Ability to create a psbt without syncing a wallet in swift-bdk.

[Fonta1n3]

I am using swift-bdk to carry out some offline functionality in Fully Noded.

It would be useful to be able to build a psbt with inputs and outputs I specify without having to sync a BDK wallet object as I already have all the info needed to build the psbt.

Currently I am getting: BitcoinDevKit.CreateTxError.UnknownUtxo(outpoint: "1d5d0947fb69d6ed8220ad90a892bc1b8a693ea6e8711e99f498738c773abdd5:1") when attempting to do this.

Is there an addForeignUtxo option that could be exposed to swift-bdk?

Thank you.

[ItoroD]

Hey @Fonta1n3 ! How did you attempt to build the your psbt?

[Fonta1n3]

func createPsbtWithManualInputs(
        wallet: BDKWallet,
        utxos: [Esplora_Utxo],
        outputs: [(address: String, amount: UInt64)],
        feeRate: Float? = nil,
        network: BDKNetwork
    ) throws -> String {
        // Start building the transaction
        var txBuilder = TxBuilder()
        
        // Add each UTXO manually as input
        for utxo in utxos {
            let txid = try Txid.fromString(hex: utxo.txid)
            let outpoint = OutPoint(txid: txid, vout: UInt32(utxo.vout))
            let address = try Address(address: utxo.address!, network: network)
            let script = address.scriptPubkey()
            let amount = Amount.fromSat(satoshi: UInt64(utxo.value))
            let txOutput = TxOut(value: amount, scriptPubkey: script)
            wallet.insertTxout(outpoint: outpoint, txout: txOutput)
            txBuilder = txBuilder.addUtxo(outpoint: outpoint)
        }
        
        // Add each output
        for output in outputs {
            let address = try Address(address: output.address, network: network)
            let script = address.scriptPubkey()
            let amount = Amount.fromSat(satoshi: output.amount)
            txBuilder = txBuilder.addRecipient(script: script, amount: amount)
        }
        
        txBuilder = txBuilder.doNotSpendChange()
        txBuilder = txBuilder.manuallySelectedOnly()
        txBuilder = txBuilder.feeRate(feeRate: try .fromSatPerVb(satVb: 1))
        
        // Finalize and create the PSBT
        let psbt = try txBuilder.finish(wallet: wallet)
        
        // Return base64-encoded PSBT (standard format for sharing/signing)
        return psbt.serialize()
    }

[ItoroD]

Ahh I get what you mean. Tagging @reez @thunderbiscuit

[Fonta1n3]

Yea I got it working by adding:

let syncRequest = try wallet.startSyncWithRevealedSpks().build()
let client = EsploraClient(url: "https://blockstream.info/testnet/api/", proxy: nil)
let sync = try client.sync(request: syncRequest, parallelRequests: 4)
try wallet.applyUpdate(update: sync)

For my purposes its entirely redundant as I am already fetching the utxo info from esplora or from the users node, but FN does it via onion which I can not seem to get working as per #927

Would be really cool to just be able to build the psbt offline :)