add unspentoutput method to utxo clients

api/utxo/utxo.go

@@ -83,9 +83,17 @@ type Client interface {
 	// Output returns the transaction output identified by the given outpoint.
 	// It also returns the number of confirmations for the output. If the output
 	// cannot be found before the context is done, or the output is invalid,
-	// then an error should be returned.
+	// then an error should be returned. This method will not error, even if the
+	// output has been spent.
 	Output(context.Context, Outpoint) (Output, pack.U64, error)
 
+	// UnspentOutput returns the unspent transaction output identified by the
+	// given outpoint. It also returns the number of confirmations for the
+	// output. If the output cannot be found before the context is done, the
+	// output is invalid, or the output has been spent, then an error should be
+	// returned.
+	UnspentOutput(context.Context, Outpoint) (Output, pack.U64, error)
+
 	// SubmitTx to the underlying chain. If the transaction cannot be found
 	// before the context is done, or the transaction is invalid, then an error
 	// should be returned.

chain/bitcoin/bitcoin.go

@@ -111,7 +111,7 @@ func (client *client) Output(ctx context.Context, outpoint utxo.Outpoint) (utxo.
 	hash := chainhash.Hash{}
 	copy(hash[:], outpoint.Hash)
 	if err := client.send(ctx, &resp, "getrawtransaction", hash.String(), 1); err != nil {
-		return utxo.Output{}, pack.NewU64(0), fmt.Errorf("bad \"gettxout\": %v", err)
+		return utxo.Output{}, pack.NewU64(0), fmt.Errorf("bad \"getrawtransaction\": %v", err)
 	}
 	if outpoint.Index.Uint32() >= uint32(len(resp.Vout)) {
 		return utxo.Output{}, pack.NewU64(0), fmt.Errorf("bad index: %v is out of range", outpoint.Index)
@@ -136,6 +136,40 @@ func (client *client) Output(ctx context.Context, outpoint utxo.Outpoint) (utxo.
 	return output, pack.NewU64(resp.Confirmations), nil
 }
 
+// UnspentOutput returns the unspent transaction output identified by the
+// given outpoint. It also returns the number of confirmations for the
+// output. If the output cannot be found before the context is done, the
+// output is invalid, or the output has been spent, then an error should be
+// returned.
+func (client *client) UnspentOutput(ctx context.Context, outpoint utxo.Outpoint) (utxo.Output, pack.U64, error) {
+	resp := btcjson.GetTxOutResult{}
+	hash := chainhash.Hash{}
+	copy(hash[:], outpoint.Hash)
+	if err := client.send(ctx, &resp, "gettxout", hash.String(), outpoint.Index.Uint32()); err != nil {
+		return utxo.Output{}, pack.NewU64(0), fmt.Errorf("bad \"gettxout\": %v", err)
+	}
+	amount, err := btcutil.NewAmount(resp.Value)
+	if err != nil {
+		return utxo.Output{}, pack.NewU64(0), fmt.Errorf("bad amount: %v", err)
+	}
+	if amount < 0 {
+		return utxo.Output{}, pack.NewU64(0), fmt.Errorf("bad amount: %v", amount)
+	}
+	if resp.Confirmations < 0 {
+		return utxo.Output{}, pack.NewU64(0), fmt.Errorf("bad confirmations: %v", resp.Confirmations)
+	}
+	pubKeyScript, err := hex.DecodeString(resp.ScriptPubKey.Hex)
+	if err != nil {
+		return utxo.Output{}, pack.NewU64(0), fmt.Errorf("bad pubkey script: %v", err)
+	}
+	output := utxo.Output{
+		Outpoint:     outpoint,
+		Value:        pack.NewU256FromU64(pack.NewU64(uint64(amount))),
+		PubKeyScript: pack.NewBytes(pubKeyScript),
+	}
+	return output, pack.NewU64(uint64(resp.Confirmations)), nil
+}
+
 // SubmitTx to the Bitcoin network.
 func (client *client) SubmitTx(ctx context.Context, tx utxo.Tx) error {
 	serial, err := tx.Serialize()

chain/bitcoin/bitcoin_test.go

@@ -59,6 +59,9 @@ var _ = Describe("Bitcoin", func() {
 				output2, _, err := client.Output(context.Background(), output.Outpoint)
 				Expect(err).ToNot(HaveOccurred())
 				Expect(reflect.DeepEqual(output, output2)).To(BeTrue())
+				output2, _, err = client.UnspentOutput(context.Background(), output.Outpoint)
+				Expect(err).ToNot(HaveOccurred())
+				Expect(reflect.DeepEqual(output, output2)).To(BeTrue())
 
