cpaper_extended

Commercial paper extended example

This is an extended example of the official Commercial paper scenario

Features

• Protobuf transaction payload and event definitions
• Protobuf chaincode state schema
• Event emitting
• Unique key external reference usage

Example - Commercial Paper chaincode

Scenario

Commercial paper scenario from official documentation describes a Hyperledger Fabric network, aimed to issue, buy and redeem commercial paper.

5 steps to develop chaincode

Chaincode is a domain specific program which relates to specific business process. The job of a smart contract developer is to take an existing business process and express it as a smart contract in a programming language. Steps of chaincode development:

1. Define chaincode model - schema for state entries, transaction payload and events
2. Define chaincode interface
3. Implement chaincode instantiate method
4. Implement chaincode methods with business logic
5. Create tests

Define chaincode model

With protocol buffers, you write a .proto description of the data structure you wish to store. From that, the protocol buffer compiler creates a golang struct that implements automatic encoding and parsing of the protocol buffer data with an efficient binary format (or json).

Code generation can be simplified with a short Makefile:

.: generate

generate:
	@echo "schema"
	@protoc -I=./ --go_out=./ ./*.proto

Chaincode state

The following file shows how to define the world state schema using protobuf.

examples/cpaper_extended/schema/state.proto

syntax = "proto3";

package hyperledgerlabs.examples.cpaper_extended.schema;
option go_package = "schema";

import "google/protobuf/timestamp.proto";

// Commercial Paper state entry
message CommercialPaper {

    enum State {
        ISSUED = 0;
        TRADING = 1;
        REDEEMED = 2;
    }

    // Issuer and Paper number comprises composite primary key of Commercial paper entry
    string issuer = 1;
    string paper_number = 2;

    string owner = 3;
    google.protobuf.Timestamp issue_date = 4;
    google.protobuf.Timestamp maturity_date = 5;
    int32 face_value = 6;
    State state = 7;

    // Additional unique field for entry
    string external_id = 8;
}

// CommercialPaperId identifier part
message CommercialPaperId {
    string issuer = 1;
    string paper_number = 2;
}

// Container for returning multiple entities
message CommercialPaperList {
    repeated CommercialPaper items = 1;
}

Chaincode transaction and events payload

This file defines the data payload used using in the business logic methods. In this example transaction and event payloads are exactly the same for the sake of brevity, but you could create a different schema for each type of payload.

examples/cpaper_extended/schema/payload.proto

// IssueCommercialPaper event
syntax = "proto3";

package cckit.examples.cpaper_extended.schema;
option go_package = "schema";

import "google/protobuf/timestamp.proto";
import "github.com/mwitkow/go-proto-validators/validator.proto";

// IssueCommercialPaper event
message IssueCommercialPaper {
    string issuer = 1;
    string paper_number = 2;
    google.protobuf.Timestamp issue_date = 3;
    google.protobuf.Timestamp maturity_date = 4;
    int32 face_value = 5;

    // external_id - another unique constraint
    string external_id = 6;
}

// BuyCommercialPaper event
message BuyCommercialPaper {
    string issuer = 1;
    string paper_number = 2;
    string current_owner = 3;
    string new_owner = 4;
    int32 price = 5;
    google.protobuf.Timestamp purchase_date = 6;
}

// RedeemCommercialPaper event
message RedeemCommercialPaper {
    string issuer = 1;
    string paper_number = 2;
    string redeeming_owner = 3;
    google.protobuf.Timestamp redeem_date = 4;
}

Define chaincode interface

In examples/cpaper_extended/chaincode.go file we will define the mappings, chaincode initialization method and business logic in the transaction methods. For brevity we will only display snippets of the code here, please refer to the original file for full example.

Firstly we define mapping rules. These specify the struct used to hold a specific chaincode state, it's primary key, list mapping, unique keys, etc. Then we define the schemas used for emitting events.

var (
	// State mappings
	StateMappings = m.StateMappings{}.
		// Create mapping for Commercial Paper entity
		Add(&schema.CommercialPaper{},
			// Key namespace will be <"CommercialPaper", Issuer, PaperNumber>
			m.PKeySchema(&schema.CommercialPaperId{}),
			// Structure of result for List method
			m.List(&schema.CommercialPaperList{}),
			// External Id is unique
			m.UniqKey("ExternalId"),
		)

	// EventMappings
	EventMappings = m.EventMappings{}.
		// Event name will be "IssueCommercialPaper", payload - same as issue payload
		Add(&schema.IssueCommercialPaper{}).
		// Event name will be "BuyCommercialPaper"
		Add(&schema.BuyCommercialPaper{}).
		// Event name will be "RedeemCommercialPaper"
		Add(&schema.RedeemCommercialPaper{})
)

CCKit uses router to define rules about how to map chaincode invocation to a particular handler, as well as what kind of middleware needs to be used during a request, for example how to convert incoming argument from []byte to target type (string, struct, etc).

func NewCC() *router.Chaincode {

	r := router.New(`commercial_paper`)

	// Mappings for chaincode state
	r.Use(m.MapStates(StateMappings))

	// Mappings for chaincode events
	r.Use(m.MapEvents(EventMappings))

	// Store in chaincode state information about chaincode first instantiator
	r.Init(owner.InvokeSetFromCreator)

	// Method for debug chaincode state
	debug.AddHandlers(r, `debug`, owner.Only)

	r.
		// read methods
		Query(`list`, cpaperList).

