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Clarify what's left in handling OP_MSG checksum #2677

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merged 4 commits into from
May 24, 2023
Merged

Clarify what's left in handling OP_MSG checksum #2677

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8f77464
Write CRC32
rumyantseva May 22, 2023
1f8caa6
Checksum cleanup
rumyantseva May 23, 2023
a922e9e
Merge branch 'main' into write-crc32
May 23, 2023
1da7fd6
Merge branch 'main' into write-crc32
mergify[bot] May 24, 2023
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51 changes: 30 additions & 21 deletions internal/wire/msg_body.go
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,7 @@ type MsgBody interface {
// indicating that connection was closed by the client.
var ErrZeroRead = errors.New("zero bytes read")

// kFlagBitSize represents the size of the flag bits field.
const kFlagBitSize = 4

// ReadMessage reads from reader and returns wire header and body.
Expand All @@ -68,7 +69,7 @@ func ReadMessage(r *bufio.Reader) (*MsgHeader, MsgBody, error) {
return &header, &reply, nil

case OpCodeMsg:
if err := containsValidChecksum(&header, b); err != nil {
if err := validateChecksum(&header, b); err != nil {
return &header, nil, lazyerrors.Error(err)
}

Expand Down Expand Up @@ -122,7 +123,7 @@ func WriteMessage(w *bufio.Writer, header *MsgHeader, msg MsgBody) error {
}

if header.OpCode == OpCodeMsg {
if err := containsValidChecksum(header, b); err != nil {
if err := validateChecksum(header, b); err != nil {
return lazyerrors.Error(err)
}
}
Expand Down Expand Up @@ -150,34 +151,42 @@ func getChecksum(data []byte) (uint32, error) {
return binary.LittleEndian.Uint32(data[n-crc32.Size:]), nil
}

func containsValidChecksum(header *MsgHeader, body []byte) error {
// validateChecksum calculates checksum of the message (header + body)
// and compares it with the checksum from the last bytes of the message.
// If the flag bit for checksum presence is not set or the checksum is valid, it returns nil.
// If the checksum is invalid, it returns an error.
//
// TODO The callers of checksum validation should be closer to OP_MSG handling: https://github.com/FerretDB/FerretDB/issues/2690
func validateChecksum(header *MsgHeader, body []byte) error {
if len(body) < kFlagBitSize {
return lazyerrors.New("Message contains illegal flags value")
}

flagBit := OpMsgFlags(binary.LittleEndian.Uint32(body[:kFlagBitSize]))
if flagBit.FlagSet(OpMsgChecksumPresent) {
want, err := getChecksum(body)
if err != nil {
lazyerrors.Error(err)
}
if !flagBit.FlagSet(OpMsgChecksumPresent) {
return nil
}

// https://datatracker.ietf.org/doc/html/rfc4960#appendix-B
hasher := crc32.New(crc32.MakeTable(crc32.Castagnoli))
want, err := getChecksum(body)
if err != nil {
return lazyerrors.Error(err)
}

if err := binary.Write(hasher, binary.LittleEndian, header); err != nil {
return lazyerrors.Error(err)
}
// https://datatracker.ietf.org/doc/html/rfc4960#appendix-B
hasher := crc32.New(crc32.MakeTable(crc32.Castagnoli))

offset := len(body) - crc32.Size
if err := binary.Write(hasher, binary.LittleEndian, body[:offset]); err != nil {
return lazyerrors.Error(err)
}
if err := binary.Write(hasher, binary.LittleEndian, header); err != nil {
return lazyerrors.Error(err)
}

got := hasher.Sum32()
if want != got {
return lazyerrors.New("OP_MSG checksum does not match contents.")
}
offset := len(body) - crc32.Size
if err := binary.Write(hasher, binary.LittleEndian, body[:offset]); err != nil {
return lazyerrors.Error(err)
}
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got := hasher.Sum32()
if want != got {
return lazyerrors.New("OP_MSG checksum does not match contents.")
}

return nil
Expand Down
4 changes: 4 additions & 0 deletions internal/wire/op_msg.go
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Original file line number Diff line number Diff line change
Expand Up @@ -203,6 +203,8 @@ func (msg *OpMsg) readFrom(bufr *bufio.Reader) error {

if msg.FlagBits.FlagSet(OpMsgChecksumPresent) {
if err := binary.Read(bufr, binary.LittleEndian, &msg.checksum); err != nil {
// TODO Move checksum validation here: https://github.com/FerretDB/FerretDB/issues/2690
// It needs header data to be available.
return lazyerrors.Error(err)
}
}
Expand Down Expand Up @@ -295,6 +297,8 @@ func (msg *OpMsg) MarshalBinary() ([]byte, error) {
}

if msg.FlagBits.FlagSet(OpMsgChecksumPresent) {
// TODO Calculate checksum before writing it: https://github.com/FerretDB/FerretDB/issues/2690
// It needs header data to be ready and available here.
if err := binary.Write(bufw, binary.LittleEndian, msg.checksum); err != nil {
return nil, lazyerrors.Error(err)
}
Expand Down