Can combine PSBT

BTCPayServer/Models/WalletViewModels/WalletPSBTCombineViewModel.cs

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+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.IO;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
+using NBitcoin;
+
+namespace BTCPayServer.Models.WalletViewModels
+{
+    public class WalletPSBTCombineViewModel
+    {
+        public string OtherPSBT { get; set; }
+        [Display(Name = "PSBT to combine with...")]
+        public string PSBT { get; set; }
+        [Display(Name = "Upload PSBT from file...")]
+        public IFormFile UploadedPSBTFile { get; set; }
+
+        public PSBT GetSourcePSBT(Network network)
+        {
+            if (!string.IsNullOrEmpty(OtherPSBT))
+            {
+                try
+                {
+                    return NBitcoin.PSBT.Parse(OtherPSBT, network);
+                }
+                catch
+                { }
+            }
+            return null;
+        }
+        public async Task<PSBT> GetPSBT(Network network)
+        {
+            if (UploadedPSBTFile != null)
+            {
+                if (UploadedPSBTFile.Length > 500 * 1024)
+                    return null;
+                byte[] bytes = new byte[UploadedPSBTFile.Length];
+                using (var stream = UploadedPSBTFile.OpenReadStream())
+                {
+                    await stream.ReadAsync(bytes, 0, (int)UploadedPSBTFile.Length);
+                }
+                try
+                {
+                    return NBitcoin.PSBT.Load(bytes, network);
+                }
+                catch
+                {
+                    return null;
+                }
+            }
+            if (!string.IsNullOrEmpty(PSBT))
+            {
+                try
+                {
+                    return NBitcoin.PSBT.Parse(PSBT, network);
+                }
+                catch
+                { }
+            }
+            return null;
+        }
+    }
+}