		Query(`get`, cpaperGet, defparam.Proto(&schema.CommercialPaperId{})).

		// txn methods
		Invoke(`issue`, cpaperIssue, defparam.Proto(&schema.IssueCommercialPaper{})).
		Invoke(`buy`, cpaperBuy, defparam.Proto(&schema.BuyCommercialPaper{})).
		Invoke(`redeem`, cpaperRedeem, defparam.Proto(&schema.RedeemCommercialPaper{})).
		Invoke(`delete`, cpaperDelete, defparam.Proto(&schema.CommercialPaperId{}))

	return router.NewChaincode(r)
}

Implement chaincode init method

In many cases during chaincode instantiation we need to define permissions for chaincode functions - "who is allowed to do this thing", incredibly important in the world of smart contracts. The most common and basic form of access control is the concept of ownership: there's one account (combination of MSP and certificate identifiers) that is the owner and can do administrative tasks on contracts. This approach is perfectly reasonable for contracts that only have a single administrative user.

CCKit provides owner extension for implementing ownership and access control in Hyperledger Fabric chaincodes. In the previous snippet, as an init method, we used owner.InvokeSetFromCreator, storing information which stores the information about who is the owner into the world state upon chaincode instantiation.

Implement business rules as chaincode methods

Now we have to define the actual business logic which will modify the world state when a transaction occurs. In this example we will show only the buy method for brevity. Please refer to examples/cpaper_extended/chaincode.go for full implementation.

func invokeCPaperBuy(c router.Context) (interface{}, error) {
	var (
		cpaper *schema.CommercialPaper

		// Buy transaction payload
		buyData = c.Param().(*schema.BuyCommercialPaper)

		// Get the current commercial paper state
		cp, err = c.State().Get(
			&schema.CommercialPaperId{Issuer: buyData.Issuer, PaperNumber: buyData.PaperNumber},
			&schema.CommercialPaper{})
	)

	if err != nil {
		return nil, errors.Wrap(err, "not found")
	}

	cpaper = cp.(*schema.CommercialPaper)

	// Validate current owner
	if cpaper.Owner != buyData.CurrentOwner {
		return nil, fmt.Errorf(
			"paper %s %s is not owned by %s",
			cpaper.Issuer, cpaper.PaperNumber, buyData.CurrentOwner)
	}

	// First buyData moves state from ISSUED to TRADING
	if cpaper.State == schema.CommercialPaper_ISSUED {
		cpaper.State = schema.CommercialPaper_TRADING
	}

	// Check paper is not already REDEEMED
	if cpaper.State == schema.CommercialPaper_TRADING {
		cpaper.Owner = buyData.NewOwner
	} else {
		return nil, fmt.Errorf(
			"paper %s %s is not trading.current state = %s",
			cpaper.Issuer, cpaper.PaperNumber, cpaper.State)
	}

	if err = c.Event().Set(buyData); err != nil {
		return nil, err
	}

	return cpaper, c.State().Put(cpaper)
}

Test chaincode functionality

And finally we should write tests to ensure our business logic is behaving as it should. Again, for brevity, we omitted most of the code from examples/cpaper_extended/chaincode_test.go. CCKit support chaincode testing with Mockstub.

var _ = Describe(`CommercialPaper`, func() {
	paperChaincode := testcc.NewMockStub(`commercial_paper`, NewCC())

	BeforeSuite(func() {
		// Init chaincode with admin identity
		expectcc.ResponseOk(
			paperChaincode.
				From(testdata.GetTestIdentity(MspName, path.Join("testdata", "admin", "admin.pem"))).
				Init())
	})

	Describe("Commercial Paper lifecycle", func() {
		// ...

		It("Allow buyer to buy commercial paper", func() {
			buyTransactionData := &schema.BuyCommercialPaper{
				Issuer:       IssuerName,
				PaperNumber:  "0001",
				CurrentOwner: IssuerName,
				NewOwner:     BuyerName,
				Price:        95000,
				PurchaseDate: ptypes.TimestampNow(),
			}

			expectcc.ResponseOk(paperChaincode.Invoke(`buy`, buyTransactionData))

			queryResponse := paperChaincode.Query("get", &schema.CommercialPaperId{
				Issuer:      IssuerName,
				PaperNumber: "0001",
			})

			paper := expectcc.PayloadIs(queryResponse, &schema.CommercialPaper{}).(*schema.CommercialPaper)

			Expect(paper.Owner).To(Equal(BuyerName))
			Expect(paper.State).To(Equal(schema.CommercialPaper_TRADING))

			Expect(<-paperChaincode.ChaincodeEventsChannel).To(BeEquivalentTo(&peer.ChaincodeEvent{
				EventName: `BuyCommercialPaper`,
				Payload:   testcc.MustProtoMarshal(buyTransactionData),
			}))

			paperChaincode.ClearEvents()
		})

		// ...

	})
})