区块链Hyperledger Fabric超级账本ChainCode链码ChaincodeStubInterface深入剖析详解

chaincode的开发一般是使用GO或者JAVA，由于超级账本本身就是由go语言编写的，因此一般选用GO语言。ChainCode代码需要定义一个结构体struct，然后在该struct上实现ChainCode定义Init和Invoke两个函数。main函数作为ChainCode的启动入口。Init和Invoke方法是其两个重要的方法。应用程序请求运行智能合约fabcar后，Invoke方法被调用。在Invoke的时候，由传入的参数来决定我们具体调用了哪个方法，所以需要用GetFunctionAndParameters解析调用的时候传入的参数。

首先给出如下的示例：
type Foo struct {
}

func (this *Foo) Init(stub shim.ChaincodeStubInterface) peer.Response {
return shim.Success(nil)
}

func (this *Foo) Invoke(stub shim.ChaincodeStubInterface) peer.Response {
return shim.Success(nil)
}

在Init和Invoke方法中都会传入参数stub shim.ChaincodeStubInterface，这个参数提供的接口为我们编写ChainCode的业务逻辑提供了大量实用的方法。

获得调用的函数
GetArgs() [][]byte 以byte数组的数组的形式获得传入的参数列表
GetStringArgs() []string 以字符串数组的形式获得传入的参数列表
GetFunctionAndParameters() (string, []string) 将字符串数组的参数分为两部分，数组第一个字是Function，剩下的都是Parameter
GetArgsSlice() ([]byte, error) 以byte切片的形式获得参数列表

增删改查State DB
ChainCode核心的操作就是对State Database的增删改查，对此Fabric接口提供了3个对State DB的操作方法。
增改数据PutState(key string, value []byte) error
删除数据DelState(key string) error
查询数据GetState(key string) ([]byte, error)

ChaincodeStubInterface 定义如下所示：

type ChaincodeStubInterface interface {
    // GetArgs returns the arguments intended for the chaincode Init and Invoke
    // as an array of byte arrays.
    GetArgs() [][]byte

    // GetStringArgs returns the arguments intended for the chaincode Init and
    // Invoke as a string array. Only use GetStringArgs if the client passes
    // arguments intended to be used as strings.
    GetStringArgs() []string

    // GetFunctionAndParameters returns the first argument as the function
    // name and the rest of the arguments as parameters in a string array.
    // Only use GetFunctionAndParameters if the client passes arguments intended
    // to be used as strings.
    GetFunctionAndParameters() (string, []string)

    // GetArgsSlice returns the arguments intended for the chaincode Init and
    // Invoke as a byte array
    GetArgsSlice() ([]byte, error)

    // GetTxID returns the tx_id of the transaction proposal, which is unique per
    // transaction and per client. See ChannelHeader in protos/common/common.proto
    // for further details.
    GetTxID() string

    // GetChannelID returns the channel the proposal is sent to for chaincode to process.
    // This would be the channel_id of the transaction proposal (see ChannelHeader
    // in protos/common/common.proto) except where the chaincode is calling another on
    // a different channel
    GetChannelID() string

    // InvokeChaincode locally calls the specified chaincode `Invoke` using the
    // same transaction context; that is, chaincode calling chaincode doesn't
    // create a new transaction message.
    // If the called chaincode is on the same channel, it simply adds the called
    // chaincode read set and write set to the calling transaction.
    // If the called chaincode is on a different channel,
    // only the Response is returned to the calling chaincode; any PutState calls
    // from the called chaincode will not have any effect on the ledger; that is,
    // the called chaincode on a different channel will not have its read set
    // and write set applied to the transaction. Only the calling chaincode's
    // read set and write set will be applied to the transaction. Effectively
    // the called chaincode on a different channel is a `Query`, which does not
    // participate in state validation checks in subsequent commit phase.
    // If `channel` is empty, the caller's channel is assumed.
    InvokeChaincode(chaincodeName string, args [][]byte, channel string) pb.Response

    // GetState returns the value of the specified `key` from the
    // ledger. Note that GetState doesn't read data from the writeset, which
    // has not been committed to the ledger. In other words, GetState doesn't
    // consider data modified by PutState that has not been committed.
    // If the key does not exist in the state database, (nil, nil) is returned.
    GetState(key string) ([]byte, error)

