github.com/kchristidis/fabric@v1.0.4-0.20171028114726-837acd08cde1/docs/source/chaincode4ade.rst

Chaincode for Developers
========================

What is Chaincode?
------------------

Chaincode is a program, written in `Go <https://golang.org>`_ that implements a
prescribed interface. Eventually, other programming languages such as Java,
will be supported. Chaincode runs in a secured Docker container isolated from
the endorsing peer process. Chaincode initializes and manages the ledger state
through transactions submitted by applications.

A chaincode typically handles business logic agreed to by members of the
network, so it similar to a "smart contract". Ledger state created by
a chaincode is scoped exclusively to that chaincode and can't be accessed
directly by another chaincode. Given the appropriate permission, a chaincode may
invoke another chaincode to access its state within the same network.

In the following sections, we will explore chaincode through the eyes of an
application developer. We'll present a simple chaincode sample application
and walk through the purpose of each method in the Chaincode Shim API.

Chaincode API
-------------

Every chaincode program must implement the
`Chaincode interface <http://godoc.org/github.com/hyperledger/fabric/core/chaincode/shim#Chaincode>`_
whose methods are called in response to received transactions.
In particular the ``Init`` method is called when a
chaincode receives an ``instantiate`` or ``upgrade`` transaction so that the
chaincode may perform any necessary initialization, including initialization of
application state. The ``Invoke`` method is called in response to receiving an
``invoke`` transaction to process transaction proposals.

The other interface in the chaincode "shim" APIs is the
`ChaincodeStubInterface <http://godoc.org/github.com/hyperledger/fabric/core/chaincode/shim#ChaincodeStub>`_
which is used to access and modify the ledger, and to make invocations between
chaincodes.

In this tutorial, we will demonstrate the use of these APIs by implementing a
simple chaincode application that manages simple "assets".

.. _Simple Asset Chaincode:

Simple Asset Chaincode
----------------------
Our application is a basic sample chaincode to create assets
(key-value pairs) on the ledger.

Choosing a Location for the Code
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If you haven't been doing programming in Go, you may want to make sure that
you have :ref:`Golang` installed and your system properly configured.

Now, you will want to create a directory for your chaincode application as a
child directory of ``$GOPATH/src/``.

To keep things simple, let's use the following command:

.. code:: bash

  mkdir -p $GOPATH/src/sacc && cd $GOPATH/src/sacc

Now, let's create the source file that we'll fill in with code:

.. code:: bash

  touch sacc.go

Housekeeping
^^^^^^^^^^^^

First, let's start with some housekeeping. As with every chaincode, it implements the
`Chaincode interface <http://godoc.org/github.com/hyperledger/fabric/core/chaincode/shim#Chaincode>`_
in particular, ``Init`` and ``Invoke`` functions. So, let's add the go import
statements for the necessary dependencies for our chaincode. We'll import the
chaincode shim package and the
`peer protobuf package <http://godoc.org/github.com/hyperledger/fabric/protos/peer>`_.
Next, let's add a struct ``SimpleAsset`` as a receiver for Chaincode shim functions.

.. code:: go

    package main

    import (
    	"fmt"

    	"github.com/hyperledger/fabric/core/chaincode/shim"
    	"github.com/hyperledger/fabric/protos/peer"
    )

    // SimpleAsset implements a simple chaincode to manage an asset
    type SimpleAsset struct {
    }

Initializing the Chaincode
^^^^^^^^^^^^^^^^^^^^^^^^^^

Next, we'll implement the ``Init`` function.

.. code:: go

  // Init is called during chaincode instantiation to initialize any data.
  func (t *SimpleAsset) Init(stub shim.ChaincodeStubInterface) peer.Response {

  }

.. note:: Note that chaincode upgrade also calls this function. When writing a
          chaincode that will upgrade an existing one, make sure to modify the ``Init``
          function appropriately. In particular, provide an empty "Init" method if there's
          no "migration" or nothing to be initialized as part of the upgrade.

Next, we'll retrieve the arguments to the ``Init`` call using the
`ChaincodeStubInterface.GetStringArgs <http://godoc.org/github.com/hyperledger/fabric/core/chaincode/shim#ChaincodeStub.GetStringArgs>`_
function and check for validity. In our case, we are expecting a key-value pair.

