Additional APIs and good defaults for Client & JSAPI.

libethereum/Client.h

@@ -235,6 +235,9 @@ public:
 	/// Get the fee associated for a transaction with the given data.
 	static u256 txGas(uint _dataCount, u256 _gas = 0) { return c_txDataGas * _dataCount + c_txGas + _gas; }
 
+	/// Get the remaining gas limit in this block.
+	u256 gasLimitRemaining() const { return m_postMine.gasLimitRemaining(); }
+
 	// [PRIVATE API - only relevant for base clients, not available in general]
 
 	eth::State state(unsigned _txi, h256 _block) const;

libethereum/State.h

@@ -192,6 +192,9 @@ public:
 	u256 execute(bytes const& _rlp, bytes* o_output = nullptr, bool _commit = true) { return execute(&_rlp, o_output, _commit); }
 	u256 execute(bytesConstRef _rlp, bytes* o_output = nullptr, bool _commit = true);
 
+	/// Get the remaining gas limit in this block.
+	u256 gasLimitRemaining() const { return m_currentBlock.gasLimit - gasUsed(); }
+
 	/// Check if the address is in use.
 	bool addressInUse(Address _address) const;
 

libqethereum/QEthereum.cpp

@@ -413,7 +413,7 @@ void QEthereum::doTransact(QString _json)
 	if (!t.gasPrice)
 		t.gasPrice = 10 * eth::szabo;
 	if (!t.gas)
-		t.gas = client()->balanceAt(KeyPair(t.from).address()) / t.gasPrice;
+		t.gas = min<u256>(client()->gasLimitRemaining(), client()->balanceAt(KeyPair(t.from).address()) / t.gasPrice);
 	if (t.to)
 		client()->transact(t.from, t.value, t.to, t.data, t.gas, t.gasPrice);
 	else