    // PutState puts the specified `key` and `value` into the transaction's
    // writeset as a data-write proposal. PutState doesn't effect the ledger
    // until the transaction is validated and successfully committed.
    // Simple keys must not be an empty string and must not start with null
    // character (0x00), in order to avoid range query collisions with
    // composite keys, which internally get prefixed with 0x00 as composite
    // key namespace.
    PutState(key string, value []byte) error

    // DelState records the specified `key` to be deleted in the writeset of
    // the transaction proposal. The `key` and its value will be deleted from
    // the ledger when the transaction is validated and successfully committed.
    DelState(key string) error

    // GetStateByRange returns a range iterator over a set of keys in the
    // ledger. The iterator can be used to iterate over all keys
    // between the startKey (inclusive) and endKey (exclusive).
    // The keys are returned by the iterator in lexical order. Note
    // that startKey and endKey can be empty string, which implies unbounded range
    // query on start or end.
    // Call Close() on the returned StateQueryIteratorInterface object when done.
    // The query is re-executed during validation phase to ensure result set
    // has not changed since transaction endorsement (phantom reads detected).
    GetStateByRange(startKey, endKey string) (StateQueryIteratorInterface, error)

    // GetStateByPartialCompositeKey queries the state in the ledger based on
    // a given partial composite key. This function returns an iterator
    // which can be used to iterate over all composite keys whose prefix matches
    // the given partial composite key. The `objectType` and attributes are
    // expected to have only valid utf8 strings and should not contain
    // U+0000 (nil byte) and U+10FFFF (biggest and unallocated code point).
    // See related functions SplitCompositeKey and CreateCompositeKey.
    // Call Close() on the returned StateQueryIteratorInterface object when done.
    // The query is re-executed during validation phase to ensure result set
    // has not changed since transaction endorsement (phantom reads detected).
    GetStateByPartialCompositeKey(objectType string, keys []string) (StateQueryIteratorInterface, error)

    // CreateCompositeKey combines the given `attributes` to form a composite
    // key. The objectType and attributes are expected to have only valid utf8
    // strings and should not contain U+0000 (nil byte) and U+10FFFF
    // (biggest and unallocated code point).
    // The resulting composite key can be used as the key in PutState().
    CreateCompositeKey(objectType string, attributes []string) (string, error)

    // SplitCompositeKey splits the specified key into attributes on which the
    // composite key was formed. Composite keys found during range queries
    // or partial composite key queries can therefore be split into their
    // composite parts.
    SplitCompositeKey(compositeKey string) (string, []string, error)

    // GetQueryResult performs a "rich" query against a state database. It is
    // only supported for state databases that support rich query,
    // e.g.CouchDB. The query string is in the native syntax
    // of the underlying state database. An iterator is returned
    // which can be used to iterate (next) over the query result set.
    // The query is NOT re-executed during validation phase, phantom reads are
    // not detected. That is, other committed transactions may have added,
    // updated, or removed keys that impact the result set, and this would not
    // be detected at validation/commit time.  Applications susceptible to this
    // should therefore not use GetQueryResult as part of transactions that update
    // ledger, and should limit use to read-only chaincode operations.
    GetQueryResult(query string) (StateQueryIteratorInterface, error)

    // GetHistoryForKey returns a history of key values across time.
    // For each historic key update, the historic value and associated
    // transaction id and timestamp are returned. The timestamp is the
    // timestamp provided by the client in the proposal header.
    // GetHistoryForKey requires peer configuration
    // core.ledger.history.enableHistoryDatabase to be true.
    // The query is NOT re-executed during validation phase, phantom reads are
    // not detected. That is, other committed transactions may have updated
    // the key concurrently, impacting the result set, and this would not be
    // detected at validation/commit time. Applications susceptible to this
    // should therefore not use GetHistoryForKey as part of transactions that
    // update ledger, and should limit use to read-only chaincode operations.
    GetHistoryForKey(key string) (HistoryQueryIteratorInterface, error)

    // GetPrivateData returns the value of the specified `key` from the specified
    // `collection`. Note that GetPrivateData doesn't read data from the
    // private writeset, which has not been committed to the `collection`. In
    // other words, GetPrivateData doesn't consider data modified by PutPrivateData
    // that has not been committed.
    GetPrivateData(collection, key string) ([]byte, error)

    // PutPrivateData puts the specified `key` and `value` into the transaction's
    // private writeset. Note that only hash of the private writeset goes into the
    // transaction proposal response (which is sent to the client who issued the
    // transaction) and the actual private writeset gets temporarily stored in a
    // transient store. PutPrivateData doesn't effect the `collection` until the
    // transaction is validated and successfully committed. Simple keys must not be
    // an empty string and must not start with null character (0x00), in order to
    // avoid range query collisions with composite keys, which internally get
    // prefixed with 0x00 as composite key namespace.
    PutPrivateData(collection string, key string, value []byte) error

