chenhg5/cc-connect · error

yuanbao: parse varint tag failed at %d

Error message

yuanbao: parse varint tag failed at %d

What it means

This error is thrown by parseFields in the yuanbao protocol codec when the protobuf wire-format tag at the current byte offset cannot be decoded as a varint. decodeVarint returns n==0 when the buffer ends mid-varint (continuation bit set on the last byte) or the varint exceeds 10 bytes, meaning the framed payload is not valid protobuf data.

Source

Thrown at platform/yuanbao/proto.go:140

	return b.bytes()
}

type field struct {
	fieldNum int
	wireType int
	value    interface{}
}

func parseFields(data []byte) ([]field, error) {
	if len(data) == 0 {
		return nil, fmt.Errorf("yuanbao: empty data")
	}
	var fields []field
	pos := 0
	for pos < len(data) {
		tag, n := decodeVarint(data[pos:])
		if n == 0 {
			return nil, fmt.Errorf("yuanbao: parse varint tag failed at %d", pos)
		}
		pos += n
		fieldNum := int(tag >> 3)
		wt := int(tag & 0x07)
		switch wt {
		case wtVarint:
			val, n := decodeVarint(data[pos:])
			if n == 0 {
				return nil, fmt.Errorf("yuanbao: parse varint at %d", pos)
			}
			fields = append(fields, field{fieldNum, wt, val})
			pos += n
		case wtLen:
			ln, n := decodeVarint(data[pos:])
			if n == 0 {
				return nil, fmt.Errorf("yuanbao: parse length at %d", pos)
			}
			pos += n

View on GitHub (pinned to 4000b2338a)

Solutions

1. Verify the bytes passed to parseFields are the complete, uncompressed protobuf message for the frame (check framing/splitting logic upstream of decodeConnMsg).
2. Log the raw bytes at the failure offset and compare against an expected encoded message to detect protocol drift after a server update.
3. Update the yuanbao adapter to match any changed server protocol version.
4. Add a length/consistency check before decoding: ensure the frame payload length matches the header-declared length.
5. If transient network truncation is suspected, reconnect and re-request the frame rather than retrying the parse.

Example fix

// before
raw := wsFrame.Payload
cmp, _ := parseFields(raw)
// after
if len(raw) == 0 || raw[len(raw)-1]&0x80 != 0 {
    return fmt.Errorf("frame truncated, refusing to parse")
}
cmp, err := parseFields(raw)
if err != nil {
    return fmt.Errorf("yuanbao: decode frame: %w", err)
}

func isDecodableFrame(b []byte) bool {
    return len(b) > 0 && b[len(b)-1]&0x80 == 0
}

func validVarintStart(b []byte) bool {
    // tag varint must terminate within 10 bytes
    n := 0
    for n < len(b) && n < 10 {
        if b[n]&0x80 == 0 { return true }
        n++
    }
    return false
}

cm, err := decodeConnMsg(raw)
if err != nil {
    slog.Warn("yuanbao: drop frame", "err", err)
    return // or resync/reconnect
}

When it happens

Trigger: decodeVarint(data[pos:]) returns 0 while parsing the tag of a message frame: input shorter than the tag's varint length, byte 0x80+ as the final byte, or a 10+ byte malformed varint. Reached via decodeConnMsg, decodeAuthBindRsp, decodeInboundPush, or decodeMsgBodyElement on any inbound frame.

Common situations: Yuanbao server protocol changed (new framing/wire format), a truncated or corrupted WebSocket frame is fed to the decoder, a caller accidentally passes plaintext or compressed data instead of the protobuf body, or a proxy splits/merges frames incorrectly.

Understand the failure class

Background: "cannot parse invalid wire-format data", "cannot unmarshal", "failed unmarshalling": protobuf unmarshal errors explained — this error's family across 10 libraries.

Related errors

• yuanbao: parse varint at %d
• yuanbao: parse length at %d
• yuanbao: length %d exceeds data at %d
• yuanbao: 64-bit truncated at %d
• yuanbao: 32-bit truncated at %d

AI-assisted analysis of chenhg5/cc-connect@4000b2338a (2026-09-06). Data as JSON: /api/errors/06644035def6bf0e. Report an issue: GitHub.