What causes "a signed proposal is required" in hyperledger/fabric?

Verify the signed proposal passed to Evaluate has its proposal bytes populated (len > 0) before calling.

a signed proposal is required

Error message

a signed proposal is required

What it means

Returned by getChannelAndChaincodeFromSignedProposal (internal/pkg/gateway/evaluate.go:115) when the signed proposal passed to Evaluate contains an empty ProposalBytes field. The gateway cannot parse a proposal with no payload, so it rejects the call before unmarshalling. It signals a malformed or unset signed proposal in the request.

Source

Thrown at internal/pkg/gateway/evaluate.go:115

			}
		case <-ctx.Done():
			// Overall evaluation timeout expired
			logger.Warnw("Evaluate call timed out while processing request", "channel", request.GetChannelId(), "txID", request.GetTransactionId())
			return nil, newRpcError(codes.DeadlineExceeded, "evaluate timeout expired")
		}
	}

	evaluateResponse := &gp.EvaluateResponse{
		Result: response,
	}

	logger.Debugw("Evaluate call to endorser returned success", "channel", request.GetChannelId(), "txID", request.GetTransactionId(), "endorserAddress", endorser.endpointConfig.address, "endorserMspid", endorser.endpointConfig.mspid, "status", response.GetStatus(), "message", response.GetMessage())
	return evaluateResponse, nil
}

func getChannelAndChaincodeFromSignedProposal(signedProposal *peer.SignedProposal) (string, string, bool, error) {
	if len(signedProposal.GetProposalBytes()) == 0 {
		return "", "", false, fmt.Errorf("a signed proposal is required")
	}
	proposal, err := protoutil.UnmarshalProposal(signedProposal.GetProposalBytes())
	if err != nil {
		return "", "", false, err
	}
	header, err := protoutil.UnmarshalHeader(proposal.GetHeader())
	if err != nil {
		return "", "", false, err
	}
	channelHeader, err := protoutil.UnmarshalChannelHeader(header.GetChannelHeader())
	if err != nil {
		return "", "", false, err
	}
	payload, err := protoutil.UnmarshalChaincodeProposalPayload(proposal.GetPayload())
	if err != nil {
		return "", "", false, err
	}
	spec, err := protoutil.UnmarshalChaincodeInvocationSpec(payload.GetInput())

View on GitHub (pinned to 2736b63f8f)

Solutions

Verify the signed proposal passed to Evaluate has its proposal bytes populated (len > 0) before calling.
If building manually, serialize the proposal with protoutil.Marshal (or the appropriate SDK helper) into SignedProposal.ProposalBytes.
Use the SDK's proposal-generation APIs (NewSignedProposal / gateway.NewProposal) instead of constructing SignedProposal by hand.
Check that the bytes weren't lost in serialization between services (e.g. base64 decoding an empty string).

Example fix

// before
signedProposal := &peer.SignedProposal{} // empty proposalBytes
resp, err := gw.Evaluate(ctx, signedProposal)
// after
proposalBytes, _ := protoutil.Marshal(proposal)
signedProposal := &peer.SignedProposal{ProposalBytes: proposalBytes, Signature: sig}
resp, err := gw.Evaluate(ctx, signedProposal)

Defensive patterns

Strategy: validation

Validate before calling

func validateSignedProposal(sp *peer.SignedProposal) error {
    if sp == nil || len(sp.GetProposalBytes()) == 0 {
        return errors.New("signed proposal has empty proposal bytes")
    }
    return nil
}

Type guard

func hasProposalBytes(sp *peer.SignedProposal) bool {
    return sp != nil && len(sp.GetProposalBytes()) > 0
}

Prevention

Always build signed proposals with protoutil.Marshal or SDK helpers, never with struct literals left empty.
Validate proposal bytes length before signing.
Keep client SDK and Fabric versions aligned.
Add unit tests asserting proposals are fully populated before submission.

When it happens

Trigger: Calling Evaluate with a SignedProposal whose proposalBytes slice is empty — typically when the caller constructed the signed proposal themselves and left the serialized Proposal field unset.

Common situations: Manually building peer.SignedProposal without calling protoutil.Marshal on the proposal; forwarding a response proposal that was never populated; client SDK version mismatch producing an empty field.

Related errors

AI-assisted analysis of hyperledger/fabric@2736b63f8f (2026-09-04). Data as JSON: /api/errors/186f869c7510e181. Report an issue: GitHub.