  .. code:: go

    // Init is called during chaincode instantiation to initialize any
    // data. Note that chaincode upgrade also calls this function to reset
    // or to migrate data, so be careful to avoid a scenario where you
    // inadvertently clobber your ledger's data!
    func (t *SimpleAsset) Init(stub shim.ChaincodeStubInterface) peer.Response {
      // Get the args from the transaction proposal
      args := stub.GetStringArgs()
      if len(args) != 2 {
        return shim.Error("Incorrect arguments. Expecting a key and a value")
      }
    }

Next, now that we have established that the call is valid, we'll store the
initial state in the ledger. To do this, we will call
`ChaincodeStubInterface.PutState <http://godoc.org/github.com/hyperledger/fabric/core/chaincode/shim#ChaincodeStub.PutState>`_
with the key and value passed in as the arguments. Assuming all went well,
return a peer.Response object that indicates the initialization was a success.

.. code:: go

  // Init is called during chaincode instantiation to initialize any
  // data. Note that chaincode upgrade also calls this function to reset
  // or to migrate data, so be careful to avoid a scenario where you
  // inadvertently clobber your ledger's data!
  func (t *SimpleAsset) Init(stub shim.ChaincodeStubInterface) peer.Response {
    // Get the args from the transaction proposal
    args := stub.GetStringArgs()
    if len(args) != 2 {
      return shim.Error("Incorrect arguments. Expecting a key and a value")
    }

    // Set up any variables or assets here by calling stub.PutState()

    // We store the key and the value on the ledger
    err := stub.PutState(args[0], []byte(args[1]))
    if err != nil {
      return shim.Error(fmt.Sprintf("Failed to create asset: %s", args[0]))
    }
    return shim.Success(nil)
  }

Invoking the Chaincode
^^^^^^^^^^^^^^^^^^^^^^

First, let's add the ``Invoke`` function's signature.

.. code:: go

    // Invoke is called per transaction on the chaincode. Each transaction is
    // either a 'get' or a 'set' on the asset created by Init function. The 'set'
    // method may create a new asset by specifying a new key-value pair.
    func (t *SimpleAsset) Invoke(stub shim.ChaincodeStubInterface) peer.Response {

    }

As with the ``Init`` function above, we need to extract the arguments from the
``ChaincodeStubInterface``. The ``Invoke`` function's arguments will be the
name of the chaincode application function to invoke. In our case, our application
will simply have two functions: ``set`` and ``get``, that allow the value of an
asset to be set or its current state to be retrieved. We first call
`ChaincodeStubInterface.GetFunctionAndParameters <http://godoc.org/github.com/hyperledger/fabric/core/chaincode/shim#ChaincodeStub.GetFunctionAndParameters>`_
to extract the function name and the parameters to that chaincode application
function.

.. code:: go

    // Invoke is called per transaction on the chaincode. Each transaction is
    // either a 'get' or a 'set' on the asset created by Init function. The Set
    // method may create a new asset by specifying a new key-value pair.
    func (t *SimpleAsset) Invoke(stub shim.ChaincodeStubInterface) peer.Response {
    	// Extract the function and args from the transaction proposal
    	fn, args := stub.GetFunctionAndParameters()

    }

Next, we'll validate the function name as being either ``set`` or ``get``, and
invoke those chaincode application functions, returning an appropriate
response via the ``shim.Success`` or ``shim.Error`` functions that will
serialize the response into a gRPC protobuf message.

.. code:: go

    // Invoke is called per transaction on the chaincode. Each transaction is
    // either a 'get' or a 'set' on the asset created by Init function. The Set
    // method may create a new asset by specifying a new key-value pair.
    func (t *SimpleAsset) Invoke(stub shim.ChaincodeStubInterface) peer.Response {
    	// Extract the function and args from the transaction proposal
    	fn, args := stub.GetFunctionAndParameters()

    	var result string
    	var err error
    	if fn == "set" {
    		result, err = set(stub, args)
    	} else {
    		result, err = get(stub, args)
    	}
    	if err != nil {
    		return shim.Error(err.Error())
    	}

    	// Return the result as success payload
    	return shim.Success([]byte(result))
    }

Implementing the Chaincode Application
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

As noted, our chaincode application implements two functions that can be
invoked via the ``Invoke`` function. Let's implement those functions now.
Note that as we mentioned above, to access the ledger's state, we will leverage
the `ChaincodeStubInterface.PutState <http://godoc.org/github.com/hyperledger/fabric/core/chaincode/shim#ChaincodeStub.PutState>`_
and `ChaincodeStubInterface.GetState <http://godoc.org/github.com/hyperledger/fabric/core/chaincode/shim#ChaincodeStub.GetState>`_
functions of the chaincode shim API.

