	// enums are encoded as `fixext1 enumType fixint<value>`
-	if enum, ok := enumRegistry[userType]; ok {
-		d.expectEnum(assignto, enum)
-		d.emit("{")
-		d.emit("v := data[%v]", d.n);  d.n++
-		d.emit("if !(0 <= v && v <= 0x7f) {") // mposfixint
-		d.emit("  return 0, mdecodeEnumValueErr(%q, v)", d.pathName(assignto))
-		d.emit("}")
-		d.emit("%s= %s(v)", assignto, typeName(userType))
-		d.emit("}")
-		d.overflow.Add(1)
-		return
-	}
-
 	// v represents basic decoded value casted to user type if needed
 	v := "v"
 	if userType.Underlying() != userType {
@@ -1203,6 +1178,49 @@ func (d *decoderM) genBasic(assignto string, typ *types.Basic, userType types.Ty
 		d.emit("}")
 	}
 
+	// zodb.Tid and zodb.Oid are encoded as [8]bin or Nil
+	if userType == zodbTid || userType == zodbOid {
+		d.resetPos()
+		d.overflowCheck()
+		defer d.overflowCheck()
+
+		// Size depends on if we have an INVALID_{TID,OID}
+		// which is encoded as NIL or if we have a valid
+		// {TID,OID} which is encdoed as Bin8Fix.
+		d.overflow.AddExpr("msgpack.TidOrOidSize(data)")
+		d.emit("if data[%v] == byte(msgpack.Nil) {", d.n)
+		d.emit("%s = %s(%v)", assignto, typeName(userType), INVALID_ID)
+		d.n += 1
+		d.resetPos()
+		d.emit("} else {")
+		d.expectBin8Fix(assignto, 8, false)
+		d.emit("%s= %s(binary.BigEndian.Uint64(data[%v:]))", assignto, typeName(userType), d.n)
+		d.n += 8
+		d.resetPos()
+		d.emit("}")
+		return
+	}
+
+	// Code argument of Error packet is not encoded as enum, but as int
+	if typeName(userType) == "ErrorCode" {
+		mgetint("", 32, "")
+		return
+	}
+
+	// enums are encoded as `fixext1 enumType fixint<value>`
+	if enum, ok := enumRegistry[userType]; ok {
+		d.expectEnum(assignto, enum)
+		d.emit("{")
+		d.emit("v := data[%v]", d.n);  d.n++
+		d.emit("if !(0 <= v && v <= 0x7f) {") // mposfixint
+		d.emit("  return 0, mdecodeEnumValueErr(%q, v)", d.pathName(assignto))
+		d.emit("}")
+		d.emit("%s= %s(v)", assignto, typeName(userType))
+		d.emit("}")
+		d.overflow.Add(1)
+		return
+	}
+
 	// IdTime can be nil ('None' in py), in this case we use
 	// infinite -1, see
 	// https://lab.nexedi.com/kirr/neo/-/blob/1ad088c8/go/neo/proto/proto.go#L352-357

go/neo/proto/zproto-marshal.go

@@ -63,21 +63,19 @@ overflow:
 }
 
 func (p *Error) neoMsgEncodedLenM() int {
-	return 3 + msgpack.ArrayHeadSize(reflect.TypeOf((*p)).NumField()) + msgpack.BinHeadSize(len(p.Message)) + len(p.Message)
+	return msgpack.ArrayHeadSize(reflect.TypeOf((*p)).NumField()) + msgpack.Uint32Size(uint32(p.Code)) + msgpack.BinHeadSize(len(p.Message)) + len(p.Message)
 }
 
 func (p *Error) neoMsgEncodeM(data []byte) {
 	data[0] = byte(msgpack.FixArray_4 | 2)
-	data[1] = byte(msgpack.FixExt1)
-	data[2] = 2
-	if !(0 <= p.Code && p.Code <= 0x7f) {
-		panic("p.Code: invalid ErrorCode enum value)")
+	{
+		n := msgpack.PutUint32(data[1:], uint32(p.Code))
+		data = data[1+n:]
 	}
-	data[3] = byte(p.Code)
 	{
 		l := len(p.Message)
-		n := msgpack.PutBinHead(data[4:], l)
-		data = data[4+n:]
+		n := msgpack.PutBinHead(data[0:], l)
+		data = data[0+n:]
 		copy(data, p.Message)
 		data = data[l:]
 	}
@@ -93,23 +91,15 @@ func (p *Error) neoMsgDecodeM(data []byte) (int, error) {
 		nread += uint64(len(data) - len(tail))
 		data = tail
 	}
-	if len(data) < 3 {
-		goto overflow
-	}
-	if op := msgpack.Op(data[0]); op != msgpack.FixExt1 {
-		return 0, mdecodeOpErr("Error.Code", op, msgpack.FixExt1)
-	}
-	if enumType := data[1]; enumType != 2 {
-		return 0, mdecodeEnumTypeErr("Error.Code", enumType, 2)
-	}
 	{
-		v := data[2]
-		if !(0 <= v && v <= 0x7f) {
-			return 0, mdecodeEnumValueErr("Error.Code", v)
+		v, tail, err := msgp.ReadInt32Bytes(data)
+		if err != nil {
+			return 0, mdecodeErr("Error.Code", err)
 		}
 		p.Code = ErrorCode(v)
+		nread += uint64(len(data) - len(tail))
+		data = tail
 	}
-	data = data[3:]
 	{
 		b, tail, err := msgp.ReadBytesZC(data)
 		if err != nil {
@@ -119,10 +109,7 @@ func (p *Error) neoMsgDecodeM(data []byte) (int, error) {
 		nread += uint64(len(data) - len(tail))
 		data = tail
 	}
-	return 3 + int(nread), nil
-
-overflow:
-	return 0, &ErrDecodeOverflow{"Error"}
+	return 0 + int(nread), nil
 }
 
 // 1. RequestIdentification