 				// Build the transaction by consuming the outputs and spending
 				// them to a set of recipients.
@@ -122,11 +125,15 @@ var _ = Describe("Bitcoin", func() {
 					confs, err := client.Confirmations(context.Background(), txHash)
 					Expect(err).ToNot(HaveOccurred())
 					log.Printf("                   %v/3 confirmations", confs)
-					if confs >= 3 {
+					if confs >= 1 {
 						break
 					}
 					time.Sleep(10 * time.Second)
 				}
+				ctxWithTimeout, cancelCtxWithTimeout := context.WithTimeout(context.Background(), time.Second)
+				defer cancelCtxWithTimeout()
+				_, _, err = client.UnspentOutput(ctxWithTimeout, output.Outpoint)
+				Expect(err).To(HaveOccurred())
 
 				// Check that we can load the output and that it is equal.
 				// Otherwise, something strange is happening with the RPC

go.sum

@@ -67,6 +67,7 @@ github.com/VictoriaMetrics/fastcache v1.5.7/go.mod h1:ptDBkNMQI4RtmVo8VS/XwRY6Ro
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+github.com/aead/siphash v1.0.1 h1:FwHfE/T45KPKYuuSAKyyvE+oPWcaQ+CUmFW0bPlM+kg=
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 github.com/akavel/rsrc v0.8.0/go.mod h1:uLoCtb9J+EyAqh+26kdrTgmzRBFPGOolLWKpdxkKq+c=
@@ -117,9 +118,13 @@ github.com/btcsuite/btcutil v0.0.0-20190207003914-4c204d697803/go.mod h1:+5NJ2+q
 github.com/btcsuite/btcutil v0.0.0-20190425235716-9e5f4b9a998d/go.mod h1:+5NJ2+qvTyV9exUAL/rxXi3DcLg2Ts+ymUAY5y4NvMg=
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+github.com/btcsuite/go-socks v0.0.0-20170105172521-4720035b7bfd h1:R/opQEbFEy9JGkIguV40SvRY1uliPX8ifOvi6ICsFCw=
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+github.com/btcsuite/goleveldb v0.0.0-20160330041536-7834afc9e8cd h1:qdGvebPBDuYDPGi1WCPjy1tGyMpmDK8IEapSsszn7HE=
 github.com/btcsuite/goleveldb v0.0.0-20160330041536-7834afc9e8cd/go.mod h1:F+uVaaLLH7j4eDXPRvw78tMflu7Ie2bzYOH4Y8rRKBY=
+github.com/btcsuite/snappy-go v0.0.0-20151229074030-0bdef8d06723 h1:ZA/jbKoGcVAnER6pCHPEkGdZOV7U1oLUedErBHCUMs0=
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+github.com/btcsuite/websocket v0.0.0-20150119174127-31079b680792 h1:R8vQdOQdZ9Y3SkEwmHoWBmX1DNXhXZqlTpq6s4tyJGc=
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@@ -172,6 +177,7 @@ github.com/danieljoos/wincred v1.0.2/go.mod h1:SnuYRW9lp1oJrZX/dXJqr0cPK5gYXqx3E
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+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
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@@ -602,13 +608,15 @@ github.com/jbenet/goprocess v0.1.3/go.mod h1:5yspPrukOVuOLORacaBi858NqyClJPQxYZl
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@@ -632,6 +640,7 @@ github.com/kilic/bls12-381 v0.0.0-20200607163746-32e1441c8a9f/go.mod h1:XXfR6YFC
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