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Add Script:dust_value() to get minimum output value for a spk #566

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merged 1 commit into from Feb 7, 2021
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Add Script:dust_value() to get minimum output value for a spk #566

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20 changes: 20 additions & 0 deletions src/blockdata/script.rs
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Expand Up @@ -325,6 +325,26 @@ impl Script {
opcodes::All::from(self.0[0]).classify() == opcodes::Class::IllegalOp)
}

/// The minimum value an output to a witness script must have in order to be
/// broadcastable on today's bitcoin network.
pub const WITNESS_OUTPUT_DUST_THRESHOLD: u64 = 294;

/// The minimum value an output to a non-witness script must have in order to be
/// broadcastable on today's bitcoin network.
pub const LEGACY_OUTPUT_DUST_THRESHOLD: u64 = 546;

/// Gets the minimum value an output with this script should have in order to be
/// broadcastable on today's bitcoin network.
pub fn dust_value(&self) -> u64 {
if self.is_op_return() {
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When looking at core it also captures the case where a script is too big making the UTXO unspendable. But that would only make this implementation more conservative which might be ok since it's such a fringe use case and not consensus critical.

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Hmm, right - are those scripts broadcastable at all or are they nonstandard?

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@sanket1729 sanket1729 Feb 5, 2021 •
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Those scripts are not possible by consensus rules all scripts(bare, p2sh, witness_v0). But post tapscript, those scripts will be broadcastable.

https://github.com/bitcoin/bips/blob/master/bip-0342.mediawiki#resource-limits

https://github.com/bitcoin/bitcoin/blob/6c6140846f37de8c132b3b6abf09f3d7940554a7/src/script/interpreter.cpp#L452

We can change the isWitnessProgram check to check only v0 programs, but this can also be done in taproot upgrade #503. But this could have easily been one of the things we forgot to add.

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@sanket1729 sanket1729 Feb 5, 2021 •
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@sgeisler Nevermind, I was wrong. This function is about scriptPubkey and not about the witness Program inside it. The witness program can be more 10,000 in Tapscript, but scriptpubkey is always 35.

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Right, I'm not even talking about if its valid (its obviously not possible to spend), but is it standard - can you broadcast a transaction with such a script in an output and have it be mined, even if the output is unspendable.

0
} else if self.is_witness_program() {
Self::WITNESS_OUTPUT_DUST_THRESHOLD
} else {
Self::LEGACY_OUTPUT_DUST_THRESHOLD
}
}

/// Iterate over the script in the form of `Instruction`s, which are an enum covering
/// opcodes, datapushes and errors. At most one error will be returned and then the
/// iterator will end. To instead iterate over the script as sequence of bytes, treat
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