Backend: implement Silent Payments sending

Implemented sending of Silent Payments (BIP-352).

Created tests for Silent Payments based on test data for
BIP-352.

src/GWallet.Backend.Tests/GWallet.Backend.Tests.fsproj

@@ -25,6 +25,7 @@
     <Compile Include="Deserialization.fs" />
     <Compile Include="ExceptionMarshalling.fs" />
     <Compile Include="MetaMarshalling.fs" />
+    <Compile Include="SilentPayments.fs" />
     <Compile Include="Program.fs" />
   </ItemGroup>
   <ItemGroup>
@@ -38,6 +39,7 @@
     <ProjectReference Include="..\GWallet.Backend\GWallet.Backend.fsproj" />
   </ItemGroup>
   <ItemGroup>
+    <Content Include="data\send_and_receive_test_vectors.json" />
     <EmbeddedResource Include="data\basicException.json" />
     <EmbeddedResource Include="data\customFSharpException.json" />
     <EmbeddedResource Include="data\realException.json" />

src/GWallet.Backend.Tests/SilentPayments.fs

@@ -0,0 +1,112 @@
+namespace GWallet.Backend.Tests
+
+open System.IO
+open System.Reflection
+open System.Text.Json
+
+open NUnit.Framework
+open NBitcoin
+
+open GWallet.Backend.UtxoCoin
+
+
+type private TestInput =
+    {
+        TxId: string
+        Vout: int
+        ScriptSig: string
+        TxInWitness: string
+        ScriptPubKey: string
+        PrivateKey: string
+    }
+    static member FromJsonElement(jsonElement: JsonElement) =
+        {
+            TxId = jsonElement.GetProperty("txid").GetString()
+            Vout = jsonElement.GetProperty("vout").GetInt32()
+            ScriptSig = jsonElement.GetProperty("scriptSig").GetString()
+            TxInWitness = jsonElement.GetProperty("txinwitness").GetString()
+            ScriptPubKey = jsonElement.GetProperty("prevout").GetProperty("scriptPubKey").GetProperty("hex").GetString()
+            PrivateKey = jsonElement.GetProperty("private_key").GetString()
+        }
+
+[<TestFixture>]
+type SilentPayments() =
+
+    let executingAssembly = Assembly.GetExecutingAssembly()
+    let binPath = executingAssembly.Location |> FileInfo
+    let projectDirPath = Path.Combine(binPath.Directory.FullName, "..", "..", "..")
+    let dataDir = Path.Combine(projectDirPath, "data") |> DirectoryInfo
+
+    [<Test>]
+    member __.``Test creating outputs using test vectors from BIP-352``() =
+        // https://github.com/bitcoin/bips/blob/master/bip-0352/send_and_receive_test_vectors.json
+
+        let testVectorsFileName = "send_and_receive_test_vectors.json"
+        let testVectorsJson = JsonDocument.Parse(File.ReadAllText(Path.Combine(dataDir.FullName, testVectorsFileName)))
+
+        for testCase in testVectorsJson.RootElement.EnumerateArray() do
+            let testCaseName = testCase.GetProperty("comment").GetString()
+            let sending = testCase.GetProperty("sending").[0]
+            let expectedOutputs = 
+                sending.GetProperty("expected").GetProperty("outputs").EnumerateArray() 
+                    |> Seq.map (fun each -> each.EnumerateArray() |> Seq.toArray)
+                    |> Seq.toArray
+            let given = sending.GetProperty "given"
+            let inputs = given.GetProperty("vin").EnumerateArray() |> Seq.map TestInput.FromJsonElement |> Seq.toList
+            let recipients = 
+                given.GetProperty("recipients").EnumerateArray()
+                    |> Seq.map (fun each -> each.GetString() |> SilentPaymentAddress.Decode)
+                    |> Seq.toList
+
+            if expectedOutputs.Length > 1 || (expectedOutputs.Length = 1 && expectedOutputs.[0].Length > 1) || recipients.Length > 1 then
+                printfn "Skipping BIP-352 test case '%s'" testCaseName
+            else
+                printfn "Running BIP-352 test case '%s'" testCaseName
+
+                let expectedOutput = expectedOutputs.[0] |> Array.tryHead |> Option.map (fun elem -> elem.GetString())
+
+                let spInputs =
+                    inputs
+                    |> List.map (
+                        fun input -> 
+                            let witness = 
+                                match input.TxInWitness with
+                                | "" -> None
+                                | hex -> 
+                                    let stream = BitcoinStream(DataEncoders.Encoders.Hex.DecodeData hex)
+                                    Some <| WitScript.Load stream
+                            let spInput =
+                                SilentPayments.convertToSilentPaymentInput 
+                                    (Script.FromHex input.ScriptPubKey) 
+                                    (DataEncoders.Encoders.Hex.DecodeData input.ScriptSig)
+                                    witness
+                            input, spInput)
+
+                let maybePrivateKeys, outpoints =
+                    spInputs
+                    |> List.choose
+                        (fun (input, spInput) ->
+                            let privKey = new Key(DataEncoders.Encoders.Hex.DecodeData input.PrivateKey)
+                            let outPoint = OutPoint(uint256.Parse input.TxId, input.Vout)
+                            match spInput with
+                            | InputForSharedSecretDerivation(_pubKey) ->
+                                let isTapRoot = (Script.FromHex input.ScriptPubKey).IsScriptType ScriptType.Taproot
+                                Some (Some(privKey, isTapRoot), outPoint)
+                            | InputJustForSpending ->
+                                Some(None, outPoint)
+                            | _ -> None)
+                    |> List.unzip
+
+                let privateKeys = maybePrivateKeys |> List.choose id
+
+                match privateKeys, expectedOutput with
+                | [], None -> ()
+                | [], Some _ ->
+                    Assert.Fail(sprintf "No inputs for shared secret derivation in test case '%s'" testCaseName)
+                | _, Some expectedOutputString ->
+                    let output = SilentPayments.createOutput privateKeys outpoints recipients.[0]
+                    let outputString = output.GetEncoded() |> DataEncoders.Encoders.Hex.EncodeData
+                    Assert.AreEqual(expectedOutputString, outputString, sprintf "Failure in test case '%s'" testCaseName)
+                | _, None ->
+                    Assert.Throws(fun () -> SilentPayments.createOutput privateKeys outpoints recipients.[0] |> ignore)
+                    |> ignore