    // DelState records the specified `key` to be deleted in the private writeset of
    // the transaction. Note that only hash of the private writeset goes into the
    // transaction proposal response (which is sent to the client who issued the
    // transaction) and the actual private writeset gets temporarily stored in a
    // transient store. The `key` and its value will be deleted from the collection
    // when the transaction is validated and successfully committed.
    DelPrivateData(collection, key string) error

    // GetPrivateDataByRange returns a range iterator over a set of keys in a
    // given private collection. The iterator can be used to iterate over all keys
    // between the startKey (inclusive) and endKey (exclusive).
    // The keys are returned by the iterator in lexical order. Note
    // that startKey and endKey can be empty string, which implies unbounded range
    // query on start or end.
    // Call Close() on the returned StateQueryIteratorInterface object when done.
    // The query is re-executed during validation phase to ensure result set
    // has not changed since transaction endorsement (phantom reads detected).
    GetPrivateDataByRange(collection, startKey, endKey string) (StateQueryIteratorInterface, error)

    // GetPrivateDataByPartialCompositeKey queries the state in a given private
    // collection based on a given partial composite key. This function returns
    // an iterator which can be used to iterate over all composite keys whose prefix
    // matches the given partial composite key. The `objectType` and attributes are
    // expected to have only valid utf8 strings and should not contain
    // U+0000 (nil byte) and U+10FFFF (biggest and unallocated code point).
    // See related functions SplitCompositeKey and CreateCompositeKey.
    // Call Close() on the returned StateQueryIteratorInterface object when done.
    // The query is re-executed during validation phase to ensure result set
    // has not changed since transaction endorsement (phantom reads detected).
    GetPrivateDataByPartialCompositeKey(collection, objectType string, keys []string) (StateQueryIteratorInterface, error)

    // GetPrivateDataQueryResult performs a "rich" query against a given private
    // collection. It is only supported for state databases that support rich query,
    // e.g.CouchDB. The query string is in the native syntax
    // of the underlying state database. An iterator is returned
    // which can be used to iterate (next) over the query result set.
    // The query is NOT re-executed during validation phase, phantom reads are
    // not detected. That is, other committed transactions may have added,
    // updated, or removed keys that impact the result set, and this would not
    // be detected at validation/commit time.  Applications susceptible to this
    // should therefore not use GetQueryResult as part of transactions that update
    // ledger, and should limit use to read-only chaincode operations.
    GetPrivateDataQueryResult(collection, query string) (StateQueryIteratorInterface, error)

    // GetCreator returns `SignatureHeader.Creator` (e.g. an identity)
    // of the `SignedProposal`. This is the identity of the agent (or user)
    // submitting the transaction.
    GetCreator() ([]byte, error)

    // GetTransient returns the `ChaincodeProposalPayload.Transient` field.
    // It is a map that contains data (e.g. cryptographic material)
    // that might be used to implement some form of application-level
    // confidentiality. The contents of this field, as prescribed by
    // `ChaincodeProposalPayload`, are supposed to always
    // be omitted from the transaction and excluded from the ledger.
    GetTransient() (map[string][]byte, error)

    // GetBinding returns the transaction binding, which is used to enforce a
    // link between application data (like those stored in the transient field
    // above) to the proposal itself. This is useful to avoid possible replay
    // attacks.
    GetBinding() ([]byte, error)

    // GetDecorations returns additional data (if applicable) about the proposal
    // that originated from the peer. This data is set by the decorators of the
    // peer, which append or mutate the chaincode input passed to the chaincode.
    GetDecorations() map[string][]byte

    // GetSignedProposal returns the SignedProposal object, which contains all
    // data elements part of a transaction proposal.
    GetSignedProposal() (*pb.SignedProposal, error)

    // GetTxTimestamp returns the timestamp when the transaction was created. This
    // is taken from the transaction ChannelHeader, therefore it will indicate the
    // client's timestamp and will have the same value across all endorsers.
    GetTxTimestamp() (*timestamp.Timestamp, error)

    // SetEvent allows the chaincode to set an event on the response to the
    // proposal to be included as part of a transaction. The event will be
    // available within the transaction in the committed block regardless of the
    // validity of the transaction.
    SetEvent(name string, payload []byte) error
}