accounts/abi/bind: use ethereum interfaces

In this commit, contract bindings and their backend start using the
Ethereum Go API interfaces offered by ethclient. This makes ethclient a
suitable replacement for the old remote backend and gets us one step
closer to the final stable Go API that is planned for go-ethereum 1.5.

The changes in detail:

* Pending state is optional for read only contract bindings.
  BoundContract attempts to discover the Pending* methods via an
  interface assertion. There are a couple of advantages to this:
  ContractCaller is just two methods and can be implemented on top of
  pretty much anything that provides Ethereum data. Since the backend
  interfaces are now disjoint, ContractBackend can simply be declared as
  a union of the reader and writer side.

* Caching of HasCode is removed. The caching could go wrong in case of
  chain reorganisations and removing it simplifies the code a lot.
  We'll figure out a performant way of providing ErrNoCode before the
  1.5 release.

* BoundContract now ensures that the backend receives a non-nil context
  with every call.

1 files changed, 35 insertions, 60 deletions

diff --git a/accounts/abi/bind/backend.go b/accounts/abi/bind/backend.go
index bec742c29..3d38f87cd 100644
--- a/accounts/abi/bind/backend.go
+++ b/accounts/abi/bind/backend.go
@@ -20,28 +20,42 @@ import (
 	"errors"
 	"math/big"
 
+	"github.com/ethereum/go-ethereum"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
 	"golang.org/x/net/context"
 )
 
-// ErrNoCode is returned by call and transact operations for which the requested
-// recipient contract to operate on does not exist in the state db or does not
-// have any code associated with it (i.e. suicided).
-var ErrNoCode = errors.New("no contract code at given address")
+var (
+	// ErrNoCode is returned by call and transact operations for which the requested
+	// recipient contract to operate on does not exist in the state db or does not
+	// have any code associated with it (i.e. suicided).
+	ErrNoCode = errors.New("no contract code at given address")
+
+	// This error is raised when attempting to perform a pending state action
+	// on a backend that doesn't implement PendingContractCaller.
+	ErrNoPendingState = errors.New("backend does not support pending state")
+)
 
 // ContractCaller defines the methods needed to allow operating with contract on a read
 // only basis.
 type ContractCaller interface {
-	// HasCode checks if the contract at the given address has any code associated
-	// with it or not. This is needed to differentiate between contract internal
-	// errors and the local chain being out of sync.
-	HasCode(ctx context.Context, contract common.Address, pending bool) (bool, error)
+	// CodeAt returns the code of the given account. This is needed to differentiate
+	// between contract internal errors and the local chain being out of sync.
+	CodeAt(ctx context.Context, contract common.Address, blockNumber *big.Int) ([]byte, error)
+	// ContractCall executes an Ethereum contract call with the specified data as the
+	// input.
+	CallContract(ctx context.Context, call ethereum.CallMsg, blockNumber *big.Int) ([]byte, error)
+}
 
-	// ContractCall executes an Ethereum contract call with the specified data as
-	// the input. The pending flag requests execution against the pending block, not
-	// the stable head of the chain.
-	ContractCall(ctx context.Context, contract common.Address, data []byte, pending bool) ([]byte, error)
+// PendingContractCaller defines methods to perform contract calls on the pending state.
+// Call will try to discover this interface when access to the pending state is requested.
+// If the backend does not support the pending state, Call returns ErrNoPendingState.
+type PendingContractCaller interface {
+	// PendingCodeAt returns the code of the given account in the pending state.
+	PendingCodeAt(ctx context.Context, contract common.Address) ([]byte, error)
+	// PendingCallContract executes an Ethereum contract call against the pending state.
+	PendingCallContract(ctx context.Context, call ethereum.CallMsg) ([]byte, error)
 }
 
