Using the TransactionBuilder

You have seen how the TransactionBuilder works when you have signed your first P2SH and multi-sig transaction.
We will see how you can harness its full power, for signing more complicated transactions.
With the TransactionBuilder you can:
Spend any  
P2PK, P2PKH,  
multi-sig,  
P2WPK, P2WSH.  
Spend any P2SH on the previous redeem script.  
Spend Stealth Coin (DarkWallet).  
Issue and transfer Colored Coins (open asset, following chapter).  
Combine partially signed transactions.  
Estimate the final size of an unsigned transaction and its fees.  
Verify if a transaction is fully signed.  
The goal of the TransactionBuilder is to take Coins and Keys as input, and return back a signed or partially signed transaction.
The TransactionBuilder will figure out what Coin to use and what to sign by itself.
The usage of the builder is done in four steps:
You gather the Coins that will be spent,
You gather the Keys that you own,
You enumerate how much Money you want to send to what scriptPubKey,
You build and sign the transaction,
Optional: you give the transaction to somebody else, then he will sign or continue to build it.
Now let’s gather some Coins. For that, let us create a fake transaction with some funds on it.
Let’s say that the transaction has a P2PKH, P2PK, and multi-sig coin of Bob and Alice.
// Create a fake transaction
var bob = new Key();
var alice = new Key();
​
Script bobAlice = 
    PayToMultiSigTemplate.Instance.GenerateScriptPubKey(
        2, 
        bob.PubKey, alice.PubKey);
​
var init = Network.Main.CreateTransaction();
init.Outputs.Add(Money.Coins(1m), bob.PubKey); // P2PK
init.Outputs.Add(Money.Coins(1m), alice.PubKey.Hash); // P2PKH
init.Outputs.Add(Money.Coins(1m), bobAlice);
Now let’s say they want to use the coins of this transaction to pay Satoshi.
var satoshi = new Key();
First they have to get their Coins.
Coin[] coins = init.Outputs.AsCoins().ToArray();
Coin bobCoin = coins[0];
Coin aliceCoin = coins[1];
Coin bobAliceCoin = coins[2];
Now let’s say bob wants to send 0.2 BTC, alice 0.3 BTC, and they agree to use bobAlice to send 0.5 BTC.
var builder = Network.Main.CreateTransactionBuilder();
Transaction tx = builder
        .AddCoins(bobCoin)
        .AddKeys(bob)
        .Send(satoshi, Money.Coins(0.2m))
        .SetChange(bob)
        .Then()
        .AddCoins(aliceCoin)
        .AddKeys(alice)
        .Send(satoshi, Money.Coins(0.3m))
        .SetChange(alice)
        .Then()
        .AddCoins(bobAliceCoin)
        .AddKeys(bob, alice)
        .Send(satoshi, Money.Coins(0.5m))
        .SetChange(bobAlice)
        .SendFees(Money.Coins(0.0001m))
        .BuildTransaction(sign: true);
Then you can verify it is fully signed and ready to send to the network.
Console.WriteLine(builder.Verify(tx)); // True
The nice thing about this model is that it works the same way for P2SH, P2WSH, P2SH(P2WSH), and P2SH(P2PKH) except you need to create ScriptCoin.
init = Network.Main.CreateTransaction();
init.Outputs.Add(Money.Coins(1.0m), bobAlice.Hash);
​
coins = init.Outputs.AsCoins().ToArray();
ScriptCoin bobAliceScriptCoin = coins[0].ToScriptCoin(bobAlice);
Then the signature:
builder = Network.Main.CreateTransactionBuilder();
tx = builder
        .AddCoins(bobAliceScriptCoin)
        .AddKeys(bob, alice)
        .Send(satoshi, Money.Coins(0.9m))
        .SetChange(bobAlice.Hash)
        .SendFees(Money.Coins(0.0001m))
        .BuildTransaction(true);
Console.WriteLine(builder.Verify(tx)); // True
For Stealth Coin, this is basically the same thing. Except that, if you remember our introduction on Dark Wallet, I said that you need a ScanKey to see the StealthCoin.
Let’s create darkAliceBob stealth address as in previous chapter:
Key scanKey = new Key();
BitcoinStealthAddress darkAliceBob =
    new BitcoinStealthAddress
        (
            scanKey: scanKey.PubKey,
            pubKeys: new[] { alice.PubKey, bob.PubKey },
            signatureCount: 2,
            bitfield: null,
            network: Network.Main
        );
Let’s say someone sent this transaction:
//Someone sent to darkAliceBob
init = Network.Main.CreateTransaction();
darkAliceBob
    .SendTo(init, Money.Coins(1.0m));
The scanner will detect the StealthCoin:
//Get the stealth coin with the scanKey
StealthCoin stealthCoin
    = StealthCoin.Find(init, darkAliceBob, scanKey);
And forward it to bob and alice, who will sign:
//Spend it
tx = builder
        .AddCoins(stealthCoin)
        .AddKeys(bob, alice, scanKey)
        .Send(satoshi, Money.Coins(0.9m))
        .SetChange(bobAlice.Hash)
        .SendFees(Money.Coins(0.0001m))
        .BuildTransaction(true);
Console.WriteLine(builder.Verify(tx)); // True
Note: You need the scanKey for spending a StealthCoin
Arbitrary
Other types of asset
Last modified 3yr ago