.. code:: go

    // Set stores the asset (both key and value) on the ledger. If the key exists,
    // it will override the value with the new one
    func set(stub shim.ChaincodeStubInterface, args []string) (string, error) {
    	if len(args) != 2 {
    		return "", fmt.Errorf("Incorrect arguments. Expecting a key and a value")
    	}

    	err := stub.PutState(args[0], []byte(args[1]))
    	if err != nil {
    		return "", fmt.Errorf("Failed to set asset: %s", args[0])
    	}
    	return args[1], nil
    }

    // Get returns the value of the specified asset key
    func get(stub shim.ChaincodeStubInterface, args []string) (string, error) {
    	if len(args) != 1 {
    		return "", fmt.Errorf("Incorrect arguments. Expecting a key")
    	}

    	value, err := stub.GetState(args[0])
    	if err != nil {
    		return "", fmt.Errorf("Failed to get asset: %s with error: %s", args[0], err)
    	}
    	if value == nil {
    		return "", fmt.Errorf("Asset not found: %s", args[0])
    	}
    	return string(value), nil
    }

.. _Chaincode Sample:

Pulling it All Together
^^^^^^^^^^^^^^^^^^^^^^^

Finally, we need to add the ``main`` function, which will call the
`shim.Start <http://godoc.org/github.com/hyperledger/fabric/core/chaincode/shim#Start>`_
function. Here's the whole chaincode program source.

.. code:: go

    package main

    import (
    	"fmt"

    	"github.com/hyperledger/fabric/core/chaincode/shim"
    	"github.com/hyperledger/fabric/protos/peer"
    )

    // SimpleAsset implements a simple chaincode to manage an asset
    type SimpleAsset struct {
    }

    // Init is called during chaincode instantiation to initialize any
    // data. Note that chaincode upgrade also calls this function to reset
    // or to migrate data.
    func (t *SimpleAsset) Init(stub shim.ChaincodeStubInterface) peer.Response {
    	// Get the args from the transaction proposal
    	args := stub.GetStringArgs()
    	if len(args) != 2 {
    		return shim.Error("Incorrect arguments. Expecting a key and a value")
    	}

    	// Set up any variables or assets here by calling stub.PutState()

    	// We store the key and the value on the ledger
    	err := stub.PutState(args[0], []byte(args[1]))
    	if err != nil {
    		return shim.Error(fmt.Sprintf("Failed to create asset: %s", args[0]))
    	}
    	return shim.Success(nil)
    }

    // Invoke is called per transaction on the chaincode. Each transaction is
    // either a 'get' or a 'set' on the asset created by Init function. The Set
    // method may create a new asset by specifying a new key-value pair.
    func (t *SimpleAsset) Invoke(stub shim.ChaincodeStubInterface) peer.Response {
    	// Extract the function and args from the transaction proposal
    	fn, args := stub.GetFunctionAndParameters()

    	var result string
    	var err error
    	if fn == "set" {
    		result, err = set(stub, args)
    	} else { // assume 'get' even if fn is nil
    		result, err = get(stub, args)
    	}
    	if err != nil {
    		return shim.Error(err.Error())
    	}

    	// Return the result as success payload
    	return shim.Success([]byte(result))
    }

    // Set stores the asset (both key and value) on the ledger. If the key exists,
    // it will override the value with the new one
    func set(stub shim.ChaincodeStubInterface, args []string) (string, error) {
    	if len(args) != 2 {
    		return "", fmt.Errorf("Incorrect arguments. Expecting a key and a value")
    	}

    	err := stub.PutState(args[0], []byte(args[1]))
    	if err != nil {
    		return "", fmt.Errorf("Failed to set asset: %s", args[0])
    	}
    	return args[1], nil
    }

    // Get returns the value of the specified asset key
    func get(stub shim.ChaincodeStubInterface, args []string) (string, error) {
    	if len(args) != 1 {
    		return "", fmt.Errorf("Incorrect arguments. Expecting a key")
    	}

    	value, err := stub.GetState(args[0])
    	if err != nil {
    		return "", fmt.Errorf("Failed to get asset: %s with error: %s", args[0], err)
    	}
    	if value == nil {
    		return "", fmt.Errorf("Asset not found: %s", args[0])
    	}
    	return string(value), nil
    }

    // main function starts up the chaincode in the container during instantiate
    func main() {
    	if err := shim.Start(new(SimpleAsset)); err != nil {
    		fmt.Printf("Error starting SimpleAsset chaincode: %s", err)
    	}
    }

Building Chaincode
^^^^^^^^^^^^^^^^^^

Now let's compile your chaincode.

.. code:: bash

  go get -u --tags nopkcs11 github.com/hyperledger/fabric/core/chaincode/shim
  go build --tags nopkcs11

Assuming there are no errors, now we can proceed to the next step, testing
your chaincode.

