Get addresses from transparent outputs in zcash_script

[mpguerra]

Motivation

lightwalletd uses the getaddresstxids, getaddressbalance, and getaddressutxos RPCs.

These RPCs return the transparent address that receives funds from a transparent output:

• Add transparent address indexes to zebra-state #3150

zcashd Implementation

Here is how zcashd gets the output addresses using out.scriptPubKey.AddressHash(), and builds its address indexes:

• https://github.com/zcash/zcash/blob/c76b756a688bfa0a4396a45355814cdc9f9a47e3/src/main.cpp#L3232

zcash_script needs to return the same addresses for:

• the provided cached parsed transaction, and
• the provided transaction data.

Example Code

The new functions are similar to the SigOps functions in:
zcash/zcash@31bd2ba

Something like:

uint160 zcash_script_transparent_output_address(tx, nOut, ...) {
    // parse tx if needed

    if nOut >= tx.number_of_transparent_outputs {
        // set the error to "invalid output index"
        return INVALID_ADDRESS;
    }

    const CTxOut &out = tx.vout[nOut];
    CScript::ScriptType scriptType = out.scriptPubKey.GetType();
    if (scriptType == CScript::UNKNOWN) {
        // set the error to "invalid script"
        return INVALID_ADDRESS;
    }

    // set the error to "no error"
    return out.scriptPubKey.AddressHash();
}

[ftm1000]

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[conradoplg]

@teor2345 could you please add more details to what is required here? What I deduced is that we need to add a new function to zcash_script that receives an output and returns the address from it. Is that correct?

[teor2345]

@teor2345 could you please add more details to what is required here? What I deduced is that we need to add a new function to zcash_script that receives an output and returns the address from it. Is that correct?

zcash_script operates on transactions, so we want to pass the transaction and the transparent output index. Then we want to do the same thing zcashd does to build its address index.

I expanded the explanation and filled in some example code.

I'm hoping we can return a uint160 as a Rust [u8; 20] without having to allocate memory. But I guess we'll see.

[conradoplg]

Those two PRs mentioned above close this issue. (The zcashd one won't be merged into main and we will keep pointing to that branch, until we create a PR upstream and it's accepted)