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Add some comments to Script.java

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Mike Hearn 2012-11-01 15:18:49 +01:00
parent 050d70cf15
commit 35ff3e1735
1 changed files with 16 additions and 3 deletions
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19
core/src/main/java/com/google/bitcoin/core/Script.java
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@ -1476,7 +1476,7 @@ public class Script {
}
/**
* Verifies that this script (interpreted as a scriptSig) correctly spends the given scriptPubKey
* Verifies that this script (interpreted as a scriptSig) correctly spends the given scriptPubKey.
* @throws VerificationException if this script does not correctly spend the scriptPubKey
*/
public void correctlySpends(Transaction txContainingThis, long index, Script scriptPubKey, boolean enforceP2SH) throws VerificationException, ScriptException {
@ -1496,8 +1496,21 @@ public class Script {
if (!castToBool(stack.pollLast()))
throw new VerificationException("Script resulted in a non-true stack");
if(enforceP2SH && scriptPubKey.isPayToScriptHash()) {
// P2SH is pay to script hash. It means that the scriptPubKey has a special form which is a valid
// program but it has "useless" form that if evaluated as a normal program always returns true.
// Instead, miners recognize it as special based on its template - it provides a hash of the real scriptPubKey
// and that must be provided by the input. The goal of this bizarre arrangement is twofold:
//
// (1) You can sum up a large, complex script (like a CHECKMULTISIG script) with an address that's the same
// size as a regular address. This means it doesn't overload scannable QR codes/NFC tags or become
// un-wieldy to copy/paste.
// (2) It allows the working set to be smaller: nodes perform best when they can store as many unspent outputs
// in RAM as possible, so if the outputs are made smaller and the inputs get bigger, then it's better for
// overall scalability and performance.
// TODO: Check if we can take out enforceP2SH if there's a checkpoint at the enforcement block.
if (enforceP2SH && scriptPubKey.isPayToScriptHash()) {
for (ScriptChunk chunk : chunks)
if (chunk.isOpCode && (chunk.data[0] & 0xff) > OP_16)
throw new VerificationException("Attempted to spend a P2SH scriptPubKey with a script that contained script ops");