Testing Using dev mode
^^^^^^^^^^^^^^^^^^^^^^

Normally chaincodes are started and maintained by peer. However in “dev
mode", chaincode is built and started by the user. This mode is useful
during chaincode development phase for rapid code/build/run/debug cycle
turnaround.

We start "dev mode" by leveraging pre-generated orderer and channel artifacts for
a sample dev network.  As such, the user can immediately jump into the process
of compiling chaincode and driving calls.

Install Hyperledger Fabric Samples
----------------------

If you haven't already done so, please install the :doc:`samples`.

Navigate to the ``chaincode-docker-devmode`` directory of the ``fabric-samples``
clone:

.. code:: bash

  cd chaincode-docker-devmode

Download Docker images
----------------------

We need four Docker images in order for "dev mode" to run against the supplied
docker compose script.  If you installed the ``fabric-samples`` repo clone and
followed the instructions to :ref:`download-platform-specific-binaries`, then
you should have the necessary Docker images installed locally.

.. note:: If you choose to manually pull the images then you must retag them as
          ``latest``.

Issue a ``docker images`` command to reveal your local Docker Registry.  You
should see something similar to following:

.. code:: bash

  docker images
  REPOSITORY                     TAG                                  IMAGE ID            CREATED             SIZE
  hyperledger/fabric-tools       latest                               e09f38f8928d        4 hours ago         1.32 GB
  hyperledger/fabric-tools       x86_64-1.0.0                         e09f38f8928d        4 hours ago         1.32 GB
  hyperledger/fabric-orderer     latest                               0df93ba35a25        4 hours ago         179 MB
  hyperledger/fabric-orderer     x86_64-1.0.0                         0df93ba35a25        4 hours ago         179 MB
  hyperledger/fabric-peer        latest                               533aec3f5a01        4 hours ago         182 MB
  hyperledger/fabric-peer        x86_64-1.0.0                         533aec3f5a01        4 hours ago         182 MB
  hyperledger/fabric-ccenv       latest                               4b70698a71d3        4 hours ago         1.29 GB
  hyperledger/fabric-ccenv       x86_64-1.0.0                         4b70698a71d3        4 hours ago         1.29 GB

.. note:: If you retrieved the images through the :ref:`download-platform-specific-binaries`,
          then you will see additional images listed.  However, we are only concerned with
          these four.

Now open three terminals and navigate to your ``chaincode-docker-devmode``
directory in each.

Terminal 1 - Start the network
------------------------------

.. code:: bash

    docker-compose -f docker-compose-simple.yaml up

The above starts the network with the ``SingleSampleMSPSolo`` orderer profile and
launches the peer in "dev mode".  It also launches two additional containers -
one for the chaincode environment and a CLI to interact with the chaincode.  The
commands for create and join channel are embedded in the CLI container, so we
can jump immediately to the chaincode calls.

Terminal 2 - Build & start the chaincode
----------------------------------------

.. code:: bash

  docker exec -it chaincode bash

You should see the following:

.. code:: bash

  root@d2629980e76b:/opt/gopath/src/chaincode#

Now, compile your chaincode:

.. code:: bash

  cd sacc
  go build

Now run the chaincode:

.. code:: bash

  CORE_PEER_ADDRESS=peer:7051 CORE_CHAINCODE_ID_NAME=mycc:0 ./sacc

The chaincode is started with peer and chaincode logs indicating successful registration with the peer.
Note that at this stage the chaincode is not associated with any channel. This is done in subsequent steps
using the ``instantiate`` command.

Terminal 3 - Use the chaincode
------------------------------

Even though you are in ``--peer-chaincodedev`` mode, you still have to install the
chaincode so the life-cycle system chaincode can go through its checks normally.
This requirement may be removed in future when in ``--peer-chaincodedev`` mode.

We'll leverage the CLI container to drive these calls.

.. code:: bash

  docker exec -it cli bash

.. code:: bash

  peer chaincode install -p chaincodedev/chaincode/sacc -n mycc -v 0
  peer chaincode instantiate -n mycc -v 0 -c '{"Args":["a","10"]}' -C myc

Now issue an invoke to change the value of "a" to "20".

.. code:: bash

  peer chaincode invoke -n mycc -c '{"Args":["set", "a", "20"]}' -C myc

Finally, query ``a``.  We should see a value of ``20``.

.. code:: bash

  peer chaincode query -n mycc -c '{"Args":["query","a"]}' -C myc

Testing new chaincode
---------------------

By default, we mount only ``sacc``.  However, you can easily test different
chaincodes by adding them to the ``chaincode`` subdirectory and relaunching
your network.  At this point they will be accessible in your ``chaincode`` container.

.. Licensed under Creative Commons Attribution 4.0 International License
   https://creativecommons.org/licenses/by/4.0/