thanos-io/thanos · error

proto: wrong wireType =

Error message

proto: wrong wireType = %d for field ChunkCount

What it means

Same generated gogoproto Unmarshal guard as error 932, but for field 3 (ChunkCount) of the Statistic message in pkg/status/statuspb/rpc.pb.go:1747. It fires when the incoming wire bytes encode ChunkCount with a non-varint wire type, proving a schema/codec mismatch between sender and receiver.

Solutions

  1. Align both peers on the same Thanos version / generated statuspb code
  2. Regenerate pkg/status/statuspb with matching protoc and gogoproto versions
  3. Confirm ChunkCount is field 3 with proto type varint in the sender's rpc.proto
  4. Capture and inspect the raw gRPC frame if the mismatch persists after version alignment

Example fix

// before: receiver compiled with stale rpc.proto
// after: regenerate and rebuild both sides
make proto
go build ./pkg/status/...
Defensive patterns

Strategy: try-catch

Validate before calling

if !semverCompatible(peerVersion, minSupportedVersion) {
    return fmt.Errorf("peer %s version %s incompatible for TSDB statistics", peer, peerVersion)
}

Try / catch

if err := proto.Unmarshal(buf, &stat); err != nil {
    if strings.Contains(err.Error(), "field ChunkCount") {
        return fmt.Errorf("schema mismatch (ChunkCount): %w", err)
    }
    return err
}

Prevention

When it happens

Trigger: Unmarshaling a Statistic message where field 3 is received as length-delimited (2), fixed64 (1), or fixed32 (5) instead of varint (0).

Common situations: Thanos component version skew; receiver's generated rpc.pb.go out of date relative to the sender's proto; interop with a non-Thanos service that reuses field numbers differently.

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

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/b6974178ca63e0b5. Report an issue: GitHub.

Appendix: source

Thrown at pkg/status/statuspb/rpc.pb.go:1747

			}
			m.NumLabelPairs = 0
			for shift := uint(0); ; shift += 7 {
				if shift >= 64 {
					return ErrIntOverflowRpc
				}
				if iNdEx >= l {
					return io.ErrUnexpectedEOF
				}
				b := dAtA[iNdEx]
				iNdEx++
				m.NumLabelPairs |= int64(b&0x7F) << shift
				if b < 0x80 {
					break
				}
			}
		case 3:
			if wireType != 0 {
				return fmt.Errorf("proto: wrong wireType = %d for field ChunkCount", wireType)
			}
			m.ChunkCount = 0
			for shift := uint(0); ; shift += 7 {
				if shift >= 64 {
					return ErrIntOverflowRpc
				}
				if iNdEx >= l {
					return io.ErrUnexpectedEOF
				}
				b := dAtA[iNdEx]
				iNdEx++
				m.ChunkCount |= int64(b&0x7F) << shift
				if b < 0x80 {
					break
				}
			}
		case 4:
			if wireType != 0 {

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