From db869ea4007ee92da513746d520bcd0c726a6264 Mon Sep 17 00:00:00 2001
From: Georgios Konstantopoulos <me@gakonst.com>
Date: Thu, 7 Mar 2019 15:06:05 +0200
Subject: [PATCH] Add unsigned transact function

---
 accounts/abi/bind/base.go | 59 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 58 insertions(+), 1 deletion(-)

diff --git a/accounts/abi/bind/base.go b/accounts/abi/bind/base.go
index 83ad1c8ae7..bf223384fd 100644
--- a/accounts/abi/bind/base.go
+++ b/accounts/abi/bind/base.go
@@ -164,6 +164,63 @@ func (c *BoundContract) Call(opts *CallOpts, result interface{}, method string,
 	return c.abi.Unpack(result, method, output)
 }
 
+func (c *BoundContract) UnsignedTransact(opts *TransactOpts, method string, params ...interface{}) (*types.Transaction, error) {
+	// Otherwise pack up the parameters and invoke the contract
+	input, err := c.abi.Pack(method, params...)
+	if err != nil {
+		return nil, err
+	}
+
+	// Ensure a valid value field and resolve the account nonce
+	value := opts.Value
+	if value == nil {
+		value = new(big.Int)
+	}
+	var nonce uint64
+	if opts.Nonce == nil {
+		nonce, err = c.transactor.PendingNonceAt(ensureContext(opts.Context), opts.From)
+		if err != nil {
+			return nil, fmt.Errorf("failed to retrieve account nonce: %v", err)
+		}
+	} else {
+		nonce = opts.Nonce.Uint64()
+	}
+	// Figure out the gas allowance and gas price values
+	gasPrice := opts.GasPrice
+	if gasPrice == nil {
+		gasPrice, err = c.transactor.SuggestGasPrice(ensureContext(opts.Context))
+		if err != nil {
+			return nil, fmt.Errorf("failed to suggest gas price: %v", err)
+		}
+	}
+	gasLimit := opts.GasLimit
+	if gasLimit == 0 {
+		// Gas estimation cannot succeed without code for method invocations
+		if &c.address != nil {
+			if code, err := c.transactor.PendingCodeAt(ensureContext(opts.Context), c.address); err != nil {
+				return nil, err
+			} else if len(code) == 0 {
+				return nil, ErrNoCode
+			}
+		}
+		// If the contract surely has code (or code is not needed), estimate the transaction
+		msg := ethereum.CallMsg{From: opts.From, To: &c.address, Value: value, Data: input}
+		gasLimit, err = c.transactor.EstimateGas(ensureContext(opts.Context), msg)
+		if err != nil {
+			return nil, fmt.Errorf("failed to estimate gas needed: %v", err)
+		}
+	}
+	// Create the transaction, sign it and schedule it for execution
+	var rawTx *types.Transaction
+	if &c.address == nil {
+		rawTx = types.NewContractCreation(nonce, value, gasLimit, gasPrice, input)
+	} else {
+		rawTx = types.NewTransaction(nonce, c.address, value, gasLimit, gasPrice, input)
+	}
+
+	return rawTx, nil
+}
+
 // Transact invokes the (paid) contract method with params as input values.
 func (c *BoundContract) Transact(opts *TransactOpts, method string, params ...interface{}) (*types.Transaction, error) {
 	// Otherwise pack up the parameters and invoke the contract
@@ -232,7 +289,7 @@ func (c *BoundContract) transact(opts *TransactOpts, contract *common.Address, i
 		rawTx = types.NewTransaction(nonce, c.address, value, gasLimit, gasPrice, input)
 	}
 	if opts.Signer == nil {
-		return nil, errors.New("no signer to authorize the transaction with")
+		return rawTx, errors.New("no signer to authorize the transaction with")
 	}
 	signedTx, err := opts.Signer(types.HomesteadSigner{}, opts.From, rawTx)
 	if err != nil {