What causes "failed assembling endorsers of channel %s" in hyperledger/fabric?

Inspect the wrapped inner error (use github.com/pkg/errors Cause/Unwrap) to find the real failure

failed assembling endorsers of channel %s

Error message

failed assembling endorsers of channel %s

What it means

response.mapEndorsers wraps any error produced while mapping endorsers for a specific channel with "failed assembling endorsers of channel %s" via errors.Wrapf. The underlying error comes from mapEndorsersOfChannel (descriptor count/chaincode mismatch, missing layout group, bad endorser envelopes, etc.). The wrap adds the channel name so the caller knows which channel's chaincode query result failed to assemble.

Source

Thrown at discovery/client/client.go:469

	chaincodeQueryMapping map[int][]InvocationChain,
) error {
	for ch, index := range channel2index {
		ccQueryRes, err := protoext.ResponseEndorsersAt(r, index)
		if ccQueryRes == nil && err == nil {
			return errors.Errorf("expected QueryResult of either ChaincodeQueryResult or Error but got %v instead", r.Results[index])
		}

		if err != nil {
			key := key{
				queryType: protoext.ChaincodeQueryType,
				k:         ch,
			}
			resp[key] = errors.New(err.Content)
			continue
		}

		if err := resp.mapEndorsersOfChannel(ccQueryRes, ch, chaincodeQueryMapping[index]); err != nil {
			return errors.Wrapf(err, "failed assembling endorsers of channel %s", ch)
		}
	}
	return nil
}

func (resp response) mapEndorsersOfChannel(ccRs *discovery.ChaincodeQueryResult, channel string, invocationChain []InvocationChain) error {
	if len(ccRs.Content) < len(invocationChain) {
		return errors.Errorf("expected %d endorsement descriptors but got only %d", len(invocationChain), len(ccRs.Content))
	}
	for i, desc := range ccRs.Content {
		expectedCCName := invocationChain[i][0].Name
		if desc.Chaincode != expectedCCName {
			return errors.Errorf("expected chaincode %s but got endorsement descriptor for %s", expectedCCName, desc.Chaincode)
		}
		key := key{
			queryType:       protoext.ChaincodeQueryType,
			k:               channel,
			invocationChain: invocationChain[i].String(),

View on GitHub (pinned to 2736b63f8f)

Solutions

Inspect the wrapped inner error (use github.com/pkg/errors Cause/Unwrap) to find the real failure
Verify the channel name and that peers have joined and gossiped state for it
Ensure the requested invocation chain's chaincodes are installed on peers in that channel
Retry the discovery query once peers have stabilized membership
Check discovery client/server version compatibility (Fabric v1/v2 descriptor semantics)

Example fix

// before: prints only the wrapper
log.Println(err)
// after: extract cause
log.Printf("%v: %+v", err, errors.Cause(err))

Defensive patterns

Strategy: try-catch

Validate before calling

// Ensure requested channels and chaincodes exist before querying
if len(channel2index) == 0 || len(chaincodeQueryMapping) == 0 {
	return errors.New("no channels or chaincode interests to query")
}

Try / catch

if err := resp.mapEndorsers(ch2idx, r, ccMapping); err != nil {
	var chErr error
	if errors.As(err, &chErr) {
		log.Printf("assembling endorsers failed: %+v (cause: %v)", err, errors.Cause(err))
	}
	return err
}

Prevention

Always unwrap errors with errors.Cause/Unwrap to see the underlying failure
Log the channel name from the wrapper message before remediation
Keep client and peer Fabric versions aligned
Verify peers have stable gossip membership before issuing queries

When it happens

Trigger: Any failure inside resp.mapEndorsersOfChannel while processing a channel's ChaincodeQueryResult during a discovery SendDiscoveryQuery — too few endorsement descriptors returned, chaincode name mismatch, a layout group without endorsers, or a peer whose gossip envelopes fail to unmarshal/validate.

Common situations: Mixed channels where one channel has stale/incomplete discovery data; invoking a chaincode chain (collections or chaincode-to-chaincode) that the server's descriptor list doesn't line up with; peers in the middle of joining a channel so envelopes are missing.

Related errors

AI-assisted analysis of hyperledger/fabric@2736b63f8f (2026-09-04). Data as JSON: /api/errors/023b840a847904f3. Report an issue: GitHub.