 // ContractTransactor defines the methods needed to allow operating with contract
@@ -49,64 +63,25 @@ type ContractCaller interface {
 // used when the user does not provide some needed values, but rather leaves it up
 // to the transactor to decide.
 type ContractTransactor interface {
-	// PendingAccountNonce retrieves the current pending nonce associated with an
-	// account.
-	PendingAccountNonce(ctx context.Context, account common.Address) (uint64, error)
-
+	// PendingCodeAt returns the code of the given account in the pending state.
+	PendingCodeAt(ctx context.Context, account common.Address) ([]byte, error)
+	// PendingNonceAt retrieves the current pending nonce associated with an account.
+	PendingNonceAt(ctx context.Context, account common.Address) (uint64, error)
 	// SuggestGasPrice retrieves the currently suggested gas price to allow a timely
 	// execution of a transaction.
 	SuggestGasPrice(ctx context.Context) (*big.Int, error)
-
-	// HasCode checks if the contract at the given address has any code associated
-	// with it or not. This is needed to differentiate between contract internal
-	// errors and the local chain being out of sync.
-	HasCode(ctx context.Context, contract common.Address, pending bool) (bool, error)
-
-	// EstimateGasLimit tries to estimate the gas needed to execute a specific
+	// EstimateGas tries to estimate the gas needed to execute a specific
 	// transaction based on the current pending state of the backend blockchain.
 	// There is no guarantee that this is the true gas limit requirement as other
 	// transactions may be added or removed by miners, but it should provide a basis
 	// for setting a reasonable default.
-	EstimateGasLimit(ctx context.Context, sender common.Address, contract *common.Address, value *big.Int, data []byte) (*big.Int, error)
-
+	EstimateGas(ctx context.Context, call ethereum.CallMsg) (usedGas *big.Int, err error)
 	// SendTransaction injects the transaction into the pending pool for execution.
 	SendTransaction(ctx context.Context, tx *types.Transaction) error
 }
 
-// ContractBackend defines the methods needed to allow operating with contract
-// on a read-write basis.
-//
-// This interface is essentially the union of ContractCaller and ContractTransactor
-// but due to a bug in the Go compiler (https://github.com/golang/go/issues/6977),
-// we cannot simply list it as the two interfaces. The other solution is to add a
-// third interface containing the common methods, but that convolutes the user API
-// as it introduces yet another parameter to require for initialization.
+// ContractBackend defines the methods needed to work with contracts on a read-write basis.
 type ContractBackend interface {
-	// HasCode checks if the contract at the given address has any code associated
-	// with it or not. This is needed to differentiate between contract internal
-	// errors and the local chain being out of sync.
-	HasCode(ctx context.Context, contract common.Address, pending bool) (bool, error)
-
-	// ContractCall executes an Ethereum contract call with the specified data as
-	// the input. The pending flag requests execution against the pending block, not
-	// the stable head of the chain.
-	ContractCall(ctx context.Context, contract common.Address, data []byte, pending bool) ([]byte, error)
-
-	// PendingAccountNonce retrieves the current pending nonce associated with an
-	// account.
-	PendingAccountNonce(ctx context.Context, account common.Address) (uint64, error)
-
-	// SuggestGasPrice retrieves the currently suggested gas price to allow a timely
-	// execution of a transaction.
-	SuggestGasPrice(ctx context.Context) (*big.Int, error)
-
-	// EstimateGasLimit tries to estimate the gas needed to execute a specific
-	// transaction based on the current pending state of the backend blockchain.
-	// There is no guarantee that this is the true gas limit requirement as other
-	// transactions may be added or removed by miners, but it should provide a basis
-	// for setting a reasonable default.
-	EstimateGasLimit(ctx context.Context, sender common.Address, contract *common.Address, value *big.Int, data []byte) (*big.Int, error)
-
-	// SendTransaction injects the transaction into the pending pool for execution.
-	SendTransaction(ctx context.Context, tx *types.Transaction) error
+	ContractCaller
+	ContractTransactor
 }